Use high-pressure air to blow parts dry after cleaning. It can also be used to pressure test clutch pack operation. By applying air to the fluid supply holes, you can pressurize the passages with air, verify apply piston movement, and check that there is no leakage at the seals.
An air ratchet also comes in handy for these tasks, but it is not as fast as an impact gun. Impact guns can be used to remove stubborn fasteners such as those that attach the tail housing or rear transmission mount to the case. A smaller 3/8-inch impact gun can be used to remove oil pan and valve body attaching bolts.
An angle grinder equipped with abrasive discs is one of the best inventions of modern times for cleaning off stubborn gaskets from machined surfaces. The discs are available in several different materials so they do not damage the soft aluminum surfaces.
Air tools can take a lot of time out of a transmission build. Even so, make sure they are going in the correct direction when removing bolts, which are easily stripped out in the soft aluminum cases.
Considering the age of many of these cases, and the fact they are aluminum, it’s usually best to avoid using an impact gun to tighten fasteners, even though it does save a lot of time. A spin-handle wrench is nearly as quick, and removes the possibility of stripping case threads. If, for any reason, an impact gun is used to tighten fasteners, it should be at its lowest setting; just enough to snug them up. Use a torque wrench for any final torque applied to minimize the possibility of stripping the threads in the case.
A variety of punches and chisels are required for transmission work. They are used to “stake” parts in place, as well as to remove and install roll pins. Many bushings are difficult to remove without splitting them first, especially if they are in blind holes.
A round punch can be ground at a slight angle and used to catch the edge of the bushing. This drives it down on one side and facilitates removing it from its hole. Before removing any bushings, measure the depth at which they’re set so you can correctly install the new bushing.
Punches and chisels are handy items for transmission building. You may encounter roll pins that must be removed or installed; you may have to split a bushing to get it loose from its bore.
Jeweler’s files are used to remove sharp edges. In almost all cases, the manual shaft needs some work to get it out of the case to access the manual shaft seal. Some metal on the nut at the end is usually raised up enough so that it does not pull through the case. It also leaves a knife-edge that needs to be removed or it will cut the new seal upon installation.
Files may be required to remove material from the manual shafts so they can be removed from the case. Most manual shafts have a lip that prevents them from sliding out of the case (to access the manual shaft seal). A few seconds with a small jeweler’s file removes any excess material so that the shaft will slide right out of the case.
Lip seals are used on apply pistons and servos to keep hydraulic fluid and pressure behind the piston. The lip on the seal is pushed tight against the bore in which it rides to create a positive seal. Lip seals can be somewhat difficult to install because you generally have to work with both an inner and outer seal for each piston.
Use a razor blade or razor knife to remove old rubber seals from apply pistons and Teflon sealing rings from accumulators and servos.
Custom molded hard plastic apply piston installation tools are available for most transmissions, but they are not required to rebuild a TH350 transmission. They are precision fit and sized for each apply piston and usually sold in sets for each type of transmission. They are rather expensive, but are still a good idea if they are within your budget, or if you plan to build numerous units.
The factory was kind enough to provide chamfered edges to help with seal installation. You still need to help the seals get past the edges without damaging them. A piece of small diameter wire crimped in some tubing makes a great lip seal installation tool. A feeler gauge with a bend on the lower portion works equally as well.
Seals, O-rings, and Teflon seals can be difficult to remove from apply pistons and accumulators. A razor blade, razor knife, or a small pocket-knife with a very sharp blade comes in handy here. Cutting the rings off the apply piston or accumulator is preferred instead of prying them off with a small screwdriver. The aluminum is less likely to be damaged, which could, in turn, have cut or damaged the new seal.
Special seal installation tools are available for all transmission models. They prevent the lip seals from tearing during the installation process. The factory machines a slight chamfer on the edge of each drum to help with seal installation. Instead of buying special seal installation tools, you can use a feeler gauge or make your own seal installation tool from a piece of small copper or steel tubing and smooth wire. Insert a loop of wire into the open end of the tubing and crimp it tightly. The loop of wire is used to get the lip of the seal that you are installing past the chamfered edge without tearing it. Inconel or music wire works best because it is more rigid than soft metal wire.
Use a blowgun and compressed air to do a function test of the forward and direct clutch packs prior to installing them in the case. It’s better to find a problem now, rather than after the transmission is placed in service.
It takes some practice and patience to install lip-type seals without damaging them. The key here is to never force them into place or try to push them past a sharp lip without using some sort of installation tool. Air checking the seal once the drum is assembled ensures that you have not ripped or damaged the seals. Air checking simply involves applying compressed air to the supply passage in the drum where pressurized transmission fluid would normally move the apply piston. Some drums can be pressure tested on the workbench before installation. Alternatively, you can place the transmission oil pump in a soft-jawed vise with the drums and sealing rings in place, and then apply pressurized air through the appropriate supply holes at the pump’s mounting surface.