1990 Won't Shift into Overdrive
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From: Avon CT
1990 Won't Shift into Overdrive
I have a 1990 Convertible with a Vin # 8 350 engine with automatic . The car has 57,000 miles and I have had it for two months now . Up until yesterday the transmission was shifting into overdrive at about 42 miles per hour , no problems . I thought I had a bad power brake booster and since I replaced that . The transmission won't shift into overdrive . I don't know if I did something or just a coincidence ? Help
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From: Avon CT
Tell what the TV cable is and I will answer . I had trouble with the cable for the speed control unit , under the brake booster . Ok got out My Haynes Repair Manual . Found the TV cable looks ok to Me . I can pull it out and it returns with the cable stop against the linkage . The transmission shifts through the gears ok , just doesn't go into overdrive . I thought that was controlled by the ECM ?
Last edited by TomP.; Aug 29, 2010 at 05:23 PM.
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How many gear changes are you getting?
Not on a '90 .Gear shifts only controlled by TV cable
Last edited by vetteoz; Aug 29, 2010 at 06:58 PM.
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From: Avon CT
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From: Avon CT
Yes I mean converter lock up , its not happening . The transmission is shifting all four times , but the converter never locks up . The Haynes manual I have shows three wires from the ECM controlling the converter lock up . Does anyone know which wires they are at the ECM ?
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If you put your foot on the brake it cuts the power to trans and TCC disengages
Vac switches are for cruise control release ; seperate system to TCC
Last edited by vetteoz; Aug 30, 2010 at 06:52 AM.
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Tan/ blk at ECM is TCC control .( Grounds TCC solenoid wire )
Blue wire is feedback to tell ECM trans is in O/d (4th gear )
Check to see if you have 12V on the purple wire at trans ; key on
Last edited by vetteoz; Aug 30, 2010 at 06:54 AM.
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Ditch the Haynes and get the correct Factory Service Manual (FSM) for your Corvette off Ebay. You'll thank us later. 
Le Mans Master
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From: Tampa Florida
I agree-
Bingo - when you changed the booster out you messed up the gap on the brake switch swipe. Your cruise control shouldn't work either at this point since it use the contacts in the same switch. What you need to do is get the pedal off the brake switch - just becaue the brake lights are not "on" doesn't mean your totally off the switch since there are multiple contacts within that switch.
You might have gotten it just a hair off the gap. Get up to 50 MPH in OD and stay steady on the gas pedal - lift "up" on the brake pedal with your left foot and see if your OD kick in while your holding it up with your foot.
Your going to need to pull the booster to adjust the end play gap or remove the driver side lower knee bolter/hush panel to manually adjust the switch swipe.
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From: Avon CT
OK Let Me say to all thanks for the help . The wiring diagram is the greatest !! I'm going to go out to the garage and find the problem now . So thanks again for all the help .
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From: Avon CT
I want to THANK ALL AGAIN for all the help !!!!!
I will look into the correct Factory Service Manual for the 1990 Vette as recommended here .
