Transmission Spotter’s Guide

We’ve complied info on the most popular automatic and manual four-wheel-drive transmissions and give you a look at their overall shapes. We’ve also included peculiarities that’ll make it easy to pick them out in a crowd. The photos and illustrations are the easiest way to tell each of the trannies apart, but here are some pointers.

Automatic Transmissions
The easiest way to identify anything is by process of elimination. With transmissions, your first step is to look at the bellhousing and the oil pan on the bottom. If you’re lucky, the tranny will have the model number on the case. However, often it has been removed, and then things get interesting. You have two choices for narrowing down the juicebox: bolt pattern or oil pan. The following page shows exactly what each pan looks like for the most popular automatic trannies, as well as each bolt pattern.

In terms of specifics, let’s start with the GM trannies. Most of the four-speed TH700-R4s, or 4L60s, have a four-prong terminal on the driver side, although the ’93 4L60 has a five-pin connector. You might be able to ID it by codes MD8 or MXO that might be cast into the case. Later models have a 30-spline output shaft. The three-speed TH350 is the most common transmission in GM 4x4s and can be easily identified by its small size. The ID stamping (if still intact) can be found on the driver side. The three-speed TH400 looks similar to the TH350, so the easiest way to tell the difference is to head straight for the oil pan. The TH400’s is Texas-shaped. The GM Powerglide is a two-speed tranny that says Powerglide (or GM) on the passenger side.

The three-speed C4 Ford transmission can be differentiated from the C6 (also a three-speed) by its smaller size and thin, almost cylindrical case. There are two versions of the C4, a flare case and a step case. The flare-cased C4 tranny’s bellhousing bolts directly to the transmission case with five bolts, and the oil-pump bolts are separate. The case flares out to meet the bellhousing. The step case uses the same bolts for the oil pump and the bellhousing, and there’s a ¼-inch gap between the case and the bellhousing. Also, there’s no drain plug in the oil pan. The C5 looks identical to the C4, but the oil pan has a hump, versus the C4’s flat pan. The AOD (automatic overdrive) four-speed looks nothing like the C4, C5, or C6. The E40D four-speed came behind computer-controlled engines only. The Chrysler 727 TorqueFlite is a three-speed with no case markings—it’s smooth with a long output shaft. Originally it had a cast-iron case but was later built with aluminum. It looks just like the 909 (not shown in this story).

Manual Transmissions
Unlike the automatic transmissions, identification of the manual kind can’t be made simply by looking at an oil pan. Let’s start with the Borg-Warners. The good news is that you can tell them apart by the casting number in the case. The T5 overdrive tranny is a five-speed, top-loader case with a 1352 casting number. Top-loader simply means the gears are loaded into the tranny through the top when the tranny is rebuilt. Some trannies are side-loaded, meaning the gears go in through the side. The other easy way to spot the T5 is by its aluminum casting—important since the front of the case is the same as the T4’s (not shown in this story). The T15 three-speed is a top-loader and has either a side- or top-mounted shifter. Its casting number is 1307. The four-speed T18 looks identical to the T98 (which we’re also not discussing), so check for casting number 1301. The three-speed T90 is a top-loader and can have either a side or top shift, and the casting number is 1318. Also, the short-input-shaft T90s were used behind four-cylinders, while the longer ones were used behind the sixes.

The four-speed Muncie SM465 used in GM trucks is a top-loader and features an iron case and cover. The difference between it and the four-speed SM420 is the output shaft; the SM420 has a journal-design countershaft. It has an iron case and cove, like the SM465, and is a top-loader.

New Process made it simple to tell the NP833 and NP435 apart: The four-speed NP435 has an aluminum top cover, a cast-iron case, and a tower shift and is a top-loader. The four-speed NP833 has a side shift cover.

The Tremac 150 has the same case configuration as the Tremac 176, so watch for the four-speed 176’s butterfly bolt pattern and aluminum case. The 176 also has a top cover with shift forks, while the three-speed 150 is a top-loader and has a tower shift and cast-iron case. Check out the box above for a look at each of these transmissions.