Saginaw 4-Speed Bearing and Seal Overhaul Kit T301R

The Motive Gear T301R is the bearing and seal overhaul package for GM's Saginaw manual transmission, covering both the 3-speed and the 4-speed version of the case. These are the cast-iron, side-cover-shift boxes GM put behind small blocks in Chevelles, Novas, Camaros, Firebirds, and light-duty pickups, and they are still the cheapest four-speed to keep alive in a street car. When one starts howling in a specific gear or leaves a puddle under the bellhousing, it is almost always bearings and seals rather than gear teeth.

Use it on a full teardown. With the case on the bench, pull the side cover and shift forks, slide a dummy shaft through the cluster gear so the roller bearings and thrust washers stay put while you drive the countershaft out the back, then unbolt the front bearing retainer and pull the main drive gear with its bearing. Everything that spins gets replaced out of this kit: the front and rear main bearings, the mainshaft support, and the seals at the input retainer and tailhousing. Set the cluster gear endplay with the original thrust washers before you close it up.

The two failure patterns this fixes are a whine that changes pitch with road speed in every gear but fourth, which points at the cluster and countershaft bearings, and gear oil weeping down the back of the bellhousing or out the tailshaft, which is the input retainer seal or the extension housing seal. Both are cheap to fix on the bench and expensive to ignore, because a collapsed bearing puts steel through the gear set. Motive Gear backs the kit with a 1-year, 50,000-mile warranty.