Only have 1 & 2 and R gears??

Discussion in 'GM Powertrain' started by Dactyl, Jul 26, 2010.

  1. Dactyl

    Dactyl Member

    Was just driving along and out of no where lost drive, but 1st,2nd and R gears still worked. Bringing it to AAMCO tomorrow anyone have this problem before?
     
  2. Wolfman

    Wolfman New Member

    I had almost exactly the same thing happen to my 1990 3/4 ton 2wd w/700R4 behind bone stock 350.
    I was on my way back from about a 350 mile trip towing a 14 foot landscape trailer. At 100 miles after
    leaving on return trip, at about 60-65 mph going into a flat long curve suddenly it was like shifting
    into neutral. I slowed to around 20 mph and it downshifted and acted almost normal including shifting
    to drive and overdrive. Then a couple miles and same thing and this time it would go from 1st to second,
    and to 30 or so and letting of the throttle it would free wheel, but not upshift to 3rd. I had lost the 3-4
    clutches and limped it to the nearest place I could call for a tow (on a trailer) home. I did a ton of research
    on the truck and the transmissions offered after the turbo 400. That is, the 4l60/700R4, 4l60e, and several
    variations including 4l65e,4l70e, 4l80e, and others.
    I suspect that you have the same problem and although this could possibly be repaired with a replacement
    for the clutch pack, it is not advisable due to potential debris in trans and torque converter as well as fluid
    lines and cooler. This trans has a very bad reputation for failure from parts and components that were weak
    or poorly designed for it's intended use. When rebuilding the 700r4 or the 4l60e it is advisable to upgrade the
    servo to at least the corvette servo and the 3-4 clutch pack, a larger pressure valve and there is available a
    larger overdrive servo. These upgrades will help your trans take the use and abuse it was intended to, and last
    much longer also. When repairing or rebuilding these units after clutch failure, there is almost always debris
    throughout the fluid sytem from the trans to torque converter to lines to and from cooler. The torque converter
    should always be replaced and the cooler and all lines ahould be flushed to prevent this debris from damaging
    the trans in a very short time. These transmissions can be made to be reliable, durable and long lasting with
    the right parts and the proper maintainence (fluid changes every 20k and when towing anything for more than
    a couple of blocks use drive not overdrive, and install an auxillary cooler to help keep fluid temps down.
    I wish you success with your shift problems whether it is rebuild time or (hopefully) something minor. Find
    a reputable repair facility and be sure to get a thourough and complete diagnosis from two or more shops and
    ask lots of questions. One last thing, never use a transmission additive that claims to stop leaks. It will
    soften the seals so much that it turns the seals to mush.
    Good Luck and Happy Truckin'.
    Wolfman
    "I remain, as always, dazed and amazed, used, abused and then finally Amused by it all."
     

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