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
| 1st | 2nd | 3rd | 4th | R |
| 6.55 : 1 | 3.58 : 1 | 1.70 : 1 | 1.00 : 1 | 6.09 : 1 |
Muncie SM465 Transmission Specs
| Transmission | Muncie SM465 | |
| Type | 4 speed manual transmission | |
| Manufacturer | General Motors | |
| Applications | 1968 - 1991 Chevrolet/GMC pickups, Blazers, and Suburban, 1982 - 1991 6.2L GM diesel equipped trucks |
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| Synchronized | Synchronized in all forward gears and reverse | |
| Case Material | Cast iron case & top cover | |
| Case Length | 12.00" | |
| 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 |
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| Weight | ~ 175 lbs | |
| Fluid Type/Spec | 50W or 80W-90 non-hypoid gear oil Recommend Amsoil Severe gear 80W-90 full synthetic gear oil |
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| Identification | 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. Transmission has passenger and driver side PTO provisions. |  |