Longevity of the rear axle mount

[awolff280sl]

About 15 years and 40,000 miles ago I replaced the motor mounts, subframe mounts, tranny mount, and the rear axle/diff hanger mount. All mounts were MB. About 6 months ago I started getting a clunk at times, but only when starting off from a complete stop in 1st gear. No clunks at any other time. I checked the usual suspects and all the other mounts, but never suspected the rear axle mount because I thought it was still too new. I was also worried that it was coming from the diff itself which is a harvested 3.27.
When I at last checked the rear mount there was only 1-2mm of space between the plate and the mount. Changing it out eliminated the clunk.
Is this normal wear for this mount? All the other mounts still look good. Could increased wear be caused by a 3.27 and/or 15 inch wheels?

[Ferrolanoman]

Can you please take a pic and show us the rear axle mount you replaced? I also have a clunk starting out in first gear and a lesser one when shifting into second, then no more clunks. I've looked under the car on a lift and cannot find the likely culprit.
thanks in advance.

[stickandrudderman]

15 years seems like a good innings for a hard working rubber part.

[awolff280sl]

Here's the old mount, and a pic of the new one in place. I don't see any gross difference from the new one when on the bench. It's only once installed that the space went from 1-2mm to about 10mm.
Previous postings on the forum have noted that the symptoms of a worn rear mount include clunking when gong over bumps. I would be interested to know if your clunk from a stop to 1st gear is also cured by replacing the mount.
It is indeed a hard-working rubber part.

[kampala]

Since "clunk" has been mentioned - is it not this other differential tubular bushing that is often also related to the "clunk?"

I have this tubular bushing, but have not found the courage to replace it.

photo borrowed from mbclassics

[awolff280sl]

The traditionally named "clunk bushing" in the diff hanger.
When does it clunk? With bumps, with shifting, with turns?

[wwheeler]

Andy,

Thank you a thousand times for posting this! I have had the same clunk in my W111 for the last year or so and has been driving me crazy! I put my car on a lift and checked everything and could find nothing. Last month I said oh well, I guess I will have to live with it. Mine clunked mainly when coming to a stop and when downshifting from second to first. Sometimes when driving , but not as often. I replaced mine in 2010 or just over 11 years ago. It was an MB part as well.

So thanks to this post, I took off the mount cover in the trunk for an inspection. Sure enough, I barely have more than a mm of clearance! In fact, there is white dust on either side (the waxy UV protection that rubber parts have) all over on the sides. Looks like the rubber just collapsed.   

I will order a new one and see what happens.

Thanks again.

Wallace

[kampala]

Mine clunks when starting in 1st gear and occasionally in second.  It’s not the same clunk I was getting before replacing the trunk mount.

As a test, I tightened the two bolts on the tubular bushing to see if the sound changes and it absolutely changed.  It was less for a short while.  For me, this means most likely the tubular bushing. 

Trunk Mount -  when I bought mine from mbclassics in Germany, Alexander sold both, aftermarket and Mercedes, but recommended aftermarket for longevity. As I recall he said Mercedes is a little softer so the ride may be a touch different but aftermarket, from his experience, lasts longer.  I installed aftermarket and so far it’s fine.

[Ferrolanoman]

Thank you very much for the pics and the diagnosis. Don't know which of the two bushings mine needs but hopefully it's the trunk one.

[awolff280sl]

Now I'm wondering whether it might be good preventative maintenance to tighten the 2 bolts holding the tubular clunk bushing ever so slightly at a certain mileage before it starts to clunk. If that bushing wears steadily over time then tightening the sleeve may slow down the wear.
Having to replace it is out of the question, until it isn't.

[kampala]

Now I'm wondering whether it might be good preventative maintenance to tighten the 2 bolts holding the tubular clunk bushing ever so slightly.

I was very cautious tightening those two bolts -- I did not know the torque and could not find it readily but I was nervous to not crack anything.   The bolts were not loose but moved them about 1/4 turn max. Not certain I should have done it, but wanted to find out which bushing it was - so did it as a test.
 
 JA17, Stick, Benz Dr, or other well informed - -  may know a lot better.   

[ja17]

Hi Oz, Those two bolts at the horizontal bushing are "cinch" bolts which grab the bushing and locate it fore and aft. In addition they are critical for preventing rotation of the bushing and are used to set left side rear wheel camber. They should always remain tight unless repairs are required.

[wwheeler]

Oz,

Just curious which aftermarket mount you bought?

[kampala]

Wallace

I bought from mbclassics in Germany.   Here’s the link to the aftermarket trunk mount.  He also has aftermarket tubular mount. 


https://www.mbclassics.de/rubber-mount-rear-axle-W108-110-111-113

[wwheeler]

Thanks Oz and it is ordered. I have bought from MB Classics before and is a good company. I drove my W111 to a local classic MB shop to show them the collapsed mount. They were were like, oh yeah, that is shot. After only 11 years........MB is selling theirs for $200 or so and the repro is $87 US with the current exchange rate. Even with shipping to the US from Germany, that is a no brainer. Hopefully it will last more than 11 years.

BTW, there were a couple of W113 cars there today and I looked at those mounts. Easily a 1/4" gap between the top washer and the base. Mine has basically nothing. I hope that cures the clunk.

[wwheeler]

I have my old mount out and have the new repro mount. I took a picture side by side. The old one is on the right and the new on the left. Like Andy's, my old mount had the lower part (facing down) push out quite a bit versus the new on. The first pic is with the upper washer on the old mount. The second pic is the upper washer on the new mount. A fair amount of difference. We will see if it gets rid of the clunk.

When removing the mount, the axle carrier post pushed to the right just a bit in the trunk floor hole. I am going to readjust my axle and center the post so that it is perfectly centered before installing the new mount. 

[stickandrudderman]

When removing the mount, the axle carrier post pushed to the right just a bit in the trunk floor hole. I am going to readjust my axle and center the post so that it is perfectly centered before installing the new mount.

You should read the technical manual on this subject before doing anything. The positioning of the axle hanger is important and well documented.

[Harry]

What space between the plate and the mount is being referred to?

[awolff280sl]

hey Wallace, my clunk is back.
The clunk is so dependent upon how I accelerate off of a stop, and thus so intermittent, that it never was cured by replacing the mount. It came back as I became less mindful of how I accelerated off of a stop that had already become second nature. I heard it one time while turning left. I hear it as coming from the right rear.
Over time I've checked the exhaust for hitting, the brake caliper bolts for loosening, the diff centering rod bolts, and the driveshaft play in the diff. All are good.
Maybe it has something to do with the right axle.
Or maybe it's the problem that Joe Alexander has identified in some 3.27 axles where "the large pin which holds the spider gears in the casting wears its mounting holes oblong causing differential "slop and clunk"?

[wwheeler]

Thanks for the info Stick and yes I will read that. I also checked everything under the car and found nothing that would cause a clunk. There are a couple of local experts that have been messing with these cars for years and years. They looked at it too and also came up empty. My rear axle has been rebuilt as is everything from the transmission going back. I am only semi confident that the mount is the problem but is pretty easy to replace and worth a shot.

The only other thing I found is the right axle bearing it is has a bit of play where as the left is solid. I have the self centering bearing on the right and am thinking that is what is causing that. I am thinking that is normal though.

Or maybe centering the rear axle combined with the new mount will resolve the clunk. We shall see. 

[awolff280sl]

Wallace, the diff hanger will not necessarily be centered in the hole in the trunk when the rear wheels are lifted off of the ground. Proper centering is based upon what stickandrudderman referred you to.

[ja17]

Hi Andy, the clunk can be caused by a badly deteriorated horizontal cylindrical bushing on the rear axle. This is the round steel/rubber bushing that holds the round hinge tube of the rear swing axle.

[wwheeler]

My diff mount update. Installing a new mount increased the clearance of the washer to the mount base in the trunk significantly. Hopeful this would eliminate the clunk. Well it did sort of.

I have had a clunk (more of a knock) driving around town and then a clunk that only happened when the car was coming to a stop and downshift into 2nd gear. The knock driving around town is gone for sure and must have been the mount's washer hitting the base plate. The clunk is still there though. So it is better but I think the clunk is in the axle internals and have been told that can be normal and not to worry too much about it. I guess it is also possible the trans pressure is set a bit too high. BTW, the 3 position solenoid works as it should.

The pivot bushing that Joe speaks of is only 7 years old and should be ok.

Oh well, good enough for me. 

[ja17]

Wallace, I think Andy's clunk is a different situation than yours. I do think that you can adjust the trans pressure to soften the last downshift.

[wwheeler]

Thanks Joe. I have never had a psi gauge on it to know for sure. Every once in a while the trans would "double shift" from second to fourth under very specific conditions. Raising the pressure a bit seemed to help that. Not sure what the cause of that was.

In your experience, do you feel the self adjusting axle bearing on the right side could contribute to the noise? It is new but has a bit of play side to side where as the left side is solid.

Thanks.