Clunk sound on acceleration
 

I'm hearing a very distinctive single tap/clunk sound when I tap the gas. It doesn't continue to make noise as you accelerate but it is very repeatable especially at very low speed. . It will also sometimes make the noise on a low speed downshift (auto th350). No vibration and the tranny shifts perfect.

There is some play at the yoke. Not a ton but seems like more than there should be?

I thought about u-joints and I will replace them just because, but after taking the drive shaft off they are moving very freely so i'm skeptical.

I replaced the tranny tailpiece bushing. It didn't look bad but I was in there so I did it. No improvement.

I'm thinking maybe the spline bushing in the tranny? Or maybe an engine mount? The mounts look OK to me.

GM used to sell a grease called spline grease through the parts department. I don't think you need this but a coating of wheel bearing grease would be worth a try. Easy enough to do. GMC and Chevy trucks had a rough time with driveline lash, clunk as you describe it. The fix for that was inserting a small "super ball", remember those?, inside the slip yoke to absorb the shock along with the grease. It actually worked! I would try grease first, then a small "super ball" if needed. If that doesn't work, you can take the drive shaft off the list as the source of the problem. If you try the "super ball", make sure you still have movement in the slip yoke when reinstalling the shaft. You don't want it jammed in tight. That could damage the transmission.

And your motor mounts are both good?

Where can you hear the sound coming from? I had the same exact issue on my car, turned out the ears on 3 out of 4 of the outboard disc brake pads were not cinched down tight to the caliper after they were installed as they're supposed to be. Because of this, they had excess radial clearance and wound clunk around every time I braked/accelerated, and would create a rhythmic clunk when coasting at lower speeds.

I don't think so. I didn't see any obvious problem with the mounts. It feels very "power train".

So is the theory that the spindle moves into the yoke and taps the end?

I have seen cases where the pin that holds the spider gears is loose in the differential case. Try to locate the area where the noise is coming from.

Check all the trailing arm or spring eye bushings. May have one that’s bad.

Just to echo Steve, I had some bad clunking going into gear. Particularly reverse. I figured my driver’s side mount was bad since I have a shaker and could see the motor movement. When I got in there the mount bolts were loose and some were partially backed out. They are a pain to get to also. Worth checking.

Sam

Was it not the transmission mount? My 1987 GTA had the exact same kind of situation where there was a clunk in similar circumstances, it was an easy fix as the transmission mount was perished. It went from a very noticeable clunk to completely smooth afterwards!

Put the trans in park, and rock the car back and forth, see if you can hear it.

No - Mgarblik is describing a "spline lock clunk".

The splines have radial load on them, so the driveline is bound up at that length.

Releasing the bind with grease (or the ball), or accelerating, allows the driveline to move into position - hopefully without the clunk.

K