1990 GMC Sierra Transmission

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

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  1. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    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 New Member 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 New Member 1000 Posts 100 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 Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    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 Super Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    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 New Member 1000 Posts 100 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 Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    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 New Member 1000 Posts 100 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 New Member 1000 Posts 100 Posts

    Chris,

    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 New Member 1000 Posts 100 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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