[cctroupe09]

Hey guys, my 77 Vette has the 3 speed automatic in it, I was wondering what would be making it shift hard from park/neutral to reverse/drive, it jerks pretty hard and troubles me that it may be going out or hurting something inside.

Also, My halfshaft U Joints need replacing, and I'm going to do the driveshaft U joints while I'm at it. Can anyone tell me what size they are?

[toobroketoretire]

Originally Posted by cctroupe09

Hey guys, my 77 Vette has the 3 speed automatic in it, I was wondering what would be making it shift hard from park/neutral to reverse/drive, it jerks pretty hard and troubles me that it may be going out or hurting something inside.

Also, My halfshaft U Joints need replacing, and I'm going to do the driveshaft U joints while I'm at it. Can anyone tell me what size they are?

Your idle speed should be around 550 rpm in DRIVE or about 750 rpm in PARK. If it's much higher than that it will make a pretty good clunk when you put it in gear. Your parts store should be able to look up the correct u-joints if you tell them what engine size you have. The big 454's and TH400's use one size larger than the 350's and TH350's use. And I only buy Spicer u-joints with the grease zerks.

[cctroupe09]

My D idle is 550 and P idle is 700, so it's not that it's idling too high, it still jerks pretty hard, usually when the car is cold and has been sitting.

Any opinions?

[bluedawg357]

Dose it clunk when you put it into reverse from park or drive from nuetral? if so it could be a ujoint getting slopy. could also be the differential bushing wearing out.

[cctroupe09]

Yes, when I shift into R or D, it going into gear with a nice loud clunk and the car moves enough to feel it. I know my U joints are worn, I'll be replacing them soon.

I was just curious about it as I was concerned it may have been a transmission problem or differential problem. (my differential is leaking a bit, I'll have to fix that next).

[bluedawg357]

if your differientail pinion seal is leaking then the ujoints are probably bad enough that you shouldn't drive it. just food for thought.