upgrades, and places that require close attention when rebuilding these units. They are not overly complicated, or difficult to rebuild. As with any other transmission-rebuilding project, close attention to detail, good parts, and careful assembly is required.
You will also notice that I am replacing all of the bushings in every transmission rebuild. Most of the plastic or metal/brass thrust washers are also replaced. This is not a common practice among transmission builders. I have also found that the factory bushings (in units such as the TH350) may pass a visual inspection, but just about fall out of their locations with hand pressure during removal. This is especially true for the two bushings located in the sun gear, as they get “worked” pretty hard over the life of the unit. Typically, bushings are given a visual inspection and left in place, as some are somewhat difficult to remove and install.
Thrust washers are also reused in most cases, provided they pass a quick visual inspection. From a rebuilding standpoint, it is a good idea to spend the additional time and funds to replace all of the bushings and thrust washers. The results from doing this are all positive for the transmission. Having less fore/aft and up/down movement between the parts reduces gear noise and improves sealing of the rings, which produces a final product that runs quieter, shifts better, and lasts longer.
So, let’s get started . . . .
This chapter is one of the most important in this book.
Transmission rebuilding is not overly difficult, but it does involve attention to detail, and exact precision in every area. This does not mean that completely and correctly rebuilding an automatic transmission is beyond the scope and capabilities of the average automotive enthusiast. Automatic transmissions have always had a mystique about them that keeps away even the most skilled automotive technicians. There is no need to carry your TH350 off to a shop or to someone with more experience. A complete and correct rebuild can be accomplished in a small shop or garage. Anyone taking on the task simply needs to be armed with good information, a few tools that I describe, and good parts.
At the very top of the list of necessary items is a clean work area. An automatic transmission is a hydraulic or fluid-drive system. All parts must be kept dirt free and working smoothly for correct function. The person rebuilding the unit is essentially returning the main components to the same location, while, as necessary, replacing parts that wear out.
My goal is to outline the tools and equipment that help get the job done, showing tools that are often already part of the average automotive enthusiast’s toolbox, and tools that can be obtained easily, modified, or fabricated to get a particular task accomplished, without having to spend a lot of money buying them.
It is true that a few special tools may be required for certain operations on several of the units I cover. The good news is that the majority of the tools required are simply plain old hand tools, or tools that are easily fabricated if a procedure requires something not typically found in the average toolbox.
The biggest hurdle to overcome when rebuilding TH350 transmission is removing the low/reverse piston’s snap ring and spring cage from the case. That part of the build will require some sort of spring compressor. One can be fabricated easily from a long threaded bolt or piece of threaded rod, a couple of pieces of flat steel, and a nut.
It’s surprising the amount of tools you can accumulate over nearly four decades of transmission rebuilding. The good news is that most of what is needed to rebuild the TH350 transmission is already in the average homeowner’s toolbox, or can be fabricated quickly from readily available materials at minimal cost.
Compress the spring cages on the high and forward drums. You can use the same type of tool for the direct drum, but the forward drum becomes more of a challenge because of its attached shaft. This requires a press or spring compressor that holds the direct drum in position and allows a compressor to center over the spring cage to compress. Then you can remove the snap ring.
First and foremost on your list should be safety equipment. Automatic transmissions use pressurized fluid. During the rebuild, you come into contact with transmission fluid and cleaning solvents. You will also be using compressed air for drying parts as well as air pressure for testing clutch packs, servos, etc.
Eye protection is a must anytime compressed air is used. Nothing is worse than getting high-detergent transmission fluid into your eyes, or a piece of dirt or debris when you are blowing off parts.
A good pair of safety glasses with plastic or impact resistant lenses is a must for transmission work.
Chemical-resistant gloves help protect your hands from chemicals such as cleaning solvents, automatic transmission fluid (ATF), and assembly lubricant.
Nitrile gloves are a good idea for keeping solvents and transmission fluid off your hands. They also provide some protection against cuts from the jagged edges inside the cases. The quality of the gloves currently available varies considerably. The better-quality gloves are thicker and more resistant to solvents such as brake cleaner (which works well to remove oily residue from parts before assembly).
Heavy-duty and chemical-resistant gloves also provide protection. Wear them while cleaning the transmission case with heavy-duty degreasers or other harsh chemicals.
Heavy-duty gloves should be worn if using a parts washer and solvents. They also offer some degree of protection when handling transmission cases during the cleaning process. Sharp edges can leave some pretty nasty cuts.
Hearing protection is a must when hammering bushings in place and blowing off parts with compressed air. The tiny passages found in transmissions can produce high-pitched noises when hit with high-pressure compressed air; it can seriously damage your hearing.
Hearing protection is also a very good idea. During the rebuild, compressed air is used to clean parts and dry them. For example, when high-pressure air is blown into the case passages, it often creates a high-pitched sound that can damage your hearing.
General Motors used both metric and SAE fasteners throughout the years of production. Later units have metric fasteners; some units have both SAE and metric on the same unit. A complete socket set with 1/4-, 3/8-, and 1/2-inch-drive sockets is needed. Make sure to have extensions for each drive.
An
