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  1. #1
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    Default Trasmission shift points

    I was wondering if anyone knew why the shift points on the Automatic trans for a 1990 corvette seem so "gentle" for lack of a better word. It is normally in OD at anything past 25MPH and will not shift into second at anything past 45-50MPH. I know its not recommended but I have put mine in 2 and romped it at 50MPH and its night and day compared to having it in OD and letting the computer do it. I guess my main question is why doesn't it shift lower if it can? Is it bad for the l98 to reach those RPMs or is it just too much strain on the engine in general. Is there a way to change the factory shift points to shift to a lower gear at a higher speed or is that pretty bad for the engine? It almost feels like chevy designed it not to drop that extra gear to be safe but it really makes my corvette feel "Slow". Any help with this question would be appreciated. I know its pretty random. Thanks!

  2. #2
    Member DonB's Avatar
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    Sam I have a '90 too and you need to reset the TV( control cable at the throttle. The TV cable as GM calls it stands for Transmission Valve control. In layman's terms it is the "kick-down" cable. There is an easy procedure for it. Google it or look it up in the search here. It's also listed in the FSM. There are numerous articles on it.
    Last edited by DonB; 09-02-16 at 09:26 PM.

  3. #3
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    Default OD shifting

    I noticed in my '88 Vette that on occasion when in OD there is momentary power slippage similar to a slipping clutch. However when I'm not in OD my car runs normal with full power, no slippage.

    Is the OD "slippage" something that can be corrected adjusting the TV cable? My Vette has about 60,000 miles. Also when Shifted into OD at driving speeds it doesn't engage for awhile or may randomly disengage.

  4. #4
    Member DonB's Avatar
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    Quote Originally Posted by garyg View Post
    I noticed in my '88 Vette that on occasion when in OD there is momentary power slippage similar to a slipping clutch. However when I'm not in OD my car runs normal with full power, no slippage.

    Is the OD "slippage" something that can be corrected adjusting the TV cable? My Vette has about 60,000 miles. Also when Shifted into OD at driving speeds it doesn't engage for awhile or may randomly disengage.
    It may. That's hard to say(but I doubt it). The TV cable adjusts mainly shift points. Try it. You have nothing to loose...
    When"s the last time you changed the fluid & filter in the trans.?

  5. #5
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    Default

    I had the transmission fluid levels checked and topped within the last 200 miles however I printed out from the GM service manual the Std and OD trans filler plugs diagram page since my car is older then the mechanics that serviced it. I'm sure they didn't drain and refill the OD unit in fact I'm not sure they even addressed the OD.

    I must admit I'm not aware of the need to clean and/or replace the filter in the OD tran.

  6. #6
    Member DonB's Avatar
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    Quote Originally Posted by garyg View Post
    I had the transmission fluid levels checked and topped within the last 200 miles however I printed out from the GM service manual the Std and OD trans filler plugs diagram page since my car is older then the mechanics that serviced it. I'm sure they didn't drain and refill the OD unit in fact I'm not sure they even addressed the OD.

    I must admit I'm not aware of the need to clean and/or replace the filter in the OD tran.
    O.K. What trans do you have? Is it the 4 speed automatic, which is what the conversation with the TV cable is about.

    Manual transmissions don't have one. It sounds like you have the 4+3 manual. This is a T-10 with an overdrive unit because you mentioned trans and O.D. filler plugs. That sounds like a manual trans with the O.D. to me. Automatics do NOT have filler plugs. They have a single filler tube with a dipstick.

    So basically,..What I telling you is, If your car has a CLUTCH pedal, there is NO TV cable. TV cables ONLY control the throttle valve body in an automatic transmission. PERIOD!

    Therefore, if your O.D. is slipping, R.T.F.M., on adjustment(if any) or take it to some one who is familiar with that trans and O.D. My guess would be, if it slips on the initial engagement, the linkage needs adjustment(or it's just cold). If the O.D. slips all the time, you may need more than an adjustment.
    J.M.H.O!

  7. #7
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    Thanks, right I have a Std. trans and OD model, 4 + 3. I miss read the TV cable mention.

  8. #8
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    Quote Originally Posted by garyg View Post
    Thanks, right I have a Std. trans and OD model, 4 + 3. I miss read the TV cable mention.
    I just ordered a new OD trans filter. Hopefully it is simply a filter problem since the car does go into overdrive.

  9. #9
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    84-85 4+3 DO have a TV cable. The 86-88 do not. I have no idea how to set it even though I've owned an 85 4+3 for 32 years. Never had to mess with it.

    NEVER "adjust" shift timing, feel or quality in the automatic with the TV cable. There is only one correct setting for it. The TV setting affects line pressure under all conditions. If set wrong, low pressure will result in burn-ups. If you want to change shift timing, quality, or feel, you make changes to governor, separator plate, accumulator bushings and springs, even friction material and clutch-pack clearances.

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