vibration at 65 - rear axle cause???

[sms]

I have a very noticeable vibration in my '87 560sl that starts at 45mph and gradually gets worse and peaks at around 65mph. I've had the wheels dynamically balanced 2x and had the front end checked and aligned. It also has new tires. My shop went back and looked at the wheels (original 15") again and found one that was slightly bent. They replaced it, but car still vibrates.

I've eliminated the drive train as the cause (engine & transmission) since car still vibrates at 65mph even if I use different gearing. The only thing left, I'm told, is the rear half shafts or the drive shaft. Half shafts have 75k miles on them and boots are intact, but dry rotted. No signs of leaking oil yet! How likely is it that the half shafts could be causing the vibration???

Thanks,

Steve

[jay3000]

The driveshaft center bearing, and support could be the cause.. Apparently a fairly common failure at over 100K miles..
I posted a "how to" article on replacing them a while back on a 300sel..

You did not say what kind of tires you have. The description you offer indicates tire problems. I would suggest that you go to: www.gsp9700.com and find the machine near you. This machine can analyze your tires for excessive road force variation (stiff spots.) It is the next step for your situation.

Driveshaft vibration usually is at its worst under acceleration and is at a much higher frequency than tire vibration.

Best of luck,

[jay3000]

Try this.. Have your wife lay on the rear floor, and put her ear on the driveshaft hump right behind the console.. If it's the center bearing, the noise will be very loud, and you will be able to feel it at that point..

If a tire is bad on the front, you will feel it in the steering wheel.. If you think have a bad tire on the rear, move it to the front.. If you don't feel it in the steering, it's probably not the tire..

On mine, the Center bearing made a low pitch roar/vibration at 35-70 mph coatsing, or under load and became less noticable at speeds above 80.

[sms]

I've owned plenty of cars and have never had a vibration problem that couldn't be simply resolved. I've had both American RWD autos and foreign fwd cars. I currently have a 1987 Maxima with 200k miles and is as solid on the highway @ 75mph as it is around town. It's had its share of parts replaced like tie rod ends, struts, ball joints, cv joints, etc., but it didn't list for $60k and it didn't have these problems until atleast 125k miles. I've never had a bad wheel or tire and have been getting them at the same place for 15yrs. So what's the mystery with this Mercedes? Tires, wheels, bearings, and front end have been looked at over and over again. I'm now looking at exotic things like rear axle, drive shaft bearings, u-joints, flex disks, cv joints, and differential. Can a car that cost $60k new and only has 75K miles and that hasn't been abused (not a beater) have these issures and which one is most likely???

TIA,

Steve

[jay3000]

Did you try what I suggested??? The car has a two piece driveshaft, with only one universal joint (in the middle)..
It has a slip joint , and center bearing/ support in the middle of the shaft also.. On either end of the shaft there is a rubber disk that connects the shaft to to the tranny, and diff...


Over time, not necessarily miles, the rubber parts deteriorate, and the grease in the bearing becomes old, and brittle.. That may well be the source of your vibration..

When I disassembled mine, it was obvious..

[sms]

Are the deteriorated rubber parts that you mention called flex disks and does one usually fail sooner than the other?

[jay3000]

Yes.. The parts that connect the driveshaft at either end, are called flex discs..

My bet is still on the center bearing, and support however..

You can visually inspect the flex disc at both ends for cracking, and deterioration..

[sms]

Do you need to drop the exhaust to inspect the bearing and what else might need to be removed?

Thanks,

Steve

[jay3000]

See if this link will work...

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=480995&sortby=lastpost&sortorder=descending

[jay3000]

If you search around for center bearing, and for driveline vibration, you will find lots of reading..

[sms]

Hi,

Provide an update on this problem. The shop I took it to inspected the shaft, flex disks, and wheel bearings, but could find nothing unusual. They removed the rear shafts and noticed that one was binding. Had the shafts rebuilt and once installed about 90% of the vibration is gone. I think that what's left is either the normal road feel for these cars or could be rear subframe bushings?

Steve