1962 C20 Tranny - The 1947 - Present Chevrolet & GMC Truck Message Board Network

DBear · 10-02-2011, 02:54 AM

Does anyone have an opinion on the 4 speed manual trans that came as a option in a '62 C20. Trying to figure out who was the manufacture, and model #. Also, was wondering how the performance is with them. Thanks

*blackedoutharley* · 10-02-2011, 06:48 AM

If you're talking about the "granny gear" 4 speed trans it should be the Muncie SM420... the easiest way to tell (vs. the SM465 from later years) is where reverse gear is located.

SM420 = towards your leg and down
SM465 = towards your passengers leg and down.

As far as "performance".... well, lets say that while the SM420 is virtually indestructible it is not a racing transmission by any stretch of the imagination.
With proper maintenance it serves as a great transmission for a truck and will handle a substantial amount of power.

I have the original SM420 in my '65 and it has held up behind a healthy small block for 125K with no issues and plenty of abuse.

The biggest problem I find with these transmissions is that the oil was changed by previous owners about as often as the rearend was and it usually wasn't enough.

For more info on the transmission check out:
http://www.novak-adapt.com/knowledge/sm420.htm

They are a popular transmission for the off road crowd due to a very steep 1st gear ratio.

10-02-2011, 02:54 AM	#1
DBear Registered User Join Date: Nov 2008 Location: Rowlett, TX Posts: 867	1962 C20 Tranny Does anyone have an opinion on the 4 speed manual trans that came as a option in a '62 C20. Trying to figure out who was the manufacture, and model #. Also, was wondering how the performance is with them. Thanks

10-02-2011, 06:48 AM	#2
blackedoutharley Account Suspended Join Date: Jul 2007 Location: Plumas Lake, Ca. Posts: 1,009	Re: 1962 C20 Tranny If you're talking about the "granny gear" 4 speed trans it should be the Muncie SM420... the easiest way to tell (vs. the SM465 from later years) is where reverse gear is located. SM420 = towards your leg and down SM465 = towards your passengers leg and down. As far as "performance".... well, lets say that while the SM420 is virtually indestructible it is not a racing transmission by any stretch of the imagination. With proper maintenance it serves as a great transmission for a truck and will handle a substantial amount of power. I have the original SM420 in my '65 and it has held up behind a healthy small block for 125K with no issues and plenty of abuse. The biggest problem I find with these transmissions is that the oil was changed by previous owners about as often as the rearend was and it usually wasn't enough. For more info on the transmission check out: http://www.novak-adapt.com/knowledge/sm420.htm They are a popular transmission for the off road crowd due to a very steep 1st gear ratio.



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