Rebuilds the GM SM465 4-speed granny-low manual with all bearings, seals, gaskets, small parts and synchronizer rings for 1968-and-newer Chevy and GMC trucks.
The SM465 is the cast-iron granny-low 4-speed behind the small blocks, big blocks and diesels in Chevy and GMC C/K pickups, Blazers, Jimmys, Suburbans and vans, and it is one of the few old manuals worth rebuilding instead of replacing. If yours howls in every gear, grinds going into second or third, jumps out of fourth or drips from the front and rear seals, this USA Standard Gear kit replaces the bearings, seals, gaskets, small parts and synchronizer rings that wear out, so you can reuse the gears and case that almost never do.
Power comes in through the input shaft, which rides on the front bearing in the case and carries the mainshaft pilot bearing inside its nose. The countershaft (cluster) gear spins on needle bearings and thrust washers, and every forward gear is driven through it, so a worn cluster bearing makes noise in first, second and third but goes quiet in fourth, which is a direct 1:1 lock-up. The mainshaft rides on the rear bearing at the back of the case, and the reverse idler spins on its own needles. Second, third and fourth are synchronized: brass synchronizer rings rub against cones on each gear to match speeds before the slider engages. First gear in the SM465 has no synchronizer at all, which is why it is meant to be selected only when stopped. When the rings wear smooth, the gears clash going in, and once the bearings loosen, shafts move out of line and the box howls and can pop out of gear.
Grinding into first while the truck is rolling is normal for an SM465, since first gear is not synchronized; this kit does not change that.
Check the oil level first; these boxes leak at the top cover and seals and often run low for years. Then listen in each gear: noise that stops in fourth points to the countershaft, noise that stays points to the main bearings. With the truck off and in neutral, check for input shaft play at the clutch. Our SM465 problems and rebuild cost guide covers the common failures and what a rebuild runs, the countershaft bearing failure guide explains the gear-by-gear noise test, and if you are weighing rebuild against replacement, see automatic vs. manual transmission repair cost.
This kit fits the SM465 with the cast-iron case and cast-iron top cover and the 0.68 inch wide input bearing, which covers 1968-1987 Chevrolet and GMC pickups and vans and 1969-1984 Blazer, Jimmy and Suburban. These are the cases with two PTO side covers, and the kit includes gaskets for both. Late 1988-1991 trucks use an aluminum top cover with a wider 0.83 inch input bearing and need a different kit, so look at the top cover before ordering: if it is aluminum, this is the wrong kit. If you are not sure, send us the year and a photo of the top cover and we will confirm it. If your gearbox is actually a passenger-car Muncie M20, M21 or M22 rather than the truck SM465, see the 1966-74 Muncie bearing kit with synchros. Browse every manual transmission and differential rebuild kit.
Included: input, mainshaft and countershaft bearings, needle bearings and thrust washers, input and output seals, all case and cover gaskets, snap rings and small parts, and synchronizer rings. Not included: gears, synchro hubs, sliders, shift forks or the synchro key and spring sets. Inspect gear teeth, the cluster and fork pads during teardown, and replace keys and springs if they are worn.
Bench rebuild it on a clean surface with the GM shop manual for your year. Press bearings on square and seat every snap ring fully. Lap each new synchronizer ring on its gear cone and check the gap between ring and gear dog teeth; a ring that sits too close to the gear means the cone is worn and the new ring will not last. Measure countershaft and mainshaft end play with a dial indicator and magnetic base and set it to the manual's specification. Refill with the gear oil specified for your year; our GL-4 vs GL-5 guide explains why a GL-4 rated oil such as Red Line MTL 75W-80 GL-4 is kinder to brass synchro rings. With the transmission out, replace the clutch release bearing and pilot bushing at the same time.
| Type | Manual transmission bearing, seal and synchro rebuild kit |
| Fitment | GM SM465 4-speed manual, 1968 and newer Chevy and GMC trucks |
| Input bearing | 0.68 inch wide, cast-iron top cover units |
| Includes | Input, output and countershaft bearings, needle bearings, seals, gaskets, small parts and 3-4 synchronizer rings |
| Also includes | Two PTO cover gaskets for truck cases |
| Does not include | Gears, synchro hubs, sliders or shift forks |
| Brand | USA Standard Gear |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Probably not. Late 1988-1991 SM465s use an aluminum top cover with a wider 0.83 inch input bearing and take a different kit. This kit is for the cast-iron top cover units with the 0.68 inch input bearing. Check the top cover material before ordering.
First gear in the SM465 has no synchronizer. It is a granny low meant to be selected at a stop. Grinding into first while rolling is normal and new synchro rings will not change it. Grinding into second or third is a synchro problem this kit does fix.
No. The kit includes synchronizer rings but not the key and spring sets, hubs, sliders, gears or shift forks. Inspect those at teardown and replace keys and springs if they are worn.
That pattern usually means worn countershaft (cluster) bearings, because fourth is a direct drive that does not load the cluster. This kit replaces the countershaft needle bearings and thrust washers.
Use the gear oil specified for your year in the GM manual. A GL-4 rated manual transmission gear oil is the safe choice for the brass synchro rings, and keep the level at the bottom of the fill plug.
A press, snap ring pliers, a bearing separator and a dial indicator for end play are the minimum. The SM465 is a straightforward rebuild for a careful home mechanic, but if you lack a press, a shop can press the bearings for you.
