Mysterious occasional noise - '81 240D - PeachParts Mercedes-Benz Forum

Hosenpants · #1 09-19-2006, 02:53 PM

My wife and I have a noise from our '81 240D (automatic) and we could use some educated guesses.

The noise seems to come from the middle/rear of the car, I'll say near the middle as it can be heard from either side while we're driving in the beast. The sound is a kind of clunk-clunk, or thunk-thunk, that increases/decreases with the speed of the vehicle.

The sound has sounded on three occasions, each time after the car has been driven for at least an hour on the freeway, bombing along at 75+ , but only on those three occasions, not on short freeway drives.

This weekend, head up to Ventura, car spinning like a top, an hour later pull off the freeway, wait at stoplight, pull away from stoplight - thunk-thunk-thunNK-THUNK...!!??

Stop car, look underneath, nothing dragging or hanging. Wife says: this is what it did a month ago when I came back from Fresno! We walk away from car for five minutes, come back. Start car again, still making noise (quietly as we're moving slowly into a gas station parking lot). I get out so she can drive a short distance while I try to pinpoint where the heck the noise is from. After I get out - no noise. Rest of weekend, local driving and a 20 minute freeway blast, no noise. Car runs just fine.

Monday come home from Ventura. An hour later, pull off freeway, stop at light, pull away: thunk-thunk-thunNK-THUNK...!!?? She hops out and runs alongside, thinks its coming from the middle/rear of the car.

She has yet to drive the car today, but I won't be surprised if the noise is gone again.

To recap:

Noise from rear/middle of car (our best guess)
Regular beat - i.e., not a lug nut in a hub cap (happened to the Olds once)
No obvious sensation of anything hitting the bottom of the car
Happened a month ago after long sustained freeway blast - went away almost immediately.
Happened this weekend twice - after hour long freeway blasts - went away.

Did not happen after 20 minute freeway blast.
Not an object poking out of the tires.

I apologize for apparent laziness, we live on an incline with no garage or jack stands. I slid under the car looking for sheered metal, oily stains, anything that would look suspicious to a noob. Nothing but dirty and solid (looking) hunks of car under there.

We have a shop with a good reputation in the area who I probably should be giving this info to, but thought to run it past the members. Anyone care to take a guess?

#2 09-19-2006, 03:18 PM

Have the shop take a look at the CV joints, that would be my first guess.

rrgrassi · #3 09-19-2006, 04:14 PM

Also take a look at the center driveshaft bearing, called a center carrier bearing by some. A lot of times the rubber surrounding the bearing fails resulting in that noise, with no noticeable parts dragging.

Also check your flex disks.

barry123400 · #4 09-19-2006, 05:21 PM

Check for any oil leaks around the rear end and outer cv joints. What you describe seems to occur after parts are warmed up. Could be lack of lubrication. Kinda sounds like a cv joint perhaps a little dry as after the car sits awhile it seems to return to normal. You might also want to check the wheel studs to make sure they are not loosening off but thought that would result in less noise after wheel warms up.

dmorrison · #5 09-19-2006, 05:34 PM

It's definately the drive shaft. Probably the center bearing rubber diaphram. While your there check the front and rear flex discks. Mercedes uses flex disks instead of universal joints. I have had this same noise ( clunking while accelerating or slowing) on 2 of my cars, center bearing support was torn.

Dave

Diesel4me · #6 09-19-2006, 07:30 PM

And to add to what everyone else has said, you should check/get this fixed immediately. I would not drive the car at all till this is fixed. If that thing comes loose (center carrier bearing or either flex disc) it can ruin your day pretty quickly.

Hosenpants · #7 09-19-2006, 10:15 PM

Thanks for the time and brain power y'all.

We'll take Putty in tomorrow - two indy shops nearby have been recommended by different peeps. I'll report back when the dust settles.

Hosenpants · #8 09-28-2006, 01:50 PM

Our 240D came back from the shop last night - fingers crossed.

In addition to our first repair to our new ride, we were also test driving a local indie shop.

Short version: flex disks, drive shaft center bearing, sway bar links (old plastic I'm told) and the biggie, the driver side rear axle all replaced.

Longer version: Good impression of the mechanic and shop - basically means nobody was a jerk. We describe sound and symptoms. Mechanic gets under car, grabs driver side rear axle and moves it back and forth along its length axis. Common problem on older cars says he. Pass side feels ok - after inspecting during the driver replacement he feels the pass-side axle good for a while yet.

Flex disks were old and cracked, center bearing was making slight noise and rubber was old - replaced. He said that the sway bar links were original plastic and he felt it was best to replace 'em while this was all going down.

$850.00 later I won't truly believe it cured anything until we DRIVE for an hour and see what happens.
At the same time, the response to my original question and some research on the forums and this TIPS book I bought from Bergsma, and the local mechanic all mentioned flex disks, center bearings and axles as probable cause and/or definite items to check/replace on older cars. I guess I'm trying to convince myself that it was all work that needed to be done.

Additionally, the replacement fuel return lines I applied are holding and do not weep like the old ones and our MILEAGE BADGE showed up two days ago. I had an idea what the packaging would be like but my wife did not; she thought she'd get a plastic badge in a padded envelope. She has just started a new job - with a bit of a learning curve and mild stress that comes with - and the certificate and presentation BLEW HER MIND! She almost teared up she was so touched.

Nice job MBUSA.