Transmission & Drivetrain

It was the 1930s, the era of the Great Depression, a time when America was facing hopelessness and desperation as the prospects of war slowly grew to a boiling point over in Europe. And, amidst all that, the automatic transmission was born.

First brought to market by General Motors and popularized by the Hydra-Matic and its successors, automatic transmissions differed from their manual counterparts through the addition of a self-sufficient hydraulic fluid-based automatic shifting system, allowing cars to shift gears without driver input, versus the classic manual or stick shift system.

Ever since automatic transmissions hit the market, the same debate has been raging on for decades: which drives better? Which goes faster? Which transmission type, between the automatic and the manual, is the superior one?

Before we go into what the answer is and why, let’s delve a little deeper into the debate.

What’s Under the Hood?

Car transmissions are pretty complicated when you get down to the molecular level, but superficially, it’s simple stuff. Fuel and air go into the engine, things go boom, and the energy generated by the combustion travels through the input shaft into a metal case filled with differently-sized gears. The torque from the input shaft is translated into power through the gears that the transmission currently has engaged, out through the output shaft and into the rest of the car, depending on how it’s built.

But not all transmissions are made equal. Some have clutches, others have torque converters. Some work very differently from others, even if the end goal is the same – and little efficiencies here and there, such as optimized gear ratios, better torque conversion, improved cooling and better material can turn a 30-year-old piece of junk into a tranny powerful enough for modern-day drag racing. Between the big types, though, you’re largely looking at three major transmissions: the automatic, the manual, and the continuously variable transmission. There are others, of course, but today we’ll just tackle the first two. So, first up, our introductions:

The manual transmission came first, and its history goes back to the days of the very first real gearbox. The concept is simple, even though the application may have changed throughout the years: a shift lever attached to the transmission lets you shift from one gear/speed to another, but only after the clutch, which can be found between the transmission and the engine, is released. The clutch holds the current gear in place – to shift with a stick, you have to disengage the clutch by pushing down on a pedal next to the brake, then reengage the clutch by letting go.

Driving stick is a matter of several things, including knowing when to shift to which gear, and timing your clutch to prevent too much wear-and-tear. Engaging the clutch too slowly will wear the disc out – on the other hand, engage the clutch too quickly while stationary, and the engine might stall.

In the other corner, we have the automatic transmission. GM and Ford first came out with these – transmissions that were built largely like manual transmissions, except that they allow for an automatic shift in gears without any input from the driver, through a monitoring system which takes into account the car’s speed, engine rpm and throttle pedal.

In the past, this was done hydraulically – today, it’s all electronics. Most automatic transmissions come with a little computer in them. You can still pick up an old 7004R or any other among a series of powerful non-electronic automatic transmissions, and refurbish them for modern use – but the concept is the same.

An automatic transmission comes with a host of convenient quality-of-life benefits, including less maintenance (generally speaking) and improved, smoother driving in stop-and-go traffic. It’s easier to drive an automatic as well, given that you don’t have to worry about the clutch at all, and you don’t have to run the risk of stalling the engine. Under heavier engine load, however, automatic transmissions can get a little sluggish – and if mismatched or left non-optimized, plenty automatic transmissions forego the whole “smooth” driving experience.

Manual Transmissions vs. Automatic Transmissions

Manual transmissions involve the use of a clutch and a shift lever to switch gears, and you can’t rely on the car to do it for you. Automatic transmissions use a series of electronic sensors and hydraulic fluid to shift gears automatically. In the past, manual transmissions were the better answer for sheer performance and fuel efficiency – the ability to determine when to shift gears gave manual transmission drivers the upper hand on fuel, and a manual transmission handled well accelerated faster.

Today, technology has basically caught up with the stick shift, and there’s little reason to go manual if your intent is to leave the other driver in the wind. Automatic transmissions come in various types, but they’re winning in almost every single department: there are more automatic transmissions out there than manual transmissions, and the newest models are just as fuel efficient and accelerate just as well.

Who’s Winning the Race?

The race between the automatic and manual transmission is wholly based on the year it takes place in. If we take the world’s fastest cars, one from each camp, then the automatic transmission is the flat-out winner.

Automatic transmissions have long caught up with stick shift manual transmissions in both acceleration and fuel efficiency, and given the massive popularity of automatic transmissions in America, the overall cost difference has gotten drastically smaller. The wear and tear on automatic vs. manual transmissions is also a matter of experience, as a manual

Sure, it’s still definitely more expensive to grab a complex CVT, but in some cases, you can find cars that cost more with a manual transmission than with an automatic.

However, manual transmissions are still fun to drive – and if you’re limiting your options to older transmissions, then a competent driver behind the wheel of a stick shift can still pull ahead in a race. That being said, there is still one thing the manual has over the automatic: coordination and skill. Driving stick is still a skill, and a good skill to have. And if you’re sick of the clutch, just grab an automatic manual transmission.

The 4L70E is one of several GM-produced electronic automatic transmissions developed as a successor to the Turbo-Hydramatic line of transmissions, some of which continue to be excellent transmissions for plenty of performance builds looking for a good stock transmission with a TV cable over electronics.

Alongside the 4L60E on one spectrum, and the 4L80E on the other, the 4L70E sits between two ends of spectrum of transmission needs.

Depending on what you want, it may be an excellent transmission and just the thing you’re looking for. It’s all a question of specialization. Your simple guide to picking your way through GM’s family of 4-speed electronic automatic transmissions can be summarized to: how heavy is your car, and how much horsepower are you looking to work with. Heavier builds steer towards the larger, more imposing, power-hungry and powerful 4L80E, and the smaller your car is, the more you should be skewing towards the 4L60E.

But life isn’t always simple, and in this case, there’s more to it than just that. Here’s a quick little rundown on the 4L70E, its relative history in the world of GM transmissions, and its potential – potential that transmission experts can take, unlock, and transform into pure performance.

History of the 4L70E

GM’s transmissions play a big part in the history of American automobile manufacturing, and alongside Ford (a “friendly” competition that survives to this day), the automatic transmissions of the late 70s and early 80s pioneered the inclusion of accessible overdrive – a new gear made more accessible to transmissions after that point, designed to allow a car to maintain speed while cutting down on RPM and fuel usage, for a much better fuel economy.

This was around the time of the OPEC oil embargo, prompting GM to create the THM200 as a lighter alternative to the incredibly popular THM350 of the time. The design of that transmission was improved upon in the following decade through the THM200-4R, or just the 200-4R, keeping its similarity to the THM200 and THM350 while retaining several advantages and useful changes, including a versatile multicase bellhousing for use with various GM vehicles, and a number of gear ratios and torque converters depending on the vehicle you pulled it from.

Following the success of the 200-4R, the next-in-line kept the new designation, and the 700R4 transmission was born in 1982. This is the first of our new automatic transmissions, as the 700R4 eventually was renamed into the 4L60, in keeping with a new GM naming scheme, in 1990. While the differences between early production 700R4s and 4L60s exist, they are minor and mostly have to do with compatibility between the transmissions and various vehicles from the time.

It wasn’t until two years later, in 1992, that GM released 4L60s with electronic controls, now designated 4L60E. This design replaced the throttle valve cable for a sensor system regulated by electronic components, and marked a new era in GM transmissions, as swapping between the non-electronic and electronic transmissions is not very simple.

Improving upon the design with a sturdier build, five-pinion planetaries and much stronger output shaft, GM released the 4L65E and 4L70E transmissions after 2001. Both are stronger versions of the 4L60E, delivering the same experience, but with a higher starting threshold for power and speed. The only difference is the speed sensor located in the pump of the 4L70E, and the convenience you personally have in picking between one and the other depending on your available resources, market prices, and any existing deals.

4L70E Transmission Stats

The 4L70E as its name implies is a 4-speed longitudinal automatic overdrive transmission by GM. The E in its designation indicates that it uses electronic controls over a throttle valve cable, and it sets itself apart from the previous 4L60E by providing a sturdier build, including both five-pinion planetaries over the 4L60E’s four-pinion planetaries, and an improved output shaft. Its outer case material is aluminum, and it clocks in at about 133 lbs. dry, without any transmission fluid.

Although it is improved, it shares the same stock case design with the 4L60E, and its close cousin the 4L65E. All 4L__Es utilize a torque converter lock, and the 4L70E is no exception.

The gear ratios for the 4L70E are:

• 1st gear: 3.06
• 2nd gear: 1.62
• 3rd gear: 1.00
• 4th gear: 0.70

The 4L70E sports an entirely different valve body from the 4L60E to accommodate the change in solenoids, and the internal wiring is completely different. Care needs to be taken when deciding how to install a 4L70E in cars that originally used an older GM transmission – while it often bolts just in, the car may not be compatible with the electronic components in the 4L70E if it’s a model before 1996. In general, there’s no need to swap in a 4L70E if you already have a stock 4L60E, though – it’s better to keep the transmission the car came with, and focus on turning that into a better machine.

4L70E vs. 4L60E vs. 4L80E

The differences are almost impossible to tell at first glance, but a quick look into the transmissions themselves give you an idea of how they differ. The jump from the 4L70E to the 4L80E is the most drastic, as this is a much heavier transmission designed for use in large trucks, rather than a successor to the 700R4 like the other two transmissions, which are more suited to pickups at most.

The 4L80E weighs 178 lbs. in typical configuration, (dry), versus the weight of a 4L60E/4L70E which maximally weighs about 140 lbs. Your best bet towards visually distinguishing between the 4L60E and the 4L70E is checking the service parts identification sticker if it’s the stock transmission in a GM vehicle. Look for M70, which denotes the 4L70E. Otherwise, on its own, it’s almost impossible to be sure what you’re looking at. They all use the same oil pans and the designations are interchangeable depending on the year and build of the transmission.

Between the 4L60E and the 4L70E, the biggest difference is time. The 4L70E is a straight upgrade to the 4L60E, appearing on the market several years after the 4L60E has had time to shine. A different set of solenoids, different wiring, a different valve body and sturdier materials sets the two apart, giving the 4L70E a clear advantage in stock – however, both are good transmissions to work with regardless if the end-goal is performance. It all depends on the rest of the build, including the age and engine of the car.

The 4L65E transmission is built for Chevrolet, as an improved iteration of the 4L60E, and a successor to the 700R4. Unlike its predecessors, the 4L60E and later 4L65E is an electronic automatic transmission, with a five-pinion gearset, overdrive, and a stock torque limit of about 380 ft.-lbs. torque.

With some elbow grease, the right aftermarket parts and a good deal of experience with GM transmissions, a dedicated and qualified specialist can turn the 4L65E into a workhorse of a transmission, with a total 650 horsepower and matching 650 ft.-lbs. of torque. The 4L65E is ideal for such a high amount of torque, as its five-pinion design, 3-4 clutch and improved hydraulic fluid capacity make it a clear winner over the 4L60E for heavier builds with more required power.

But it takes more than that to justify buying a 4L65E over another transmission, or even figuring out which one you’ve currently got in your own Chevy. From the Turbo-Hydramatic 700R4, to the 4L60E, the 4L65E, and more recent 4L70E, GM has come up with several different ways to refine the design of the old-time classic TH350. However, as similar as these transmissions might be, they each come with different gear ratios, valve bodies, torque converters, and more. Some are interchangeable – others aren’t.

History of the GM 4L65E Transmission

The history of the 4L65E goes as far back as the 1960s, when General Motors introduced the Turbo-Hydramatic 350 as a new and improved automatic transmission, a successor to the Powerglide. The TH350 could be found under the hood in most GM trucks and rear-wheel drive cars up until the mid-80s, due to its reliability, sturdy build, and compact size.

While small at under 22 inches in length and roughly 120lbs in weight, it was a transmission that at the time packed enough of a punch to drive a Jeep. Typically produced without a torque controller until the TH350-C in ’79, the transmission was eventually succeeded by GM’s 700R4.

The 700R4 made the leap into the four-speed automatic transmission market, introducing overdrive as a new feature for the more fuel-conscious America of the early 80s and beyond. With fuel prices up and the automobile still in hot demand, the 700R4 allowed GM vehicles to ride more efficiently, while incorporating many of the features that made the TH350 so great, including durability and power.

While still being a non-electronic transmission, access to overdrive and general better fuel efficiency allowed the 700R4 to help GM meet stricter emission guidelines, and help save customers money on fuel costs. To this day, aftermarket modifications allow the 700R4 to act as a premium stock transmission to modify and stick into big block racing vehicles without electronic controls.

Designated as a 4L60 in the early 90s (after its 4 speeds, longitudinal positioning and 6000 lbs. GVW), the 700R4 was eventually succeeded by the 4L60E in 1997, GM’s first automatic overdrive transmission with electronic controls. Sporting the same length, weight and overall bellhousing, the main difference between the two was the introduction of electronic controls, and an adapted valve body and actuation system to accompany the new solenoids and actuators.

Different versions of the 4L60E hit the market over the course of its lifetime, differentiated through their tail housing, and presence or lack of removable bellhousing. Due to a change in solenoids and a six-bolt tail shaft, 4L60E transmissions built after 1996 are incompatible and non-interchangeable with older models.

Finally, a stronger updated version of the 4L60E was introduced in 2001 with a five-pinion planetary carrier and improved input shaft. Also sporting a different torque controller, the 4L65E comes with a hardened sun shell and has an overall better potential as a big block performance transmission due to its planetary carrier.

Specs on the 4L65E

Sporting a five-pinion planetary carrier, a 300mm input shaft over the 4L60E’s 298mm input shaft, and a better 3-4 clutch, the 4L65E comes with the following gear ratios:

• 1st gear: 3. 06
• 2nd gear: 1.62
• 3rd gear: 1
• 4th gear: 0.69

Ultimately, the upper limit for the 4L65E even with a lot of tender, loving care is 700hp – anything beyond that is better off swapping for a 4L85E, which although much stronger, is also pricier and more power-hungry.

What Sets the 4L65E Transmission Apart?

Identifying a 4L65E from other similar transmissions, such as the 4L60/700R4 and the 4L60E, takes a little practice and know-how. Despite a thicker input shaft and a different sun shell, identifying the 4L65E without opening it up requires knowledge of the alternate designations for the transmissions (M30 for the 4L60E, M32 for the 4L65E), and a few key cosmetic differences.

Older 4L60E transmissions come with a four-bolt tail housing, versus the 4L65E’s six-bolt. However, some later 4L60E transmissions also came with a six-bolt tail housing, as well as a removable bellhousing. Performance versions of the 4L60E are sometimes also designated with M32.

Ultimately, your best bet towards identifying a 4L65E is to bring it to a shop. You can check transmission codes, designations and even try and gauge the difference between input shafts, but the key differences are only visible inside the transmission.

Pushing the Limits

The beautiful thing about aftermarket parts is that even a transmission that operates on a mediocre level performance-wise can be brought up to spec with a full redo. When it comes to a custom-built 4L65E transmission, there’s a lot that can be done – from completely replacing and improving the torque converter, to installing new vanes, pump rings, thrust washers, bearings and solenoids.

Replace the input shaft, outfit the tranny with a completely revamped electronic control system and speed sensor, a custom shift kit, better cooler to prevent overheating under pressure and extra capacity pan for up to 14 quarts of transmission fluid, and you’ve got yourself a completely different piece of equipment.

Ultimately, choosing the right transmission for your car – and choosing the right set of custom modifications to said transmission – is a job in and of itself. You must consider the size and traction of your tires, the power your engine develops, the exact purpose of the car and the kind of performance you’re looking for, etc.

In some respects, a 4L60E might beat out a 4L65E simply because it happened to be what your car came with, or because you got a much better deal for it from the boneyard. Choosing between the two is a matter of circumstance, and budget. If you don’t need the extra power afforded by an extra pinion, jumping to a 4L65E might not be worth it. On the other hand, a heavier build seeking more torque and horsepower would do better with something stronger.

If you are looking for a way to upgrade your classic muscle car’s Powerglide or TH350, then you would be hard-pressed to find a better answer than the 700R4, or the 200-4R. Yet while the 700R4 is often seen as the more popular successor to the throne of the TH350, the 700R4 is not going to squeeze into every build, not is it necessarily the best fit for your car – especially if you are going forward with a lot of aftermarket work in mind.

If you are looking for an upgrade to your old muscle car and want something that both packs a punch and substantially improves your fuel efficiency, then the 200-4R is the right place to start. Its bellhousing, drive shaft, and mechanical speedometer make it a superior fit for vintage cars, and its sturdier build and better torque capacity make it the better non-electronic 4-speed overdrive transmission for classic GM performance builds.

It is not very costly, can still be found scrap/salvage yards and in junk shops, and is reasonably affordable. And remember, if you snag yourself a late-model 200-4R from one of the more recent productions, it will handily outdo the stock 700R4 found in older vehicles.

It is by no means a perfect transmission and the 700R4 will typically outdo it, and even if you pick up a newer stock version from the wrecking yard at a bargain you will still have some ways to go to making it race-worthy, but a little magic and some elbow grease will turn the 200-4R into your personal holy grail of power and fuel efficiency.

History of the GM 200-4R Transmission

The 200-4R was a continuation of the Turbo Hydramatic line of GM transmissions, specifically being the successor of the TH200, a light-duty TH350 designed to improve fuel efficiency in the face of the oil embargo of 1973.

Years later, in 1981, the TH200 was replaced by the newly-introduced 200-4R, a 4-speed automatic overdrive transmission used in high-power GM trucks and cars, including the Buick Grand National and Pontiac Firebird Trans-Am. The 200-4R can be found in various GM B-body vehicles, C-body vehicles, G-body vehicles, and D-body vehicles.

Similar in build to the TH350, the 200-4R proved to be a great update to the outdated 3-speed transmission in builds where an overdrive gear was a must. Eventually, in 1990, the 200-4R was phased out for the 700R4, and later iterations of the same transmission including the 4L60 and 4L60-E.

Rundown on the Numbers

The 200-4R is a 4-speed automatic overdrive transmission by GM, capable of fitting into most Chevy’s from the 80s and before, built similarly to the TH200 and TH350, as well as the 2-speed Powerglide transmission. Build with a torque converter lock, a 27-spline input/output shaft, 11-quart fuel capacity, a case length of about 27” and a width of about 19”, and an aluminum outer casing, its torque capacity outdoes even the reliable 700R4 of the time. Its gear ratios are:

• 1st gear: 2.74
• 2nd gear: 1.57
• 3rd gear: 1
• 4th gear: .67

The 200-4R uses a throttle valve cable, which can be replaced based on the exact specifications and compatibility of your car. A mismatched throttle valve cable can wear the transmission out faster, so make sure your cable matches your car’s throttle bracket and carburetor.

Telling a 700R4 apart from the 200-4R is thankfully quite easy, and doesn’t require you to look under the hood. The 200-4R comes with a unique-looking 16-bolt transmission pan, much like the 700R4 and 4L60 but completely different in design. The pans on the 700R4 and 4L60 are square, whereas the 200-4R tapers off on one side. The TH350, on the other hand, looks much like the 200-4R but comes with only 13 bolts.

Because of the similarities in both the size and design of the 200-4R and the TH350, the 200-4R offers a much simpler update to a 4-speed overdrive transmission in your older car than the 700R4 does.

Why Choose the 200-4R Transmission?

The primary reason for picking a 200-4R over the 700R4 boils down to what kind of car you have, and what you are building for. The 200-4R comes with better torque capacity and is a much more straightforward fit into cars that originally sported the 3-speed TH350 or 2-speed Powerglide, but its availability and lack of durability vs. the 700R4 means it may not be a good fit for newer vehicles from the time.

The gearing on the 200-4R is also much more similar to that of the TH350, giving it another plus point as the ideal upgrade to 4-speed overdrive on older Chevy’s. For the most part, even the biggest incompatibilities would require very little modification for a bolt-in.

Versus the 700R4, the fourth gear (overdrive) is slightly more aggressive, rotating at about 3% lower RPM and thus making for a more fuel-efficient transmission. Versus later electronic models (such as the 4L60E), the 200-4R is both more affordable and simpler to work with, although concerns around the integrity of the TV cable and difficulties that often arise when trying to adjust it are always factors to take into consideration.

Of course, there are plenty of reasons to admire and pick the 700R4 over the 200-4R – if the circumstances are right. There is no definitive answer – it always depends on what you have got on-hand, and what you are aiming to accomplish. Even if the 700R4 happens to be a slightly better fit for you, you might end up saving more if you find a late-model 200-4R for a better bargain.

Modernizing the 200-4R for Better, Higher Performance

As good as a transmission can be in its pure and intended form, nothing beats what a custom build can get you. And with the right aftermarket parts and some effort from a GM transmission expert, the 200-4R can go from being an aluminum transmission straight out of the 80s, into being a 21st-century powerhouse for performance-oriented muscle cars, complete with a reliable overdrive and heavy-duty materials.

When power becomes a necessity, a customized 200-4R transmission with the appropriate torque converter can hit over 700hp and 675 ft.-lbs. torque, coming in complete with the works, from a high-capacity 30,000 GVW transmission cooler, hardened input shaft, stator shaft and bearings and rings, to a high-capacity pump assembly, 10-clutch direct drum assembly, brand new transmission pan and much more.

When adjusted with proper gear ratios and a set of the right aftermarket parts, the 4L60E can be just the high performance transmission you’re looking for.

Transmissions ultimately determine how the output of an engine’s power is translated throughout the rest of the vehicle. A transmission is built to prioritize – and there are plenty of things to prioritize. Do we need speed? Power? Efficiency? Weight? Cost-effectiveness? Throughout the decades, automobile companies have come up with increasingly fine-tuned and advanced examples of this, working off older concepts and introducing new ones along the way, such as electronic control and fine-tuning.

But when it comes to matching cost with performance on a Chevy, you can’t go wrong with an older, customized transmission. While there’s nothing wrong with refurbishing a classic muscle car with a new and improved Turbo 350, you’re more likely going to see cars from the 90s and beyond outfitted with the more modern set of 4L60s and 4L60Es – four-speed automatic transmissions that are basically descendants of the Turbo-Hydramatic 700R4, a powerhouse of a transmission.

The 4L60E is an automatic transmission with electronic control (E), 4 forward gears (and 1 reverse), longitudinal rear-wheel drive, and a 6,000 lbs. maximum gross vehicle weight limit.

Yet the 4L60E isn’t the only transmission of its kind produced by GM at the time. It began as the non-electronic 4L60, installed in most GM trucks (like the Pontiac) before the introduction of the 4L60E, and other transmissions include its successors the 4L65E and 4L70E for large heavy-duty trucks, and stronger transmissions built with different gear ratios for even larger vehicles, such as the 4L80E.

Why the 4L60E Transmission?

The 4L60E transmission remains a common choice for many Chevy enthusiasts looking for a stock transmission to begin with when working on a performance-friendly car. Its main advantage above other transmissions includes the inclusion of digital interfacing and control over the 700R4’s TV cable (which was often a fault rather than an advantage of any kind), and the fact that it’s generally cheaper at stock than a 4L80E or lower, yet still more than enough for any competent transmission expert to turn into a performance-friendly powerhouse.

Take someone experienced, and the 4L60E can easily become the ideal starting transmission to work on a Chevy drag racer.

Choosing the right 4L60E is the most important bit. The latest versions of the 4L60E are built with the modern LS GM engine family in mind, which was introduced in 1998 more than five years after the introduction of the 4L60E. They also come with a larger 300mm torque converter, much thicker than what was previously installed on older 4L60Es. This update, and the fact that the 4L60E was such a common transmission at the time (and continues to be a favorable tranny for LS engines), means that regardless of if your performance car comes with an LS engine or if you’re installing the engine block in a classic muscle car for modern-day performance, you’re most likely going to be working with a 4L60E as well.

Aside from the latest version, which is recommended for newer vehicles, try and match your car to the ideal iteration of the 4L60E. Differences in the bellhousing and torque converter are the most obvious ways to tell them apart: the first 4L60Es came with their integrated bellhousing, and the 1996-1999 versions featured removable bellhousing.

Taking the 4L60E Into the 21st Century Performance World

The main hiccup on the 4L60E is its gear ratios – 3.06 in first and 1.62 in second, which meant you were getting a massive amount of torque in first gear, before dropping down to about half that power in second. Third gear, of course, is at 1:1, and the fourth is reserved for overdrive. The 4L80E on the other hand features 2.48 in first and 1.48 in second, with a 440 lb.-ft. torque rating in stock vs. the 4L60Es 380 lb.-ft. torque rating.

But we’re using the 4L60E here, not the power-robbing 4L80E, and adapting the gear ratios to be more efficient for performance is key when optimizing a transmission.

By changing the 4L60Es gear ratios to match a rear axle ratio of 3.73:1, with a 2.84 first and 1.55 second, you get a final drive ratio relatively close to 10:1 at first (specifically 10.59:1). Doing so means switching to a six-pinion planet over a four-pinion (or the five-pinion used in the 4L65E) – together with a few other aftermarket parts, you can easily turn this roughly 380 lb.-ft. torque, 400± HP transmission into a tranny capable of putting in work on Chevy cars with well over 700 horsepower.

Kitting out a 4L60E to the max means completely changing the transmission, installing new shift, EPC, PWM and control solenoids, a new transmission pan, a new gear set, new bearings, a 13-vane pump assembly, hardened stator shaft and rings, a brand-new cooler, and much, much more.

Knowing Your Gear Ratios

Gear ratios refer to the ratio between two perspective gears. When calculating performance, you must consider your car’s rear axle gear ratio (often ideally set to 4.10:1), and the gear ratio for your transmissions drives. Different ratios produce different outcomes. Other things to consider include tire diameter (larger tires take longer to turn, to put it simply), sticky tires (traction improves overall performance) and terrain.

Ideally, you’ll want a final drive gear ratio of about 10:1 in first gear. The 4L80E’s 2.48, when multiplied to the rear axle ratio of 4.10:1, yields a close 10.16:1 – whereas the 4L60E’s gear ratios are harder to work with, even with another rear axle ratio like 3.73:1. Changing the gear ratio can improve the car’s performance, yield better engine rpm, make more efficient use of the engine’s output and ultimately improve speed – which, in the end, is exactly what you want.

Geared for Performance

When adjusted with proper gear ratios and a set of the right aftermarket parts, the 4L60E can be just the transmission you’re looking for. However, straight out of the box, it’s hard to argue for it vs. the more efficient, yet typically costlier 4L80E.

Both transmissions have their pros and cons, and have different jobs. The 4L80E is built to drive massive heavy-duty trucks – the 4L60E can make itself a cozy home in classic Chevy muscle hot rods and modern engines alike. The key lies in building it just right for your own car – and that’s where the experts come in. The right transmission needs the right car and engine. Creating a car suited for performance is all about optimizing mechanical relationships, and finding harmony in it.

The 4R70W is a Ford transmission, and generally considered an evolution to the AODE, a transmission that it is often interchanged with. Both are improvements on the AOD, Ford’s first 4-speed automatic overdrive transmission, and its answer to the fuel efficiency issues first brought to light in America by the oil embargo of the 70s.

Since then, improvements in technology and stringent regulations improving fuel efficiency and air quality have demanded better and better transmissions, while still providing opportunities for top notch performance, even if only through a few modifications.

No stock transmission is perfect, but if you’re looking for a small-body Ford transmission with potential for insane performance and no need to mess with pesky throttle valve cables or old-school controls, then the 4R70W is a good place to start – but by no means the best place to end. Here’s a quick overview of the 4R70W, it’s relationship to other popular Ford transmissions, and a few things you should know about it, including its basic strengths, glaring weaknesses, and ways to improve on it and make it both more reliable and better for performance.

Quick Overview of Ford 4R70W Transmissons

It was around the 70s that automobile manufacturers started coming out with better, more fuel-efficient cars. These sacrificed some of the performance and speed of the gas-guzzling large-displacement carbureted V8 models of the past, in exchange for the ability to go long and fast at a much lower cost. While overdrive and general fuel economy were considerations for decades before the oil embargo, it was the steep increase in gas prices introduced by that decade that drove a change into American car manufacturing. It was around then that Ford first produced the AOD, its 4-speed automatic overdrive transmission, in 1980.

The AOD was new, for sure, but mostly incorporated old designs. It didn’t change much from the FMX 3-speed automatics, save for a direct overdrive, and still used the Ravigneaux gear train and other common FMX components. It’s dependable and sturdy due to the inclusion of many of these true-and-tried components, but it’s the additions that make the AOD a liability. With a rather frail overdrive band lacking in proper width, it’s not uncommon for it to wear down quickly versus its newer alternatives.

In comes the AODE. This was Ford’s improvement on the AOD, complete with a new valve body and computer controls to replace the classic throttle valve function and AOD valve body. The AODE was introduced in 1991, known simply as the AOD Electronic Control. It featured a completely revamped valve body, torque controller, front pump assembly, and a single input shaft rather than the primary and intermediate shafts of the AOD.

Specs on the 4R70W

By 1993, an updated version of the AODE hit the market with a different name, although these two transmissions are mostly interchangeable. The 4R70W comes with:

• 4 forward speeds
• Rear-wheel drive
• 700 lb.-ft torque rating
• Wide gear ratio

Here are the gear ratios for the 4R70W, in comparison to the AOD (in parenthesis):

• 1st gear: 2.84 (2.40)
• 2nd gear: 1.55 (1.47)
• 3rd gear: 1:1 (1:1)
• 4th gear: 0.70 (0.67)

The valve bodies and cases of the AOD, AODE and 4R70W are all different enough to warrant specificity – while you can take the gear train of the AOD and shove it into an AODE, you can’t switch their valve bodies.

So, Which Is Better?

While the 4R70W is unquestionably better than its predecessors in many ways, that doesn’t always mean it’s the best option for you at the time. If you already have a stock AOD to begin with, there’s a lot you can do with some spare cash without having to invest in a completely new electronic transmission. While the 4R70W can be adapted even to older classic muscle cars, it does take a bit of work and a bit more cash than updating and reworking your stock AOD.

The same goes for cars with the AODE in the 90s. The only time you might want to switch for the 4R70W is if you can afford it, and if you need the improvements.

Better Overdrive, Computer Control

The main benefits of the AODE and 4R70W over their older version is the inclusion of a sturdier, wider overdrive band, better front pump, a solid input shaft, a switch from split-torque overdrive lock-up to the use of a locking torque converter, and finally, much improved pinpoint precision and control through computer-controlled components versus the oft clunky manual control given by a throttle valve function.

Despite a thicker and improved valve body, the electronic AODs also come with a lighter case, built with aluminum rather than steel, improving weight and thus performance and fuel efficiency.

The Good, the Bad and the Ugly

The 4R70W is a good transmission, but it has its pros and cons. Let’s look over some of its best qualities, and some of its faults and issues.

For one, it has a much better and improved overdrive band. Despite being a newer transmission and having a completely different case, the 4R70W is still compatible with a vast number of Ford vehicles without too much reworking or adaptation. You can easily retrofit it into many classic muscle cars, giving older vehicles a much-needed boost in both efficiency and performance.

However, as powerful as it is, be careful not to overload this transmission. There’s a limit to its torque and power, and knowing exactly what it can and can’t do is the difference between an overheated transmission and one that will last you for decades. That, and as with any other transmission, you still need to maintain it regularly.

A Diamond in the Rough

Still, for all its merits and the improvements made upon the 4R70W after decades spent on feedback from the AOD and AODE, there are still flaws in the transmission that must be addressed through aftermarket improvements.

A specialist in Ford transmissions can set you up with an improved 4R70W, with as much as 750hp, an improved torque controller, a much-needed improved cooler with a better GVW of 30,000, and countless reinforcements to improve durability, maximize performance in the long-run, and prevent some of the faults that eventually lead to complete transmission breakdowns in the future. Examples include an improved carbon fiber overdrive band, new pump assembly, higher capacity clutch, updated solenoids for better electronic functionality, and more.

Be sure to only work with specialists who guarantee the quality of their transmission, and do their best to test the integrity of their work every time.

There’s no doubting the air of Americana around a classic 50s-70s GM ride. In the golden age of American automobile manufacturing, we turned building cars into an art form, and ever since it’s been an intrinsic part of our culture – but even in today’s age of hybrid vehicles, electric cars and fuel-efficient family minivans, anyone with the keys to a classic GM ride knows that there’s nothing that quite compares to riding behind the wheel of one of Detroit’s best.

However, there are also few cars that compare when it comes to sheer fuel consumption. The 50s weren’t exactly known for extreme frugality, and fuel economy wasn’t on the mind of the average American automotive owner. Instead, we focused on speed, on style, performance.

But then the oil crisis kicked in, and car owners quickly realized that they’d have to account for a steep increase in fuel prices. The result? We needed a new approach to fuel consumption, one that would emphasize a more frugal cruise. That’s where the popularity of overdrive came into play.

How Overdrive Works in an Automatic Transmission

Overdrive is when the car’s cruising speeds are maintained while the engine’s RPM are reduced, leading to better fuel efficiency at the cost of performance, or speed. This is done through a faster output speed than input speed, through a specific gear set. This allows you to travel long distances with a much lower fuel cost, and various different automatic transmissions offer different levels of fuel efficiency.

By “over-gearing” and sacrificing the car’s top-speed at that point in time for a lower RPM, you end up burning less fuel while maintaining cruising speed on a flat road. This can’t typically be done on rough or uphill terrain, as the car loses power in overdrive.

Typically, when achieving top speed, a car needs to continuously produce more power to match the increase in air resistance produced by an increase in speed. The ideal gear ratio for speed is the one that matches travel speed with engine speed. But when fuel efficiency becomes the goal, another set of gears is needed to reduce engine RPM but maintain cruising speeds. This, in essence, is the overdrive.

Evolution of the Automatic Overdrive Transmission

Overdrive transmissions in North America were an option in pre-automatic transmissions as far back as the 50s, but it wasn’t until the corporate average fuel economy legislation in 1975 that basically every single American transmission was built to include overdrive.

If you’re planning on riding your classic GM, then an automatic overdrive transmission (AOD) is a basic necessity unless you like watching your tank evaporate like a puddle on a blazing hot day.

Choosing the Right Overdrive Swap for Your GM

When the oil crisis called for new transmissions with a focus on fuel efficiency and compatibility with most of the existing vehicles on the market, GM and other car manufacturers got to work on implementing the overdrive. Throughout the 80s and beyond, automatic overdrive transmissions became a norm on most GM vehicles, from classic Chevy pickup trucks to muscle cars.

Choosing among GM’s selection of overdrive transmissions from back in the day is a matter of two things: compatibility and expectations. Stock automatic transmissions are only built to handle a certain amount of torque and horsepower, and trying to push one beyond its limits is a surefire way to slipping gears, burning through your overdrive and making a mess of things. Here are a few good GM AODs, and some things to keep in mind when choosing among them.

700R4

The 700R4 is widely considered the best 4-speed automatic overdrive transmission out there, and can be seen as one of GM’s best and most reliable AOD transmissions. It first hit the road in the early 80s as a replacement to the TH350 (Turbo-Hydramatic), although this early version doesn’t compare to later 700R4s typically installed in Chevy vehicles before 1993, when it was replaced with the electronic 4L60E.

While it’s a solid transmission, it can be easily tweaked and built for better performance and much better durability. Some issues commonly found in the 700R4 include its often faulty or frail TV cable, and a tendency to overheat. A better cooler, a torque controller and a few aftermarket bits and pieces can turn this into an extremely solid piece of engineering.

200-4R

The 200 4R is possibly the ideal transmission for early GM vehicles, due to compatibility and a comparable strength to the 700R4. Seriously, this thing will bolt in nearly every Chevy chassis on the market, with very little necessary modification.

Like with the 700R4, a TCI kit or a custom job by any trusted transmission expert can make this tranny run much better, with a repositioned TV cable and torque controller being some minimum additions to consider. However, with heavier modifications, you can take this thing even further.

4L60E, 4L65E, 4L80E & 4L85E

GM’s later overdrive transmissions included the 4L60E, 4L65E, 4L70E, 4L80E and 4L85E. Each of these were a continuation of the Turbo 400 and Turbo 700R4, built for rear-wheel high performance. The differences largely lie between the 4L60E and the 4L80E.

Key differences are size and performance. It wouldn’t make much sense to stick a 4L80E into anything smaller than a Chevy truck, especially with the considerable price difference between these two transmissions.

However, if you’re going with a stock 4L60E but have a vehicle capable of going pas 300 horsepower, you’re liable to see that tranny break. A custom 4L60E will get the job done, as will a stock 4L80E.

These are electronic overdrive transmissions, which makes them trickier to install in older vehicles, but not impossible. The alternative is to opt for the older 4L60 transmission, which is not as powerful, but doesn’t include electronic shift controls. That may be more up your alley if you prefer manual shift, too.

Overdrive Transmission Install

If you’ve got the equipment and the experience, then installing a new transmission is just a matter of getting all the right bits and pieces. For that, the Internet is an amazing source of aftermarket parts, reviews and more. But if you’re looking for someone to get the job done for you, you’ll need a more experienced crew.

Instead of a stock overdrive transmission installed straight into your ride, consider a stronger, performance-based custom tranny. Some select performance transmission experts have the skill and the reputation to work on some of GM’s finest old-school AODs, and turn an old stock transmission into a power house ready to put in work on the race track.

The motoring world is full of competition, both on and off the track. If people aren’t competing to be the fastest in speed, they’re competing to bring out the best driving tech possible. That’s why it’s very surprising to some that GM and Ford are both working on 10-speed transmissions, which will make a huge difference to modern luxury cars.

When Competition Meets Collaboration

Although this news may be surprising to some, it’s not the first time that these two companies have worked together. In fact, they collaborated on creating six-speed transmissions just in the last decades. Legally, this is a sound plan. Car companies can collaborate on designing new tech, but when it comes to the manufacturing process, they have to break apart and do this separately. This has led to many companies using the same engines in the past. For example, Mitsubishi, Chrysler and Hyundai all used similar engines in the last decade, after they worked together on designing them.

Why 10-Speed Transmissions?

So, it’s not unusual for companies to work together on new tech. However, many readers will be wondering why they’re even bothering. After all, it sounds like they’re focusing on something that doesn’t really matter, in the grand scheme of things. What will this do for motorists?

A highly tuned transmission can make all the difference to your driving experience. A transmission with more speeds can improve both mileage and performance when done correctly. It doesn’t just rely on the speeds available though, the software controlling it needs to be done well too, in order to help you get the most from your car.

A car with several speeds can be created with some overdrive gears, that are designed to improve fuel performance. These gears will keep the engine running especially slowly, even if the car is driving at speed, such as down the highway.

The art of creating such engines for enhanced speed, without creating the annoying ‘jerking’ feeling that some engines get when you change gears. It’s still to be decided whether GM and Ford can do this together, though.

Alternatives to Multi-Speed Transmissions

Although large advances are being made in creating multi-speed gearboxes, some companies are taking a different approach. For example, companies like Subaru, Honda and Nissan are going a different direction, creating CVTs. These are created with a belt-drive configuration that use variable diameter pulleys. These constantly adjust the ratio to create the correct setting for the driver.

While these are great for some drivers, others don’t enjoy the feeling of gearless driving. Because of this, some developers have programmed in modes that mimic the feel of driving multi-speed cars, or let the driver pick from several different modes. While there are a lot of benefits to CVTs, many drivers still prefer the way multi-speed gearboxes feel to drive.

History of Multi-Speed Transmissions

Of course, this partnership isn’t the first time that a new style of multi-speed gearbox has been created. At time of writing, Chrysler Group are putting nine-speed gearboxes into the Dodge Dart, and the upcoming 2014 Jeep Cherokee. They’re also a pioneer in using eight-speed gear boxes in their line ups, such as in the Ram pickups.

Seven and eight-speeds are actually quite common right now with luxury car brands, so you may already be familiar with them. With 10-speed transmissions being worked on now, we can now expect to see some great leaps forward in how multi-speed gearboxes work.

The Financial Incentives of Co-Creation

GM and Ford say that by developing their new engine together, they can help save the consumer a lot of cash. This is especially true of those who drive smaller cars. With a 10-speed gearbox, the driver will have more control over fuel consumption, meaning they’re spending much less at the gas pumps.

Of course, it’s not just the driver who’s saving money. By choosing the develop this new technology together, GM and Ford are saving themselves potentially millions of dollars in development cash. Of course, whether they pass the savings on to the customer remain to be seen.

Either way, such collaborations offer many benefits to consumers. There’s no word on when the new 10-speed will be made available to the public yet, as it’s still in the planning stages. However, if more companies follow the lead seen here, we could see some new and exciting changes in motoring before long.

They say a car is the sum of its parts – if you take but one piece out, then a well-made racing machine just flat out won’t work. Racing rigs are built for performance and sheer efficiency – there’s nothing superfluous about a car made to go well over a hundred miles per hour.

But some machinery deserves a little more credit for the demanding work a car goes through to attain such speeds, and maintain them. And while every layman focuses on the engine, it’s the transmission where the real magic happens.

A transmission is more than a few gears and an input and output shaft. It’s a complex system of components built with the specificity of an orchestral piece made for the climax of a classic opera performance – ideally, transmissions are made to perform in certain environments and under specific conditions. A race car and a van will have differently built transmissions, and transmissions come as automatic, continuously variable, automated manual, dual-clutch, and more.

That’s why it’s so important to have the right transmission for the job – and if you’re looking for a classic, no-fuss overdrive automatic transmission with four speeds, then a solid choice is to start with a stock 700R4 and go from there.

The reason that’s such great news is because if you’re driving a Chevy (from your uncle’s old pickup to a hot 90s Camaro), chances are you’ve already got a 700R4 sitting pretty in your rig, and working with what you have – one of the finest pieces of GM workmanship in terms of sheer reliability as an AOD – is going to save you the small fortune you might’ve had to spend on a brand-new transmission.

Trust us: you’re not cutting into your car’s potential with a 700R4. In the right hands, you’ve got yourself a serious racing transmission. But it’ll take some surgery to get it there.

Evolution of the GM 700R4 Transmission

Behind every great piece of machinery is a lengthy line of trials and errors, experimentations, innovations and breakthroughs. The 700R4 is no different, and its popularity is owed mostly to the fuel economics of the late 20th century, when gas-guzzling was becoming a heavy hit on many an enthusiast’s wallet.

Unlike many other transmissions at the time, the 700R4 is an automatic overdrive transmission, which means it’s far more fuel-efficient, giving you much more mileage out of a full tank – as much as 30% more. Those savings are only possible through the transmission’s overdrive, which allows a car to basically drop down its engine’s RPM and reduce horsepower needed on flat land while maintaining speed.

The 700R4 was introduced as a replacement to the TH350, built for car and truck platforms. It went through a name change in 1990 as the 4L60, but never actually transitioned from being the same transmission as it always was, until GM ushered in the 4L60E as an electronic replacement to the automatic manual transmission.

The 700R4 is compatible with most Chevrolet 90-degree small block and big block patterned engines, although a different version of the 700R4 exists for 60-degree patterned engines. These aren’t what you’re looking for, and they’re also typically much rarer. The only real difference visually is the front bell

Racing with a stock 700R4 while in overdrive risks the integrity of the O/D band and limits your performance in a drag race, and can ruin the transmission. But a custom built 700R4 is made of sterner stuff, and reduces the lag time introduced by sloppy and sluggish shifts.

700R4 Improvements for High Performance Racing

It may have come out in the 80s, packed into a 1982 Corvette, but the 700R4 is as solid an AOD transmission as you’re going to get even today, all without the need for computer finetuning like more modern transmissions. But it’s still got plenty of flaws, and out of the box (straight from stock), your 700R4 isn’t going to hold a candle to a well-furnished custom.

It takes a little bit of magic and ton of experience (and aftermarket parts), but you can turn a 700R4 into a 650 hp, 600 ft-lbs power house, complete with an upgraded transmission cooler to avoid overheating, a brand-new torque controller, and several hardened and heavy-duty replacement parts, including the casing itself, the O/D ring, stator shaft, new bearings and more.

To turn it this sluggish but reliable piece of GM machinery into a respectable racing transmission, the first step is to address its flaws. And it has quite a few common ones.

Addressing 700R4 Flaws

No transmission is perfect, even if it can be damn reliable, and the 700R4 is no exception – such as the infamous problematic TV cable that frequently needs to be readjusted, or replaced. Most racing and performance transmission suppliers will put the 700R4 under the knife extensively, upgrading this classic piece of GM machinery to match today’s expectations on the track. Here are a few ways for upping the performance on a 700R4 transmission.

Transmission Case

One of the perks of the 700R4 is its light but durable aluminum body. But if you’re pushing past 600 horsepower, you want a little more durability. A reinforced transmission case isn’t always necessary, depending on the kind of installation you’re looking for. In fact, it may be unnecessary unless you’re packing the extra power.

Valve Body

The valve body is an automatic transmission’s brain, and the separation plate is a plate of holes designed to direct the flow of hydraulic fluid, which is meant to facilitate shifting. As good as the 700R4 is, you want an updated valve body separation plate for firmer shifts.

Transmission Cooler

The 700R4 is prone to getting a little hot, so an updated cooler is a must. Overheating is an easy way to destroy your automatic transmission, and if you’re driving your car hard on the track (or driving a pickup off the track, for that matter), getting an aftermarket transmission cooler in there is necessary.

That’s just a few examples. Ultimately, the 700R4 is open to many upgrades depending on exactly what you want it to do. You can replace the oil pan, add a custom torque converter, or replace the stock input and output shafts with sturdier ones (especially if you’re pushing the transmission’s limits).

Custom High Performance 700R4 Transmission Rebuild

The 700R4 is a stock transmission found in most Chevrolet vehicles from back in the day, before the introduction of the 4L60E and its descendants in 1993 and onwards. But if you want to turn your Chevy into something worthy of burning rubber on the dragstrip, you’ll want a custom job.

Making the most of a 700R4 is a matter of not just knowing the transmission inside out, but also knowing what kind of engine it’s going to work with. As mentioned previously, a car is the sum of a whole, that whole must be coherent and harmonic. If you want the best results, then roll up to a shop you trust and talk to their most qualified technician.

There was perhaps nothing more exciting out of the 80’s than the inception and incorporation of overdrive into automatic and manual transmissions. How can anyone forget?

History & Evolution of AOD Transmissions

The 80’s were notorious for implementing overdrive-equipped automatic transmissions as original equipment for new automobiles those years.

Aside from being one of America’s favorite vehicle innovations of its time, overdrive manufacturers involved automatic overdrive (AOD) transmissions as an industry standard to lower emissions and improve fuel economy.

Overdrive as a concept is pretty awesome – typically displayed as a switch or a button, a quick flick or press can reveal what seems like a hidden source of power. By definition, overdrive can be explained as the utilization of a faster transmission shaft speed output than the rotation speeds of the engine’ input shaft. Meaning, the torque is being multiplied or “overdriven”, which creates a smooth and effortless driving experience.

As the 80’s came and went, transmission manufacturers and aftermarket companies heard the cries of overdrive enthusiasts who dreamt of incorporating this same efficiency into their classic vehicles. In the years following, conversion kits and overdrive automatics arrived on the market.

Thanks to these manufacturers and aftermarket companies, converting your classic car or truck to an AOD transmission has been made simple. Conversion kits and packages are now readily available depending on the type of vehicle you are building. You won’t have any problems finding the right parts or conversion packages for your mainstream vehicle. If you’re looking at something a little lower in popularity by numbers, you may have to turn to the skills of a professional fabricator in order to achieve the job.

Whether you consider yourself capable of DIY, or decide to take advantage of the vastness of the Internet in search of an AOD transmission, aftermarket companies offer something for everyone when it comes to converting your automatic transmission to overdrive.

From fully equipped AODs that are engineered for your particular application to stall speeds, torque converters and shift programs, industry providers have all the automotive aftermarket parts and components needed to help make your classic vehicle AOD transmission conversion a transformational success.

If you’re gearing up to make the switch, here’s what’s available aftermarket as well as some helpful, tried and true tips for an effective transition.

What to Look for in an AOD Transmission

When you’re out shopping for your rebuild kit or AOD, you’re going to want to pay special attention to the parts that it contains – even if you are on a tight budget you want to avoid budget parts. You don’t want to run the risk or endure the costs of having to do your project over again when something fails. Your focus should be on high-end steel plates and clutches. Your internal and external seals will depend on the type of driving you intend to do, as well as the anticipated amount of power.

Keep in mind that any automatics that are electronically controlled deserve a fresh set of electrical components from the inside out. Harnesses, switches, and solenoids should all be new. If you choose to go with a reputable transmission builder, ensure that they employ all new electrical components in their build.

When comes to AOD transmissions, you have a limited options. You can find a local shop with a reputable core to accomplish the rebuild, or you can turn to the mass of aftermarket trans rebuilders who can set you up with a warranty, bullet-proof components, solid high-performance automatic overdrive, and more.

If you’re the DIY type of person, tons of shops have a complete line of parts and transmission overhaul kits, which includes everything you need for your AOD rebuild. Your kit will include: seals, bushings, bands, plates, and clutches. While you are at it, it is recommended that you order parts for your front pump (rotors or gears) including the torque converter.

AOD Transmission Installation

As you prepare for your AOD transmission swap, don’t forget about the peripherals. You’re going to need a variety of other items, such as backup light switches and neutral safety, along with sensors. These types of items are not normally included in overdrive transmission packages.

Ensuring your transmission’s functionality and longevity begins with, and lies at, the root of proper installation. The installation of your transmission should involve as much care as the transmission build itself. For example, a poorly built or installed transmission might have issues with the bell housing seating against the engine squarely, or the torque converter seating on the front pump. Thus, to avoid potential pitfalls, both economically and mechanically, be sure to research with due diligence before committing to a transmission installer, builder, and/or rebuilder.

Whatever you decide to do, remember to do your research in purchasing quality parts from reputable manufacturers – so that you get the safe, efficient, and long-lasting classic overdrive conversion you’ve always wanted.