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September 2021

What Is Rear End Gear Ratio and How Is It Calculated?

Rear End Gear Ratio - Gearstar

Rear end gear ratio is boiled down to lower numerical values giving better acceleration, torque, top speeds, and better fuel economy.

The first time you wade into the gears’ universe, you will encounter several terms such as gear ratio, rear end, gear systems or ‘trains,’ etc. Knowing how to calculate the rear end gear ratio to choose the right one is not a must but an advantage, and this is because you can find the gear ratio in the product description.

However, if you understand precisely how it works, your choice becomes much more calculated. Let this article serve as a guide or flashlight into this universe, and you will never get lost.

Let’s get started with the basics, shall we?

What is a Rear End Gear Ratio?

Most automobiles use gear ratios in the drive axle and the transmission to multiply power. When you multiply the two ratios, it equals the final drive ratio.

When you hear car drivers refer to numbers – such as 3.08:1, 3.73:1, or even 4.10:1 – they discuss the ring-and-pinion gears’ ratio within the rear axle. This ratio refers to the number of teeth on the ring – i.e., driven gear – divided by the number of teeth on the pinion – i.e., the drive gear.

Therefore, this implies that a ring gear with 41 teeth and a pinion with ten teeth results in 4.10:1. In other words, for every single turn of the ring gear, the pinion rotates 4.10 times. The rear end gear ratio has to do with the relationship between the pinion gear and the ring gear. 

But is there a chance that the system may incorporate more than two elements? Yes, the intermediate gears are known as ‘idlers.’ They can be used to keep – or change – the direction of rotation.

You can easily apply the gear ratio formula to every pair of wheels, but the truth is that you do not have to do so. Regardless of how many idlers there are within the train, the final gear ratio is between the ‘driver’ and the ‘driven’ wheel.

How Gears Work

The wheel was first invented before the gear came into play. Gears became functional for any of the following reasons:

  • To accurately reverse the direction of rotation
  • To decrease or increase the rotation speed
  • To synchronize the rotation and keep it that way
  • To change the rotational motion to a different axis

Although gear systems came into play as far back as four ages BC in China, many still believe that the first invention could be much older. Gear systems have developed over the centuries and are readily divided into dynasties.

The primary purpose of rear end gears is to multiply the torque the engine and transmission delivers. If you think of gears as complex mechanical levers, you won’t be far off the mark. This is because gears provide mechanical advantages that swiftly multiply torque in order to assist the engine’s power in moving the automobile.

Therefore, high gears are thought of as short mechanical levers that provide less mechanical advantage, while low gears are just like longer levers with more mechanical advantage.

Calculating the torque multiplication that your axle gears provide is quite easy. You can do this by multiplying by the gear ratio. For instance, if both the engine and transmission deliver up to 100 ft./lbs. of torque to the pinion gear and the gear ratio of the ring-and-pinion is say 4.12:1, the output torque is 412 ft./lbs. i.e. 100 x 4.12.

In the same vein, if the gear ratio is 3.04:1, the output torque will be 304 ft./lbs. As you can see, the lower 4.12:1 gears invest more power to the ground than the higher 3.04:1 gears.

Note that no changes occur in the engine’s power, though the available torque to the tires has done so.

How to Calculate Gear Ratio

The first gear that is attached to the motor shaft is known as the ‘drive’. But the ‘driven’ gear is the one that is attached to the load shaft gear.

In order to calculate the gear ratio, you need to do the following:

  1. First of all, get each part and count the number of teeth they have. Let’s say the small drive has up to 21 teeth while the driven gear has 28 teeth. Bear in mind that when experts discuss spur types, the one with more teeth is referred to as the ‘gear’ while the other one with fewer teeth is called the ‘pinion.’
  2. Divide the number of the driven gear teeth by the number of the drive gear teeth. In this example, it is 28/21 or 4:3. 

This gear ratio indicates that the smaller ‘driver’ gear must rotate or turn up to 1.3 times to get the much larger ‘driven’ to make just one complete turn.

Take note that a high numerical gear ratio is referred to as a ‘low gear.’ But a low numerical gear ratio is called a ‘high gear.’ Low gears engender fast acceleration and are highly appropriate for smaller engines.

However, high gears cause higher top speeds and better cruising and are suitable for more powerful engines.

You should heavily consider the following factors – which can affect the gear ratio – before changing the existing rear end gear ratio:

  • Tire diameter
  • Transmission type as well as individual gear ratios
  • Torque converter stall speeds (automatic), etc.

This is why it is highly essential to learn how to choose the right gear ratio for your drag racer or muscle car. 

What Do ‘Short Gear’ and ‘Tall Gear’ Mean?

The terms’ short gear’ and ‘tall gear’ can be somewhat misleading; this is why clarifying them is important.

A ‘tall gear’ gives you much better-cruising speed as well as fuel economy, while a ‘short gear’ always gives you excellent acceleration but at the cost of efficiency and cruising speed.

The Advantages That Geared Transmissions Offer

The geared transmission offers several advantages compared to other forms or types of transmission. 

First of all, a geared transmission provides incredibly high performance when efficiently transmitting motions and forces along with high reliability and extended service life.

However, what makes geared transmissions stand out from others is the astonishing accuracy of their gear ratio. This means that they can easily be utilized in precision machinery since gear ratios in geared transmissions are incredibly precise.

Moreover, unlike mechanisms – such as pulleys or chains – the size of geared transmissions is small. This makes it easy to install them in large and small machines and spaces and places that are somewhat difficult to access readily.

Finally, their maintenance is not complex in any way, and this is why geared transmissions remain one of the most prevalent systems within the automotive – and other – industries today.


Learning gearing lingo is important, especially if you want to know more about rear end gear ratios and how it calculated, how gear ratios affect mileage and acceleration, etc.

Rear end gear ratios can be boiled down to one statement: higher ratios – i.e., with lower numerical value – give better acceleration/torque and lower ratios yield to better fuel economy and higher top speeds.

An Overview of The GM Turbo 350 Performance Transmission

Turbo 350 Transmission - Gearstar

Many experts consider the Turbo 350 Transmission perfect for light trucks, rally races, and entry-level sports vehicles. What makes this transmission unique is its tough parts and high performance, which give it the capacity to tackle several use cases.

Gearstar innovatively produces level two, three, and four automatic transmissions heavily backed by a full warranty.


The Turbo 350 Transmission – better known as the Hydramatic 350 – is a 3-speed automatic that debuted as a joint Chevrolet/Buick project in 1969. The primary objective of this project was to replace the Super Turbine 300 2-speed Powerglide automatic.

The project also spawned several transmissions, including the 250, 250c, 350c, and 375b GM transmissions.

Identifying the GM Turbo 350 Performance Transmission

When General Motors introduced the Turbo 350 to the world, the latter was encased in a one-piece aluminum alloy housing unit. This unit measures 21.75 inches long and is comparatively light as it weighs up to 120 lbs.

It comes with a custom-made oil pan that fits in perfectly, as well as a chamfer at the rear passenger side. You can find the modulator by looking at the back of the case.

General Motors installed a lock-up torque converter in vehicles made from 1979 to 1984. This converter utilized electronic converters to make the vehicle and transmission much more fuel-efficient, especially when moving at highway speeds.

Drivers can identify the lock-up converter via an electrical plug on the driver’s side of the transmission. A plug on the left side shows you have a 350-C on your hands. Adding aftermarket conversions to these transmissions can still be worthwhile today, with up to 10 percent more fuel efficiency.

Turbo 350 Performance Transmission: Specs

General Motors introduced the Turbo 350 Transmission to conveniently replace the highly revered Powerglide 2-speed automatics in the 1960s. The following are the gear ratios the Turbo 350 features:

  • First gear: 2.52 to 1
  • Second gear: 1.52 to 1
  • Third gear: direct drive, i.e., 1.0 to 1
  • Reverse: 2.07 to 1

The Turbo 350 has no overdrive gear available.

On the contrary, the Powerglide came with the following gear ratios:

  • First: 1.82-to-1 /1.76-to-1
  • Second: 1.00-to-1

The Turbo 350 powers classic American muscle and its venerable specifications are as follows:

  • Level 2, Level 3, and Level 4 performance
  • The ability to take on as much as 700 horsepower
  • The capacity to control as much as 400 lb-ft. of torque

The power of your classic American muscle determines the horsepower you need, as much better engines will require a minimum Level 3 transmission. Due to considerable modifications, the particular transmission that handles your build with strong parts and high-quality build is always available.

The Turbo 350 shares several components – including the torque converter – with the Buick Super Turbine Powerglide and the Turbo 400. This transmission remained in production for up to 15 years until it was fully replaced in 1984 by the 700R4.

In 1980, the lockup torque converter was added but pulled four years later because of its downshifting and inconsistent acceleration.

The Turbo 350 Transmission: Construction and Size

The Turbo 350 Transmission is a single-piece transmission with a bell housing perfectly integrated into the transmission body. The entire transmission casing is made of cast aluminum.

The Turbo 350 is renowned for its short length, making it one of the lightest transmissions ever made. It takes up to 4 quarts in a pan and may require a little extra based on the torque converter in action.

When combined with a 9.5-inch converter, the overall requirement is about 10 quarts.

The additional gear the Turbo 350 came with made a no-brainer choice compared to its predecessor. This is why it is widely employed in nearly all rear-wheel vehicles – from General Motors – at the time.

Its strength, compactness, and versatility have made many vintage or classic car owners retain the transmission’s use to this day. Most vintage cars sold today also come with this powerful transmission, with minor alterations.

Turbo 350 Transmission: Benefits

The Turbo 350 empowers every driver to take their hobbies to a higher level. Only a few drivers are privileged to start their journey with the best available vehicle or the most horsepower.

If you are very new to the sport or looking to power your daily driver conveniently, the Turbo 350 is an excellent option.

The most profound benefit that the Turbo 350 brought to the table was its extra gear, one up from its predecessor. This transmission is also compact, strong, and versatile.

The Turbo 350 only had one notable weakness: the wobbling of the direct clutch drum.

Most Common Uses of the Turbo 350 Transmission

The Turbo 350 Transmission found excellent use in Pontiac Firebirds, GMC trucks, Chevrolet Camaros, Monte Carlo, and the Caprice. This transmission remarkably matches GM automobiles with small-block V-8s as well as the small Iron Duke 4-cylinder models, the block-block 396 V-8s, and V-6s.

The BOP (Buick, Oldsmobile, and Pontiac) is an offshoot version of the standard Turbo 350 that works with the Pontiac V8. You can easily differentiate one from the other by looking at the block flange. The BOP version comes with a valley, while the Chevrolet model showcases a peak.

General Motors also created several derivatives of the Turbo 350, including lock-up torque converter models with the smaller TH375, TH 250, and TH20.


The Turbo 350 Transmission works remarkably well with many modestly powered vehicles. It was versatile in the 1960s since it had no fixed center support and could be used in several experimental vehicles.

Even though the Turbo 350  is no longer in production, it is still employed by several classic vehicle builds. It comes with extra gear, which gives it a significant advantage over its predecessor.

The Turbo 350 Transmission is also versatile, strong, and compact. During its time, its overall strength and versatility made it popularly used in many rear-wheel automobiles from General Motors. It is still in use in several vintage or classic vehicles today.

5 Symptoms of a Bad Coolant Temperature Sensor

Coolant Temperature Sensor - Gearstar

A coolant temperature sensor remains one of the most vital engine management sensors. Learn why and symptoms of a bad sensor.

The coolant temperature switch – otherwise known as the coolant temperature sensor – is primarily responsible for monitoring the engine coolant’s temperature. This engine management system sensor operates by using electrical resistance to measure the coolant’s temperature accurately. 

The signal generated is automatically transmitted to the computer so that necessary changes can be made. This includes changing the engine’s timing as well as the fuel calculations for premium performance. Most automobile engines require more fuel when they are cold but require less when fully warmed up.

If the computer detects that the engine’s temperature is too high, it will automatically scale back engine performance settings. This occurs to prevent overheating, which can damage the engine severely.

As you can see, temperature plays such a crucial role in the performance calculations of your engine. And this implies that if the coolant temperature sensor malfunctions, it may translate very quickly to engine performance hiccups.

This post discusses some of the common symptoms of a bad coolant temperature sensor. These symptoms should alert you of potential problems with your automobile and push you to have it checked out thoroughly.

Symptoms of a Bad Coolant Temperature Sensor

Overheating Engine 

If you notice that your engine overheats, the coolant temperature sensor could be the problem. At times, the coolant temperature switch may fail such that it starts transmitting hot signals permanently. 

This causes the computer to erroneously counterbalance the signal, thereby causing the engine to misfire or overheat. 

Poor Fuel Economy

Poor fuel economy is another symptom that indicates your coolant temperature sensor is malfunctioning. 

If the coolant temperature sensor malfunctions, it can transmit a false signal to the computer. And the response of the computer may unbalance the timing and fuel calculations. 

It is also common for a coolant temperature sensor to fail without warning and send permanently cold signals to the computer. The computer mistakenly assumes the engine is cold, even when it is not. 

This will cause the automobile to use up more fuel than is necessary, thereby reducing fuel economy. And this will ultimately hamper engine performance.

‘Check Engine Lights Turns On

If the ‘Check Engine’ light suddenly comes on, this could imply a hitch with the coolant temperature sensor. If the computer detects an unsavory development with the sensor’s circuit or signal, it may set off the ‘Check Engine’ light. And the light will not go off until a specialist readily addresses the issue. 

Black Smoke Emitted from the Engine

Few drivers hardly notice this crucial coolant temperature sensor symptom. But if your vehicle’s exhaust starts emitting black smoke, the coolant temperature sensor could be the culprit.

The coolant temperature sensor can fail and transmit cold signals to the computer. This action confuses the computer and stimulates it to enrich the fuel mixture unnecessarily. This can cause the fuel mixture to be vibrant such that during combustion, the fuel can’t be adequately consumed within the chamber.

This leads to the burning up of your vehicle’s exhaust pipe, thereby causing black smoke. This can be so severe that driving the vehicle in such a condition may result in environmental or excessive air pollution.

Poor Idling

A faulty sensor can cause the fuel mixture to adjust. This causes the engine to shake or vibrate when the vehicle is at low speed and can even bring about strange behaviors, power losses, etc.

Engines are highly sensitive, especially to inappropriate air-fuel mixtures at idle. This is a pointer that something is wrong with your coolant temperature sensor and must be checked out by a certified professional.

Defective Electrical Cooling Fans

Some vehicles’ coolant temperature sensors control the electric cooling fans. Most automobiles come with two different temperature sensors for the fans, engine management and dashboard gauge.

However, if your vehicle only has a single coolant temperature sensor and it becomes faulty, your electrical fans may not function at all.

Where is the Coolant Temperature Sensor Located?

Different car manufacturers and brands have distinct ways of installing the coolant temperature sensor. Its exact location also depends on its overall design.

However, the coolant temperature sensor is often located right on the cylinder head or engine block. You will find it installed conveniently on a plastic hose on the coolant’s inlet.

Some automobiles come with more than one coolant temperature sensor. This is because sometimes, these different switches can be used to send signals to the cooling fan control, dashboard, and control unit of the engine system.

If your vehicle comes with two sensors, the one that transmits signals to the control unit is often known as the coolant temperature sensor.

Diagnosing a Malfunctioning Coolant Temperature Sensor

Diagnosing should be the job of a certified technician. However, this shouldn’t stop you from examining the engine component if you suspect it is malfunctioning.

You may have to get your hands on a repair manual for the model of your vehicle. This will enable you to find the measurement values that a functioning coolant temperature switch should exhibit.

Check the service manual of your vehicle to locate your coolant temperature sensor. When you set eyes on it, disconnect the connector plugs.

If your sensor has two pins, determine the ohm measure between the pins. Then compare the value with the correct ohm-value – at a given temperature – in your repair manual. If the value does not tally, it means you need to replace the coolant temperature sensor.

If the values add up or tally, consider checking the connectors and wirings between the sensor and the engine’s control module.

You can also make use of an OBD2 Scanner to look for related trouble codes. Check the live data to see the temperature of the sensor. If the temperature is off the range, check the wirings of the sensor or replace the engine component.


The coolant temperature switch remains one of the most vital engine management sensors. This is because it plays a crucial role in numerous calculations that ultimately affect your engine’s performance.

This is why you shouldn’t waste any time if you suspect that the coolant temperature sensor is malfunctioning. Get a professional or experienced technician to inspect your vehicle as soon as possible.

The technician should be able to analyze or diagnose your automobile and determine if there will be a need for the replacement of the coolant temperature sensor or not.


Our Favorite High-Performance Transmissions

High Performance Transmissions - Gearstar

Gearstar specializes in high performance transmissions. Find out which are our favorite! Get started with Gearstar and learn what makes us different.

Are you shopping around for a GM high-performance transmission? You are welcome since this is the right place to get one. Gearstar is highly committed to engineer and builds the most satisfactory GM and Chevy high-performance transmissions that are hand-built and customized to handle as much as 1000 ft.-lbs. torque and 1200 horsepower.

Each high performance is put together by one technician – from scratch, i.e., from start to finish – using premium-quality parts on the market today. The transmissions are perfectly engineered and built to the horsepower, rear gear ratio, and torque specs of every engine it will be matched with. 

Every high-performance transmission undergoes a thorough dynamo test for up to 1000 miles to validate its excellent working condition before leaving the Gearstar facility. Each driveline component is built with the highest quality constituents, including the latest updates.

Why Refer to a Transmission as ‘High Performance’?

A high-performance transmission is usually – and much more likely – utilized for engineered and built engines for performance and speed. 

This gear mechanism used to be limited to only vehicles used exclusively for racing on the drag strip or street racing. However, over the years, there has been a lot of blurring of the line.

Many car enthusiasts these days are no longer reserving specific vehicles for those times. They are now outfitting their unique daily drivers to make them versatile enough to conform to numerous roles.

This often implies restoring and modifying their existing muscle automobiles to meet both objectives – i.e., be a reliable daily driver during the day and tear up the street or track by night or on weekends.

Matching the Engine and High-Performance Transmissions

It is vital to match your vehicle’s transmission to its engine; therefore, do not spend too much money on modifying the engine.

This is where high-performance transmission comes on the scene. To fully utilize your car engine, you must get the converter and transmission to back it up. 

High-performance transmissions provide both the speed and power that you need to get or reach peak performance, thanks to your racing engine. This includes other high-performance types of engines.

This is why you need to ensure that your high-performance transmission builder and engine builder agree or are on the same page from the beginning of the project until it is completed. 

When you are crystal-clear upfront about what you expect regarding speed, power, durability, and performance, the two builders can work together and produce the results you need in record time.

This makes Gearstar different, as you will always get the specs you request without any alteration.

The Different High-Performance Transmissions Gearstar Offers

Gearstar offers a wide range of high-performance transmissions that you can select to match your engine. Here are some of Gearstar’s lineup of GM high-performance transmissions highlighted in no particular order:

  • Ford – AOD: Level 2, 3, and 4 transmissions
  • AODE: Levels 2, 3, and 4 transmissions
  • C4: Levels 2, 3, and 4 transmissions
  • C6: Level 4 transmission
  • E4OD: Level 3 transmission
  • 4R70W: Levels 2, 3, and 4 transmissions

You will also find the following high-performance transmissions on Gearstar:

  • GM – Turbo TH350 (Level 2, 3, and 4): Stage 1 TH350 can take up to 450hp. Stage 2 holds up to 550hp. It can take from 300-350 ft./lbs. torque.
  • Turbo 400 TH400 (Level 2, 3, and 4): It can take up to 400-450hp and is rated at 450 ft./lbs. input torque.
  • 700R4 (Level 1, 2, 3, and 4): It is suitable for up to 550hp max but can do as much as 625hp. Its torque varies considerably according to its production year. But it is known to generate a maximum engine torque of about 350 ft./lbs. as well as a maximum gearbox torque of 650 ft./lbs.
  • 200-4R (Level 2, 3, and 4): It can handle up to 350-400hp on the street and 400-450hp on the track, as well as 675 ft./lbs. torque.
  • 4L60E (Level 2, 3, and 4): It is rated 450hp and 425 ft./lbs. torque.
  • 4L65E (Level 2, 3, and 4): It can handle up to 425-450hp. Built solely for Chevrolet, it has a stock torque limit of up to 380 ft./lbs. torque.
  • 4L65E C5C6 (Level 4): It can handle up to 650hp and up to 650 ft./lbs. torque.
  • 4L70E (Level 4): It can handle as much as 375hp and 350 ft./lbs. torque.
  • 4L80E (Level 2, 3, and 4): It is powered with a magnificent 800hp and generates up to 700 ft./lbs. torque.
  • 4L85E (Level 4): It is powered by a whopping 1000hp and up to 460 ft./lbs. torque.

Each Gearstar high-performance transmission is available at different price points. The power your classic vehicle has will determine the horsepower you will need, and much better engines will require a Level 3 transmission at least.

Gearstar makes every high-performance transmission that can ably handle your build with strong parts and premium-quality steel.

Every high transmission needs regular maintenance, repair, or replacement. Transmissions generally wear away every 150,000 to 200,000 miles. If your transmission has reached either limit, it is high time you changed it.

Fortunately for you, Gearstar has several new options available at affordable prices. An industry-leading warranty and thorough inspection heavily back these high-performance transmissions.

High-performance transmissions give profound peace of mind as your classic racer keeps running, and there’s zero stalling on and off the track.

High Performance Transmissions: Conclusion

As you can see, Gearstar has an excellent lineup of premium-quality, high-performance transmissions designed to match any engine of your choice. Every transmission is engineered, custom-built, and optimized – from scratch or start to finish – by a master technician, so there’s zero room for errors.

Every high-performance transmission that Gearstar features is designed and built per the torque, horsepower, and rear gear ratio specs of the particular engine it is created for.

Since every high-performance transmission is dyno-tested for an equivalent of up to 100 miles for best performance metrics, Gearstar’s products are warranted against failure for up to 36,000 miles or three years, whichever comes first right from the date of shipment.

So, what are you waiting for? Order your high-performance transmission from Gearstar today!

The Ultimate Guide to the 4L80E Transmission

Overview of the 4L80E Transmission - Gearstar Performance

The 4L80E transmission is an automatic transmission designed by General Motors. Learn more about this legendary transmission.

The 4L80E transmission was introduced in the GM C/K Trucks line-up – to the delight of motorists – in 1991. The legendary TurboHydramatic TH400 automatic transmission was the 4L80E transmission’s immediate predecessor. It is constructed to a great extent on the 400 in strength and parts. The 4L80E also features a lock-up torque converter, an added overdrive gear, as well as state-of-the-art electronic controls. This automatic transmission has remained in production through the 2009+ model year.

In this post, you will learn more about the 4L80E transmission and its variant, i.e., the 4L85E. The latter is constructed such that it can efficiently handle heavy-duty use. Every reference to the 4L80E also applies to this variant, except where stated otherwise. 

Note that the terms’ 4L80′ and ‘4L85’ may be used without adding the suffix, ‘É.’ This is because every GM automatic is electronically controlled now and, therefore, doesn’t need differentiation. 

Let’s get to the meat of the matter.

The Development of the 4L80E Transmission

As mentioned briefly earlier, the 4L80E automatic transmission was directly developed from the TH400 transmission. The latter is a challenging and enduring transmission at GM – as well as other marques. It was practically the last hold-out of the entire old-school automatics with no overdrive or lock-up converter.

GM quickly recognized a gap revealed by the rapidly expanding success of the 4L80E/700R4 automatic transmission. Although the 700R4 was a tough transmission, it could not hold a candle to the TH400 transmission. 

And for this particular reason, GM had no choice but to start developing a pretty heavy-duty automatic overdrive.

GM relied heavily on – and used – several parts or components and designs derived from the TH400 transmission when developing the 4L80E. But the added overdrive gear gave the 4L80E an edge over its predecessor, even though it required a somewhat longer case and an extra gear set.

The rear tail housing bolt pattern was not tampered with in any way. However, its indexing bore diameter was efficiently changed. The 4L80E transmission features a large 32 spline output shaft – much like the TH400 transmission – in the numerous 2WD and 4WD applications.

The 4L80E features a die-cast aluminum case, just like most other GM automatics. However, the 4L80E never featured a removable bell housing, unlike the 4L60E automatic transmission. Instead, the 4L80E transmission showcases an integrated bellhousing with the Chevrolet 90-degree engine bolt pattern only.

In 1991, GM trucks rolled out into the market, bearing the 4L80E automatic transmission. This included the Silverado, Sierra, Suburban, Hummer H1, etc.

The 4L80E automatic transmission is by no means perfect and has its share of glitches. However, it became a huge success and continued to be enhanced throughout its production span, even with extra changes entering when required.

In 2002, the 4L85 automatic transmission entered the market. A few differences between this transmission and the 4L80E include a 5-pinion reaction gearset, a 5-pinion output gearset, etc.

GM specified a brand-new automatic transmission fluid formulation in 2006, though this development was not regarded as a transmission change. The company required this fluid formulation’s warranty in the 4L80E series. Dexron VI, another brand, highly superseded its previous transmission fluids, claiming that it has significantly improved the transmission performance as well as a more extraordinary fluid life and transmission.

The 4L80E Automatic Transmission Technology

Every 4L80E automatic transmission makes use of electronic controls, which are generally from the Powertrain Control Module. Some vehicles using this automatic transmission come with shift maps that the driver can select, based on usage, including towing, etc. 

Part of the Powertrain Control Module’s strategy includes shift stabilization, which contributes significantly to reducing hunting.

The torque converter – when applied in factories – is heavily controlled via a PWM lock-up solenoid for seamless lock-up action. Despite this, several performance aficionados always prefer to efficiently reprogram the 4L80E automatic transmission in order to run as a very simple, ON-OFF solenoid.

The H1 received a 4L80 along with its dedicated T42 transmission computer in 2004. This automatic transmission also arrived with a considerably enhanced Park/Neutral safety switch and modified transmission line pressure solenoid. Other General Motors applications are still going to follow soon.

The TCM (Transmission Control Module) refers to the highly adaptive learning computer smartly integrated within the transmission valve body. It communicates efficiently with the Engine Control Module through the onboard vehicle CAN bus network. 

This is a departure from – and a return to – preceding automotive control systems within the industry. This is because the earlier versions of electronic transmissions made use of a separate control module. This module was later integrated right into the Engine Control Module and is now known as the ‘Power Control Modules.’

But now, this high-speed CAN network permits an incredibly high rate of data sharing between these units. This occurs in order to reach a collaboration between transmission and engine functions.

Since the 4L80E automatic transmissions are – on certain occasions – used in conversion applications with the earlier non-PCM-controlled engines, GM as well as aftermarket control modules are necessary. And they are now used to control the operation or function of the transmission in these specific scenarios.

The Specifications

When you see the nomenclature of the 4L80E, it readily informs users that this is a longitudinally-mounted, 4-speed transmission designed for vehicles that weigh nothing less than 8000 lbs. The 4L80E has an RPO code – i.e. ‘MT1’ – manufactured domestically in GM’s Willow Run and Ypsilanti plants.

Here are the 4L80E ratios it features in each gear:

  • First: 2.48
  • Second: 1.48
  • Third: 1.00
  • Fourth: 075
  • Reverse 2.07

The maximum output torque of the 4L80E transmission is 885 ft. lbs. 

While the top engine input torque is 440 ft. lbs. Die-cast aluminum is the transmission’s case. And it was designed for vehicles that weigh up to 8,000 lbs. GVWR as well as with engines up to 440 ft. lbs. of torque.

However, the 4L85 was primarily designed for automobiles that weigh up to 16,500 lbs. GVWR as well as with engines up to 460 ft. lbs. of torque. This transmission has an incredible towing capacity as it was up-rated to 22,000 lbs.

The 4L80E series requires a shifter with a 7-position quadrant: P, R, N, OD, D, 2, 1. The torque converter on this automatic transmission is a fluid turbine drive, much like those found on its predecessors, e.g., the 700R4, 4L60, TH350C.

The 4L80E also comes with a lock-up pressure plate for direct, mechanically-coupled driving from the engine crank. It is 26¼ inches long and boasts a 310mm torque converter.

Applications of the Transmission

The 4L80E automatic transmission has several applications, such as:

  • Speed-sensing
  • Transfer case adaptability
  • Jeep conversions
  • Engine compatibility

Final Thoughts

By now, you already know that the 4L80E automatic transmission is intelligently designed to meet transmission challenges. This implemented automatic transmission from the legendary General Motors has an extraordinary record in conversion situations and will always leave you super-impressed.

545RFE Transmission Specs and Schematic

545RFE Transmission - Gearstar Performance Transmissions

The 545RFE transmission is an electronically controlled unit that was great for its time until it was replaced bu the 65RFE and 66RFE. Read below for specs and more information.

The automobile universe witnessed the introduction of the 545RFE/45RFE transmission in 1999 Chrysler models. The transmission was a perfect fit for 2-wheel-drive vehicles as well as all-wheel-drive automobiles. 

The 545RFE transmission, formerly known as the 45RFE – introduced and popularly seen in the Jeep Grand Cherokee of 1999 – is highly notable for its three planetary gearsets instead of 2 planetary gearsets commonly used in a 4-speed automatic.

The 545RFE also features the following:

  • Three multiple disc holding clutches
  • Three multiple disc input clutches
  • A dual internal filter system (one filter for the fluid cooler return system and the other primary filter for transmission sump)

The 545RFE transmission, based primarily on the 45RFE automatic, was used extensively in Chrysler’s entire fleet of rear-wheel heavy-duty trucks, except for coupes and sedans.

545RFE Transmission: Specs

But back in 1998, Chrysler has introduced the 45RFE in the 1999 WJ Jeep Grand Cherokee. This transmission was paired remarkably well with the 4.7 L PowerTech V8 engine. The ’45’ refers to its torque rating, i.e., ‘5,’ while ‘4’ represents the number of forward gears. ‘RFE’ refers to the ‘rear-wheel-drive application and full electronic controls.’

But by 2001, the 545RFE transmission was produced due to a taller, extra overdrive ratio and programming changes. The new transmission had a standard axle ratio that resulted in 2000 revolutions per minute at the engine, allowing you to cruise at 110 km/h (70 miles per hour).

The 545RFE transmission found its way to several SUV and truck applications from 2001 to 2012 with Jeep Commander and Jeep Grand Cherokee models that sport higher output Hemi engines. It could also be found in several Dodge Durango models within this period.

Although the engine yield was 200 rpm less than the 45RFE, the outcome was a considerable decrease in noise and fuel consumption. Now, the 545RFE transmission had six forward speeds and one reserved for kickdowns.

The engineering of the 545RFE transmission closely resembles that of the solid Torquefiles or an up-to-date version. The 545RFE transmission had a tall 3.00:1 first gear for initial acceleration.

The reverse was designed to be equal to first gear to accommodate heavy loads easily. When the 545RFE transmission was launched, it had the broadest range of gear ratios within its class. Even the factory where the transmission was made was also brand-new.

According to experts, the 545RFE comes with 2 overdrive gears. These are relatively close to each other due to the available size. The top 0.67:1 was probably chosen since that was the largest one that could easily fit without enlarging the transmission, making it too big for the organization’s automobiles.

To be clear, the following are the 545RFE gear ratios:

First gear – 3.00:1

Second gear – 1.67:1

Second gear (Prime) – 1.50:1

Third gear – 1.00:1

Fourth gear – 0.75:1

Fifth gear – 0.67:1

Reverse – 3.00:1

The capacity of the 545RFE transmission is 10.5-11 l, while the fluid type is Dexron 3-6 or MOPAR +4.

Some models with the ‘Tow/Haul’ mode were able to make faster shifts to cut wear on the 545RFE transmission. This considerably minimized the search for gear by holding the lower gears for extended periods. It was also possible to choose lower gears when traveling downhill to boost engine braking.

The computer-controlled 545RFE transmission comes in a burnished, one-piece die-cast aluminum casing. The casing was ribbed to increase torsional rigidity. Early transmission units took up to 6.6 quarters (6.2 liters) of ATF+3 fluid, while later versions took the same amount of ATF+4 fluid.

The gear ratios were designed to provide reserve torque as the transmission was highly suitable for the large torque band of the VM 2.8 diesel, Hemi V8, 4.7 V8, and 3.7 V6.

However, in 2009, the computer was programmed so that drivers could easily select the highest gear the 545RFE transmission would shift to. This made it easier for vehicles with this transmission to tow other vehicles, climb hills, and descend without any issues.

Common Issues with the 545RFE transmission

Here are some of the common problems that the 545RFE transmission showcases:

Solenoid Pack

Since the this transmission has zero transmission bands, the 545RFE – which is electronically controlled – relies heavily on a solenoid switch pack to efficiently direct fluid to the proper clutch pack for smooth gear engagement.

If something goes wrong and the solenoid pack becomes defective, there will be no gear engagement, failure to engage overdrive, stalling of the engine seamlessly, and ‘limp mode.’


This is another common challenge when moving parts within the transmission generate much more friction heat than the ATF can siphon away.

The primary cause of this problem involves the towing of heavy loads, multiple shifting of transmission on mountain roads, and driving in heavy stop/go traffic.

Delayed and Slipping Gear Engagement

The 545RFE transmission pump comes with a bit of a valve mechanism, which controls the fluid pressure that the torque converter transfers.

If the valve mechanism becomes faulty, you will experience significantly delayed gear engagement, stalling, torque converter/transmission overheating, reduced fuel economy, and slipping.

Harsh or Delayed 3-4 or 4-5 Shifts

Users of this transmission may experience a severe or unusual delay of 3-4 or 4-5 gear change. In such instances, it appears as if the transmission is reluctant to go into that specific gear.

This problem is linked to valve body issues in which the material used for making one of the check balls has somehow broken down so severely that fluid easily gets past and engages the underdrive clutch during the shifts.

The only way to solve this problem will be to install an upgraded #2 check ball made of a tougher material.

Four and five-speed automatic transmissions have up to 90 percent of interchangeable parts, and this makes it easy to perform repairs. The 545RFE transmission is reliable and highly durable, making serious damage a scarce thing. 

Although it was originally developed and designed to be used by heavy-duty engines, it is very compact. The use of highly active electronic control systems significantly reduced the valve body and drive shafts. 

Differences Between the 45RFE and 545RFE Transmission

The 45RFE and the 545RFE transmissions are mechanically identical. The notable difference comes down to software.

The 545RFE transmission has an electronically activated fifth gear. You will also notice that the unit control module and solenoid pack is different in both transmissions.


This transmission was excellent in its heydays. It was an electronically controlled unit that Chrysler produced and used extensively until it was replaced by the 65RFE and 66RFE automatic transmissions. For information on other performance transmissions and torque converters, contact us today.