Muncie SM465 4 Speed Transmission

SM465 Transmission Specs & Ratios

The SM465 is often considered the successor of the Muncie SM420. It is a fully synchronized, four speed manual transmission found in many GMC and Chevrolet pickups. Having been used for several decades, it is readily available and replacement parts are plentiful. The SM465 has a standard "H" shift pattern with reverse being to the passenger and downwards.

The SM465 is likely one of the most well known, most popular heavy duty 4 speed transmissions within the realm of the four wheel drive and off-road community. It was made from 1968 to 1991, with the 1968 to 1978 units considered early models and the 1979 - 1991 transmissions considered the late model do to minor changes. The early SM465 had a 10 spline output shaft for 4WD models and a 35 spline output for 2WD models, while the late model 4WD transmission used a 32 spline output shaft. In 1988, the cast iron top cover was replaced with a cast aluminum one, and it also was fitted with a different input shaft and bearing design. The "SM" in SM465 designates it as a GM synchro-mesh transmission. It is top loaded, extremely rugged, and has an impressive 6.55 : 1 "Granny" gear.

Muncie SM465 Transmission Ratios






6.55 : 1

3.58 : 1

1.70 : 1

1.00 : 1

6.09 : 1

Muncie SM465 Transmission Specs


Muncie SM465


4 speed manual transmission


General Motors


1968 - 1991 Chevrolet/GMC pickups, Blazers, and Suburban,
1982 - 1991 6.2L GM diesel equipped trucks


Synchronized in all forward gears and reverse

Case Material:

Cast iron case & top cover

Case Length:


Input Shaft:

1 1/8" 10 spline input shaft, 6.5" stick-out

Max Input Torque:

465 lb-ft

Output Shaft:

• Early 4WD - 10 spline
• Early 2WD - 35 spline
• Late 4WD - 32 spline
• Late 2WD - 35 spline


~ 175 lbs

Fluid Type/Spec:

50W or 80W-90 non-hypoid gear oil
Recommend Amsoil Severe gear 80W-90 full synthetic gear oil


Top loading transmission, early style had a cast iron top cover, while the later model had an aluminum top cover (both had a cast iron case). Standard H shift pattern with reverse toward the passenger and down. Trans has passenger and driver side PTO provisions.

SM465 transmission top cover bolt pattern