acr2001

I bought Posi Quiet semi metallic brake pads for the front and back of my 2005 C240. I did not replace the original rotors (they have 25k miles on them).

On the fronts the new pads don't appear to be making full contact with the rotor - I can see that the inner portion of the rotor is the usual proper color (smooth and dark with a hint of blue) while the outer portion of the rotor is a lighter whiter color. This problem did not occur on the rears. I notice that it takes a fair amount of added pedal force to stop compared to the stock pads I had.

Does this make sense? Is this a common issue, and do I just need new front rotors? The new pads have about 1000 miles on them so far with no improvement.

Oh and I did bed them in to the point of smoke coming off of them without improvement!

I'll post a picture of the rotors soon...

Glyn M Ruck

These cars do 80% plus of their braking on the front. Your discs have obviously worn unevenly. The new pads will bed in completely finally. Sounds like they have a bit of wearing to do to achieve that. If you are not getting 100% contact it is probably the main reason you have to push a bit harder. Softer pads do require less pedal pressure however.

If you are seeing abnormal blueing you could be getting some localised overheating.

Did you do a pad break in? I must say it's something I never do & have never had a problem.

acr2001

First I put about 800 miles on them, then after they still didn't feel right I tried breaking them in (bedding them in). At this point I'm out of patience, I'm going to order R1 concepts E-line drilled rotors for the front. I just wish I could get the performance of the stock pads without all the damn dust.

I think the rotors are damaged at this point from overheating because the new pads are making contact with less than half of the rotor unless I'm doing hard braking at which point I do get full contact. I'm just starting to feel a pulse in the pedal from a high spot.

I guess this is why MB says to always replace the pads and rotors at the same time, would have saved me time money and frustration.

acr2001

I was just reading some more on the Posi Quiet pads and apparently they don't have anything close to the bite of stockers, so I'm going to put stock pads back on and deal with the dust. This was a stupid waste of money... someone needs to create a website with comprehensive reviews of brake pads because as it is now theyre all a ****ing gamble!! :

Glyn M Ruck

MBSA never replace discs until they are at limit. I'm on my second set of stock pads & all is well apart from the darn dust. People I trust in the US tell me that Porterfield pads are the perfect compromise between performance & dust on stock rotors. Remember all rotors are not equal either. You will find that certain friction materials work well with some rotors & others with other - metal surface porosity, crystalline structure & hardness all come into the equation.

When people recommend a pad they should tell you what rotor it is running on. In my racing days I found that the friction material required for a straight Brembo ventilated steel disc was quite different from that required by a Japanese plasma coated disc - as an example.

acr2001

I've been reading about this stuff all over for the past few hours, even went through the huge 48 page brake thread.

I think the moral of it all is that N-O-T-H-I-N-G has the same bite as the stock pads, and anyone who says otherwise is either mistaken or lying.

I had read that MB recommended new rotors when changing the pads. My stock pads have 80% of their life left on them, I only changed them to stop the dust. Looks like they're going back on since they are worn at the same angle as the rotors.

Glyn M Ruck

I think this statement is correct. They are a damn good quiet pad with the downside being dust. I've been told that the Porterfield ceramic pads do require a little more pedal pressure but otherwise perform very similarly with about 25% of the dust. The only down side is that they don't achieve to bring the vehicle to a dead stop with quite the finesse of the stock pad - slight snatchiness at very low speed. I'm going to try some with stock rotors next time round - the dust has a negative effect on my disposition.

The truth is that, as usual, Benz have worked & balanced the compromises very well - I like the feeling of the stock brakes for normal everyday use - nicely progressive & all. I was talking to a very bright young Prof who is one of SAs top tuners the other day. The subject of ECU tuning arose. He recons that Benz ECU tuning is just about perfect & that messing with it takes away more than it gives in all round performance. I think there is a lesson in there somewhere.

BTW - splinter posted the MB rotor condemning limits a few weeks back.

LILBENZ230

I posted a thread similar to this a few weeks ago. The outer ring of my front rotors appears to be a different color. It looks like the pads aren't making contact with that outer ring. So what I did was make large dots in that ring with a permanent marker, and then back the car down the driveway. The dots were wiped away which means the pads are making contact, but as Glyn told me - no way to prove the pads were making contact with the same pressure.

And my car is running stock pads! Very weird to me. I'm starting to get a slight vibration (19k miles on the stock pads) so I'll be redoing brakes soon.

mleskovar

The FIRST thing you do with new pads is break them in. I don't get the 'color' of the rotor statement. Pics?

acr2001

I hate to disagree, but most websites say that bedding in can be done at any time. Either way, I figured out the issue after taking the pads off...

They were not making full contact - I know this because as you get closer to the outer edge of the pad, its worn in less and the original surface is partially visible.

I think I figured out why too - on the front brakes, the pistons are totally flat but the MB pads come with shims attached that have cut outs only at the bottom where the piston makes contact. These cut outs cause the piston to hit the brake pads at a very slight angle. Because of this the pads / rotors wear at that slight angle. The new brake pads did not have the same design, and instead had totally flat shims.

On top of all of that, I had two mechanics tell me today that the stock rotors are made of a custom material which is soft and designed for the material used on the stock pads. They told me aftermarket pads need to be used with aftermarket rotors on these cars.

TemjinX2

did you resurface the rotors when you changed the pads? Its usually recommended you change the rotors with the pads but if you don't you need them resurface so there even again.

I always swap the rotors and pads together just as a precaution. Since brakes isn't something you want to be too laxed on. I bought akembo ceramic street pads with oem rotors. I noticed the ceramics stop slightly better then oem but no dust. Only bad thing is that in the cold mornings they do make noise until you drive about 40yds and they heat up.

I've done some canyon carving and they've held up well under strong braking and heat...no brake fade at all.

Glyn M Ruck

There is no doubt that pad & rotor materials need to be matched up for optimum performance.

mleskovar

Link us to some of those sites that say that. By definition bedding in is the first thing you do with new pads if you want them to operate properly. You may be confusing the often touted "slam the brakes on a few times from speed and the noise and shimmy will go away" bogus fix with bedding in. Here's a good explanation of the reason why it's important to bed in new brake pads. http://www.stoptech.com/tech_info/wp...rakedisk.shtml The author of the white paper has excellent credentials in the field of automotive braking.

acr2001

I actually read that when I was searching. I didn't save any links, but I'll take a look later.

My point is that I did bed them in, just not immediately after installing them and it didn't help, I don't think waiting made any difference. One website actually recommended driving a few hundred miles normally before bedding.

Even if bedding them first is better, as I said the MB pads were designed differently so that they wore at an angle, all the bedding in the world wouldn't fix that - the pads would have required at least few thousand miles of wear before they would have made full contact.

To further the point, I think bedding them probably did more damage than it did good because of the partial contact. It created hot spots on the rotor during the bedding process.

acr2001

I asked about resurfacing the rotors and I had the same two mechanics tell me that MB rotors "never come out right" if you try to resurface them. I think this is why MB says not to do it.

mleskovar

Please read the whole white paper in the link I posted. Pads and rotors will not work properly until a transfer of material is made through the bedding in process. Waiting only sets you up for failure with and incomplete or random transfer.

Your assumption is that the pads were designed wrong? You need to step back and really look at what happened. Either the pads were installed incorrectly or there was a problem with the rotor to hub interface that wasn't corrected. If a pad isn't making full contact there is a problem. If they wear at an angle there is a problem in the mechanism, not the pads. If you knew how pads are manufactured you would rule out the thought that the pads are crooked on the backing plates.

acr2001

I don't know how you can say that without explaining why the MB back plates are angled (while the aftermarket pads are not).
Do you know what I'm talking about when I say that the MB shims have a partial cutout in them? I wish I could find a picture. This will cause a slight angle as the pads and rotors wear in, there is no question about it. And I can tell you that all 4 front pads on my car have this angle. The left and right side match perfectly, so I don't think it's a defect.

9 out of 10 drivers and mechanics I know do not bed new pads in at all, so regardless of whats said on the web, you're not going to CAUSE damage by not bedding the pads in. The main cause of my problem was the angle that the MB pads and rotors wore at.

Obviously if I installed new rotors I wouldn't have had that problem.

Another bit of info: the stock front pads are different on the left and right - you cannot install a pad for the drivers side on the passengers side with the stock pads. This is because of the cutout I mentioned. It lines up differently with the piston on either side. With the aftermarket pads (at least the ones I used) the front pads were all the same.

acr2001

Here are some photos of what I'm talking about with the stock pads.

On a side note, how bad is it that I reused the caliper bolts and 'clips' on the front? I also reused the pins on the rear brakes.
I know you're supposed to toss at least the bolts and install new ones.

Glyn M Ruck

No problem reusing bolts & clips

mleskovar

Eventually the clips will fail in the front. The symptom is a clicking noise when you release the brake pedal. It's the pad falling and hitting bottom after the braking action has moved the pad up. BTW, you can't buy just the clips. I tried and couldn't find them anywhere (if you know of a place please post!).

mleskovar

You win, obviously you know what you're doing and the problems you're experiencing are caused by faulty manufacture or design of parts.

acr2001

I assume you're being sarcastic...
I wasn't trying to prove you wrong, I'm just looking for an explanation because the facts seem to speak for themselves - the MB pads result in a slight angle compared to the pads I bought which are completely flat. The photos show it.

I know you have a ton of experience with this stuff (plenty more than I do), but until someone can explain this I believe my reasoning makes the most sense as far as the different backing plates are concerned. Obviously MB is spending extra money to cut those notches into them (where the piston touches) for some reason, while the aftermarket pads don't bother with it.

mleskovar

OK, now I think I know what you are trying to explain. You're talking about the shim that's attached to the backing plate....correct? And the about 120 degree circular piece cut out of the shim on the pads that go on the inside, against the piston....correct? The piston never enters that cutout and the force of the piston is distributed to the working pad face by the remaining part of the shim against the backplate. When you removed the old pads weren't they evenly worn? I <think> those cutouts are an attempt to reduce the area of the shim to piston contact thereby reducing the chances of vibration....the squealing noise you sometimes hear from brakes. Incidentally, proper break in reduces the chances of squealing as well.

acr2001

Don't hate me mleskovar, I'm only telling you what I saw (I wish I took pictures before I put the pads back on the car). On both sides, when I took the MB pads off and thoroughly cleaned them, you could see exactly where the piston was contacting that back plate / shim. It was contacting inside that cut out area and the edges of the shim (you could tell because it took a bit of the paint off of the plate).

So to put it another way, roughly half of the piston was making contact with the pad, and the half making contact was the half that was inside that cutout in the back plate. This is why I made the assumption that MB added that cutout in order to create a slight angle when the piston hits the pads. If mine wore wrong then they did so on both sides exactly the same amount. Maybe mine did wear wrong, because what you're saying sounds like it makes more sense now that were both on the same page. My brakes are working great again now that I put the original pads back on.

mleskovar

No hate :-) Sometimes it's very frustrating explaining things on the internet and understanding what others are saying. And that works both ways. I'm no expert and have been wrong many times. I no longer use the stock pads, couldn't stand the dust and short life (but the 'feel' was excellent, hot or cold). But my original MB pads wore evenly and I do remember the cutouts because the after market pads I installed did not have them. Maybe the witness marks you saw within the cutout were caused by pad dust buildup and then being compressed? If the piston is forcing the pad to **** and apply more pressure against the inner part of the rotor like you think then what about the pad on the other side? There's no cutout there. If the caliper were being cocked then the opposite would happen to that pad....more pressure on the outside of the rotor.There's enough piston to shim contact to evenly distribute the force and disc brakes rely on evenly distributed pressure across the face of the pad to work correctly. Otherwise you'd have temperature variations across the pads and rotors and the stopping power would be seriously compromised.