Cruz 86

The torque converter on my 86 locks up only in 4th at 67 mph. I changed from 2.59 gears to 3.07 gears and it still locks up at 67 mph so I guess its set by speed and not rpm. Is this programed into the PROM? Is my setting (67 mph) normal. I dont know if the car has an after market chip or not. Dont the converters usually lock-up in other gears besides 4th? Can I control this manually with a switch?

J Z06

I don't recall what mine used to lock up as stock with 2.59s and a stock motor. It now in "D" locks at 41 MPH. That's about all I can tell you.

drive it

Yes, the prom controls the lockup. The original gm program had it locking at 15 mph. There is a lockup constant for low gear and high gear, but I found mine would only lock once its in fourth-don't know if thats the tranny or they all do it. Hypertech etc. usually program it at 40mph. Personally I set mine at 45mph-smoother for me as far as driveability. 67mph is too high-if it doesn't lock its slipping which is producing heat, and heat kills your tranny. There are also tables for unlocking and locking the tq according to throttle position; if you step on it you want it to unlock and then relock as you let up off the throttle. It sure sounds like the prom is changed but I can't imagine why anyone would set the lockup so high-but if its consistant in lockup speed then it doesn't sound like a short. Yes you can wire a switch to manually lockup the tc but thats a pain to use daily-if you forget to unlock it as you stop it will stall out. Better to try a stock chip, or burn a new one with better parameters in it. If someone did try a self burn and didn't know what they were doing you may be better off to try a different one.

c4paul

On my '84, when driving normally, it locks up at about 43 MPH. The lockup is higher if I'm getting on it.