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problems with a 1991 gm truck tranny

Discussion in 'Chevy Trucks' started by 80heavyhalf, Apr 4, 2005.

  1. 80heavyhalf

    80heavyhalf Junior Member
    Messages: 4

    i'm new to this site and can't find the problem so i am asking for some advise. I have a 1991 3/4 ton truck which is a 2500 series ext.cab and long box with a 4 speed automatic, overdrive. My tranny is ok and runs normal until i get up to 80KM on the highway and then it just kicks out like it is in neutral. If i let off the gas it kicks back in but won't let me past 80. If you guys have any suggestions i would appreciate it.
     
  2. 80heavyhalf

    80heavyhalf Junior Member
    Messages: 4

    anybody? does anybody no why?
     
  3. William B.

    William B. Senior Member
    from S.E. IA
    Messages: 978

    When was the last time the fluid and filter were changed/ checked?

    William
     
  4. sonjaab

    sonjaab PlowSite.com Addict
    Messages: 1,425

    What you have is the "speed limiter" kicking in and its built in to EVERY
    newer GM truck. My late model GM trucks will only do around 100 mph
    before they start to "freewheel"............Its normal !!!!!!

    Why?...Because GM and big brother don't want you to exceed the
    speed rating of your stock tires.

    Many vehicles have these nowadaze... :realmad: ....geo
     
    Last edited: Apr 8, 2005
  5. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377


    Naw, 80km/h is only 50mph.... if the speed limiter is set that low it must have come with BMX bicycle tires :p

    I don't think a 1991 is fully computer controlled yet.... I don't know what the problem could be.
     
  6. sonjaab

    sonjaab PlowSite.com Addict
    Messages: 1,425

    DEREK.........Me bad.............Forgot the km difference ! More is less
    in mph :sleeping:
     
  7. ratlover

    ratlover PlowSite.com Addict
    from IL
    Messages: 1,325

    Are you shure its not the converter unlocking? Duno exactly why it would do that.......

    What happens if you go WOT from a stop or darn near?

    Is it when it goes to shift into OD that it does this?
     
  8. sonjaab

    sonjaab PlowSite.com Addict
    Messages: 1,425

    FYI: From memory..........MY 90/94/97 1/2 tons also would "freewheel"
    at about 100 mph also.
     
  9. 80heavyhalf

    80heavyhalf Junior Member
    Messages: 4

    Yea, as soon as it gets to shift into overdrive it kicks right out, just like it is neutral. Like i said earlier it works normal until you get highway driving. When i get up to 80km/h it just kicks right out. You can accel as fast as you want it is normal put it just kicks out. thanks for everythin guys!
     
  10. sonjaab

    sonjaab PlowSite.com Addict
    Messages: 1,425

    Heavy........One of the tech guys at the truck forums sez it
    is most likely your converter solenoid. If it goes bye-bye
    the converter will NOT lock up causing the problem you
    describe when the tranny hits OD.

    Common problem............What tranny do you have ?
    700r4?.

    A tranny shop can fix ya up.....Avoid AAmco or the dealer!
     
  11. heather lawn spray

    heather lawn spray PlowSite.com Addict
    Messages: 1,206

    Also possibly speed sensor in trany; not a big deal; trany shop can do it in a couple of hours for a couple of hundred
     
  12. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    These trucks either have the 700R4/4L60 or the TH400. Since he mentions overdrive, I am assuming the first one (they are the same thing, different name. A 4L60E is electronically controlled...)

    A lockup torque convertor solenoid going bad will not cause a freewheel condition, it will prevent the torque convertor from locking up, making the tranny 'slip' a little just like first, second, and third. You will still have overdrive with this condition.

    When it shifts to overdrive, does it do it immediately (as in, as it is shifting?) or a delayed reaction?

    If it does it immediately there is something physically wrong with the tranny, either the overdrive clutch pack or in the hydraulic circuit in the valve body.
     
  13. 80heavyhalf

    80heavyhalf Junior Member
    Messages: 4

    i'm pretty sure it's the 4L60. thanks for the post guys. any opinons on what to do would be good then that'll be all i'll need. thanks