1991 Chevy 1500, 350, 5-Speed

Discussion in 'Transmissions' started by mark mabry, Jun 2, 2019.

  1. mark mabry

    mark mabry Newbie

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    Can someone tell me what transmissions interchange? Thank you in advance :)
     
  2. JCribb

    JCribb Old Army truck mechanic

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    for the 1/2 ton like you have, 88-95, because those are external slave cylinder versions like you have. 96 and up switched to internal slave cylinder, meaning you have to drop the whole transmission to change the hydraulics out.

    I prefer the external setup over internal.
     
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  3. Gramps

    Gramps I'm Awesome

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    If I remember right, 88-90 are the same, then 92-93/4 and 93/4-95.

    There was a couple iterations in there, I think all COULD work, but will take some modifications, ie not a direct swap.
     
  4. DerekTheGreat

    DerekTheGreat I'm Awesome

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    I once thought the 5LM60 was '88-'91 (RPO MG5) but we recently picked up a '92 C1500 that also has this transmission.. Another oddity is that its the first GMT400 I've seen which was factory built without smog stuff. What RPO code might that be or how did someone opt out of all that?
     
  5. JCribb

    JCribb Old Army truck mechanic

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    My 94 was born with the 5LM60/NV3500. According to the only transmission guy I trust, he said they’re the same with only very few differences between them. I do know that my RPO code was MG5. However, after destroying three of them, I had to step up my game to the NV4500, which has two RPO options one being MT8.
     
  6. 91c1500sleeper

    91c1500sleeper Newbie

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    I swapped an NV3500 from a 93' 1500 into my 91'. Used the donor driveshaft with new universal joint, wiring pigtails and was able to use my crossmember from the auto trans. Bought all new clutch, FW, pressure plate and hydraulics.
     
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  7. DerekTheGreat

    DerekTheGreat I'm Awesome

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    Aren't the cases different? Aside from the tailshaft, this '92's transmission looks just like my '89's.
     
  8. JCribb

    JCribb Old Army truck mechanic

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    That I don’t know, but if you had a 5 speed it was the light duty 1/2 ton variant, whatever the nomenclature was.

    I know the heavy duty 5 speed didn’t come out until 1992, which was the NV4500.
     
  9. DerekTheGreat

    DerekTheGreat I'm Awesome

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    I definitely know what one of those looks like, had the provisions for a PTO & such, big honker by comparison.

    Both of our transmissions exhibit some sort of growling when getting into the throttle harder below 1,100 rpm or so, hers less so than mine. Sounds typical of the front bearing failure they say the 5LM60 or somethingsomething290 is prone to. I've put over 15,000 miles on mine like this though so I'm not worried, least not any more haha.
     
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  10. JCribb

    JCribb Old Army truck mechanic

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    Yup, and the three I killed all suffered from bearing failures or shift rail failure. I learned that transmission really had no business behind a V8, because it cannot sustain the torque beating it receives. With that said, if you don’t have a stock engine like I do, you learn this the hard way. The longest surviving transmission was 8,000 miles behind my built engine. I bought mine through smart parts in Minnesota, and as the third transmission was dying it’s slow death, I finally spoke to someone who had a brain. He was knowledgeable with engine power, and after our exchange of words, he said if I had spoken to him the first time he would have steered me away from the NV3500 and straight to the NV4500.
    He said at best the light duty one will hold up to 300-320 ft lbs of torque, whereas the heavy duty one will hold up to 450.

    So if you have engine modifications or you plan to have them, save yourself the frustration and go bigger when it comes to the manual transmission.
     
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