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Hunting trans. UPDATE

Discussion in 'The Garage' started by southernspeed, Jun 24, 2006.

  1. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    I did a search but couldn't find my specific problem.

    If I drive at a steady speed on a light throttle the trans will kind of 'hunt'. It seems to be the TCC locking and unlocking every couple of seconds or so giving it the feeling that it's hunting between gears but it's not.
    It will do it locked down in 3rd and in o/d at a higher speed
    It's a 700r4 box, just rebuilt with TCI superpro kit, inc a shift kit and Jet 1/2 and 3/4 apply servos. It also has the valve that supposedly holds onto O/D longer.
    Any ideas?
     
    Last edited: Jun 28, 2006
  2. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    One of the first questions you'll probably get is, "Was the TV Cable correctly adjusted?", assuming that the cable was unhooked if the trans was removed for the rework.
     
  3. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    You're right! yes, and double checked. But I'm sure it's the TCC not a gear hunting problem.
     
  4. Wingnutt

    Wingnutt 1/2 ton status

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    the TCC is commanded by the computer, so unless you modified the chip, I don't think it's the TCC lockup (unless the converter is about ready to bite the dust). I'm thinking that the TV cable may not be correctly adjusted. If you have a tach on it, watch and see how the rpms change. If you are seeing about a 500 rpm change, it probably is the TCC, if the change is closer to 1200 rpms it's hunting thru the gears.
     
  5. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    On my second trip this weekend I took my laptop and ran winaldl. The ecu is commanding tcc lock-up correctly and the revs are rising and falling around 300 rpm.
    If you put your foot down slightly so that the clutch disengages, the trans acts normally. It is just when the clutch is supposed to be locked.
    It's a new TCI RV converter in there so it should be good!
     
  6. gmcjimmy90

    gmcjimmy90 Registered Member

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    Have you checked the fluid? Mine will kick in and out of lockup when it gets about a half a quart low.
     
  7. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Several times! Thanks for the suggestion anyway.
     
  8. NateInChandler

    NateInChandler 1/2 ton status

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    Check the brake switch, Depending on the year GM put brake switches on the trucks so when you hit the brakes it unlocks the convertor, if its not adjusted right it will do exactly like what your talking about (or not lock up at all).. Nate
     
  9. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Yeah I thought about that but when I ran winaldl it showed the ecm as commanding lock up continuosly while it should. I'm pretty sure that if the brake switch was at fault, the ecm would reflect that in it's TCC command.



    (does that make any sense at all:D )
     
  10. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Come on Dorian, you must know the answer to this!!
     
  11. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Oh this is almost unbelievable. I just found out from talking to TCI that the company over here has sold me a th400 converter instead of an rv/towing 700r4 converter.

    Talk about ruining your day!:mad:
     
  12. mouse

    mouse 1/2 ton status

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    I hope they are replacing it free of charge. I kow its a major pain to drop the trans again. If you have a place you can use a hoist and tall trans jack, you could just slide the trans back and save a little time.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Sorry, didn't have a clue on this one, nor did I see it in time. :) But i can comment on the TCI statement.

    If TCC is being commanded, and you are seeing the RPM difference from the "lock/unlock" occurring, how is it the wrong converter? No TH400's with TCC!
     
  14. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Unfortunately they're not taking any responsability saying I must have ordered a th400 converter! Even though I've never owned a th400 and didn't have a catologue so I asked them for a converter for a '91 with a 700r4....but it's my problem!
    They said they'd sell me the 700 one at the same price as the 400 so I'm saving nearly £200 by not going else where but I really wanted to tell them where to stick it! Good customer relations eh? I've spent over £1000 with them over the last year or two and I still get shafted like this!
    I'm not happy but what can I do? It was all done over the phone so there is no order on paper to prove anything.
    There's a lesson there!!!
     
  15. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    I figured it was diverting fluid to lock up a non existant clutch and maybe that was causing the TCC valve to shuttle back and forth, that in turn dumping pressure from the pump enough to make an rpm difference of 175 to 200 rpm?
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    Not a tranny expert, but the drop in RPM's occurs because the TCC locks the converter, stopping the converter "slipping" that normally occurs. (I know, rudimentary knowledge, just thought process here) If the RPM's drop when TCC is commanded, and there is nothing to increase the load on the engine (again, lack of slipping in the converter) I don't see how RPM's would decrease.
     
  17. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Yeah, I hear what you're saying and I'm just clutching at straws. I just thought that the high pressure being directed through to the clutch must be hitting a dead end somewhere and maybe backing up causing the tcc valve to shuttle. I can kind of imagine this backing up to the pump and causing back pressure?
    Like I say, clutching at straws (no pun intended!)
    According to the people who supplied the converter I def have a 400 one so I'm screwed anyway.
     
  18. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Dorian, location:now?guess!......hey if you're in England, come and drop this trans for me!
     
  19. dyeager535

    dyeager535 1 ton status Premium Member

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    Umm, no? :P

    I'd come visit if I were there though. :)

    Now that I think about it, the input shaft for TCC apps is special, it's longer. A TH350 converter will not seat on a TH350C trans, and although I have no proof, I don't see why a TH400 converter would seat on a TCC application either.

    What exactly clues them in that they sold you a TH400 converter? Either they sold you the wrong converter, or sold you the right one and don't know it...either way not real professional or detail-oriented are they? :)
     
  20. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    TCI asked me what converter i was using as I'd emailed them for help telling which shift and rebuild kit I had. I couldn't find the invoice for the converter so I phoned the company that sold it to me. They had it on there system and gave the part number which turned out to be this th400 one.
    I'm going to be REAL pissed if I change these converters over and they're the same ones!
    I'll get the new one either next week or in 2 weeks depending if I caught the truck out of Chicago or not.
    Watch this space!

    In the meantime, if anyone knows any tranny experts, see if they know if a 400 converter will mesh to a 700 box! Thanks.
     

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