Some bushings are installed below flush for a reason. Before removing any bushing that is not flush, take a moment to measure the depth in the bore. Make sure to duplicate the depth when installing the new bushing. This eliminates the chance that any lube oil passages are blocked off and ensures that the bushing supports the correct corresponding part of the shaft or component.
Another measuring device is a micrometer. Use ball micrometers to measure round surfaces and quickly determine bushing thickness. Flat-tipped micrometers (for measuring diameter) can tell you the diameter of a valve in the valve body
A feeler gauge is used to measure the free travel of the clutches in the forward and direct drums. This ensures that the transmission functions correctly, that you have put the correct number of frictions and steels in each clutch pack, and that they are the correct thickness.
A standard caliper is a great tool to measure friction and steel plate thickness, as well as the total thickness of clutch packs. It can also be used to measure the bushings’ diameter (both outside and inside), as well as the thickness of apply pistons, steel plates, and frictions.
A standard 1-inch micrometer works equally as well for measuring frictions and steel plates, as well as the total thickness of a clutch pack.
You should also add a feeler gauge to your list. They are used to check clutch pack endplay in the forward and direct drums. A feeler gauge is also used to install the apply pistons in the forward, direct, and intermediate drums.
Several of the units covered in this book require a piston spring compressor inside the case. The TH350 and 4L60, specifically, use a low/reverse piston in the lower portion of the case. A snap ring holds the spring cage in; it must be compressed in place for removal.
You need a spring compressor to remove the snap ring inside the case on the TH350 transmission. You can fabricate one in minutes with a long threaded 3/8-inch bolt and a couple of pieces of flat bar.
You can use these to compress spring cages on other components, provided those pieces have a center hole. For drums without a center hole, the component must be held stationary and some sort of spring compressor used to push down on the spring cage to facilitate the removal of the snap ring.
You can use a shop press to compress the spring cages on the forward and direct drums with a piece of flat steel and a couple of sockets that are the same height. Pretty much anything that compresses the spring cage evenly and does not distort it will work here. Be extremely careful here, because a shop press has enough force to distort the spring cages and damage the drum if the cage hangs up on the snap ring groove for any reason.
A spring compressor is a required tool for transmission building. Shown here is a homemade unit fabricated from square stock and angle iron. A spring compressor allows the transmission builder to gently compress spring cages just enough to remove and install the retaining rings without damaging the spring cage.
A larger tabletop bench-mounted spring compressor is needed for building clutch drums. A shop press works equally as well, although this type of press tends to be much more difficult to set up and a lot slower to use.
Many years ago, I made a spring compressor from two pieces of flat steel bar left over from other projects in about 5 minutes. It has served me well for decades and the total investment in the part was only a few dollars. Similar tools can be fabricated from steel flat plate and longer pieces of threaded rod. It mounts easily in a large shop vise for clutch drums with a protruding shaft. If necessary, a hole can be drilled through the workbench to accommodate these drums, which allows the tool to be used on a flat work surface if a large vise is not available. If you don’t want to build your own, spring compressors are also available through most commercial tool supply stores.
While certainly not required, a transmission holding fixture, if available, makes the build go much easier. However, being able to turn the transmission in any direction and lock it there really helps with the disassembly and assembly process. Several different types are available.
General Motors was kind enough to cast bosses into the case to accommodate a special holding fixture. Two round pins engage the case, one on each side, and then a long threaded bolt is tightened against the top of the case. Because no oil pan bolt holes are used, the entire transmission can be taken apart and reassembled while in the holding fixture.
Most universal holding fixtures use a couple of bolts that bolt into the pan rails. They still provide stability for the unit and the ability to lock it into any position, but the tool must be removed to install the oil pan and complete the rebuild.
A suitable working surface is a must for building transmissions. Use a heavy-duty table or workbench to effectively support the weight of the transmission if a holding fixture is used. The more surface area on the top of the bench the better, as it allows you to keep the parts separated and organized during the procedure.
A roll-around cart makes a great place to keep your rebuild kit and other parts clean and separated from the work area.
If a holding fixture of any type is to be used, it needs to be securely attached to a heavy-duty table or workbench. The workbench may need to be counterbalanced to offset the weight of the transmission. A simple heavy-duty workbench can be easily constructed from a couple of 4 × 8-foot sheets of plywood, 4 x 4s, several 2 x 6s and some good wood screws. The benches I use in the shop have storage space under them. The weight of the parts on the lower shelf provides enough stability so that the weight of the transmission doesn’t cause the table to fall over. The 4 x 8 work surface provides plenty of room to spread out all the parts removed from the transmission.
Several types of holding fixtures are available for transmissions. General Motors was kind enough to cast bosses on all TH350 and TH400 cases to accommodate the appropriate holding fixture.