I hear a clunking noise, any diagnostic guesses welcome. Here are the details. 72 Vette 55,000 neglected miles, 4 spd.

The clunking noise is most noticible at light throttle 30 mph, or coasting around a corner.

Among other items I have repaired/replaced since purchase last July, all front/rear suspension bushings have been replaced with Poly from VBP. Half shaft U-joints replaced, less than 1000 miles. ront wheel bearings replaced. Rear bearings re-greased with tool on spindle bolt. Drive shaft original u-joints, appear tight/greased/good. Parking brakes rebuilt with VBP SS Kit. O-ringed SS Sleeved brakes, new SS lines, and master cylinder. Drained/replaced trans fluid twice. Suctioned/replaced diff fluid with posi GM additive.

Known issues: Eighth to Quarter inch movement at diff yokes with wheels off the ground and rocked at 6/12 o-clock position by hand. Very slight movement (~1-2 mm) at transmission driveshaft yoke, when pushing up and down hard by hand on front of drive shaft (is this an issue, seems like this may be normal?).

I have noticed the issue after driving the car hard over the past couple of days; been power shifting 1-2-3 a bit and flooring it quite a bit. Wanted to break anything that might be weak, was contemplating driving the car from NJ to Tampa, FL in June when I relocate there. Guess I will be trailering the car there now...

My guesses are the diff bearings and/or yokes are the problem - or the transmission tailshaft bearing.

Any ideas for further diagnosis of the problem are appreciated. I already lifted the car and used jack stands under the rear shock mounts to support the t-arms; the tires spun by hand without any indication of the noise. The rear bearing seem OK, no significant movement at 9-6 o-click at the wheels and no growling/squeeking noise. The noise sounds just like when the outer u-joints were bad, before I replaced them.

 

consider a cheap attempt for a solution and change the gear oil in your differential...don't forget to add the posi additive...8oz I believe

 

I changed the diff gear oil and GM additive already. I don't think it is a posi clutch pack issue, because the noise is evident in a straight line, as well as during turns.

There is no noticable noise when accelerating, just at cruise and deceleration. The posi works, at least a bit. Two black lines on the pavement are possible, though not necessarily consistently applied.

 

Two pounds of hamburger will quiet it down,but won't correct excessive gear lash.

 

If you've got 1/8 to 1/4 inches of play on your halfshaft yokes you're probably in big trouble. Your housing may be shot by now too. Ask me how I know.

 

Sounds like you checked a lot of the common things. The side yoke play is way too much and they need to be replaced.

One thing you could check again is the front snubber bushing. If you already used a poly bushing go back to a rubber one. Some of the poly bushings were under size and may be giving you the problem you describe.

There should be no in/out play in the differential front yoke, if so the crush sleeve may be wrecked or the pinion nut loose.

How were the U-joint flanges? if bent I would think you wouldd get a vibratin more then a clunk?

If you broke a spider gear or ring gear tooth you might get that too but the tooth usually gets caught up and destroys the rear end. If it were me I would replace the side yokes- because they're worn and rebuild the rear end. When you open it up you'll get a better idea of whats going on in there. If you need any help let me know.



Gary

 

FYI, when I replaced the rear end in my Chevelle with a 12 bolt posi I used Amsoil rear end fluid . . . did not need the GM additive, it already had it in it. I even called Amsoil to verify this, not sure if it was some sort of special fluid or just their regular fluid so please verify with them whcih product it is before anyone takes my word for it.

Chris

 

I'd suspect a worn spider gear... I think that you'll need a diff. rebuild..

 

Drove around the neighborhood, clunking is most prevelant at cruise (25mph) during slight right turns, and to a lesser degree while decellerating lightly in a straight line.

Rechecked the new poly pinion mount, pried on it with a crowbar, looks tight.

I pulled the half shafts. One is binding a bit at the outer flange. I hope this is the immediate problem. Already bought a new u-joint to install and some new bolts for the outer flanges.

With the shafts out, the wheel bearings seem OK and the diff seems to operate smoothly spinning it by the driveshaft or yokes.

Even if the stiff ujoint is the problem, a diff rebuild can't be too far off in the future due to the yoke looseness, soon as funds permit (selling/buying house, intrastate move, and new career path). At least I will be moving close to Vansteel in a couple of months.

Thanks for the info...