Rear end "clunk"',.....I'm at a total loss!!

[dltalfa]

OK,..so I have rear end "clunk". Happens when you release the clutch. Evident at every shift change, of course more prominant in the lower gears and at initial take off.

I had read that this was usually the differential mount, so I replaced it. Clunk still there.

I then read that it could be a U-Joint. So I crawled under the car and did notice some "very slight" movement in the right rear axle half shaft. So,..I replaced the u-joints on both sides, all four. While I was at it, I decided to proceed and replace the drive/prop shaft u-joints too.

You guys may have read my previous thread about all the trouble this caused, as I had to lower the exhaust and remove the sway bar to get the drive/prop shaft in and out.

So, while the sway bar was out, I also replaced the sway bar bushings.

To recap:

I have all new half shaft u-joints.

All new drive/prop shaft u-joints.

New sway bar bushings.

New front differential mount,

AND the clunk is no different!!!!!!

What am I missing?

What else could it be?

[Diseazd]

Check the tightness of the 2 nuts that attach the mustache bar to the frame and the 2 nuts that attach the diff to the mustache bar.

Edited February 18, 2012 by Diseazd

[Zed Head]

Could be a bad strut, or a loose strut mounting point, or a loose gland nut. A broken motor mount will also feel like something broken in the back.

[5thhorsemann]

Also check to ensure the exhaust isn't hitting the floor pan, as mine was.

[Carl Beck]

Agreed - "check the tightness" - means use a torque wrench and set them to the higher end of the torque spec. Even though the nuts on the studs that go though the mustache bar are of the "self locking" type - I remove them and apply locktite to the threads - then torque them down.

Another "clunk" cause can be bushings that are shot or bolts/nuts lose on the inside /outside of the lower control arms.In which case you will hear them sliding fore/aft.

FWIW,

Carl B.

[dltalfa]

Thanks for all the suggestions.

I just came back from the garage. I jacked the car up again, secured it on jack stands, and crawled under the car.

With the car in gear, you can move the rear tire to take up the slack. Even by hand you can hear a slight "clunk",..but I can't see anything moving.

I had my son get in the car, start it up, and "bump / release" the clutch. You can hear the "clunking" very load,...but I still can not see ANY movement anywhere.

Could it be inside the differential itself? Are these diffs known for having internal problems?

It does not whine or groan like a bad rearend should. It's very smooth and quite except for the "clunk" at clutch release.

[olzed]

G'Day dtalfa. I have narrowed mine to backlash in the diff, and now I just live with it. Seventies technology???? I dunno.

People have replaced the diff mount and swear by that, but did'nt work for me. I have done everything else as you have.

Everything is tight under the car, 100,000 miles, drives like a dream, apart from the clunk.

[LeonV]

Did you check the differential strap which goes over the top of the diff nose? Make sure it's in good shape and not stretched out. Put in an RT mount for extra insurance.

[jmortensen]

It's almost never the differential. You can pull the diff and check the backlash with a dial indicator, but if you look through past posts you'll see others who have replaced the diff or worked on it and had the same problem. You can't run any diff without backlash, so it's not a matter of old tech vs new tech.

When you put the car in gear and bump the clutch, you're hearing slack from the transmission gears and bearings, both driveshaft u-joints, the ring and pinion, the spider gears, the splines for the diff output shafts and the side gears, the halfshaft U-joints, the splines for the stub axle and companion flanges, and the wheel bearings. Similarly twisting the driveshaft or the wheels by hand also gives a false impression of slack in the diff that really probably isn't there.

Seems that the most common issues are:

Front diff mount/strap

Bushings

U/joints

bolts connecting diff to mustache bar and/or the cover bolts

Edited February 18, 2012 by jmortensen

[ConchZ]

I had another thing causing a clunk that seemed to be coming from the rear end whenever I released the clutch. A loose nut on the backside of the T/C rod. Because it clunks against the frame, and your biggest connection to the frame is through the seat, you feel it underneath and a bit behind you, making you think it comes from the back end.

[Arne]

Mine was in the transmission itself. The woodruff keys that locate the drive gear on the front of the countershaft were worn, allowing the the gear to move on the countershaft. Clunk once under forward torque, and thud back under the reverse. Sounded for all the world like the clunk was coming from much farther back.

My issue was a bit unusual, but the moral of the story is that you may have to cast a wider net of troubleshooting to find this, as there are several potential causes.

The full story of my transmission clunk starts on this page - http://1971.240z.home.comcast.net/~1971.240z/2007/07-08.html

[Zed Head]

Don't forget the transmission mount either. There are three points of contact, all rubber mounted, unless you have an early mount.