Corvette 1989 OE Manual

TH700R4 Transmission Performance Rebuild 1: Theroy & Upgrades

TH700R4 Transmission Performance Rebuild & Upgrades

TH700R4 Transmission Performance Rebuild

 

TH700R4 Transmission Performance Rebuild

Some basic information on the 700r4. Today the 700r4, 4L60, 4L60E are used in many upgrade and performance applications and many of us wish to rebuild them ourselves to be sure the correct parts are used and the transmission is what you think it is. With these transmissions its easy to find someone to rebuild them. Now finding someone that will care as much about the transmissions long life as much as you will is not that easy. Since its hard to see whats inside the transmission lots of people have purchased full out race transmissions only to find out they were even a good rebuild.

The Primary Focus

Now for my primary focus this will be on the TH700R4 as its not computer controlled and uses the simplest setup and wiring. Most of us will not want to use a computer controlled transmission on a car with a carburetor. If the car is fuel injected the 4L80E is a much better choice if your going to buy and install a computer might as well get the strongest transmission to go with it.

TH700R4 is considered to be a TH350 with and overdrive

The TH700R4 is considered to be a TH350 with and overdrive gear and a short first gear. This give the transmission great off the line power even for cars with less than ideal gearing. Now it also lets the engine run low RPM’s at highway speeds. Even with low gears like 4.11:1 the TH700R4 can run less than 3000 rpm on the highway at 70 MPH. Depending on tire size you may even be less than 2000 RPM at 65 or 70 MPH. If you drive a lot of highway miles this can be the biggest upgrade to the MPG problem large high power V8’s suffer from. This simple low RPM at road speeds makes for better gas milage and a lower first gear for more off the line power. This type of upgrade is well suited for many muscle and performance cars and trucks.

EFI and the TH700R4

Now if you are using an EFI based engine that is equipped with factory style computers or compatible versions. The larger TH400 based 4L80E is the best way to go. Since the cost of the trans is just about the same as the TH700R4 and sometimes a lot cheaper since a low mile 4L80E can be used in cars with good power and not fail. The same cant be said for the TH700R4. With the bolt in ability to take 400 or more hp. This is one great upgrade. Now lets talk about the draw backs. The computer system is expensive. There are a few aftermarket and junk yard solutions that work well. But that is for another article.

TH700R4 older no computer shifts

My primary focus of this article is the TH700R4 and its none computerized shift and lockup controls. TH700R4 becomes on of the best choices for a heavy muscle car or classic cruiser. Its relatively simple and cost are not in the extreme. A good built TH700R4 can handle the 400+ hp most of us crave and still produce a smooth ride along with long life. It is also a good choice for weekend racer or street strip applications with good support form the aftermarket. Stronger bands and several different types of torque converters are available. High RPM stall converters are pretty costly but can be worth the investment. Depending on your needs the TH700R4  can fill the need in your budget and your ride.

max effort racing the TH700R4??

As for all out max effort racing the TH700R4 is not for you. You can not get a 5K RPM stall converter that has lockup. Many of the converters made for the TH700R4 are based on street car performance levels. They can be made to push your heavy car down the drag strip quite well for the most part. But when it comes to cars running large shots of N2O or high levels of boost the TH700R4 can fail even when its well built.

With proper parts these transmissions can take a good amount of power and put it to the ground effectively. There are lots of good aftermarket parts that can make them work well. They are just not a replacement for a pro built bullet proof power glide at the drag strip. Nor will they take the place of a good 6 speed on a road course or time trail. Same is true for large rock crawlers and other extreme vehicles.

The right parts for the build

Now with that said they can do all most as well in some regard once built properly they are strong and will take a significant amount of abuse without failure. In stock trim with w stock engine in front of them they will also last a ling time. I have a 1989 corvette with 300K miles on the odometer and has only had the transmissions rebuilt once.

I am writing this article because the first TH700R4 that came in my Corvette lasted for 250K miles the rebuild is failing at 50K miles and should not be. If it was built properly common since says it should have lasted another 250K miles. Now we get to the reason you want to do the work your self. If your like me this type of failure drives you nuts. Money poorly spent. It should not be failing I did not ask for a crappy job nor did I ask for any money to be saved during the rebuild simply ask to have it rebuilt to factory spec with all new parts including hard parts know as steels and soft parts know as fibers and bands.

Parts are every where and the broken trans complete is very cheap

It is easy to see the parts either were not replaced or were replaced with cheaper none oem standard parts. This can be very costly way to save money as now its got to come out again. In the 1989 Corvette the transmissions is not as easy as some car and easier than others. This particular car does not have a cross member. It uses a brace that is connected to the rear end forming a strong single unit from the engine to the rear end and it works very well. Just not the most fun to remove and reinstall. Because of this I am very disappointed with the failed transmission.

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Here are some exploded diagram from the manual. The first one is the exploded diagram of the parts outside of the transmissions. The second is the internal clutch parts including the clutch packs, sprags and sun gear.

TH700R4 Transmission Performance Rebuild

 

TH700R4 Transmission Performance Rebuild

 

A Clean dis-assembly

As you can see the transmission contains a lot of parts and pieces. At first look it appears to be extremely complex. With a little review its not an impossible job to complete. The parts are straight forward and many of the parts only install in the one direction. Of course there are many that can be installed incorrectly. Care should be taken to make sure things are assemble correctly as you go. Slow and steady is the way to go.

During dis-assembly you should snap pictures with your cell phone as you go just to make sure you have something to refer to during reassembly. You can also find many videos and pictures on the internet to help reference the build.  I will post some links below so you can find them quickly during the build.

 

Look for the next post were we get into the removal of the transmission with pictures and advice on cleaning the transmission on the bench. Making it ready for bench top Service/Rebuild. Click on the link below to see the next installment of this article.

TH700R4 Transmission Performance Rebuild 2: Removing From 1989 Corvette