2. GM SM465

   In 1968 the 20 year reign of the SM420 transmission came to an end. An understandable apprehension spread throughout the GM community as to its new replacement. The concerns were quickly dismissed as the SM465 proved worthy of its predecessor in strength and reliability. The brawny SM465 deserves to be considered as one of the best transmissions ever offered by General Motors.

  The SM465 is commonly referred to in the off road community as a Granny 4 speed, It also carries the nickname “Bulldog”. Much like other 4 speed truck transmissions, the SM465 offers an impressively low first gear of 6.54:1. This transmission is ideal for the off roader who needs the added benefits of “the crawl” and demands the respected strength offered by the SM465.

 

 The shift pattern has the standard H pattern with reverse being down and to the right. As with most truck transmissions, the granny gear is seldom used for street use. The shift pattern itself gives misconceptions to many as it indicates L-1-2-3-R, which many consider as a 3 speed.

 

 The SM465 transmission comprises of both a cast iron case and top cover. The cover is retained by 8 bolts. The transmission measures in at a large but acceptable 12” in overall length. The case itself features impressive reinforcement ribs traveling in both a longitude and latitude fashion. This transmission also features dual PTO ports. The input shaft measures 6-1/2” of stick out length from the front of the transmission case. The clutch splines on the input shaft were 1-1/8” 10 splines, which was the typical standard for many of GM’s transmissions. The pilot tip of the transmission retained the customary .590 pilot tip.

  

We have also encountered a few 1-3/8” 10 spline input shafts over the years. These oversized inputs seem to be isolated to some heavier 2 ton applications. The 1-3/8” 10 spline seems overkill for most applications, it is however common for tractor pull vehicles to upgrade to this shaft.

 

     One of the key identification attributes of the SM465 is the enlarged front bearing retainer. Most GM 4 speeds consisted of a bearing retainer with the base measuring 4.686” in diameter. The SM465 retainer features a base of 5.125”; therefore, the bell housings offered in front of SM465 transmissions were machined with a larger hole in the center of the bell housing. The snout area of the retainer for the throw out bearing remained the standard 1.34” As with most GM transmissions during this era; the SM465 retained the standard GM Saginaw 4 bolt pattern on the front of the transmission.

 

 It should also be noted that during the last years of the SM465, the transmission was offered with an aluminum top cover. These transmissions also featured a unique “cruise” feature. The transmission basically had a forth gear switch that could activate a cruise mode feature. It was used in conjunction with the ECM to offer a leaner mode of engine operation for added fuel economy. These transmissions were commonly used 1989-91 C/K trucks.

 

 Over the 25 year span of the Sm465, there were three primary SM465 output shafts offered. It is important to discuss these differences due to the fact that many of AA’s adapters utilize existing output shafts. The SM465 transmissions were used in both 2 and 4wd vehicles. The 2wd transmissions featured a 35 spline output shaft where a corresponding yoke was bolted. The 35 spline was robust and somewhat short making it ideal for conversions.

 

 The early 4wd transmissions were offered with a short 2-1/2” stick out 10 spline output shaft. These output shafts where commonly used in conjunction of the NP205. Since the transfer case also utilized a 10 spline male shaft, the two coarse splined shafts were mated via a female to female splined tube. These tubes are commonly known as “power sleeves”. The transmission and np205 were mated by a 7” long cast iron adapter.

 

 In 1982, GM began the initial and gradual phasing out of the NP205 on some of their vehicles. Design changes to the SM465 would be needed to offer the transmission behind the new NP208. The revised SM465 offered a long 32 spline output shaft and adapter. This became the standard application for up to ¾ ton trucks. GM rightfully decided not to offer the NP208 in their 1 ton and dually applications.   Larger trucks still maintained the earlier 10 spline NP205 application for the time being. 

 

 In 1984, GM introduced an updated version of the NP205. The figure eight bolt pattern and 10 spline shafts were retired. The new NP205 would now offer the same round 6 bolt pattern and 32 spline input as the NP208. The decision to offer both transfer cases with the same bolt pattern and spline counts would allow GM to streamline production of the SM465 transmission.  All 4wd SM465 transmissions were now offered as 32 spline only. Although the 32 spline output shafts are impressively large and strong, the overall length of these output shafts cause length issues for most conversions, and therefore routinely require the installation of shorter output shafts.

 As the early 1990s approached, GM increasingly saw the American consumer s’ desire for more fuel efficiency. The future was going to be overdrive and that meant 5 speeds. GM retired the SM465 in 1991 and ushered in the NV4500 5speed.