Rear Brake Pads wore down to METAL in 24k miles!
 

I was shocked today to brake and at low speeds the entire rear end vibrated.

I checked the rear brake pads today and one side the disk is SCORED from metal on metal, and the other side is 95% to metal.
I replaced these on my Excel document @ 140k. I have 164k now.

How in the heck does a set of REAR brake pads wear down to zero in 24k miles? My last set was put on at 75k...so they lasted 65k (and I remember they still had some life left on them maybe 5-10k more), but this set lasts 24k?
They were Textar pads.

Any ideas? If it were ONE side I would think bad caliper, but both rear corners are gone.

I also replaced the fronts at 140k as well and there are tons of pad life left (I checked that last week because I was searching for a sticky caliper for my steering pull to the right).

Wow. Sticking calipers would be my first thought.

But I will say I bought Mercedes boxed originals. Textar were cheaper and I knew they were OEM but I really wanted the reduced dust and to be certain they would be OEM.

Well when they came, they were stamped Textar with MB stamping. Go figure I thought. Not a big deal though, its not like the OEM were too much more.

These are the worst pads I have ever had. Like yours mine are wearing out way to fast. But for me its the fronts that are worst. Also the amount of dust they produce is 100 fold worse than the ones I pulled out (which were also OEM Benz stamped). I can wash my wheels and have them black a week later. Front calipers are rebuild ATEs.

Mercedes like most cars today utilizes a dual circuit master cylinder, in the case of 124 cars the circuits are front and rear. Maybe the brake pressure being applied by the divided circuits is not proportioned correctly for some reason?

Disappearing rear brake pad could be attributable to, too much rear circuit pressure being applied or too little front circuit pressure being applied. Either of those would lead to the greater loss of pad material in the rear.


With a deficiency at the front brakes the rear brakes would have to be working and wearing harder to stop the car so that could be a contributing factor as well.

I've used Textar pads front and rear on my 300TE, and old 260E for a good number of miles. Its definitely not the pads.

Since the pads wore within 95% of each other, I think the odds that the calipers BOTH sticking at the exact same time is extremely slim.

BatteredBenz -- The master cylinder makes sense. Is there a way I can test if the M/S is the issue?

I don't know how you could easily measure to see if there is a difference. I saw your post on another thread about rear subframe suspension and a pulling in a direction other than straight forward when travelling at speed, so at this point I'd be inclined to get new pads and think about what other things or combination of things might be happening or not happening.

It seems like you didn't notice anything until the pads were toast so there wasn't much warning which would indicate the system was otherwise operational from a driving and braking stand point.

I wonder if something else could be causing something, ABS?

I know you take a serious interest with your car so it seems unlikely as two calipers or two hoses causing both brakes to stick so something in common is more likely.

If the brakes were dragging you'd think it would have been noticed as less mileage, if they were wearing away over 24K!

Could be just crappy pads that were not what you wear expecting, AutoZone pads I wouldn't be surprised, but you'd expect more than with decent parts.

If your pads were metal to metal, this has been going on for some time at least. Your post about the car pulling to the right is less than a month ago I believe, so the rear brake issue has to be several months in the works. First thing first: get those rotors and pads replaced ASAP. Never rule out both rear calipers sticking at the same time, there is nothing that says that it can't happen, so make sure you test both calipers. Not sure how you would test the circuits/brake pressure, but what you can do is get a helper to assist you and get the 2 fronts off the ground and have someone apply the brakes while you try to rotate by hand, do that with front and rear.This will at least tell you if there is pressure on the fronts, though it may not tell you much else. Also check the condition of brake fluid. 24k miles ago puts you at close to 2 years (unless you're like me, that puts you at about 6 months :-). Hopefully this is linked to your pulling to the right because you've went from that, to cracked sub frame bushings, to a failed switch over valve....Hopefully you can get these issues sorted out and start enjoying your s124. Keep us posted.

When was the fluid changed?
Brake hoses?

Brake hoses were done at 140k.

I've always done brake fluid every 2 years.

There were no signs of any lost fuel economy...or at least it was negligible 1 mpg at most.

Did YOU replace the brake pads?

i.e. You know for sure they were actually replaced?

Elek- excellent question.

Yep. Did them myself. I do 99% of all work on my cars.

Edit...you made me second guess myself but I found the receipt from purchase October 2013 so definitely did it. There's no way I reused old pads on new rotors when I bought the pads anyway lol. Definitely wore down to zero in 24k miles.

Receipt shows I bought rotors pads and hoses so inline with my maintenance document.

Based on the above it sounds like a fluid restriction.

I Googled the problem and everything kept saying proportioning valve but I can't find anything for MB on that term. Is it integrated in the master cylinder or abs unit?

Rebuild the rear calipers?
 

MB brake systems are bullet proof for obvious reasons. The rebuilding process for calipers is really nothing more that replacing the O-ring inside the piston sleeve and the rubber collar that surrounds the sliding piston. with my 90 300E, I found that some corrosion had formed a ring around the piston causing both pistons from each side to stick so much that they would not move forward to engage the brake pad. (The previous owner, never changed the fluid it seems). I gently took the corrosion off with an abrasive pad and followed up with a fine steel wool to get the side as smooth as possible, replaced the O-ring and collar for both caliper for less than $25 (while at it, I went ahead and replaced the hoses, and cleaned up the caliper sliding surfaces). Now all is well again.

Good luck.

Seems like the master cylinder is the best guess so far. It's $165 new but I got very lucky and found a brand new ATE one on ebay without the box for $50. Done deal!

I will probably get it some time next week so I will report back after I install it to see if I notice any difference in the feel of the car or braking.

How are your rear wheel bearings? If the bearings are shot and the hub/rotor is allowed to change angles while turning or following different road crown slopes, the rotor will shift back and forth a few .001" of an inch and quickly wear down the brake pads. Every time you push the brake pedal the pistons will move out and the gap will be reduced, and then the wear cycle starts anew.

Roll down your windows and listen while making turns at around 20 or 25 mph (so there's no wind noise), do you hear the sound of the rotors brushing on the pads?