I've been helping a friend trying to diagnose some shifting issues. It's a '70 cuda with a 440 and a 727. The complaint was early up shifts and no kickdown at any speed.
First we figured kickdown linkage issue so we tried adjusting the kickdown linkage. Took it for another drive and it worked great. Shift timing was good and it kicked down whenever we asked it to.
Then on the way back it stopped kicking down and started shifting early again. Took it back to the shop and hooked a pressure gauge to the line pressure tap. With the car idling in gear we had 55-60 psi. Moved the throttle pressure lever back and forth and the pressure didn't change. Pulled the VB and checked out the throttle valve & kickdown valve. Both move freely in their bores however the throttle valve showed some wear. I had another VB laying around so I took the throttle valve out of that one and put it in this one. Put it all back together, hooked up the pressure gauge and then had good line rise with it idling in gear and moving the kickdown lever back and forth.
Took it for another test drive and seems to work right most of the time but still won't kickdown sometimes. And whenever it won't kickdown, it has early shifts. When it does kickdown, shift timing is perfect.
I'm thinking maybe the valve body bore where the TV valve rides is worn. That's all I can think of. Anybody else out there have any ideas?
