Suspension clunk - goes away with weight in bed

[k2rm]

I have a 1970 C20, trailing arm rear, stock height with front disk conversion and font sway bar.

I have been fighting a clunk for quite some time. If I brake hard I hear the clunk. If I then accelerate, regardless of speed, it clunks. If I accelerate slowly or brake gradually, no clunk. It is more pronounced turning either right or left. I can also feel it through the floorboard when it clunks.

Yesterday I hauled a dresser, maybe 150lbs. No clunk! Somehow adding a little bit of weight makes it disappear. Any ideas of what it may be?

Thanks!

[dwcsr]

check the trailing arm bushings, also check the center bearing on the drive shaft, lastly check the ubolts on the axle.

[k2rm]

Thanks for the suggestions. The trailing arm bushings are about three years old. I have the ECE trailing arms that came with polygraphite bushings. I checked the ubolts on the axle and they are torqued greater than 150 ftlbs.

The carrier bearing is about 5 years old. How is the best way to to check it? The driveshaft seems solid with no play if I grab it and try to move it.

[Hart_Rod]

Check your shock mounting bolts...

[smashingchuck]

Originally Posted by Hart_Rod

Check your shock mounting bolts...

x2 on the shock bolts..........

[k2rm]

Thanks for the suggestions. Still haven't been able to figure it out. All bushings appear good and shock bolts are tight.

[72MARIO]

Are you sure its not the rear brakes grabbing sticking and then releasing ? Are the axel seals dry ?

[dwcsr]

I'd start looking at the front.

[jjzepplin]

Check steering box bolts and frame behind box for cracks? Idler arm? Put jackstands under each front control arm and try to move the wheels up and down left to right while someone looks at suspension with flashlight on bushings etc. Should be no play. Had one mysterious clunk turn out to be the frame though behind the steering box. Also one I had shank style lug nuts on old Crager rims and they would come loose. Acorn from now on.

[suspect]

Take the shock bolts out and make sure they're not wore out from constant movement. Also check the holes on the mounts. Even if they're tight, they can just appear that way until the weight of the truck moves them.