jack up a back wheel and block it up properly for your
safety. my dad tried putting a wheel under for'safety' and used a stock volvo jack and almost killed himself. use a suitable stand..
put it in gear.
turn the free wheel back and forth to it's limit make it hammer but not excessively
while you do that, feel each U joint for play between the two yokes.
nice if a helper turns the wheel if not use your foot to turn the wheel.

if one feels loose you can replace it, or all of them.

id soak /clean them with solvent and oil or WD-40 remove any screw in grease nipples while you fit them together. it will help. some have no nipples.

i use some sockets to press with and bigger sockets for the caps to have a void to go into.. in a bench vice. it's a bit of a struggle.. you can use a hydraulic press if you have access to one. don't hammer on them.

Check the bushings on the two torque arms, four bushings in all. Also the trailing arm bushings. https://www-ese.fnal.gov/People/wilcer/volvo_trailing_arm_bushing_tool.htm
--
Art Benstein near Baltimore

“Wonder is the beginning of wisdom.” -Socrates

Hi,


The easiest and most likely guess is it an universal joint and since there are two or three of them, it could a little of all, “joining” forces!
It will probably do it going backwards but will be less of a sound or of different magnitude because the rolling elements or needles inside, are crunched and packed in one direction and they will not shift as much.

The design says the bearings are suppose to pivot with the two axis’s of rotation. In these cases, the spider frame mass is doing the “floppy de-go-see!” (:-)

Good news is, Since so many of these are produced for millions of drive lines they have stayed rather inexpensive to buy!

If you decide to replace these your self, draw or scrape a line across one side of the two adjoining joints to keep the driveshaft in alignment for the “dynamically balanced” purposes. Otherwise you might get a whop whop noise or vibrations after you think you “whipped” that sucker and have to take it back out!

With all that considered, you might have a bad transmission mount or even motor mounts so don’t just jump on the joints without twisting and pulling on things to see how solid the whole drivetrain is holding up!

Hope this helps you isolate the clunk as you can also look at rear suspension bushings, especially the trailing arm and torque rods but since you did not mention a pop while going over driveway entrances you might be safe there!

Good luck and tell us what you find?
“Armchair diagnostics” are usually incomplete, as so, the fact that “True Gremlins” can be intermittent and are green or white, when it comes to the electrical side of things.

So at least you are on the other side of that, with it doing it every time you move forward!

Phil

Check all the u-joints. Look for any rust trails coming from them if you can't actually feel any play. Also check the TABs (Trailing Arm Bushings) - those are the large ones under the rear axle. It is difficult to see them unless they're completely blown out. They should be centered up on the cross bolt. In a worst case scenario there could be too much play in the differential. -- Dave