rel="nofollow" href="#ulink_acfc0696-fc79-5c3c-9ee2-75a2b5eaae90">Case Cleaners
Once the transmission is completely stripped down, the case needs to be cleaned. Cases are often coated with mud, dirt, grease, undercoating, and road tar. A quick trip to a local carwash gets rid of most of the heavy debris. Some additional time spent with a screwdriver and small wire brush loosens the stubborn dirt and grease. Some solvent, such as brake cleaner, may be required to get the tar and undercoating off of the case. Brake cleaner also helps to dry the case; it doesn’t leave an oily residue. It also works quite well for cleaning internal components.
A gasket scraper, small screwdriver, and wire brushes also help with case cleaning. They help remove really stubborn deposits such as undercoating and road tar that the transmission has encountered through years of service.
Brake cleaner helps dry and degrease the case prior to assembly. It doesn’t leave any oil or other chemicals behind that could prevent paint from sticking, and it doesn’t damage the rubber seals on the TH350’s low clutch-pack apply piston.
A power washer makes a great transmission case cleaner. Using a zero tip, a good power washer blasts off dirt and grease to make the cleanup process a lot easier.
Dirt can enter the assembly in a lot of places when you are power washing the cases. It’s not really practical to tape up all of the potential entry points to try to keep the water and dirt out prior to power washing, so I usually save the cleaning for after the cases are stripped all the way down. Even so, some common sense applies here, and a case completely covered with mud from a 4x4 or off-road application is certainly one I’d want to clean up some before taking it apart.
Several very good degreasers are available to clean up transmission cases and tail housings that may be covered with dirt and grease. Soak the transmission for several hours and then blast the case with a power washer or take it to a local car wash.
Several companies make heavy-duty degreasers specifically designed for this purpose. Applying these cleaners before power washing or hand cleaning helps to loosen heavy greasy deposits from the case. Some of these products produce fumes so they should be used only in a well-ventilated area. Also use a good pair of thick chemical-resistant gloves.
Bushing Removers and Installers
Automatic transmissions have numerous bushings. Some are relatively easy to access for removal and installation, while others may be quite difficult to get to. If a bushing is readily accessible and driven in flush with the top surface of its hole, removal and installation is relatively easy. Just about any suitable flat driver can be used to flush-mount a bushing.
Bushing drivers can be fabricated from just about anything with a wide flat surface and some sort of a handle on it, such as old engine valves.
A good bushing driver set is not inexpensive, and really not needed if you are only doing one or two units. Most bushings are driven in flush, so any suitable driver with a broad flat surface and some sort of a handle works. For bushings that are driven in below flush, you can split an old bushing and use it in combination with a flat driver. Complete bushing driver sets, as shown here, have the necessary drivers to set any bushings to specific depth.
Some bushings are driven in below flush. They may be, for example, deep enough that they are below the lube oil supply hole. Careful measurement and care must be used to install these bushings to the same depth at which they were originally installed. This requires a bushing driver slightly smaller than the hole into which the bushing is driven. If a bushing is located in a blind hole, it may be difficult to remove. A sharp punch ground on a slight angle can be fabricated to catch the edge of the bushing and drive it down. The bushing turns sideways in the bore and can then be pried out with a large screwdriver.
The lower case bushings for the TH350 and TH400 transmissions should be driven in from the front. You need an extension with a suitable bushing driver to gain access to them.
A long tapered punch is a must for bushing removal. Grind an angle to the tip as shown. The sharp edge catches the bushings and helps remove them from their bore. Even bushings in blind holes can be turned sideways and pried out using a tapered punch.
Instead of using a tapered punch, you can remove the TH350’s output shaft bushing with a starting tap. Thread the tap into the bushing and continue until it hits the bottom of the bore. It pushes the bushing out of the bore without damaging anything.
The lower case bushings on TH350s and TH400s may require a long extension to drive the new bushing in place. You need a large piece of solid steel pipe to help drive them in. The front output shaft bushing in the TH350 transmission can be effectively removed with a large tap. Tap the bushing and continue to turn the tap until it hits the bottom of the hole; it pushes the bushing out of the output shaft. This bushing is difficult to remove by any other method.
Use a large punch ground at an angle (as described above) to remove this bushing. You need a shop vise with soft jaws to effectively hold the output shaft. With a hammer and angle-ground punch, drive down on the edge of the bushing. Locate the seam if possible, and collapse the bushing; it can then be removed from the output shaft. Use care for this procedure to avoid damaging the inside of the bore where the bushing is located.
Heli-Coils and Bolt Extractors
The transmissions that I discuss here are cast aluminum alloy. Steel fasteners attach the various parts, such as the vacuum modulator and oil pan. It is not uncommon to strip the threads out of the case in one or more places; this usually occurs with the oil pan attaching bolts. In some cases, a longer bolt can be used to reach new threads. Another option is to use a larger-diameter bolt.
However, the best repair is to install a thread insert
