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1990 GMC Sierra Transmission

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Crawdaddy, Apr 22, 2010.

  1. Crawdaddy

    Crawdaddy ↑↑↑ Has no life Staff Member 5+ Years 1000 Posts Platinum Contributor

    Hey all!

    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!
  2. Greg84

    Greg84 Rockstar 100 Posts

    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.
  3. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    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.
  4. Crawdaddy

    Crawdaddy ↑↑↑ Has no life Staff Member 5+ Years 1000 Posts Platinum Contributor

    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. :party:
  5. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    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.
  6. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    I have done trannies in a 1988 2wd, 1991 2wd, and a 1992 4wd, and a 1994 4wd. They were all 700R4 trannies except for the 1994, and i was looking into a 4L60E for the 1992 since i was thinkning the same thing and went to the junk yard as they were brining me the 700R4 out of a K3500 with a 350 in it.. I was confused till i looked at it and sure enough it was the same. So someone might correct me but hey i dont claim to know everything.....
    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: Apr 23, 2010
  7. Crawdaddy

    Crawdaddy ↑↑↑ Has no life Staff Member 5+ Years 1000 Posts Platinum Contributor

    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.
  8. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    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..
  9. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts


    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.
  10. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    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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