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#57047 02/25/2006 7:50 PM | Joined: Mar 2005 Posts: 92 Wrench Fetcher | | Wrench Fetcher Joined: Mar 2005 Posts: 92 | Is there any way to figure out what year SM420 transmissions are? I have two different trannies and I want to date them (no I don't mean dinner and a movie.) Thanks in advance,
Steve O | | |
#57048 02/25/2006 7:52 PM | Joined: Nov 2001 Posts: 481 Shop Shark | | Shop Shark Joined: Nov 2001 Posts: 481 | | | |
#57049 02/25/2006 9:04 PM | Joined: Oct 2003 Posts: 5,152 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Oct 2003 Posts: 5,152 | I'm pretty sure there are casting numbers that can help sort it out. Somewhere I have a book that should have the numbers.
But a few other things things will help narrow the range.
Only in '67 did they have a backup switch mount near the shifter.
If its setup for a torque tube its '54 or earlier. The inverse is not necessarily true, one setup for open drive might have been for an early big truck.
Post the casting numbers and I'll look for my book. If I don't post back email or PM me.
1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble... | | |
#57050 02/25/2006 10:35 PM | Joined: Mar 2005 Posts: 92 Wrench Fetcher | | Wrench Fetcher Joined: Mar 2005 Posts: 92 | Thanks for the response and I think I figured it out. They have a casting code similar to the engine for dating. one of the trannys had a last number of "8" and the other was a "9". So they could have been either or both late '40's or '50's. The early 420's didn't have a neopreme seal on the input shaft. So I pulled the front bearing cover and found out I have a '49 and a '58. I had replaced the '49 one in my '50, so it was probably the original tranny. The '58 has an extra cast tab on the upper left rear with a threaded hole. Don't know what that is for. The casting number is 3761930. I wouldn't mind if this could be looked up for application.
Thanks,
Steve O | | |
#57051 02/26/2006 3:06 AM | Joined: Sep 2003 Posts: 343 Member | | Member Joined: Sep 2003 Posts: 343 | According to the Novak site: http://www.novak-adapt.com/knowledge/sm420.htm The casting number would indicate a 64-67 SM420, since it is a 7 digit number starting with 37xxxxx. Apparantly all the trannys prior to 64 only had 6 digit casting numbers. The following passage was taken from this webpage: http://members.cox.net/cglabe1/SM420/sm420.html "You can determine the date of manufacture of your sm420 by decoding the casting mark on the top of the drivers side. The code starts with a letter that stands for the month (A-L), followed by two digits for the date and two digits for the year. In the example below, H3061 means August 30, 1961." I just noticed that your casting number matches my SM420 trannys casting number. I just finished rebuilding my SM420 recently, that is why I am so familiar with the sites I posted above. I have some pics of my tranny being rebuilt, but I need to put some more pics in the album showing the completed tranny. Here are some pics: http://community.webshots.com/photo/546614518/2646378880052948230tEJbXV Jim
1954 GMC 1/2-ton Longbed
1971 Pontiac LeMans Sport
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