albert101

Had the same long pedal travel on my car when I did a brake service. Apparently, the proper bleed procedure typically requires you to actuate the ABS/DSC valves while performing a full bleed to release any air that might be trapped in the ABS/DSC unit. On my C-class we weren't able to actuate the valves (since I don't have the MB Star system) so, while the car was on the lifter and all the wheels suspended, I put the car into drive, allowed the wheels to spin and then applied the brakes multiple times to actuate the ABS. This should actuate the ABS valves. We then re-bled the system in the usual fashion to get any air that was released by actuating the ABS valves. The pedal feel was as good a new after that.

Glyn M Ruck

Any air in the system would obviously cause a low pedal. How did air get into the ABS block? Did someone let the reservoir run dry?

albert101

The place where I had my brakes serviced that caused my long pedal travel was at the dealers. I took the car back to the dealers to try and cure the problem yet after three times, same issue. I later then took my car to a buddy of mine's auto shop where we did the procedure I mentioned in my previous post to induce the ABS and force the air out of the system. It worked like a charm and my brakes feel as good as new now. I assume the procedure they did at the dealer's wasn't done right?

Lonemetalman

I own an Alfa Romeo and that has happened to me. Just needed to say thank you because you were the first one to really Know that problem and solution.
Now i have a day of brake fixing to do Cheers mate!

Glyn M Ruck

Good luck! It's a pain. I owned 7 Alfa's in a row at one time & had this issue with most of them.

NewShockerGuy

OK OLD thread but this is extremely important since it's one of the FEW threads I found.

Just did a brake upgrade on our w211 (09), and I completely dissasembled and redid all piston seals and dust covers. When I installed them on the car I pushed ALL the pistons all the way.. BUT I bleed the system and used the brake pedal to push the pistons against the pads/rotors.

Now it looks like what you are describing is what I am experiencing.

The pedal will go all the way down before it engages the brakes. IF I pump the brakes quickly then the pedal engages at half way point.

I had my wife start pushing the pedal on the car while it was on and I had it on my lift. I noticed that the pistons ONLY started to move as she was at the bottom movement of the pedal.. Then when she lets go of the pedal I can see the pistons by about 1mm not touching the pads....

I am guessing this is happening on all 8 piston fronts (amg) and 4 piston rears (amg).

What are your thoughts on the matter?

Glyn M Ruck

A classic case of caliper over return!

NewShockerGuy

Welp that's good t know. I was thinking my master cylinder was bad or worse the calipers. It's funny I've done many calipers before but never had this happen.

So I removed the pads on one caliper at a time and had my wife push the brake pedal until I could see the pistons moving out of that specific caliper that I was working on. Then I had to ever so slightly push the pistons back in, in order to fit the pads in.. some were an extremely tight fix. Zero movement between the pads and rotor now, where before there was maybe a 1-2mm slop after removing the retaining pins.

I have to go get another bottom of MB dot4 plus fluid tomorrow so I can't bleed the brakes. However when I reading the how to on w211, the pressure should be set to 2 bar (29psi) and my power bleeder I only went up to 13psi. When I hooked up my compressor with the motive power adaptor for the Merc, and set it to 29psi I cracked open the rear passenger caliper and per the instructions while it's pressurize it's very important for someone to be pushing the brake pedal down as well. Needless to say there was some air bubbles coming out. Not a lot but I think the higher PSI and the fact that someone was also pressing the brake pedal was helping.

I will be doing the same tomorrow to the rest of the calipers once I get the fluid.

I'm hoping this helps...lol

-Nigel

Carsy

Good news ,thanks for the feedback.JC

NewShockerGuy

Welp going to bleed them today after I pick up some fluid. Couldn't make it to the MB dealer on Monday.


Going to ask a painfully stupid question. As the brake pads wear what is to prevent the caliper piston over return?


IE: How is it different if I pushed them in too far last time but as the pads will wear with time wouldn't the pistons suffer from the same thing since they are being pressed up against the pads/rotor, eventually wouldn't they pull back in?


I'll report back here by noon hopefully everything will be as it should.


Thanks
-Nigel

Glyn M Ruck

Not a stupid question at all. You have to hope in daily use that the D seals slide & don't stick to the caliper bore.

I'm having that issue with my CLK right now. Had a perfect pedal with new front pads. They are now about half worn and my pedal is no longer as good & has more travel than when pads were new. Due for a service & will fix!

NewShockerGuy

Welp bled the brakes last night. Went through the entire bottle to make sure everything was out from before. A few air bubbles on the front right caliper and rear left caliper came out. Nothing crazy. Went and drove the car today. The pedal does NOT go to the floor!!

THANK YOU for actually having knowledge in this and posting about it. I can't stress that enough! I had zero clue as to why this was like it because I've never heard or experienced it and figured the master cylinder was bad or something even though the previous calipers were OK..lol

I did several test stops and hard stops to bed the brake pads in. Zero issues. Car stops and stops quite well now... surprisingly quick actually.

Doing exactly what you said worked. I took out the pads in each caliper one at a time, had the wife push the brake pedal and I was controlling which pistons were coming out (so that all 8 weren't flying out at the same time) and then did each side of the fronts then did the rears. Pads were hard to put back in because there was zero play/gaps like there were before. I am confident that everything is how it should be. No leaks of brake fluid and no air bubbles. And best of all no caliper piston over return!

I'm a happy camper :-)

-Nigel

Glyn M Ruck

Hi Nigel. Ah! I'm delighted for you. Yeah ~ lots of pistons to worry about. Thank you for reporting back so we increase our knowledge base.

Pleased you are a happy camper.
KR
G

Brent H

Hi, I seem to be having the return problem described in this thread. The question I have is how to correct as there seems to be at least 3 approaches. Disassemble - no thank you. Old break pads without friction material and stomping on brakes to move piston its full travel distance and then slowly return just until you can get your new pads in...is this trial and error until they fit?? Option 3 seems similar but brake pedal was pressed (without pads??) I assume this was done very carefully moving the piston only 1 or 2 millimeters. Is there a preferred method? How do you know you've moved the piston enough or conversely how do you know if you haven't moved the piston too far back in? Hope my question makes sense

Glyn M Ruck

The safe way is to remove the pads. Put a spacer in place so that the pistons can't come all the way out. Put you foot on the brake to move all the pistons forward. Then press back gently so that you can just slip a new pad in. Then bleed from longest to shortest brakeline.

Good luck!

Extreme Dimensions

If it's spongy than 9 out of 10 it's a bad bleed job. Unless the mechanic was negligent on the install.

Brent H

Sorry for being thick but I don't get the "push back gently" part...I'll need a c clamp, I believe, to push the piston back in unless I open the bleeder valve?? Is there something I'm missing...a trick or something. Once again excuse my ignorance, I've done many brakes before but not on a mercedes.

Flarearrow

Its not rocket science. If you've replaced pads and flushing brake lines on other cars, it's the same process

Glyn M Ruck

You can generally push them back with a large screwdriver. If you have trouble crack the bleed nipple slightly.

Caliper over return is common on Benz cars. My CLK is developing it again as front pads wear & D seals don't slide down the caliper bore. Most people don't understand it & you can pressure bleed until you are blue in the face with no improvement.

NewShockerGuy

So make sure the brake reservoir cap is open, this will help when you are gently pushing the pistons back.


As Glyn mentioned the spacer idea is great. When this happened with me I only did one side first. I had my wife get in the car and I had her SLOWLY pushing the brake pedal down. I could see 4 pistons moving on one side and the ones that were coming out a little TOO fast I simply used a smaller wood dowel rod to stop those pistons from moving so that the others could move a slightly forward. What would happen is that they would move out just a TAD too far and I would not be able to put the pad in. I used the same dowel rod to gently push against the caliper so that the piston would go in 1mm-2mm at a time until I could JUST squeeze the pad in. It was still quite difficult to put the pad in compared to other vehicles that I've had where it just slips in. After doing that bleed the entire system all over again starting with the furthest most caliper/bleed screw. Then go all the way around ensuring the that the brake reservoir doesn't run dry and that you are not introducing air into the system.


By doing exactly what Glyn recommended earlier I went from having the pedal go practically to the floor before the brakes engaged to a normal engagement of how the brake pedal should normally feel.


Hope that helps.


-Nigel

Brent H

Well I'd like to report success and say a big thank you to all that have contributed to this topic and especially Glyn - Thank You!! A couple of "tweaks" or alternatives to consider for the process. Before starting take a "visual" as to where the piston is currently sitting so you have a good idea as to where you will need to retract it. As for pushing the piston out, old pads are the way to go if you still have them but I'm sure the wood shim idea would work fine. I did not have to move the piston too far out (maybe 1 cm). I then used a c-clamp to retract the piston close to where it needed to be (based on the visual). On one side it was a bit loose so it went on fine and there was no issue with over return), on the other it was too tight but with a bit of side to side rocking motion (the pads are bevelled at top and bottom) I was able move the piston a bit more to get the pads on. The only other thing I'd say is I placed the caliper back over the rotor to push the pistons out although I suppose you could do it without placing over the rotor, just make sure your shims are the right size!!!

Glyn M Ruck

Pleased you are sorted.

I always do this with the caliper over the rotor/disc. You certainly don't want a piston to pop right out of it's bore. Then you are faced with a further problem.

Brent H

So, I had the over return problem and fixed it with the suggestions in the thread. I thought I was all good but then after about 5 KM of driving I started to notice a noise. It sounded like a low hum, possibly a vibration. Most of the time it goes away when I step on the brake. So I took apart the front driver side again, cleaned everything up even more, drove the piston out and back in again, put it all back together and still the same thing. I did notice after the first "adjustment" of the piston and a bit of driving, that I could still see at least a milimeter of space between the rotor and pad which struck me as odd. It's almost like the pad is slightly binding (although I'm not sure how). I'm at the point now where I'm thinking of getting some new seals and "rebuilding" the caliper as I'm speculating the over return problem is still there and there's enough space for the pad to move slightly ajar and then vibrate off of the rotor.

Would appreciate it if anyone had any ideas

Carsy

Maybe a little grease or a small piece of emery paper between caliper & pad to stop the vibration. This was a fix in the old days !!

Just204

I typically just use real big channel locks to push the Pistons in but I bought this for my merc and it's great!

It's not perfect but the best design imo for pushing in the pistons. Pushes them in evenly and is a solid tool. It would also prevent pushing the pistons in too far.

On a side note, reading the diy abs bleeding procedure. I assume you crack the bleeder very slightly and then do it? Or is there a bleeder port in the abs unit?