I own a 1983 300D turbo diesel. when I drive it sometimes when I hit 20MPH the back right starts making a really loud thumping noise, but when i get over around 23MPH the sound stops. I was wondering if anyone else had similar problems and what it turned out to be? any ideas would be helpful.

 

ok, that makes sense ill try to get that replaced.

 

I also have an 83 300D and I had a thumping noise and all speeds that turned out to be my right CV boot in the rear axle had torn and was running dry for who knows how long. As I was replacing the right rear axle the left boot broke and I ended up replacing the left rear as well. The loud thumping noise went away but I still hear an occasional noise at low speeds. Especially on bumpy roads.

I'm wondering if this low speed noise is possibly this same thing. Maybe the same noise coming from my center support bushing and bearing? I do have 2 brand new axles and everything seems nice and tight within the differential.

 

To check the center support bearing hold the drive shaft both side of the bearing, and push up and down on it if it dosen't return to center, or rattles when moved, replace it.

 

All rotating elements have a balance point, and a point where they are severly out of balance. Without support on both ends of a shaft it will wobble until it reaches the balance point, then smooth out. That point is different on each shaft, hence different viabrations at different speeds. When it is supported properly, the balance viabrations are absorbed by the bearing, and the rubber mount ring around it
Thanks ForcedInduction for mentioning cracks and tears, I should have thought of that.

 

awesome thanks I ended up getting a junkyard u joint assembly that looked pretty decent. And that seems to have solved the problem. Thanks for all the help.

 

My noise is more noticeable on bumping roads and lower speeds. Still the same problem you think? I'm going to put her up on a rack this week so I'll end up checking the center bearing and rubber. Is there anything else in the rear end that can cause the noises? My really loud noises went away when I replaced the rear axles and this noise is also one of those irritating noises that just drives me crazy. I only wish I had a way to record it.

 

I dunno, it was cheap and I figured it would be better than just the bearings.

 

While you have it on the rack, check the whole drive train and motor mounts, everything you can check while you don't have to slide arouhd on your back to check it