W123 rear end clunk sound. Causes??
 

A member in another forum suggested I send VSTECH a message about my inquiry for rebuilding rear axles on my '85 300D. I sent him a PM and got a prompt reply but I think he wants me to start a thread and get others' opinions.

While changing rear brake pads last month I noticed a clunking sound when I rotated the rotor especially when I changed the direction of rotation or when the rotor was turning and I stopped it. The best I could determine, the sound was coming from the outboard axle boot.

Upon inspection of the boost I noticed them being kind of dry rotted but there were no tears so I'm comfortably sure that the lubricant is still intact. This is what made me begin to research axles as far as remanufactured, after-market, etc. and whether it was a DIY project I could perform. It was in this process that I end up at VSTECH's doorstep, so to speak thinking that my problem was the axles.

VSTECH has raised a couple of queries about my situation and some other possible explanations for the clunking sound which I only seem to notice while driving slow or when the car is slowing to a stop and makes the final downshift. It's not loud; it doesn't jolt the car but there is that clunk sound and I can feel it through the car.

Other than axles what could this be? I can't really inspect the differential bushing but was going to change it out with the axle job. Flex joint looks good upon inspection with no obvious issues noted. The transmission shifts smoothly on acceleration even at full throttle and there is no noise while traveling down the road unless I just can't hear it because of the sounds of going down the road but I also don't feel the clunk either. All the noise comes from the rear.

I'm all ears!

I'm glad to read you got in touch with VStech with regards to his axle booting service.

I had assumed from your thread on BW (Homokinetic or annular? - Mercedes-Benz Forum) that you knew that the axles were at fault.

Rear end clunking is often a result of a dodgy axle however there are other things to consider such as

(off the top of my head and in no particulaer order)

1) anti-roll bar links - often made from plastic and they can snap
2) broken / rusted through trailing arms
3) stuck / sticking rear brakes / parking brakes
4) forgein objects clanking about that shouldn't be there! (road kill?)
5) problems with SLS if fitted - passenger side on a LHD vehicle is where the leveling valve sits
6) loose wheel bearings
7) loose shock absorber
8) broken spring (not all that likely on the back of a W123)
9) excessive play in the differential
10) loose wheel nuts
11) loose exhaust
12) worn bushings in the trailing arms
13) worn UJ in propshaft
14) excessive play in gearbox / transmission - in particular output yoke nuts have been known to come off
15) worn propshaft centre bearing

...can anyone else think of another?

There must be more!

If is not the axles then it must be one of #'s 12-15 as Stretch suggested. I will get my car up on jack stands after lunch and investigate. Hopefully it is not #9 as that will surely be a big job.

I will post with my findings.

STRETCH, your advice and suggestions are greatly appreciated. I may have led you to believe that my problem was the axles because that it was I thought it HAD to be. You gave the best advice with info I gave you.

Is this what would be called a 'trailing arm'? When I shake these they clunk. The hushing is shot. This was #12 on Stetch's list to check. I did not have to yank on them get hard. They clunk on both sides. Is the bar that goes across the vehicle to both points the sway bar?

I would be interested to know how many miles are on the car, as a point of reference.

Also an observation that a broken or completely worn out sway bar link can make a pretty nasty clunk. I would go there first before worrying about anything else.

Of course, this is assuming you have checked and double-checked that there is no junk in the trunk (including in the spare tire well) that could be the cause. :D (Voice of experience.)

You answered while I was typing my other reply.

Those are the sway bar links. Happy news. They are by far the least expensive fix, assuming that is what you are hearing. And an easy DIY.

Yes, that is the sway bar running from one side of the car to the other.

When buying replacements, buy Lemforder if possible, second choice TRW, Febi third. (Or of course, OE Mercedes if you are inclined to spend a few more $$$.)

Avoid MTC, Meyle, Trucktec and URO or APA branded items (which may turn up first in your parts searches).

Note: in parts listings it will probably say "stabilizer bar link."

Ok... when are you bringing the car my way?

I ordered parts before reading your post. Fortunately I paid a few extra $ and got the MB part. Went ahead and got sway bar bushings too since I'll be under the car.

Agreed, looks to be an easy fix. Afterwards I'll have the axles rebooted before they fail. 107K miles on my car.

I'm new at the MB game but have learned my lesson with URO parts, particularly door strikes. Eventually I removed the rubber bushing from them and put them in the original metal housings.

Glad to hear it was a simple fix

Haven't fixed it yet Stretch. I have ordered parts. I hope that is all it is as that seems to be fairly easy to remedy. I'll let you know how it turns out. Thanks again.