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Thread: 1990 GMC Sierra Transmission
04-22-2010, 12:37 PM #1
1990 GMC Sierra Transmission
I'm just trying to confirm my research. I'm trying to get a replacement transmission for a 1990 GMC Sierra 2500. From visual inspection, it appeared to have a Chevy 350 and a TH700R4 tranny. A 700R4 in a 3/4 ton truck doesn't seem quite right, but I don't think it's ever been swapped. So, I decided to look up the RPO codes in the glovebox. According to the RPO codes, it has a 305 and a 700R4. Wow, a small motor AND a 700R4 transmission in a 3/4 ton. So, I just need to know if it makes sense that it has a 700R4 transmission in it, and not a 4L60E or a 4L80E. I thought they went electronic by then, but I swear it looked like a 700R4. Am I right? Junkyard, here I come!Christopher
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04-22-2010, 01:06 PM #2
1990 would still be a 700r4. The speedometer signal should be electric instead of mechanical (first year for that), but the rest of it wouldn't be electronic.
04-22-2010, 01:24 PM #3
The 700R4 had an electric speedo from 1988 on i know for sure.. But yes a 305, and 700R4 is a 3/4 ton sounds about right i have seen a few ext cab 2wd 3/4tons running about with 4.3Ls and autos in them..
The 4L60, and 80Es werent available till 1993-1994 from my understanding.Mike
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04-22-2010, 01:55 PM #4
For some reason, I thought pickups moved to the 4L60E in 88 along with the body change. I know the 700R4 was kept in Suburbans until 1991, but so was the 80s bodystyle. Cool. I might also get a spare 700R4 out of this deal then.
04-22-2010, 07:35 PM #5
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Yea that combo was available in the 2500, pick-ups of that year too.
I always though it was a little light for a 3/4 ton but a lot of trucks were equipped like that and they seemed to do ok.
04-23-2010, 08:31 AM #6
But hey a spare 700R4 is never a bad thing to have around. Id build the heck out of it if its laying around and upgrade it as you go...
Oh and tbplus10, mine is a little on the under powered side.. So a TBI350 in these things is just what i would consider adaquate. I would be scared to run with the V-6. The 305 is kinda in the same boat as the 350 as far as i am concerned.
Last edited by murdog94; 04-23-2010 at 08:33 AM.
05-07-2010, 09:59 AM #7
What vehicles would be suitable candidates for a transmission for the truck. Obviously vehicles that have 2wd 700R4s in them, but what vehicles would have come with a 700R4. Pickings for trucks with that transmission seem to be slim down here.
05-07-2010, 10:16 AM #8
I believe the fullsize vans came with a 700R4.. oh and i did some research into this a little bit more.. In 1992 some of them were 700R4s but most were 4L60E's... So just about anything fulsize from 1992 back will work. I am not 100% but i think the 700R4 from a 2wd S-10 with the 4.3L will work as well though i would measure the length since the tail shaft might be a bit short. And possibly the Astro vans with the 4.3L will as well.. I know that anything with the 4.3L had a 700R4 backing it up in the same years but i am not to sure if the tail shaft lengths were different.. And most RWD cars came with a 200R4 that wont work in the fullsize trucks..
05-09-2010, 08:08 AM #9
The 700 has to be from a 305 or 350 to start with. An S-10 won't work because the bell housing is different. A diesel will bolt up but won't shift correctly and will have the wrong torque converter. Lastly the 2WD and 4WD will not interchange without a teardown and shaft change.Jim
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05-09-2010, 01:56 PM #10
Thanks for clearing that up for me as well Jimmiee, i wasnt sure but did want to point it out as a possibility since some models share. However the 4.3L it is good to know for me as well.
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