Had the rotors replaced about 10,000 miles ago. At the same time, put on new AXIS brake pads (lower dust and I believe better feel). After about 9000 miles, felt a grabing and releasing on low speed gradual braking. Shop decided it was the rotors. Resurfaced rotors. Still there. Finally, after replacement of steering shock also found a bad ABS sensor. Now, under hard braking around 65 miles, steering shimmy is violent all the way to release of brakes. Under heavy or light braking at any other speed no shimmy or vibration. Tires also have been balanced. Any help?

Soccer
86 300sdl, 177k
91 300TE 4matic, 120k

Soccer,

I believe you need rotors. Turning these rotors is not a good thing, their border line thin to begin with. Turning them reduces the mass to a point where they can't hold as much heat. I believe that this led to the additional warping.

Check with the parts shop on this site. The rotors are not terribly expensive, nor very difficult to change.

Good luck,

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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

You must have some amount of rythmic irregularity in the brake disc to pads contact, but, the 126 chassis is known for problems around sixty. The common cause is weakness of the longitudinal strut mount (sometimes called rear control arm ball joint - basically the rear attachment of the lower control arm part# 126 330 13 35).

The discs should be dial indicated for run-out and probably sanded to remove glaze. You should also sand or replace the pads. The purpose here is that friction coefficient differences point to point around the circumferance of the disc can cause a pulsing force even on true discs. Both BMW and Volvo have factory bulletins out about this condition on their models that also have weak longitudinal supports.

Actually upon thinking about it, if it was in my shop I would throw away those discs. I have never seen a turned rotor that I liked. There is only 1mm (0.040") wear tolerance on each face of a new rotor so even one cut gets you very close. Also most manufacturers now recommend not turning rotors because the surface finish roughness is too great on all field service equiptment. MBs brake discs are designed to be tossed about every second set of pads.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

W126: front longitudinal strut mount: follow-up for Steve
 

Steve:

I was very intrigued by your comment indicating that the famous W126 60-70mph vibration/shake can often be related to weakness of the " longitudinal strut mount".

Thanks for the tip, which - coming from you - carries a great deal of weight.

Follow-up: Can you please advise, spcifically, which strut this is in descriptive terms, and where/how I can somehow check to see if it is unduly weak?

Thanks a million.