Thumping sound--diagnosis - PeachParts Mercedes-Benz Forum

kerry · #1 11-27-2004, 10:41 AM

Just got back from a road trip to NM. I noticed a sound on the trip. Under acceleration or decceleration, no sound. But, hold the accelerator in a partially open position and unload the drivetrain and a thumping sound occurred. It sounded like a tire with a lump but it obviously wasn't since it only happened under these precise conditions. I'm thinking it must be the center bearing on the driveshaft. Under load one way or the other it stays in position, but when free floating it thumps. Can anyone confirm or deny this diagnosis? Thanks.

81Wagon · #2 11-27-2004, 01:46 PM

Broken flex disc? Check before disaster ocurrs!

kerry · #3 11-29-2004, 09:44 AM

TTT for more opinions. Anyone think it can be anything other than either the flexdiscs or the center bearing/rubber bushing?

Zeitgeist · #4 11-29-2004, 10:03 AM

CV joint going south? Is the sound altered when taking corners? I'd also check your tires for tread separation even though it's an intermittent sound.

lrg · #5 11-29-2004, 01:34 PM

Sure sounds like the driveshaft to me. If it were the CV joints you'd probably be able to get one side to thump when making gradual turns under light throttle. The fact it goes away when the driveshaft is under pressure sounds like the key. As 81Wagon said, check the flex disks NOW and if they are OK then look at the center bearing and the surrounding carrier. One or the other is the likely villan.

nhodges · #6 11-29-2004, 09:05 PM

What car are you asking about??

Wallknight · #7 10-10-2006, 01:40 PM

What was the result? Mine is doing the same thing.

kerry · #8 10-10-2006, 02:43 PM

It was dry cv joints. I took it to StarTech in Denver and asked for a wheel bearing replacement since I had concluded from other threads at the 'Shop that it was the cause. They diagnosed it as a dry cv joint because the right side was not sliding in and out smoothly. The filled the boots with grease, readjusted the suspension height (it was too low, putting an unusual angle on the axle) and it solved the problem.

rrgrassi · #9 10-10-2006, 03:36 PM

Quote:

Originally Posted by Zeitgeist

CV joint going south? Is the sound altered when taking corners? I'd also check your tires for tread separation even though it's an intermittent sound.

Someone did pose the CV joint question. What were the condition of the boots, as it seems impossible for CV joint to be dry, if the boots are in good shape, unless they were improperly packed in the first place.

Your situation is not the norm as posted on the forum, so I'm glad you posted the cause, and we can now look at CV joint problems with new info and thanks for the added input.

vstech · #10 10-10-2006, 04:23 PM

the shop may have adjusted it, then charged you for adding grease to the CV joint...:fork_off:

kerry · #11 10-10-2006, 04:36 PM

Boots were in good shape. Don't know why they were dry. But when comparing left to right, it was obvious that the right side was not sliding in and out smoothly, but was catching. Seemed like an honest shop and the sound did seem like it was coming from back right. On a long downhill with the accelerator held in a position to unload the drive train, it sounded like a helicopter hovering over the right rear quarter of the car.
The adjustment of the rear suspension raised up the car a couple of inches so the different geometry of the cv joints could have been a factor also.

rrgrassi · #12 10-10-2006, 05:05 PM

Check your boots now and see if there is any visible changes, like where they were touched in order to remove the clamps, or if they put new ones on, just to be sure they did what you were charged for.

If the joint was dry, were there any metal shavings? Dry usually indicates some metal to metal contact. Either way I hope they inspected the dry joint by disassembly and replaced the boot.

Brian Carlton · #13 10-10-2006, 05:26 PM

Quote:

Originally Posted by kerry edwards

The adjustment of the rear suspension raised up the car a couple of inches so the different geometry of the cv joints could have been a factor also.

What, exactly, did they do to accomplish this? AFAIK, there are no adjustments to the height of the body. You have to swap parts.

rrgrassi · #14 10-10-2006, 05:39 PM

Were you in the wagon or the sedan? Brian is right about height adjusting, unless you were in the wagon. If in the wagon, IIRC, there is a level adjustment on the SLS. I do not have a wagon, but I remember reading that. I believe it was Winmutt (I could be wrong here) that posted how to adjust the SLS ride height in the rear.

OMEGAMAN · #15 10-10-2006, 05:46 PM

I had the same problem which eventually got worse and it was the right inner cv joint. Replaced the shaft and problem solved.
I too would like to know how they adjusted the ride height.