Play in Drive shaft

[Titan1021]

Just finished a 8.5 trutrac install in my 68 Camaro. Also installed ridetech 4 link. I have 2 issues. First at low speeds I can hear what I think is the driveshaft pinion invading the rear. It’s a clunk sound when I touch throttle. Only happen when car is moving not at a stop. When I get under car I can rotate drive shaft a few degrees. It does not seem normal. Might be a back lash issue.


second issue is when I’m at speed 60-70 and I get off throttle there’s a vibration if I give throttle vibration goes away. I have a new 3.5 inch aluminum DS from a Reputable shop. Any insight would be great.

tranny angle about 2 degrees down. Tranny pinion angle is about 2 degrees up.

[Z06vet]

The tru trac has a lot of play in it. First one I did years ago, I thought something was wrong. I have used 5-6 of them now in various builds, and every one allows for the driveshaft to have good bit of play. I can rotate the driveshaft by hand left to right, and back around and 1/8 of a turn. Its annoying, especially when running a manual trans when off and on the throttle. On the vibration, your driveline angle its good. Unless your car is not lowered and close to stock ride height, I think you will find the pinion needs to be close to zero. On a lowered car, the rear pinion tends to be near, or even higher, than the trans tailshaft. Youre thinking right to try to match the angles, but at lowered ride height, that creates a situation where the driveshaft slopes upward to the pinion. That creates some bad working angles. Tremec has a great app for helping you find the correct working angles using your iphone or android. I would bring the pinion down a bit, check your working angles, and test drive. If you are unable to completely eliminate the vibration with the pinion, shim the trans tailshaft up as high as possible. This has always been a great help for me.

[416velle]

I can confirm from experience that driveline angles that are wrong "typically" cause vibrations all the time at highway speeds regardless of throttle.

Assuming your work out back is right, everyone seems to get stumped at the rear and headscratch, while forgetting the driveshaft goes into the transmission, which is another place to look. What transmission are you running?

Get under the car, grab the transmission yoke or the driveshaft as far forward as possible and wiggle side to side/up and down as hard as you can. If it moves any more than rotation, then you have a problem.
I had a early 1990s 4L80 (built very well mind) and strange engineering 3" driveshaft and chased a highway speed off-throttle vibration for 3 years, replaced the tailhousing bushing 3 times....I only found the output shaft was wiggling VERY bad after I'd bought a T56 for a swap to get rid of the auto. The trans yoke was solid as a ROCK inside that T56 tailshaft.
Check and see if the driveshaft at the front wiggles; if it does, then pull the driveshaft, look at the wear pattern on the machined surface on the yoke as for some transmissions a long yoke vs short yoke makes a difference on spline engagement and yoke stability; try to wiggle the output shaft inside the transmission, if its solid then your tailhousing bushing is wasted, and if the output shaft wiggles then you're looking at a transmission rebuild.