Uneven Pad Wear Side to Side but Even on Calipers - PeachParts Mercedes-Benz Forum

TROVERMAN · #1 03-25-2004, 05:12 PM

Pulling all the wheels on the 95 E320 wagon, I noticed a few things: On one side of the car front (can't remember which now) the pads look good with decent wear left, but the annoying wear light was flashing on the dash. I figured both sides must be wearing equally. On the opposite front side of the car the pads were warn down a lot more, not to the metal part, but definitely to the min thickness or worse. This is surprising considering the car does not pull side to side when braking.
Any ideas as to why? The brakes work perfectly, and are very strong and smooth. No warning lights as to the brakes, except of course the wear light.

Also: Rotors. The front rotors are very shiny and smooth, like brand new, but there is some "lip" on both the inside and outside edges of the rotor surface. This is true for both front rotors. Is this O.K. or do they need to be replaced? I am not the kind of person who replaces rotors just because I am replacing the pads (which will be replaced this weekend) although I have heard the arguments for it.

In the rear there is a different story. The pads on both rear sides look new, and wear is equal for both. No problems there, but the rotors are confusing me. There is no "lip" whatsoever on these rotors, but the surface is not shiny either. It is relatively smooth, but you can see a whole bunch of marks all the way around the rotor where the pad has contacted the surface. The rotor is fairly smooth, though, it is not like the pad is wearing into the surface.
Any idea on the story here?

Last brake question: on this car the ABS system seems to come on quite often. It will come on when there is a snowy covering on the road, or even if the front wheels get into some mud when I am pulling into the driveway. It seems to work fine. It also seems to have a low threshold for speed, like it will work at 5mph. None of my other ABS equipped cars will do this, even the 96 BOSCH ABS equipped Volvo 960 (RWD) In fact, this is the only car I have ever had that has the ABS come on so often.

Any thoughts?

Thanks.

manny · #2 03-25-2004, 05:37 PM

As far as the uneven wear side-to-side, I would suspect a sticking piston in the caliper, maintaining too much pad/rotor contact. This may also be a partial explanation for your wonky ABS.
As far as the ridge on the rotor goes, normal.
The rotors will be marked " minimum" xxxx.
If the ridge bothers you, you could have it turned down even.
In regards to your rear brakes, they normally do very little work, as 80% of your braking is handled by the fronts.
Quite normal to see a 2 for 1 ratio ( frontpads twice, to rear pads once ).

RKreutzer · #3 03-25-2004, 10:22 PM

In addition to manny's info, the ridge indicates the original thickness and the rotor has worn behind it, so to speak. You have to measure the thickness of the rotor in the middle and see whether it is above the minimum or better yet service level. On my 126, they come with 28 mm new, the service level is 25.8 (meaning they get replaced at that level when you have the car in for service) and the minimum is 25.4 if memory serves me right.
Mine had quite a ridge and I measured 25.9.
Good luck
Reinhard Kreutzer

md21722 · #4 03-25-2004, 10:41 PM

manny,

If the slide pins in the carrier stick, would this cause one side of the pads to wear more than the others or is a sticking caliper the only way it woudl happen? I've seen many cars this way.

TROVERMAN · #5 03-26-2004, 12:40 PM

Please understand the problem: There are two pads per caliper. The problem is only on the front. On the driver's side, both pads on the caliper are worn down much more than those of the passenger side. However, both pads are worn equally on that side. (And on the other side, just less)

jcyuhn · #6 03-26-2004, 01:31 PM

I vote for a dragging caliper. If the slide pins were bad, then the two pads in the one caliper would wear unevenly. Given that the two pads are worn evenly, but more than the other side of the car, the caliper is sliding OK but is remaining applied.

I can think of two possible causes. One would be a failure of the piston to retract. Check the piston dust seal for obvious damage. You will have to rebuild or replace the caliper to remedy this problem.

The other possible culprit is the flexible brake line. These become suspect once the car reaches ~10 years of age. They can swell internally, and act as a one-way valve for the brake fluid, causing the caliper to drag just a bit.

Given that brake lines are only 15 bucks or so, I'd replace it anyway when doing to repair. It's cheaper than burning up pads and rotors.

- JimY

TROVERMAN · #7 03-30-2004, 03:28 PM

Thanks everyone--I am picking up the new pads and sensors tommorow afternoon, along with a few other misc items. The pads are like $65 and the sensors are another $15, so about $80 total. Not terrible, but not cheap, either. The other things added in make the cost go up to about $150 (new chrome door strip, two power headrest buttons which fell off, vaccuum valve, engine pan gasket) Still, if this makes the car right for a while, then all is well. I know many of you spend tons more. About the brakes--This is just a thought-the car actually has mismatched tires on the front, and has, for about 15k miles. The tires had just been replaced with 4 new Michelin Pilot Primacy tires, but one went flat almost immediately after they were put on, so the spare was put on the front, one of the original Pirelli Powergy tires. This was immediately before I purchased the car at 38,000 miles. The flat Michelin had been fixed and put in as the spare tire, while the Pirrelli remained on the front. We never switched them back because the wear across the front was about even, and the fixed Michelin had more tread. So I wonder if this could have something to do with uneven pad wear. The Pirelli is the side which has more pad left, the Michelin side on the front has far less. The Michelin is V (R) rated to 150mph+ and is a summer only sticky tire. Does this mean it gripped more than the all season Pirelli and as such wore more of the pad off? This is my idea.
The new development is that now the car has developed a light shimmy, shake, or vibration in the front end at around 75mph. I am also attributing this to the mismatched tires. Also, the front end may be out of alignment. The car was barely used in the winter, so we just left the tires as they were and used the Rover. The front tire is being replaced by a new Pilot ($130 / tire!) and the alignment ($100) will be done as well. Anyway, that's the story so far. By the way, do all of you have your alignments done by MB or can an independent do it? (Special tools, knowledge, etc?)

Thanks

guydewdney · #8 03-30-2004, 03:41 PM

let me get this right...

the pads in the left caliper (for example) are evenly worn to the minimum, but the ones in the right caliper are not worn.

the rears are both the same, unworn, and the discs themselves are not 'shiney' likle the fronts - almost as if the brakes are ddoing nothing at all?

this sounds very very much like either the master cylinder has gone south, or the load compensating valve has died.

i would go to a brake check place and have the effectivness of all four brakes tested independantly on a mini rolling road (i asume you guys have the same yearly test for safety over there on cars? the places that do that have these brake testers...

TROVERMAN · #9 03-30-2004, 05:14 PM

You are correct. However, the brakes are very strong, better than all the other cars in the signature list. The car does not pull during braking. I just wanted to know why the pads on one side of the car wore worse than on the other side.

We only have a yearly inspection here, and it is a joke. The 1st time the car was inspected, the mechanic looked at the Mercedes emblem on the hood and the mileage on the dash and passed the car. 2 minutes and $15. When the car is inspected they are supposed to check to make sure it is fit to be on the road, like no gaping rust holes, play in the front end, all lights / wipers / horn works, etc, and they are supposed to check for brake wear.