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#47137 07/02/2005 2:18 AM | Joined: Jun 2005 Posts: 6 Junior Member | | Junior Member Joined: Jun 2005 Posts: 6 | 1948 3/4 TON - WHAT YEAR 4 SPEED TRANS. WILL FIT AS A DIRECT BOLT IN to replace the tired original 4 speed? | | |
#47138 07/02/2005 2:46 AM | Joined: Jun 2001 Posts: 11 Junior Member | | Junior Member Joined: Jun 2001 Posts: 11 | The granny gear 4 speed standard from 1947 (I believe) until 1967 is called an SM420.
The tail shaft changed up a bit to fit torque tube drive trains and heavier trucks.
After 1954, the tail shafts had open yolks and driveshafts. These trannies are not hard to find, the cases changed a bit over the years, and a reverse light switch was added in '67.
SM stands for syncromesh.
Thunder54 | | |
#47139 07/02/2005 3:16 AM | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 | Thunder54,
Thanks for the info - I did not know what the SM stood for until now.
Am I correct in my understanding that the torque-tube tail shaft (fitting/housing) on the rear of oleight's '48 1/2 ton 4-speed comes off and can be used on any open-shaft SM420? Or, is this only correct for later years of 1/2 ton torque-tube SM420s - I did this with my '54 1/2 ton enclosed driveshaft SM420's "tail shaft" housing on a '54 1-ton SM420?
Thanks,
Tim | | |
#47140 07/02/2005 2:04 PM | Joined: Jun 2005 Posts: 6 Junior Member | | Junior Member Joined: Jun 2005 Posts: 6 | Are all of these trannys thru 1967 the same gear ratios? Thanks | | |
#47141 07/02/2005 5:24 PM | Joined: Jun 2005 Posts: 221 Wrench Fetcher | | Wrench Fetcher Joined: Jun 2005 Posts: 221 | The SM420 to my understandung is a heavy duty tranny GMC used them behind the big V6s the standard 4 spd tranny from a chevy is much smaller i have a SM420 in my 63 GMC it is huge compared to the 4 spd in the 68 C-10 truck i have.also have an 80 GMC 4x4 with new process 4spd The SM 420 is as big as the tranny and transfer case together. | | |
#47142 07/03/2005 3:11 AM | Joined: Jun 2000 Posts: 2,773 'Bolter | | 'Bolter Joined: Jun 2000 Posts: 2,773 | Here's the basic info on the SM420. http://www.novak-adapt.com/knowledge/sm420.htm This is a very durable tranny, and is the preferred tranny for the rock crawlers, due to it's low first gear. Unless there are major problems with yours, consider rebuilding yours. Parts are available and the job is not that hard. The factory shop manual has some good instructions. http://chevy.tocmp.com
Fred
52 3600
69 C-10
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#47143 07/05/2005 6:26 AM | Joined: Jan 2005 Posts: 35 Junior Member | | Junior Member Joined: Jan 2005 Posts: 35 | Hi since V6 Jimmy was talking about his overdrive new process 3 speed 4x4,
I just want to know if the new process a better and stronger transmission then the saginaw 3 speed OD of the late 1960s, does anyone have any ideas on what one is better to put in a newer 1973 and up GM pickup.? | | |
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