Folks,

Well a couple of updates.. My usual independent shop has their state inspector out sick (in the hospital for chest pains - yuck, a VERY nice guy). He is very qualified ( Lotus, Ferrari, Porsche, Mercedes, and Bosch certified) and the only inspector. So off to another local shop for my annual inspection. I went to MBV Euro in Charlotte, NC as recommended by another poster here. Seem like very nice folks and busy, so hopefully that is a good sign. The car passed state inspection just fine. I asked them to look / diagnos the vibration I have been feeling if possible.

BTW - I have 4 new Michelins on it in the last 6 months and have rotated them a couple of times, no impact to the vibration. I have shifted to neutral at speed and the vibration remains, so probably not engine. Vibration is worst from 40-75 and stays with power on and coasting down. The vibration feels more rapid than a wheel balance problem.

The new shop drove the car with me in it, and thought it felt similar to the center bearing, but would investigate. They have worked on many MB driveshaft issues according to the service manager that rode with me.

Off I go to teach old computers new tricks... and talk with them as I return late this afternoon. They looked, felt, inspected, .. then put the car on the lift and dropped the driveshaft shield. They ran the car up to speed on the lift and listened and looked. Given their experience here is their diagnosis:

- both flex plates are fine
- center bearing and holder is fine
- driveshaft u-joint is fine
- both axles good - some looseness but no noises (clunking) to indicate CV issues
- noise from the differential and suspect internal bearing issues, possibly the pinion gear
- checked differential lube, ( it was changed by the first independent mechanic above when I bought the car 2 years/ 50Kmiles ago). It is clean and full - so doesn't appear to be a recent lube issue.
- they think it is ok to drive, not in danger of sudden failure

Now they aren't certain, but they feel it is a differential issue. There was a "loud noise - roar like" coming from the rear end while running at speed on the lift. To the greater body of experts here...any other tests to recommend? Rebuild or find a used one?

The shop quote they have is 6 hours to R&R a used one, 9 to rebuild + parts. I can't rebuild one, but I did swap rear-ends in my 92 mustang last year. Is the MB that much tougher ( yeah there will be more bolts with the axles and mounts)? Any special alignment, balancing or tools?

Any suggestions where to look? The site here was unavailable when I got home so this is the first post I have done. I will search more after this post. (edit Wed. morning- did search this morning and have notes from several posts. R&R doesn't seem too difficult)

Any other cars that are interchangable, like maybe the 300SEL? Guessing from some rough calcs (24" tires, 3500 rpm at 80mph), I think I have around a 3.2:1 gears.

Thanks again folks. You can't imagine the stress when I came home and this site wasn't available... now I feel better. (edit - and even better after an hour of searching)

Chuck

start with the easy stuff. try driveline balance first. have you kept up on differential oil changes. sometimes its a front bearing, sometimes side cover bearings. try driveline first though. of course, that being out will probably wipe out the input bearing in the differential and that may be the noise. pull the differential cover off yourself and see if there is any crap in the oil or if it's low.

Thanks for the ideas. I do want to try and listen myself to confirm. The shop - who supposedly has done many MB driveshafts and center bearings, had it on a lift and said the driveshaft was ok. They were under the car while the driveline was spinning and said there was "noise" coming from the differential, which lead to their conclusion. They felt the axles were ok now as well.

I have some records from the previous 210K miles, but none that specifically say the rear end fluid was changed. I had it changed when I got it 2 years ago. The shop yesterday said it was full and the fluid was clean in their determination. They didn't pull the cover or do an extensive check for metal parts floating.

The only suspect thing I can think of is I did bottom out a year ago on a sandy road down at the beach. I wonder if sand got into/at the pinion bearing and caused wear. I'll get under it this weekend and explore.

I have located a used center section for a "reasonable" price, so there is an option to replace it without going broke.

Film at 11, probably an update early next week.

Chuck

I can't imagine a diffferential causing a vibration. Atleast not until after the bearings were in catastrophic failure and noisy beyond hearing for years.

Vibrations come from either the drivesahft or drive axles. Very little you can tell about either by "looking". A common problem with drivesahfts is a notchiness of the center u-joint. This can be felt if the drivesahft is removed. It can NOT be determined in the car. Drive axles can be so bad that one can visually condemn them but they will vibrate a long time before they get that bad.

One interesting fact is that if the drive axles aren't visably bad but are the vibration switching them right to left will get rid of the problem as the wear in the joint is at the original angle and by swapping them they wear on a totally different area. We have done this on a couple of early SLs (107s) and a couple of 300Ds (123). WE were given the concept by a Rolls dealer when we approached them for axles and found they had been redesigned and the replacement would cost more than a small house.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Chuck,

Sorry I cannot give you any tech help; but can you give me info on the indy shops you've used in South Charlotte?

I'm also in South Charlotte, Arboretum area, and I'm always looking for info on indy shops in the area.

You mentioned MBV Euro in Charlotte. I cannot find them in the phone book. Where are they located and what other shops have you used?

In the past year, since I've purchased my C280, I've used Max at Auto Verks with success, but the place is a bit disorganized.

Thanks,
Gene

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GeneN
Charlotte, NC
1994 C280 135K

Steve,

Thanks for the comments. I am hoping to get time this weekend with a few friends in town to get it up in the air and listen / shake some things around myself.

I guess the first step is to watch and listen. I know the dynamics will be different without any load on the car. Also will the wheels / axles dropped down and therefore at different angles than usual... this may be masking an issue. I have never run a car in the air before at speed, and not one with independent rear suspension. I'll remove the driveshaft shield and check the bushings / driveshaft as well. Two pretty good shops have done this and not recommended driveshaft or the center bearing so far, but worth looking myself now. It may well be the issue Larry discovered with wear in a particular part of the u-joint and shimming it fixes that.

Can I remove the axles and run the driveline (up in the air) to see if it still vibrates? Anything it would hurt? It may be worth a first try at switching the axles - are they interchangeable? Larry's shim recommendation may be an easy try as well.

The primary place I have taken my car is PAS Automotive on W. Palmer (near the Panther's Stadium). Mike is the mgr and Kurt is the excellent mechanic. Kurt was in the hospital earlier this week. (Kurt had briefly looked at the vibration 6 months ago and did not see a clear diagnosis either). He is their only state inspector so I was looking to go somewhere else this month.

Based on a recommendation from this forum I went to MBV European Ltd. They are on Old Pineville Rd between Tyvola and Woodlawn (closer to Tyvola on the I-77 side). They looked and looked at the vibration issue and did not charge a diagnosis fee. Seemed to be an ok shop and had many Mercedes, Bmw's, and Volvo's there. Customer interactions with the Mgr were friendly while I waited... more good signs.

Chuck

It's my belief that there is usually very little to see and running it unloaded won't help much. With the drive axles hanging you are likely to cause vibrations.

The best view is experience. Experience gained through lots of wasted time doing a bunch of wrong things and from feeling a lot of u-joints (driveshaft out) that were then replaced with proper results. An experienced MB tech should be able to decide whether the problem is driveshaft or drive axle related. The only thing to do at that point is to pull it and feel the joint out of the car. If one gets to the point of knowing it is a driveshaft problem I would get an exchange unit from Beyer Motor Works in Mesa AZ (800-824-0809). We have gotten hundreds of them from them (mostly for BMWs). Some of the real hot rod BMW shops have been known to send factory new units to Beyer to have them gone through before installation. They remachine the center yoke to accept a replacable u-joint and do straightening and balancing par excelance.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician