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Overachieving Overdrive With a 700R4 Transmission Rebuild

By March 30, 2022How To's
Powerful performance with a 700R4 transmission rebuild

A good 700R4 transmission rebuild will leave you with a ride that is more powerful, durable, and with firmer shifts.

In terms of power, you can get over 450 lb-ft of engine torque output than what the stock transmission offers.

But first, you may want to dyno test your current 700-R4 transmission to know if it is in dire need of a rebuild, especially if it has been subjected to severe usage.

If it needs a rebuild, you may notice a decline in Second, Third, and Fourth gears.

The transmission may also start releasing fluid from the breather.

Therefore, you need the right parts to get a 700R4 that is more than impressive instead of switching to a new unit.

Now walk with us as we show you how to rebuild the 700R4 transmission to overachieve overdrive.

Why Rebuild the 700R4 Transmission Instead of a Replacement?

You may be wondering if it is entirely needful to rebuild the 700R4 transmission instead of upgrading to another transmission such as the three-speed automatic, Turbo 400.

If that’s the case, here are some reasons why the 700R4 transmission rebuild is more ideal in a street-strip car.

First Gear:

The 700R4 transmission’s first gear is 3.06:1, which means a car that features a 700R4 and 3.55:1 rearend gearing would move like a car with a Turbo-400 transmission and 4.38:1 rearend.

On the other hand, the Turbo-400 has a first gear of 2.48:1.

Fourth Gear:

A look at the 0.70 overdrive gear of the 700-R4 shows that it provides a cruise rpm, which is the same as the Turbo 400’s 1:1 third gear with 2.48:1 rearend gearing.

Lockup Converter:

A lockup converter is evident on the 700-R4 and this component helps to lock the drive and driven sections of the converter with a clutch above 38 mph.

Consequently, overheating and slippage are totally eliminated.

Fewer Components:

The 700-R4 transmission has fewer components compared to electronically controlled 4L60 or 4L80.

As such, you have fewer electronics to deal with. You do not have to spend more to acquire a transmission controller and wiring harness.

How to Rebuild the 700R4 Transmission

Although the 700R4 transmission is reputably known to be a reliable trans, a rebuild can enhance its performance.

Accordingly, you can rebuild the 700R4 transmission using these tips.

Disassembly:

The first thing you’re going to do is to carefully disassemble the 700-R4 to see if there are possible areas that are in dire need of repair.

You may notice a brownish fluid and varnish on the internal components of the transmission due to overheating.

The heat is often produced by the torque converter and at higher converter stall speed, more heat is created before lockup.

Overheating, on the other hand, can cause transmission failure, which is why you should consider using an external trans fluid cooler and a temperature gauge.

The temperature gauge will tell you if your transmission is overheating.

In this case, if the automatic transmission fluid (ATF) has a temperature above 185 degrees F, it may prevent proper fluid flow and component lubrication.

Replacement of Internal Components:

Certain components in the transmission can prevent it from shifting between gears properly.

For instance, if there’s a sticking governor with coated trans-fluid varnish, there may be shifting issues.

Accordingly, proceed to replace the internal parts of the transmission.

You may also want to link the trans cooling lines and radiator heat exchanger to a cleaning machine.

Increased Line Pressure:

Take a look at the hydraulic system in a bid to increase line pressure quickly when power is applied.

The goal is also to eliminate high-rpm pressure drop-off and slippage.

In this aspect, you’ll be looking to improve the transmission pump using a new, hardened stator.

There’s a need to CNC-machine flat both sides of the pump halves to ensure that the stator is perpendicular.

It’ll also provide precision mating of the pump halves thereby eliminating internal pressure leakage.

Rings:

Hardened-steel pump-guide rings can be installed to disallow pressure drop above 5,500 rpm.

Likewise, it’ll enable the driver to manually control shift points without negative effects.

Another important installation is with a 10-vane pump rotor and an upgrade to an oversized 0.500 low-boost and 0.290 reverse-boost valves.

Also, consider the use of Teflon-coated front bushings and heavy-duty stator support bushings.

An enhancement to the pump-regulator valve and installation with a stiffer pressure-regulator spring can improve flow.

Decrease Internal Slippage:

Focus has to be given to the 2-4 gear band assembly by stepping it up to a wider 3/8-inch Kevlar band with a reinforced anchor.

This upgrade will eliminate slippage on shifts under full power and enhance the transmission’s durability.

There’s a need for an improved governor to increase automatic WOT shift points to the 5,200 to 5,600 rpm range.

Also, a heavy-duty, 29-element input sprag clutch is needed to withstand the solid shifts.

Other upgrades include the improvement of the 3-4-gear clutch pack to nine friction and nine steel plates.

Recalibration:

Improved shifting is also brought about by recalibrating the part-throttle, throttle-valve accumulator circuits in the valve body, and the spacer plate passages.

This will also provide more precise pressure regulation and firmness.

The line-bias system is upgraded in a bid to improve shifting.

Road Testing:

It is important to road test the transmission after the rebuild to see how well it works before its final use.

Conclusion

It is entirely possible to overachieve overdrive with a 700R4 transmission rebuild, especially if you do it the right way following the steps we’ve outlined.

You’ll be dealing with more power and firmer shifts after this upgrade.

The best part is, you’ll be spending less on a rebuild compared to getting an entirely new transmission.

On the other hand, it’s better to work with a car repair shop if you have little knowledge about fixing cars to ensure you don’t cause more harm than good to your unit.

It’ll save you money in the long run and help you avoid transmission failure.

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