The Stovebolt Site Forums The Shop Area Engine Shop 'Clunk' sound in rear differential

I drove Old Red ('51 3100) yesterday for the first time in 25 years. 6 miles, 15 minutes. The engine ran great, but I have two problems.

1) There is a 'clunk' sound which occurs at the rate of speed of the wheels. The faster I go, the more frequent the 'clunk'. When I'm stopped, no sound. I jacked up the rear end and put her in gear, and I believe the sound is ocming from the rear differential. It occurs in all gears. There's plenty of lube in there. Can anybody make a guess as to what the problem might be?

2) My speedometer cable makes a whining / screeching noise. Can these be serviced, or should I just buy a new one?

It was a joy driving her, but I fear the differential problem will keep me off the road.

Thanks for any help.

The speedometer cable probably needs grease. There is a special grease for speedo cables. The clunk could very well be a U-joint.

Drive her around and accelerate then let your foot off the gas. Do that several times. If you find that the clunk is noticeable you probably need to replace the u-joint.

Jeff

has it been sitting on the tires the past 25 years? I got a car going that had been sitting for 30 years and had the same thing going on. Ended up being a tire that was flat spotted really bad. Changed the tires and things were all better.

I had a Dodge van that had a spot weld come loose between the center potion and the outer ring of the rim, did the same thing. A tire and rim swap fixed ther problem.

You might have a tooth broken off the ring gear. The best way to check this is to remove the rear cover off the diffy and inspect the ring gear. If the tooth is broken it will probably (and hopefully) be laying in the bottom of the differential housing.

Thanks guys. As I mentioned, I jacked up the rear wheels and put her in gear and I still heard the noise, so I think I can rule out the effect of the road on the tires and wheels.

I will troubleshoot for the U-joint and look for a gear tooth in the diff housing.

Is a u-joint replacement a very advanced procedure (do I need to worry about tolerances, shims, etc.)? I can't devote more than a few hours at a time to these efforts, so the total elapsed time between disassembly and reassembly can be many weeks, and I have a tendency to forget how things were put together.

No, nothing major. Youll need a new gasket set thats used to shim the ball collar at the back of the tranny. Its not a hard process but it may take a good hour or so. Im not a big fan of the new replacement u-joints as I had one fail on me, so I would suggest looking for an original replacement or a good used one as they are much stronger.

If you dont have a shop manual, nows a good time to get one.

Jeff