W124 Braking Vibration
 

It's a 1994 E320 Wagon 124.092.

I had a bad vibration on the front rotors when braking so purchased new OE rotors(marked ATE on the stamping) and OE pads. The old rotors had some good mileage on them and were pretty badly glazed so I decided to replace with new. After changing everything out the vibration went away...at least when driving surface street speeds. It wasn't until about a week later on the highway that I noticed that there was still a vibration, at much faster pulsation, when braking. I have to be driving at least 55+ to really feel it. It's not as bad, but it's definitely there.

I'm wondering if the vibration is actually coming from the rears (vented on my W124)? or the rears were contributing to some of the vibration prior but I never replaced those so that's where I'm still feeling it from. If this is the case, I would be surprised. I've never had warped rear rotors before in any car or truck I have owned.

Is it possible that the rotors I bought from the dealer were bad? I've been told that quality rotors don't need to be "turned" as long as the braking system is working properly with no abnormalities.

Any thoughts?

Hmmm...

Might maybe be a front wheel bearing or front tire problem, which becomes more obvious under braking as the weight transfers forward onto the front axle.

Try swapping the tires front-to rear and paying extra attention as you go around corners and the weight transfers left to right.

Best Regards,
Rob

Try to stop just using the emergency brake with one had on the release handle. It would rule out the front brakes if there is no vibration.

Edited: On second thought, I'm not sure if the emergency brake controls the pads or just the shoes on the inside.

Test your lower ball joints or steering rods.

Don't you mean the rear brakes? I don't think they grab the disc with the pads.

Steering rod, control arm, dampener - all replaced recently.

I'm down to:
Lower Ball Joints
Rear Disc

I went through the fronts again this morning. Unmounted everything, made sure rotors were seated flat, and everything torqued back to specs. Just for my own neurosis...

Anything other possibilities other than the two aforementioned?

I went through this on my first quattro, had 5 sets of rotors and pads under warranty, blamed my wheels (BBS), which dial-indicated to less than 10% of runout spec, they eventually replaced the hubs and bearings which cured my problem to run the next set of brakes for 130,000 miles.

If you have a dial-indicator, that would be your next step IMO. If not, try spinning the wheel with something propped close to the wheel and look for lateral and radial runout at the wheel and at the tire.

Often a slow swerve left/right as you're braking will make it better/worse to indicate which side is the offendor.

Have you tried replacing the horizontal damper in between steering ends? I don't know if it will solve the underlying problem, but it may make it less noticeable, and they only cost about $65. Have you cleaned the antiskid sensors on the front brakes? Metal deposits on the sensors caused a pulsation at very low speeds for me.

you know how to check if the ball joints are bad, right? jack up the front, grab the tire at 3 o'clock and 9 o'clock and push one end forward and the other end toward you. if there's even a centimeter of 'play', the ball joint is shot and needs replacing.

Sev, I guess you meant so say " a mm of play". A cm of play would be awfully loose.

Did you THOROUGHLY clean the mating surface of the hub with a steel brush before installing the new rotors?

Also do you use tire foam? I have started seeing more and more brake vibrations as the result of this stuff. What happens is that a little gets through the wheel spokes onto portions of the rotor. It acts a lubricant that coats the surfaces on only portions of the surface changing the coefficient of friction as the rotor turns against the pads.

If you use tire foam, make a cardboard cover that fits the wheel and hold it in place as a mask to ensure that no droplets of tire foam make it to the rotors.

Dampener was replaced recently.

No play in the ball joint or runoff (checked with dial).

Yes, cleaned very thoroughly before mounting rotors.

What the hell is tire foam? I don't ever spray my tires with anything. Always cloth rag and apply.

Thanks for all the feedback. I'm starting to think it's the rear disc. It would be a first ever but I guess there is always a first for everything. What sucks is that since I have the vented rotors they are not cheap. What I may end up doing is turning the old ones to identify for sure that this is the problem and if so replace with OE if it is. Sounds like a lot of work buy I'm not going to drop dime on rear rotors only to find that wasn't the culprit.

Edit: I should add that after calling the three local MB dealers in the area and talking to the service manager they say a bad rotor, although rare, has happened to show up in their stock. So it is still possible that I may have a bad front OE rotor n

Any other ideas?

speed, it's not advisable to turn MB rotors. Not sure why you would install vented rear rotors. Solid rear rotors are stock as far as I know. Typically I buy new rotors from our local MB dealer, and have never had any quality or performance issues.

It's a 124.092 - aka wagon, and stock vented rear rotors. Only class of W124 with rear vented (well say for the W124.036). I understand and recognize about turning them but it's just to isolate the problem. It was actually a suggestion by the service manager at the MB dealer. Obvisously they don't turn them at the dealer so I'll have to take them to a service shop.

Edit: To clarify, the idea here is to turn the old rotors, remount and see if the vibration goes away. If it does, replace with OE. If not keep them on there as no harm is done (as long as I'm not below min spec). The rear rotors are more expensive than my front rotors, both OE. Go figure.

You're carefully torqueing the lug nuts to spec?