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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.
Oil pumps are designed as two halves. You have to take them apart to access the pump gears, bushing, and seal. When they are ready for assembly, you must align the two halves or the pump will not fit back into the case. Make a band from a large hose clamp or put several large hose clamps together. The pump’s bolts should remain finger tight while the band is tightened. Use a Phillips screwdriver or awl to align the bolt holes and then drop the attaching bolts through the holes while the pump’s bolts are tightened. This ensures that the halves do not slip out of alignment. Once the pump’s bolts are tightened, test fit the pump into the case, and then start all of the pump’s attaching bolts by hand. Do not install any seals for the test fitting procedure.
A couple of 5/16-inch bolts can be fabricated and used as alignment studs to install the oil pump.
General Motors threaded several bolt holes on the oil pump. Use two slide hammers to easily remove the pumps from the case without damage.
A large hose clamp can be used to align the pump halves when tightening the pump bolts. If not in alignment with each other, the pump is difficult to install in the case and the bolts may not line up enough to get them started.
Alignment studs guide the oil pump into place during final installation. Use at least two studs. Place the gasket on the case first, then hand thread the studs into the case. To make a couple of studs, simple cut the ends off a couple of long bolts and grind them to a point.
The TH350 and TH400 transmissions have two corresponding pump bolt holes tapped for a slide hammer. It is best to use two slide hammers to pull the pump evenly from the case. You can use only one hammer, but you may have to alternate back and forth between the holes in the pump to pull the pump from the case effectively. Thread a slide hammer into the pump to remove the pump from the case. Make sure to thread the slide hammer at least five full turns into the pump to avoid breaking the tool off or pulling out some of the threads.
Rebuilding the TH350 transmission effectively doesn’t require special tools. If you purchased all the special tools that you could use for a TH350 rebuild, you would quickly offset any savings from doing the rebuild yourself. For that reason, throughout this and other chapters, I provide alternatives: How you
