The Novak Guide to the GM Muncie SM465 Transmission The SM465 is an outstanding, heavy-duty truck transmission designed and used in ½, 3/4 and 1+ ton trucks. The SM465 was made by General Motors from 1968 to 1991. They are found primarily in GM and Chevrolet trucks, Blazers, Suburbans and many other models falling under the 1/4-ton to 1-1/2-ton platforms. The 465 is an intellegently designed and very well-built transmission and remains easy to locate and generally inexpensive to buy and maintain. The strength, relatively short size and the gearing of the transmission make it a good choice for a variety of on-road and off-road situations. It has a very good set of road manners contrasted by its enormous off-road brawn. The "SM" in the transmission's designation stands for Syncrho-Mesh, in the tradition of other GM gearboxes. It is also referred to as the CH-465 or CH465 by factory literature. Identification The SM465 is a top loaded, top shifting truck style transmission. This transmission is 12 " long and features a cast iron top cover that is retained by eight bolts. The SM465 case is of *cast iron. The case itself is generously ribbed both vertically and horizontally. The SM465 has a 1-1/8" diameter, ten spline input shaft that has a stick-out of 6-1/2" from the front face of the transmission. The pilot tip is ~19/32" in diameter. The front bearing retainer flange measures an unusually large 5-1/8" in diameter and the bearing retainer tube is 1-3/8" in diameter. The front bolt pattern is the consistent GM Muncie / Saginaw four-bolt pattern as found on GM bellhousings and transmissions from the 1940's through the 1990's. Features The 465 enjoys a very low compound gear at 6.55:1 and as such it is a popular choice for those wanting a very low crawling gear. The SM465 features power-take-off (PTO) ports on the passenger and driver sides of the case. The shifting pattern for the 465 is in the standard "H" pattern with reverse gear being to the right side, and down. SM465 Versions There are three principal versions of the SM465, each based on the era and configuration of the transmission. There is no known mechanical superiorities to either earlier or later versions. Earlier SM465 The earlier era of the SM465 include the 1968 - 1978 transmissions. There were both 2wd and 4wd versions. Internally, they are identical to each with the exception of the transmission mainshaft. The 4wd version of this mainshaft (or "output shaft") has a 10-spline output with a 2-5/8" stickout and an accompanying 4wd adapter housing. The 2wd version has a 35-spline threaded mainshaft compatible with a driveshaft yoke, and accompanying 2wd style tailhousing. Later SM465 The later era of the SM465 include the 1979 - 1991 transmissions. A minor internal change of the 1st gear bushing and thrust washer occurred, in addition to a change from a shorter 10-spline, 4wd output shaft to a 32-spline 4wd output shaft - coinciding with the change of bolt pattern in the New Process 205 transfer case from a figure "8" input bolt pattern to a round, six-bolt input pattern. This pattern was also found on the 208 and 241 chain-driven transfer cases. Later 2wd style SM465's also incorporated the same 1st gear bushing and thrust washer change, but the 35-spline, yoked output remained identical. 1988-1991 Versions The last years of SM465 featured a direct-drive (4th gear) switch to signal a lean or cruise mode operation to the GM Engine Control Module (ECM). These final versions had an aluminum top cover and a revised input shaft and input bearing combination. They were found in the C/K Series trucks. Suburbans, however, continued to use the earlier SM465 with the cast iron top cover.