Hi guys, my 90 coupe has a 4L60 tranny. When i reach about 40 mph overdrive kicks in, but the car starts running a little rough, or maybe even kind of jerking a little. I can hit the brakes slightly to kick the lock-up off and it smoothes right up, but now i keep it in third until i am going highway speeds and then put it into overdrive and it does fine. Do you guys know why it would do this, and is it hurting anything? Thanks for any info!

 

Couple of things. Either your lock up converter clutch is bad or one of the switches on the valve body is not holding in. Have you had the car scanned for codes? Being it does it under lower speeds because of the higher demand on the clutch, I would lean towards the torque converter. [8D]

 

I think your car is slightly out of tune causing it to bog at low RPMs. This very common, most people will just keep it in D until they're above 45mph. A good tune up may help your problem. Check your spark plugs, air filter, engine timing, maybe pour an injector cleaner in the gas tank, fuel filter. Im not saying its all of those things, but maybe just think what item of regular maintence your car is due for.

 

hey i appreciate the advice from both you guys! i will do a tune-up soon, and hopefully that will fix it, but if not i will have it scanned for any trouble codes.

 

Try adjusting your transmission cable also