1991 W126 Wheel Shake Problem?
 

I have a 1991 W126 chassis with new Michelin MXV 205/65/R15 tires that are shaking the steering wheel starting at 53 MPH. Switching rear tires to front produces same result. Tires have been Road Force balanced by tire shop and they insist tires are perfectly balanced.

My regular indie MB shop (Jarek's MB Shop of Knoxville, TN who I trust explicity) insists there is no mechanical reason for the shaking, "ball joints, tie rod ends and steering shock etc. are fine".

I'm at a stand off with the tire shop and mechanic.

Could really use some advice on this.

Thank you.


10/28/2010 UPDATE: Tires were rebalanced again using Road Force method "with special care" according to the tire shop manager. My shaking is cured now. My regular MB mechanic confirms that W126 cars need special care when balancing tires.

Have the shop check that the front wheel bearings are adjusted properly. Also, check that none of your wheels are bent.

It's possible that the new tires have slipped belts, but not likely. Michelin is a premium quality tire.

Lower control arms? What about some of the other suspension bits up front?

How are the front wheel bearings adjustable? Wheels are not bent.

My mechanic says that all the parts that could cause the problem are ok.

I'm having the same problem too. I finally replaced one of my tie rod ends and idler arm bushing, that solved it for a little while, but its back.

I stumped 2 mechanics with it too. I only knew which wheel it was by the wear pattern. (Much more and on the outside edge of the tire)

I guess the other one is going bad. You might start checking there.

ezrider, there is a specied amount of play (measured with a dial indicator in thousandths of an inch) for front wheel bearings. Ask your shop personnel if they have checked the front wheel bearing condition and the play and both are OK.

I'm not saying the wheel bearings are definitely causing the vibration, but it's possible since the shop has ruled out most other things.

Had this problem on my 90 560SEL.

Brand new tires started shaking around 60MPH.
Front end checked out, nothing obviously worn out.

First set of tires were BFGs. Had them balanced twice at point of purchase, then went to another store and did them again. Yes, I asked to have the machine calibrated for 2nd and 3rd attempt.

Tires still not balanced... Took a trip out of town. Tried again for a 4th time at yet another store, in another town. Owner was a friend of one of my Uncles, even opened up on Sunday and he did them himself. Still out of balance. Tried twice, each time machine said good to go...

After returning home, I went back to the original store and returned the tires, and mounted a set of new Michelin Pilots.

Same damn vibration.

Had them rebalanced again. No change.

Finally, took them to an old guy that had one of those on the car spin balancers.

First time he spun up one of the front tires, it looked like the headlight wiper blades were going to bounce of the lights, it was so out of balance.

He then pulled the weights and iteratively added a bit at a time until the tire spun up without vibration. Did the same with the other front. Couldn't do the rears in place, because I've got limited slip.

I went home (and could already tell a huge difference), swapped the front to rear, then returned to get the (now) front tires balanced.

He goes through the same process, and balances the other two tires...

That was five years ago, and these tires are still dead smooth, even at 80+MPH.

Go figure.

Jim

brake rotors can also cause vibration problems

The problem is the wheel hub.

All tire and wheel balancing makes the assumption that you will mount the perfectly balanced tire/wheel combo on a centerline that is perfectly concentric with the balancing axis.

This requires that the two ID's for the bearings be perfectly concentric with the mounting diameter for the hub. Since these components are not ground, it's entirely possible that the component doesn't have the concentricity necessary for a smooth ride. A deviation of only .001" would result in an unbalance of .8 ounce-inches, a value that is slightly higher than one desires to avoid feeling any vibration in the wheel at speed.

Balancing on the vehicle...........with the hub..........eliminates this issue.