Questionable noises from the rear. - PeachParts Mercedes-Benz Forum

fruitcakesa · #1 09-10-2008, 02:05 PM

I am finally getting down to tracing the noise I have been hearing form the new 81 240's rear.
I notice it most a low speed <20 mph and it feels like a rumble that is loudest as you are backed off the throttle and then back on it again. It seems to disappear when under constant load but it also may be blended with the rest of the mech clatter of the car.
I looked at the center carrier bearing and d/shaft ujoint and stuck a screwdriver into them and tried to see if there was any play in them and did not get any appreciable looseness.
I assume I will probably have to remove them to really check. Is this correct?
The driveshaft has no excessive rotary play and the flex discs look ok.
I loosened up the e brakes to eliminate any drag. The rt side adjuster is broken but turned in to the minimum and it rubs a little but that is not the sound.
There is a noticeable clunk at the diff when the clutch is released between shifts so I have drained, flushed and refilled the diff and did not see any obvious metal particles and the fluid while brown was still somewhat clear. Sound still remains.
Axle boots are intact but I have not confirmed that the shafts are ok though I also think they are not the noise.
I will be checking the rear wheel bearings next and hope it is not them as the fix looks involved.
Any help will be appreciated.

Biodiesel300TD · #2 09-10-2008, 02:09 PM

To check the center bearing you need to grab the drive shaft and see if it has any movement side to side. You should have a little, but much more than about a 1/2" is too much.

fruitcakesa · #3 09-10-2008, 04:10 PM

No excessive side play at the center bearing but when I jacked up the rear and pulled at the top of the tire and pushed at the bottom I was able to to move the wheel about 1/8 inch in a rocking motion top to bottom.
Is this too much movement?
When I spin the wheels I don't feel or hear any grinding but it is unloaded and not under power so I guess it really won't show up then.

compress ignite · #4 09-10-2008, 04:27 PM

Pumpkin!

fruitcakesa · #5 09-10-2008, 04:36 PM

You mean the problem is in the diff?
What exactly is worn, what are my options for repair, how much and what damage am I doing by locally driving it and will it get louder before it fails or just suddenly give out?

chetwesley · #6 09-10-2008, 04:36 PM

You might just want to lay off the broccoli and beans...

Sorry... title got me, just couldn't resist.

fruitcakesa · #7 09-10-2008, 05:05 PM

That's a whole other issue.

Brandon_SLC · #8 04-11-2009, 08:02 PM

I also have some noise emanating from my rear end (240D), so I'm finding all this fascinating. My car is just generally noisy, but no vibrations or rumbles so far. I have not even tried to diagnose anything yet. I've never even had my car on jack stands.

fruitcakesa · #9 04-11-2009, 10:31 PM

Ignorance is bliss; once you crack open one of these MB pandoras boxes you really can't close it and you end up chasing every little thing down.
I think I might try the "syringe full of lube through the axle boot" trick to see if that quiets it down.
These look like original axles and while the boots are intact, things still may be dry inside after all these years and if it works I will know and if not I will have eliminated another component from the equation

mobetta · #10 04-12-2009, 12:08 PM

when/if the wheel bearings wear enough, you will have some slack in the wheel. jack up car and shake the tire/wheel assy at 12 and 6 oclock, and at 3-9 oclock... you should have some play if the bearings are going...

I think most of these diffs are noisy.

fruitcakesa · #11 04-12-2009, 09:23 PM

There is some fractional play in the wheel with my hands at 3 and 9 but none at 6 and 12.
When wheel bearings start getting noisy are they nearing the end or are they at the end of their life?

leathermang · #12 04-13-2009, 01:14 AM

I would say when they get to where you can hear them they are AT the end of their life.

bodyart27 · #13 04-15-2009, 10:31 AM

You said "I notice it most a low speed <20 mph and it feels like a rumble that is loudest as you are backed off the throttle and then back on it again. "

This past month I started getting this sound under heavy throttle starts and throttle-off at low speeds.

I was thinking center bearing as well but I'm not getting a lot of vibration at the shifter (which is my quasi-way of detecting driveshaft vibration).

My next thought was to make sure the diff was topped off and not low on fluid.

Please keep us posted!

fruitcakesa · #14 04-15-2009, 11:21 AM

I took a ride down one of my favorite local twisties and noticed when accelerating hard through a right hand turn I heard a rumbly whine from the rear, possibly the right side. No sound on hard left handers or normal speed right handers.
Then when coming back up the hill to my house while going over the whoop de doos that form along the right hand turn halfway up the hill
I got the noise again. I also was going faster than usual through that turn and it was the first time that noise has occurred there.
Seems to be when pushing the car harder than normal.
Any thoughts on this development?
I drained and refilled the diff way back when I first got the car.

fruitcakesa · #15 06-04-2009, 07:04 PM

I put a new set of Michelin Harmony's and bundt wheels on the old girl, crossed my fingers and took a ride.
Oh well, it was a pipe dream to hope that this would cure the driveline noise. Not!
It still vibrates a lot from 35 to 55 and then smoothes out above that
although compared to the flatspotted, bent rimmed, boots that I was running, the car rides much smoother, quieter and sure footed thanks to the new Michies.
I am not sure of my next step since I don't want to unnecessarily throw parts at it. Any more diagnostic help would sure be appreciated.
I am loving driving the car ,vibe or not.