The CH 465/SM465 transmission is a heavy duty gearbox that was used in a number of 1/2 – 1-ton, 4×2 and 4×4 vehicles from 1968 – 1991. The latter versions were used in Chevrolet and GMC trucks, the Blazer and Suburban. It’s thought the “CH” in CH 465 stands for Chevrolet, and the “SM” in SM465 stands for either Saginaw Muncie or Synchro Mesh. Either way, this is a very durable four speed manual gearbox that is ideally suited for off-road name and towing/hauling heavy…things.
What Transmission Do I Have?
CH 465 / SM465 Transmission Applications
CH 465 / SM465 Transmission Technical Specifications
The CH 465/SM465 transmission is a heavy duty four speed manual gearbox that was used from 1968 – 1991. It’s a top loading transmission, with a 12 inch long case that was initially made from cast-iron with extra ribbing for increased strength. On later versions, the top part of the case was made from aluminum, and a hydraulic clutch release was used after 1985. Given that the CH 465 transmission was used in heavy duty applications, dual PTO ports were used on the driver and passenger sides of the transmission case. In most applications, only second – fourth gears are synchronized, with a constant mesh first gear.
CH 465/SM465 Transmission Specs
Length: 12 inches
Height: 18 inches
Weight: 175 pounds (full cast-iron case)
1988 – 1991 versions of the CH 465/SM465 transmission got a direct drive fourth gear switch to signal the ECU of a cruise/lean mode operation.
Common CH 465 / SM465 Transmission Problems
Bushing, synchro and gear failure
Due to the heavy duty nature of the CH465 transmission, most of them have seen a lot of hard use. This can result in the failure of key components like the transmission bushings, synchronizers and the gears themselves. Gaskets and O-rings can also cause the transmission to leak gear oil, resulting in the loss of lubrication and further internal damage. Some of the symptoms of these transmission problems include:
Unusual noises coming from the transmission (grinding, thumping, whining etc.)
Transmission jumps out of gear
Difficulty engaging gears
Difficulty getting the transmission out of a gear
Oil leaks
What Transmission Do I Have?
