300 E Drivetrain
 

Greetings!

I have a 1986 300E. Every once in a while when I slow down to stop, I hear a thud (like something has shifted in the trunk). If this was any other car I would look for a problem with the U-joints; but, it's not a normal car. Any suggestions where to begin? (the trunk has nothing in it).

Thanks!

Not even a spare tire? Loose jack?

You might have your drive shaft flex joints checked. Same function as u-joints except less flexible and easier to replace... once you gain access to them.

Sixto
91 300SE
87 300SDL
83 300SD

Search for "flex disk" and "center support" , "center bearing".. "clunking"

That should get you some info...

need some specs
 

Ok, I've been under the car. There seems to be a little (very little) play in the center support bearing- i can barely wiggle the drive shaft in a perpendicular direction to the shaft. I don't feel that this would cause the noise (maybe a vibration upon acceleration). Here's the strange thing, I can rotate the drive shaft almost 1/4 turn- is this normal? The noise that is made when I reach the end of travel sounds very much like the problem 'clunk' . The car is in park and on back wheel ramps. Maybe I'm not doing this right...

here are my new questions:
1. What kind of play am I looking for? if the flex disks are bad
2. What is acceptable rotational travel for driveshaft?
3. Should I be looking for something to tighten the differential?
4. Should I be using jack stands instead of ramps?
5. What is the relationship between magnetism and gravity and inertia?
:confused:

Paul

Worn flex joints will let you turn one segment of the drive shaft relative to another. The clunk in this case is the slack being taken up as you accelerate or decelerate. There can be slack at any of the joints -- transmission to drive shaft, first driveshaft to second drive shaft, drive shaft to differential, inside differential, differential to alxes. The flex joints are rubber so you'd expect them to wear first.

I don't know how much wear is acceptable. As much as doesn't cause noise is the best I can guess.

There's nothing adjustable outside of playing with shims and preloads in the differential. You don't want to go there.

It shouldn't matter that you're using ramps instead of stands except that you can't spin the axles if the wheels aren't free to rotate. If your CV joints are intact, I'd focus on the flex joints.

Magnetism, gravity and inertia are all topics in Physics. And all topics I've forgotten by now :)

If there's lateral play in the driveshaft, indicative of a worn carrier bearing, you'll more likely get vibrations or a series of thumps against the transmission tunnel when you accelerate (I know too well :eek: ). It probably won't be one clunk.

You're lucky if you can see much of your driveshaft in a 124. In a 126 most of it's covered by a shield then further covered by the exhaust pipes.

Sixto
91 300SE
87 300SDL
83 300SD

300E Drivetrain
 

I have a 300 SEL with 164K mi. Mine is diff. backlask which the car has had since 73K mi. It hasn't gotten any worse.