Rebuild Your GM Transmission

There is an especially strong snap ring holding the accumulator cover on. What worked best for us was to pry on it with the screwdriver and a pick. Jab the pick into whatever small opening you can find between the snap ring and the case, wedge the screwdriver in as soon as it will fit, and inch along until the snap ring fully pops out.

Once the case is disassembled, it's ready to be cleaned. We washed ours with some aluminum wheel cleaner and blew it dry with compressed air. From here, everything that goes back into the case needs to be clean. Use lint-free paper towels when drying everything, too.

As you disassemble the components of the transmission, come up with a system to keep everything organized. It helps when you have access to a lot of workbenches like we do. Spread everything out and keep the parts oriented up if possible. This will be a big help during reassembly.

Follow the same advice when rebuilding the valvebody. The components look similar, but put them together wrong and you'll end up with a box full of neutrals.

Inspect the components for signs of wear. The black stuff on the left side of this clutch return spring is friction material. Compare that with the other half that we wiped clean. Like brake dust, as the clutches wear, they shed their lining. This residue is washed away by the transmission fluid and hopefully trapped by the filter. Go too long between fluid changes and your whole trans will look like this inside.

Here's something we didn't expect to see: There were drops of water in our oil pump. The vent tube on our trans was missing, so we're guessing that's how the water got in. That explains the spots of rust that appeared on some of our clutch drums. While the transmission was sitting, water must have clung to these surfaces, causing them to rust. We cleaned the rust with 220-grit sandpaper and washed the assembly thoroughly with solvent.

We got our biggest surprise after disassembling the forward clutch. Automatic transmissions use multiplate clutches made up of an alternating stack of steel plates and friction discs. In this photo, the top two pieces are friction discs and the bottom two are the steel plates. Note the wear pattern on all the pieces, especially the second friction disc. There should be no bare steel showing on any friction disc, and the steel plates should be smooth. The parts in this clutch were metal on metal. Now we know the source of the metal shavings in the filter. Fortunately, B&M's Transkit comes with new frictions and steels. Some rebuild kits just give you the friction discs.

We found one more item that needed to be replaced-the low/reverse roller clutch. A roller-type clutch freewheels when turned in one direction, but when turned in the opposite direction, the rollers wedge against ramps in the clutch hub, locking it and preventing it from turning. As you can see, the cage assembly on the bottom shows heavy wear marks and the springs have collapsed. We bought a new one for just $12 at Trans1.

There are a variety of seals that separate fluid passages from one another, and these seals can be made out of a variety of materials: steel, Teflon, nylon, and rubber. Some of them are reusable, too, but you'll likely end up replacing most of them. Our oil pump seals itself with a series of locking steel rings that we replaced with new ones supplied in B&M's kit.

Installing the clutch pistons with new lip seals can be tricky. Lube the seals with clean transmission fluid and use a 0.010- inch feeler gauge to keep the seal from twisting as you push it down.

Follow the directions properly and reassembly won't be hard. Be sure to get the order of all the clutch plates correct. Usually, a steel plate will go on top of the piston, followed by a friction disc, another steel plate, and so on, usually ending with a friction disc. A steel pressure plate goes on top, held in place by a snap ring. Soak the friction discs in ATF for about 15 minutes before assembly.

Also during reassembly, be sure to check your clearances. Our clutch assemblies were all within spec.

Lube all bearings and bearing surfaces with Trans Jel. Though it probably wasn't necessary, we also gave the clutch drums a coating of ATF.

By this time, we had fashioned a more practical transmission stand than using a trash can. Stacking a set of used wheels and tires put our trans at a perfect height to finish putting it back together.

Once all the clutches are back in the case, you can install the valvebody. A sandwich of gaskets and separator plates goes between the valvebody and the transmission case. We used a light glob of Trans Jel to hold the gaskets in place and found a set of studs with the same thread pitch as the valvebody bolts to use when guiding the valvebody into proper position.

After installing the pan and gasket, the last step is to reinstall the accumulator and fill it up with the Trick Shift ATF B&M sent us. Now we just need a running engine to put this trans behind.