Clunk when TCC unlocks on heavy acceleration

This is the first 95 4L60E I have owned, I have had a 96 and a few 94's that never had this problem. I don't have any other issues with this transmission, it shifts fine. Car has 116K on it, original trans as far as I know. I just did a service on trans with flush all new fluid and filter, nothing significant was in the pan. Cruising down the road with the TCC engages just fine with no issues or shudders, but when you push the pedal down hard like when you are going to pass someone, the TCC unlocks with a bang that shakes the whole car. It does the same thing whether unlocking in 4th or 3rd gear. Any ideas?

I'm sure someone will drop in on this; but rule number 1 is: don't flush the transmission. Change the filter and fluid that drains out. Flushing causes problems.

Tom C.

It had the same issue before and after the flush

Try tapping the brake pedal enough to get the brake lights to come on and see what happens. That will unlock the converter as well.

mebbe it has other issues,. such as a trans mount,. a universal joint,.

as was mentioned the trans unlocks as the brake lights are activated,. or pretty close to it,.
the switch is next to the brake pedal switch,.

Nick

I tried tapping the pedal under light throttle, it unlocked easily with no issues. But under heavier throttle it either unlocks harshly or with less throttle it shudders then unlocks. I am thinking it may be the torque converter having issues.

Follow up to the above issue: Due to issues with my speedo not working, I decided to put a known good 94 PCM into the car to see if the PCM was making the speedo malfunction. An amazing thing happened! I had no harsh unlocking on heavy acceleration...I can't believe it. Obviously the 94 PCM isn't programmed for the PWM TCC lockup, but the car drives so much better with a 94 tune vs the 95 tune. Now if I can get this damn speedo working again!

Maybe you have a 94 trans?

Update: After racking up about 11,000 miles since I posted this issue last fall, it died. Pump went and I was stuck on the side of the freeway. That was the first time I have been left stuck by a B body in over 10 years of daily driving these cars. I had the entire trans gone through and she is back up and running great!