PeachParts Mercedes-Benz Forum - E420 Brake Questions

Hi. I have a vibration when firmly braking from above 50mph. Here is an excerpt from another web site on this topic, my questions are below.

Begin excerpt
- Robert
I purchased a used 400E with 85,000 mi., the car is great except for a vibration when the brakes are applied. The front brake rotors and pads have been replaced. I checked the front wheel bearing adjustment. Is this a problem with this model or is there a fix. Thanks for your help. Bob

- Donald
Robert, you didn't say where you felt the vibs. You've done all you can do on the outside. If you feel it in the brake pedal then check your ABS. The guide line in using ABS is SSS. Stamp,Steer, Stay. Keep constant pedal pressure when braking. I hope this helps you to find your problem.

- Robert
I feel it in the suspension, it's not the ABS feeling. It feels like a warped rotor. I checked the run out on the new rotors and they seem ok. Is there any suspension components that cause this? Thanks.

- Jack
Even with bad/warped rotor, when new brake pads are replaced, the vibration should stop for a short priod of time. Have you check the rear brakes.

- Alan
I recently purchased a used 400E with new pads and rotors and they also vibrate/shimmy.This is only a minor shimmy and it only happens when braking from 90 mph down to 55 or so. Any suggestions?

- Erich
Bob, Did you ever discover the source of the vibration? I have a 260E with the same condition.

- Paul
Warped rear rotors will also cause a pulsation when the breaks are applied.

- Jim
New rotor or old, the proper way to diagnose a pulsating pedal/vibrating brake problem is to measure the out of plane on each rotor surface with a dial indicator. This takes the guess work out of the diagnosis. The rotor surfaces should show less than 0.005" TIR. Installing a new rotor is no guarantee of solving a brake vitration problem. I have seen new rotors which exceed the 0.005" specification.

- Napoleon
I recently had to machine brand new rotors from a respected supplier because of warp ... It happens. They were magnanamous and paid for the work. What a difference.

- Edmund
Change your lower a-arm bushings. This will fix it everytime. Cheers, ED

- Napoleon
ED, Please explain.

- John
I think MB is too generous with the out-of-plane spec for rotors at .005" in cars with fixed calipers. I have had continuing vibration problems wit 4 new rotors and padsets. Replaced control-arm-bushings, tie-rod ends, idler-arm bushings with no improvement. All 4 rotors were < .003" OOP. Machined the front rotors (which I was reluctant to do) but this cured the problem temporarily. It is now back, and I must conclude that MB rotors have varying hardness and warp and wear unevenly. My next step is to switch to ATE. I have never had such problems with new rotors in any other car.

- Edmund
I have a 1997 E420 which had this vibration. It occured at about 50 to 60 MPH. I changed the rotors, break pads, new tires and several times had the tires re-balanced. With all this I could not get rid of this very anoying shaking in the front end. Only after changing the (2 per side) A-arm bushings has this been cured. Those bushings are filled with hydraulic fluid which can leak out and this will change the damping ability. When the brakes are applied stress gets put on the A-arms and when there is not the correct damping then you get a resonance which causes this vibration phenomena. I the case with my car it also caused a shimmy feeling at speeds mentioned above. I hope this helps. Cheers and a happy new year, ED

- Napoleon
ED, Thanks.
End excerpt

I have a 1994 E420 and it vibrates when braking firmly at speeds above 50 mph. I assumed it was the rear rotors since I don't feel much vibration in the wheel, but mostly hear the groan and feel a very slight vibration in the wheel and in the seat. If it is the A-arm bushings, would this repair be covered under a Starmark Warranty? If not covered, or if it does not fix the problem and I end up paying for it, is this an expensive replacement? Thanks.