Brett Richmond

Is there a way to put a toggle switch into the wiring for the overdrive unit to turn it on and off?? I have a friend that has an 86 4+3 that is stock w/Z51. He will autocross this car and when he shift it from 1st to 2nd the overdrive kicks in under acceleration. It should do this under normal driving but it will still happen under hard acceleration. Can this be done??

Bill Dearborn

There is something wrong if the OD is switching on during hard acceleration. He may need to adjust the throttle position sensor voltage. GM recommends setting the closed throttle voltage at ~ .5 volts (this can be verified in the manual). The wide open throttle setting is something that GM doesn't touch, but if you adjust the closed throttle position and then adjust the WOT voltage to 4.5 V the car will behave differently. When the car is driven normally the OD will come on when shifting to second but as soon as the throttle is moved to accelerate it will downshift to normal 2nd gear (be careful in traffic or the car might just hit somebody in the rear). Setting the TPS voltage at both limits can mean playing around a little with the TPS throttle shaft so you can get both readings but it is worth it. I did this to my 86 20 years ago and it totally changed the driving experience. After the adjustment I never had the car go into OD during high accelleration shifts. It was a great 2nd gear autocross car.

Bill