Replaces the worn bearings and seals in a GM Saginaw 4-speed or 3-speed manual box on the bench, curing gear whine and tailshaft leaks.
If the GM Saginaw four-speed or three-speed in your Nova, Chevelle, Camaro, Firebird, Vega, Monza or light truck has started to howl, rumble through the floor at cruise, or drip gear oil from the tailshaft or the front of the case, worn ball bearings and dried-out seals are the usual cause. The Motive Gear T301R is a bearing and seal overhaul kit for the Saginaw: the two main ball bearings that carry the input and the mainshaft, the input and rear lip seals, the small shift-shaft seals, and the side cover, front retainer and tail housing gaskets, as shown in the product photo.
GM and Saginaw developed the four-speed in the early 1960s using Borg-Warner T10 ideas, and it stayed in production into the 1980s. It is easy to spot: a cast-iron case with a cast-iron, seven-bolt side cover, and the reverse lever lives on that side cover rather than on the tail housing. The input shaft rides in a large snap-ring ball bearing in the front of the case, held by the front retainer; the mainshaft is carried at the back by a second snap-ring ball bearing. The 1966-87 GM Saginaw parts breakdown lists those as 6207N (input) and 6306N (rear mainshaft) sizes. Everything else, the gear stack, synchros and counter gear, depends on those two bearings keeping the shafts on center. Once they wear, the shafts move under load, the gears mesh poorly and the noise starts.
Check the oil level at the side fill plug first; a box that is a quart low will whine on its own. Then listen: noise in the lower gears that disappears in fourth means the load path through the counter gear is involved, which is a bearing and counter gear job. Noise that changes when you push the clutch in with the car in neutral is the input bearing. Drain the oil and look for brass (synchro wear) versus steel glitter (bearing or gear wear). If you are deciding whether a rebuild is worth it, our manual versus automatic repair cost guide lays out the numbers, and what to check on a used transmission helps if you are weighing a swap-meet replacement.
The T301R is listed for GM Saginaw three-speed and four-speed manual transmissions. Confirm you have a Saginaw: cast-iron case and side cover, reverse arm on the side cover, and a casting number starting with R for a four-speed or S for a three-speed. Input retainers differ between car and truck versions, and input shafts changed tooth counts over the years, so compare your old bearings and seals to the kit before the old parts go in the scrap bin. Not sure what you have? Send us a photo of the side cover and the casting number. More kits are in our rebuild kits collection.
If the shifter is sloppy too, a Hurst Comp Plus shifter rebuild kit pairs well with a freshly rebuilt box. For gasket choices and sealer tips, see our gasket and seal materials guide.
| Part Number | T301R |
| Brand | Motive Gear |
| Fits | GM Saginaw 3-speed and 4-speed manual transmissions |
| Includes | Bearings and seals for a complete overhaul |
| Warranty | 1 year / 50,000 miles |
| Ships from | USA |
Yes, it is listed for GM Saginaw three-speed and four-speed manual transmissions. Confirm you have a Saginaw (cast-iron case and side cover, reverse lever on the side cover) and compare your old bearings and seals to the kit.
No. It covers the main input and rear ball bearings, seals and gaskets. Inspect the synchro rings, counter gear needle rollers and thrust washers during the teardown and replace them separately if worn.
A Saginaw has a cast-iron case and cast-iron side cover with the reverse lever on the side cover. A Muncie is aluminum with the reverse lever in the tail housing. A casting number beginning with R marks a Saginaw four-speed, S a three-speed.
Use a manual transmission oil that is safe for brass synchronizers, such as a GL-4 rated 75W-90, and fill to the bottom of the side fill hole. Avoid GL-5 hypoid oils unless the label says they are safe for yellow metals.
That pattern points at the load path through the counter gear and the main bearings. New bearings usually cure it, but inspect the counter gear needles, thrust washers and gear teeth, since chipped teeth will still make noise.
