91 GMC pickup having problems shifting

Discussion in 'Gearhead Garage' started by Phant0m51, Jul 31, 2011.

  1. Phant0m51

    Phant0m51 From Utah, NOT mormon

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    My dads truck was running a little off for a while, somebody told him to replace the throttle body. So he finds one at a junkyard and installs it on his truck. Now the motor is running great aside from a small vacuum leak.

    So my dad is driving it on the highway yesterday going up a pretty steep hill, he pushes the gas a bit more and the truck down shifts which is normal, but at the top of the hill when it shifts back to overdrive it was like it wasn't in gear. The engine would rev like it was in neutral. He pulls the shifter down a gear and it works so he drives a bit and pops it back up to Drive and its like its in neutral again. His drive home was uneventful.

    The SES light comes on, throwing a 32 which says bad egr valve but it still throws that code after he replaced it. He was told that something with the torque converter can throw the same code. Does that even make sense to anybody?

    Any ideas what would cause the problem?
  2. 86mcss

    86mcss Devouring your Soul

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    im going to assume its a 700r4 transmission...

    First thing is first. Pull the transmission dipstick and smell the fluid. Does it smell burnt?
  3. Phant0m51

    Phant0m51 From Utah, NOT mormon

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    It doesn't smell burnt. The transmission was rebuilt about 130k miles ago.
  4. Jishory

    Jishory Junior Member

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    Torque converter unlocking is slipping too much? Is the fluid level ok? Are you checking the level while the engine is idling and in park?
  5. Phant0m51

    Phant0m51 From Utah, NOT mormon

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    I'll have him check the fluid again tomorrow. He said it was slightly low but I don't know if he followed the directions on how to get a proper check of the fluid. A mechanic told him it was something to do with an "Anti-lock torque converter" or something like that. My dad's not very mechanically inclined so he words things weird if he doesn't understand.
  6. Tacdriver

    Tacdriver Junior Member

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    I know nothing about 700R4 Trannys but, you mentioned a vacuum leak after changing the throttle body. Could that be causing a problem? If not then I go with the "Locking Torque Converter."
  7. Phant0m51

    Phant0m51 From Utah, NOT mormon

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    Thanks. He decided to have the transmission serviced instead of dealing with it. If it continues I'll look into the vacuum leak and torque converter.
  8. Justin3

    Justin3 Balls of Steel

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    That old of a transmission should be vacuum controlled, I would first look into that vacuum leak. Your torque converter may be failing but hopefully that was replaced when the transmission was rebuilt.
  9. PeNZ

    PeNZ Tweak OG

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    A 91 700r4 is elecktronik
  10. Jishory

    Jishory Junior Member

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    I thought the 700r4s were basically controlled by a kickdown cable.... None of mine had any vacuum connections? The 4L60s were the electronic version.
  11. Justin3

    Justin3 Balls of Steel

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    The one in my old S10 was Vacuum controlled, but most were Kickdown cable if I remember correctly. Not Electronically controlled though.
  12. -=Lurker=-

    -=Lurker=- **BANNED**

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    Yeah, I'd get the vacuum issue resolved first. That might solve the trans issue. It's hard to tell what it could be without the mechanical digram for your particular transmission.