E Class 2006 S211 Rear Brake Pad Replacement

[e220estate]

Hi All, Just had the 'Brake Wear - visit workshop' message which I have been expecting! Did the front pads a while ago and de-activated the SBC by disconnecting the batteries and waiting for a while. All worked OK on re-assembly. Have done the same for the rear but now I find that both rear brakes are getting hot on normal driving (therefore probably binding). Thoughts are sticking pistons (but they pushed in ok) or do I need to do something specific with the SBC other than just re-connecting the batteries? I didn't with the front pad replacements. TIA

 

[OneForTheRoad]

Hi All, Just had the 'Brake Wear - visit workshop' message which I have been expecting! Did the front pads a while ago and de-activated the SBC by disconnecting the batteries and waiting for a while. All worked OK on re-assembly. Have done the same for the rear but now I find that both rear brakes are getting hot on normal driving (therefore probably binding). Thoughts are sticking pistons (but they pushed in ok) or do I need to do something specific with the SBC other than just re-connecting the batteries? I didn't with the front pad replacements. TIA

Did you bother cleaning and lubing the caliper slide pins ?

 

[e220estate]

Took them both out and put a little copper slip on them. The caliper moved in/out freely before re-assembly. But done some more research....Am I right in concluding that installing new pads needs the SBC to be reset to allow for the increased pad thickness (I didn't do this for the front pads)? If this is the case and you don't reset then presumably the SBC will apply the brakes all the time because it 'thinks' the replacement pads are only as thick as the old pads?

 

[e220estate]

A bit more info....Have been out on short journey twice today. Both times the rear brakes overheated and the car would not role under its own weight when I got home (slight slope on the drive). Leave for ~30 mins till brakes cool and it will then easily roll under its own weight in neutral ie the brakes have backed off. When I have had this problem with other cars in the past a stuck brake usually stays stuck!

 

[OneForTheRoad]

metal expands with heat so binding will go away once cooled, ive never had to bother teaching sbc in . you could try pumping the brake with pads removed so the piston comes out about half way, pull back the rubber and clean up the piston.

 

[e220estate]

I guess my next step (before dismantling again etc) is to get a definitive answer to this question:
" in an SBC-based system, does the SBC AUTOMATICALY compensate for new (thicker) brake pads or does it need 're-activating' to achieve this?". After all, changing a battery does not require it but changing pads might, given what it does?
TIA

 

[millo777]

I had a similar experience with my w211 rear brakes. Ended up buying rebuilt calipers from ECP as they had them in stock and rebuild kits would take a week to arrive. On examination it seems that as the rear brakes take quite a while to wear down due to brake balance, by the time it comes to change the pads, the caliper pistons have been quite a way extended for several years, and in this position they still move freely. The inner part of the bore however had rusted quite badly, so when the pistons were pushed back in, they were binding on the rust and not releasing from the disk properly, hence overheating.

It's not too bad of a job to rebuild the calipers yourself, replacing the rubber boots and clips, but it depends how bad the rust in the bore is as to whether it's worth it. Also, rebuilt calipers for the rear aren't crazy expensive.

btw, the easiest way to disable SBC is to just pull the wiring loom form the pump. Where the multi plug engages the SBC pump is a plastic loop. pull that up and the multi plug slides out.

 

[e220estate]

Thanks Millo for your insight. Today (bloody freezing on the drive but MoT tomorrow!) I removed the new pads and eased the locating ears with a file, copper-slipped them again and made absolutely sure that everything external moved freely. I intend to try them tomorrow AM and if everything gets hot again it can only be the SBC on the blink or the pistons. If this happens, and based on other comments found on the web, I expect that it is more likely to be the pistons (even though they pushed in easily for pad replacement). Mine is a 2006 bought 5 years ago and this is the first time I have done the back brakes so the problem fits your scenario to a 'T'!
Question - how practical is it to DIY bleed SBC brakes? Are they 'normal'?

 

[millo777]

You should be able to bleed the rears fine. Try and clamp the hoses so you lose as little fluid as possible.

For what it's worth, MB reckon you should only use DOT4 plus from the dealer for SBC systems. Apparently its a lower viscosity than regular DOT4. Febi and few others also sell DOT 4 plus, but I haven't checked the MB spec sheet on it. I suspect if its only for the rears, regular DOT4 wouldn't cause a problem.

 

[e220estate]

Went out again yesterday AM prior to the planned MoT and the rears cooked again - cancelled MoT! As an empirical test I put back the old pads and went out again - nothing overheated so I think that pretty much points to the need for caliper replacements. Short term I will see if it passes the MoT. If it does I will do the calipers when the weather improves!
Thanks for the pointers, Millo, and ref bleeding, I have some genuine MB brake fluid so I should be ok.

 

[OneForTheRoad]

Went out again yesterday AM prior to the planned MoT and the rears cooked again - cancelled MoT! As an empirical test I put back the old pads and went out again - nothing overheated so I think that pretty much points to the need for caliper replacements. Short term I will see if it passes the MoT. If it does I will do the calipers when the weather improves!
Thanks for the pointers, Millo, and ref bleeding, I have some genuine MB brake fluid so I should be ok.

Did you bother to look under the rubber for rust on the piston end ?

 

[e220estate]

Nope - I decided that was impractical. As I said, I work on the drive at ground level and decided that the idea of being able to just push the stuck piston out enough to remove the boot (and reposition it afterwards - it is old!) and clean it would likely just fire it out of its bore because of the brake pedal pressure needed to move it, and empty brake fluid all over the drive. Plus if the bore behind the piston is the problem cleaning the bit of piston I could reach would likely not solve the problem - wasted effort. So, on balance the 'best' solution for me is replacement calipers.

 

[OneForTheRoad]

Nope - I decided that was impractical. As I said, I work on the drive at ground level and decided that the idea of being able to just push the stuck piston out enough to remove the boot (and reposition it afterwards - it is old!) and clean it would likely just fire it out of its bore because of the brake pedal pressure needed to move it, and empty brake fluid all over the drive. Plus if the bore behind the piston is the problem cleaning the bit of piston I could reach would likely not solve the problem - wasted effort. So, on balance the 'best' solution for me is replacement calipers.

No need to remove the boot , 3 presses on the pedal would of popped the piston out about an inch . They are around 2.5 inches long. Clean up the 1st 2cm would of been all it needed. You seem to know what you're doing anyways . Good luck.

 

[millo777]

You can always have a god luck at the old ones when they're off the car for peace of mind. I used a compressed air line on the brake hose attachment to pop out the piston.

 

[m80]

I haven't read all this, but picked up on the use of copper grease.
It isn't kind to rubber and can cause it to swell. If the rubber is now grabbing the sliders it might well be your issue.

A white spirit clean up might work, if you're lucky.

 

[Deleted member 159235]

Took them both out and put a little copper slip on them. The caliper moved in/out freely before re-assembly. But done some more research....Am I right in concluding that installing new pads needs the SBC to be reset to allow for the increased pad thickness (I didn't do this for the front pads)? If this is the case and you don't reset then presumably the SBC will apply the brakes all the time because it 'thinks' the replacement pads are only as thick as the old pads?

Why did you use Copper Slip? that's the wrong lubrication.

 

[W1ghty]

White silicone grease on the caliper Sliders .
Red rubber grease on or around the piston and boot or that may come into contact with brake fluid