Please help: have you seen a driveshaft do this before? 1982 300SD
 

When the car is hot, and in N or P, the driveshaft rotates back and forth, causing the whole car to shudder. If I look under the car, I can see it rotate 15 degrees forward, then back the other way. It just rotates back and forth, making lots of clunking noises until I put it back in drive and get moving. The car is fine on the highway. I'm at 202k miles. Any ideas? I couldn't find this problem in previous posts.

Other details: Around 1200 rpm there's a scraping noise coming from below the shifter, related or not... The scraping at 1200 rpm is consistent but the clunking is not, like I said, it only does it when the car is hot and idling but sometimes it doesn't do it at all. Doesn't seem to depend on how fast I stop. Also, I have to put the car in N to turn it on. But I'm convinced that all the racket is coming from the drive shaft rotating back and forth. Anyone seen this? Do I need a new transmission or differential or just to turn a bolt? Thanks!

Flex Disk & Drive Shafts
 

1984 300d Turbo 135k
Go To **************.com For Guide Books And 2 Flex Disk Kit Drive Shaft With Guide Book $85.00 May Need Center Bearing & Support. Axles $325.00 Ea New Or Rebuilts At Autozone Axles
Are Diy 3 Hrs With Guide Book

Sounds to me like you are getting some unwanted torque transferral through the transmission. If for example you have some foreign material embedded in the friction surface of the B1 band, and intermittently engaging. Remember that the input shaft in the trans is always turning when the engine is running, even in neutral or park. Secondly, there could be a valve body issue, as you say it's only happening when hot - I'm thinking somehow pressure getting fed to the B1 piston.

If it does momentarily engage in the trans, I would expect that if the driveshaft went in the forward direction it would possibly rebound off something inside and rotate backward. I wouldn't replace anything on the driveshaft yet, I'd focus on the transmission. Good luck!

bad donut?
 

.........

tom w

Thanks Peter! I'll check it out.

Maybe a rodent was attempting to stay warm on top of the heat shield, became frightened and disoriented once the engine started and when the vehicle drove off, the animal met with an untimely death due to the rotating drive-line. The carcass may be lying on the heat shield, if so it might explain the “thumping” sound you hear on the tunnel............while moving that is

:D

A thorough visual inspection will help you determine the actual cause

You didn't read the post.;)