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1969 GMC · 09-09-2004, 09:55 PM

Gm's designation of the truck 4 speed as M20 is confusing to say the least. However, there are 2 different trannies it could be. The SM420 was offered from about 1947 til 1967, it is a slightly more compact and lightweight transmission, but very durable. Parts may be hard to find.
The 2nd is the SM465, introduced in 1968. It is bigger and heavier than the SM420, and was used until at least 1991.
It did not matter what size engine for the 4 speed to be optioned, the only diff is that 67 is the last year for SM420.

09-09-2004, 09:55 PM	#2
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	Gm's designation of the truck 4 speed as M20 is confusing to say the least. However, there are 2 different trannies it could be. The SM420 was offered from about 1947 til 1967, it is a slightly more compact and lightweight transmission, but very durable. Parts may be hard to find. The 2nd is the SM465, introduced in 1968. It is bigger and heavier than the SM420, and was used until at least 1991. It did not matter what size engine for the 4 speed to be optioned, the only diff is that 67 is the last year for SM420. __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650