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At about 65000 miles I was getting the "check rear brake" notice on the instrument cluster. Yesterday I changed out the pads and was a little puzzled by what I found. The inner pads seemed to be heavily worn and the material thin while the outer pads had a ton of material left on them. I checked the sliders and they're all well lubricated and free, so I'm at a bit of a loss to explain why these pads (they are the originals installed by the factory) have worn this way.
The fact that both sides are the same strongly suggests that this is "normal", but I'm very interested to know if this is "typical" or if I need to dig a little deeper into the brake system back there.
Photo shows the pads as they were installed - left side outboard is the far left, right side outboard is the far right.
A Question:
Isn’t the wear pattern related to the automatic parking brake and also the hill/hold feature on the vehicle? Just that little bit of resistance multiplied over and over. Would this cause the unusual wear pattern?
A Question: Isn’t the wear pattern related to the automatic parking brake and also the hill/hold feature on the vehicle? Just that little bit of resistance multiplied over and over. Would this cause the unusual wear pattern?
I thought about that and I guess I could see that happening if one never used the manual brake release before moving. But I always pull the parking brake release before I take my foot off the brake and move. I only used the hill hold feature once just after I got the truck - to see whether it worked.
It's kind of a shame that they don't sell only the inner pads. The outer ones look like they'd go a few more rounds before they're ready for replacement.
Oh well, if it's normal, it is what it is.
Thanks very much for the responses. They're very much appreciated!
Not sure if you use the automatic lane departure correction (forget what Mercedes calls this particular driver assist feature) but it also applies the rear brakes to correct your course to keep you between the lane lines, using up the rear pads faster (but not sure if only the inner pads?). I had one parking brake actuator replaced because it was wearing one side faster than the other too.
Not sure if you use the automatic lane departure correction (forget what Mercedes calls this particular driver assist feature) but it also applies the rear brakes to correct your course to keep you between the lane lines, using up the rear pads faster (but not sure if only the inner pads?). I had one parking brake actuator replaced because it was wearing one side faster than the other too.
As does standard non-Distronic speed (cruise) control. It uses rear brakes to trim vehicle speed down to target in the case of descending roads or if the user has accelerated manually above the set speed.
Stability and cruise control use rear brakes to "manage" the motion / speed. Inside pad hanging is a result of caliper design, piston placement, caliper slide rail "drag". Staying with (pre electronic / computer nannies) one side piston caliper design makes for a much more inexpensive caliper cost at manufacturing time, at the expense of uneven pad wear.
GLE single piston "slider" rear
Older S 4 four piston for better pad wear and modulation
Yeah, I get the single piston deal but still don't see the rationale for having so much uneven wear on the pads. I have a 50+ year old Mustang with single piston disc brakes. Those pads wear evenly. It's hard for me to see wny there's so much difference in the Benz pad wear, other than deficient design. Any appliation of the brake should involve (and wear) BOTH pads equally in a proper design.
I suspect the problem lies in the slide rail design (grime build up), that pulls the pad in contact with the rotor on the inside, gets hung up and doesn't release/retract the same way the piston side does when the brake fluid pressure is removed from the outer pad.
The fact that the S models get 4 piston dual side clamping (no rails) says it all. It is a money saving / performance / feature decision. No performance vehicle would use a one sided single piston design for this and many other reasons.
I suspect the problem lies in the slide rail design (grime build up), that pulls the pad in contact with the rotor on the inside, gets hung up and doesn't release/retract the same way the piston side does when the brake fluid pressure is removed from the outer pad.
The fact that the S models get 4 piston dual side clamping (no rails) says it all. It is a money saving / performance / feature decision. No performance vehicle would use a one sided single piston design for this and many other reasons.
As stated in my original post, I looked at all 4 of the sliders. There was no debris or anything else in the holes or on the sliders other than the grease that the factory put on them. There are rubber booties over each assembly to keep the dirt out and they apparently work extremely well. The sliders themselves moved freely and with minimial pressure applied to them when I had the calipers off. I sort of wish I'd put the calipers on without the pads installed just to see if I could move the calipers on the sliders. But I didn't think of that at the time and I'm not going to go back in there and take one all apart again just for a science project.
I don't entirely agree with your last statement. The single piston provides a complexity saving over the multi-piston caliper and when properly designed, performs as well as the multi-piston system. The big difference comes when the rotors and pads become large and the clamping area increases to the point where a single piston can no longer provide adequate clamping force over the entire area. That's when the multi-piston units shine. For street use, the multi-piston units are, for the most part, overkill.
So inner pad wears which is against piston.
What type of driving? highway or city?
both pads should squeeze rotor equally to get "BEST or NOTHING" braking force.
When you brake piston moves out and pushes that pad into rotor which cannot move since it is sandwiched by wheel against hub.
Once this inner piston pad contacts the rotor the force from the rotor pushing back will push against the caliper and slides on the pins bringing outer Pad with it into contact the rotor
harder you press the harder the caliper and piston move together and force pads to squeeze rotor and create rotational friction to slow wheel spinning.
Why all the engineer diatribe?
to me something is wrong to have that much difference.
Yes the inner pad would be first to contact and last to release but this would not have this much wear difference.
Could be a slightly sticky piston that does not retract enough.
It retractes enough for Outer pad to release from rotor but maybe the inner is just slightly dragging all the tim.
I would really clean the calipers good and check edges where pads ride -
File burrs and rough spots away as required.
Paint them and be sure to apply brake lube.
Then clean caliper slide pins and lube up as well.
Re-assemble with new pads.
Watch brakes as someone pumps pedal slowly (do they contact rotor same time? or one first and while later other.
What happens when they release?
Look it may be normal for MB brakes but sure is crappy as you are not getting good braking from rears if you have such a difference in wear.
As long as the outer pad is not touching rotor your braking forces suck.
For street use, the multi-piston units are, for the most part, overkill.
Agree to disagree. Would be great to see a stoping comparison on same spec SUV with a one vs four piston design, I bet 4 piston will stop shorter and more consistent. Uneven clamping pressure and over heating / boiling brake fluid are two big braw backs on a single piston design. Many manufacture use it, so it is a degree of safety question, not if they are safe.
SUVs are marketed with towing in mind (though few seem to do it), unlike sedans. I tow with my AMG GLE and for that "street use", I would be much more happier with a 4 piston design. Expected better from Benz/AMG badge, but alas, not to be (thus price difference with a Cayenne or X5). Saw the same uneven, but not as bad inner wear discrepancy when I did a pad / rotor service at 40K miles. So when changing to winter tires I now inspect the inner pads for uneven wear to facilitate changing them out before it goes too far. So another date points pointing to design compromise not a unique problem to your caliper.
Towing with an SUV down 7% grades or more, with multiple needs in close repetition to scrub speed on "street use" a 4 caliper will perform better / be safer. YMWV
Inner pad has the lowest friction opposing the single piston force. The friction on the inner pad is only its own backing plate ears against the anti-rattle springs.
The outer pad has friction at its ears against anti-rattle springs plus the two slide pins, in addition to lost motion (slip or free play) in the take up between the piston, caliper bridge and outer backing plate. It doesn’t matter how clean the pins are, their presence is what matters.
Gentle braking force (caliper pressure) preferentially engages the inner pad.
I almost had the same issue Rear right side down to metal (metal to metal contact). Other side of vehicle on the rear left side had some meat left. I been slowly breaking in the new rear brakes (I replaced it on 12/27/2023). It's still screeching a little on cold rotors. It's gone once there warmed up. I can't remember if my friend helper grease the pins.
The brake pads on our 2019 GLE400 had the same wear pattern. The "sensor" pad was really worn down while the non-sensor pad still had a fair amount remaining.
I noticed this oddity for the first time on my 2007 BMW E90 some years ago when I replaced the front brake pads for the first time at 123000 km (76000 mi) - inside pads 3.5 mm left, outside pads 6.5 mm left, new pads 14mm depth. I owned about 20 cars prior to that, never saw this type of differential pad wear. I purchased this car new, mostly ever long-distance driving. Nothing seemed out of place at the calipers...Still have the car @ 84k miles. Didn't take better pics, tossed em, just took mental note of the phenomenon. So not just a Merc or BM issue then ?
Inside pads are on the right in each pair
This weekend I need to check the rear brakes on mine there still screeching at like under 5mph when I softly brakes only when the rotors are cold. It goes away when the rotors warm up. It's annoying and feel like I'm waking up the neighbors at 3am, lol.
I bet my friend helper did not put the brake paste on the back side of the pads.
This weekend I need to check the rear brakes on mine there still screeching at like under 5mph when I softly brakes only when the rotors are cold. It goes away when the rotors warm up. It's annoying and feel like I'm waking up the neighbors at 3am, lol.
I bet my friend helper did not put the brake paste on the back side of the pads.
Applied brake paste and still screeching and got allot louder. I use all OEM dealer parts. What give? Not sure, if I should get another set of brake pads or what?
The shims are revit into the brake pads.
EDIT: this morning it was 55F. From a cold start no noise from the brakes. It's confirm the cold temperature is affecting the brakes. I may take it apart this weekend and check the slider bolts, clean them and grease them and see if that will help.
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