Pulsating Brakes - the Other Cause?
 

re: 1992 400E.

What can cause brakes to pulsate? Besides warped rotors. The pulsating was quite pronounced so I put on new new Balo rotors and new pads, it was fine for a couple of months, but now it has come back and is getting worse. It's more noticeable when the brakes warm up, not so much when cold. I'm assuming there must be something wrong with a caliper - but what? The calipers must not fail often because dealers don't stock them - although they do have a caliper rebuild kit for about $60. But what could cause the pulsating to come back so soon?

Front??

If yes , check the load adjustment on the wheel bearings

Pulsating disc brakes
 

Warping the rotor can be caused by over torqueing the lug nuts also.


If it was easy everybody would do it!


Junqueyardjim

Couple things to check:

- If rotors have a darkened area, uneven surface appearance, then overheating or burned-on contaminants might be the cause.

- Not meticulously cleaning the hub face and completely cleaning off the coating on new rotors will affect the way they seat, causing eccentric rotation. This leads to uneven wear and poor braking feel.

Steve

Warped wheel/unevenly worn tire?

I'd say rotors. Brand new doesn't mean they are good. The last time my rotors were changed, we went through 4 sets right out of the box. Any they were OE by the way, not the cheap stuff.

go with the dealer, the rotors are $57 a piece pads $50
You can't go wrong with original MB parts.

Yes, front. How does one check the load adjustment on wheel bearings? Sounds promising.

I've been hand tightening the lugs - doubt if I've been overtightening. No one else has touched.

Both wheels and tires are fairly new - wheels are $100 eight hole replicas though - I don't remember the exact timing but bad wheel is possible.

If all else fails I guess I could try new rotors - but I thought Balo was as good as they get, and OEM.

I'll check the rotors out again - I didn't clean them up well when I put them on.

Thanks for all the comments. I'll report back when I know more.

That was always a problem on the 1992 400E's. SO much a problem that the fix(MB factory) back in 1993-96 was to install the front brakes fron the 1993 & later 400E/E420's. I converted at least 5 of those cars myself under that original warranty! ROTORS are the problem!

I vaguely remember that the 92s had a brake problem, with a recall or campaign or something. I just recently asked the dealer if there was any open campaigns on my car and they said no - but who knows with a car this old. Are you saying I just have to put on 93+ rotors and pads? Or more than that?

Do you use tire foam or some other dressing on your tires? If you do and you are not covering the wheel when you spray it on, you are getting an uneven film on the rotors. If this is the cause it will go away after awhile as long as you don't brake really hard while the stuff is still on there.

Good luck,

Larry may have a point, but I'd bet on the Balo brand rotors being the culprit. The Balos I had on my 92 400E didn't last long at all before they warped. I don't ever plan to try that brand again...

I am presently running ATE Power Slots on the car, but I'm not happy with the noise they make under hard braking conditions.

My shop says I should only use MB Brand rotors...

Larry, no tire foam, but I didn't clean the rotors so I'm going to do that today. If all else fails I may try the ATE rotors - cheaper than a complete rotor / caliper conversion to the 93 style. My parts guy postured the Balo as being studier than Brembo but it might be nice to try slotted rotors. Initial investigation is that 92s had 22 mm rotors (124 421 1512) and 93s went to 25mm (124 421 2412).

I cleaned the rotors this morning and picked up a clue - the passenger side wheel spins freely and quietly, but the driver's side spins not so freely and with a repetitive rubbing sound on each revolution. So something on that side is not right. The rotor looks straight but I guess it's hard to tell. I think I will try reseating the pads to see if that does anything. At least it's nice to know what side it's on. I'm also wondering if I can replace just one rotor since they are so new - less than 2k miles. Thanks for all the help.

Dean, you can certainly replace only one rotor, but if you're considering a different design (drilled or slotted) then you'd want to replace both sides. I'd try drilled rotors instead of slotted if you're convinced that the standard rotors are inadequate for your 400E. Use a dial indicator to check the runout on your existing rotors.