S211/E320 ALL Brakes binding issue

[Don22]

Hi new to forum and hopefully somebody maybe able to help ...

Car is a 2004 E320 wagon, recently a motorcyclist whom was travelling behind me, tapped on my window to tell me my brake lights were kind of erratically coming on an off when clearly I was not applying the brakes, i.e going along with no reason to brake. I thought the car kind of felt slightly odd and when I stopped and felt the temperature of the discs they were well hot.
Strange thing is every wheel was like it, left and right, front and rear. Still doing it and seems to have got worse still. The front discs are maybe abit hotter than the rears but all are obviously having brakes applied to them, when the brake is not being applied by me anyway.

You can feel the brakes also slightly stick on and I did try kind of pulling the pedal back up by hooking my toe behind it to see if it wasn't fully returning but seems it is returning fully other than brakes still remaining on. They are being applied with a fair force as they heat up fairly quickly, like after just 5 mins of driving.

Would this be the SBC pump/unit be causing the fault? Kind of reluctant to make any wrong decisions and do not want to go tearing into the mechanics of the brakes unless I am aiming in the right direction and actually fixing the problem, rather than just guessing and then having to hook upto STAR etc to fully bleed system etc.

Any help or advice greatly appreciated.
Don

 

[DSM10000]

Hello Don and welcome.

Your issue does sound like it lies within the SBC module or controls as this unit, as you know, is capable of braking individual wheels or combinations.

As you suggested, a session with Star would be the best move. Do you have a good MB independent nearby?

Please let us know how you get on

Regards

David

 

[Don22]

Hi David and thankyou for your help and fast reply.

I do have a German car specialist nearby whom is quite familiar with Mercs and has STAR as well as other diagnostics.
On that subject I do have the ICARSOFT MB2 but it seems it does not correctly interrogate the SBC system, even though it is and option on the system. Says it cannot link, so presume I am needing STAR or a better system to hook upto it properly.

I have no error screens on the dash, just that they are heating up and as the motorcyclist told me who was behind, said the brake lights were coming on and off.

 

[DSM10000]

Don.

I don't have the SBC system fitted although I do have the ICarsoft MB 2.

Possibly the lack of communication is due to a fault within the SBC?

Either way it needs someone with Star and experience of using it correctly. Hopefully your specialist will quickly find the problem.

Good luck

 

[Don22]

Yes- not sure why the iCarsoft is not linking to the SBC, maybe I need to update the firmware on it. Says 'link not available to communicate' - or something similar.
As said there are no red screens on the dash regarding the SBC.

Thanks again for the input and help DSM10000

 

[andym2]

Strangely my 2008 S211, no SBC, did something similar today. First time it's been more than about 10 miles in 2 years, so quite possibly something just got stuck.
I was driving through the cotswolds today, noticed it was struggling to get up hills. Stopped in a layby, and brakes on all four wheels were smoking. No fault lights or warnings. Left it in the shade to cool down for a couple of hours, the drove a short distance. Stopped and check and no sign of a fault or overheating so carried on for another 25 miles home with no further problem.

I'm thinking maybe something sticking in the abs, or perhaps pedal return spring if it has one...

 

[AndrewOl]

With it having so few miles over the past couple of years it may be worth checking it in for a brake service. This will find out if there is anything serious to sort out and resolve the likely problem of sticking callipers/pads for you.

 

[mersum1es]

Yeah sticking calipers is very common after pad change, but here was no 'maintenance' done?

One peculiar feature of SBC is hat it will 'dry' brakes itself - when rain sensor detects raining, one and then system slightly squeezes brakes and try keep rotors dry and more capable of sudden action. However this actuation is not happening very often, can remember exact intrvall but lets say every 2-3 minute. There are good SBC guides somewhere where this is explained.

 

[Don22]

I was driving through the cotswolds today, noticed it was struggling to get up hills. Stopped in a layby, and brakes on all four wheels were smoking. No fault lights or warnings. Left it in the shade to cool down for a couple of hours, the drove a short distance. Stopped and check and no sign of a fault or overheating so carried on for another 25 miles home with no further problem.

I'm thinking maybe something sticking in the abs, or perhaps pedal return spring if it has one...

Yes- its obviously something stuck that is common to all wheels, having all four of them boiling hot, rather than just a single caliper getting stuck or suchlike.
I have examined mine further- the fronts are getting hotter than the rears but all four are generating heat. The rears not that much really.
Its odd, the wheels actually spin fairly freely, I guess none of them are boiling hot- just hot. I just took a wheel off and can spin the disc by hand even, its like it is just gently rubbing the disc, not actually gripping it that hard.... BUT is touching it enough to generate heat over time.
I reckon its been like it a while and I have never really felt the temps of the discs as had not reason to really. From now on though with all my cars I will get in the habit of checking this.
I may take mine up the garage and get them to fully flush/ suck out all the brake fluid and put new stuff in, before doing anything else. Don't reckon the fluid has been changed in years. May have gunked something up or deposits could be jamming something from returning fully
Decided to strictly use garage / STAR for all the work on the brakes, i.e disabling SBC and also bleeding the system fully - as seems when people work on them, they are taking a chance without STAR and also the potential of air still being in system, even though they 'think' they have correctly bled system with a pressure bleeder. Too risky and not worth taking any chances with brakes at all IMO.

Just wondering, have any other owners of E Class of the same sort of period or similar felt their disc temps after say a 5 min drive ? Maybe most cars generate abit of heat as would think there is some sort of friction between the pads and the discs on most cars, i.e very lightly touching each other (or almost)? As said, its not something I have done too much, usually only do it when I KNOW there is an issue. Its just that its abit too much heat for my liking, especially when you drive the car on longer journeys and the heat gradually builds up over time. No SBC warnings on dash or anything like that and braking seems strong, other than this heat issue.

 

[Don22]

Something else I just noticed, the actual SBC/ABS unit was quite warm to the touch, hot even- which surprised me, is that normal does anyone know?
Don

 

[OneForTheRoad]

Possibly failing brake light switch ? Try running the car at tick over and see if the brake lights flicker on and off . There is a huge difference between hot discs and binding discs in terms of heat and smell. If the lights do flicker on off at tick over and the brake pedal isn't being pressed ,then there's obviously a connection somewhere.

 

[Don22]

^^ Did wonder about the brake switch and if the brakes may be somewhat normal, albeit the slight friction they seem to have. Think though they are all on slightly more than just gently touching though, even though the wheels turn reasonably free, they are still gripping the discs abit too much, hence the heat build up, especially overtime.
I'll get the fluid flushed out and re-bled using STAR and see if that changes anything and go from there. Reckon my fluid is probably well old and also reckon the previous owner may have done brakework himself without STAR, after going through the history file. Hopefully, it maybe abit gunked up somewhere in the system and something has got slightly stuck before I go down the route of SBC work or replacement.

 

[Stratman]

I have read in the (distant) past about master cylinders not fully releasing and trapping pressure in the lines. When all else has failed...

 

[Don22]

^ Yes I would imagine something like this is whats occurring. Maybe a good flush and rebleed may disturb it abit and free it up? Worth a shot I guess before undertaking more drastic and expensive work. As they say, start with the cheapest and most simplest things first, I guess ...
Don

 

[Don22]

Maybe getting to the bottom of it- seems that front discs are warped as the discs seem to touch at different points and only grab at certain points when you revolve the wheel, which proves the are off centre and warped. So its looking like the warped discs are probably what are causing the heat and the SBC is probably fine- which is abit of a relief. Would imagine when the discs wear and get thinner and then got hot, they are then more prone to warping as the heat will soften them and they have worn to minimum thickness or below, so are even more prone to warping because they are thin. The softer and thinner they are the more they will heat warp, so its like a vicious circle.... and then the brake pads wear uneven because the discs are warped ... Both the front discs seem like this which may explain it, both discs are below minimum thickness also.

Yet to inspect the rears, but suspect it maybe exactly the same scenario. The old owner seemed abit ingorant to certain work, when I enquired about brake work, he said the cars are remarkably easy on the brakes and rarely need work, which I do not agree with, being such a vital part of the car. Bet the car and discs have needed changing a year or so before- surprised it got through the last MOT, maybe they were on the limit then.
Seem to be making some sort of progress finally and glad I did not start tearing into the SBC, when there is probably nothing wrong with it!
Don

 

[190]

I have read in the (distant) past about master cylinders not fully releasing and trapping pressure in the lines. When all else has failed...

When the brakes are applied, a small amount of brake fluid moves out of the master cylinder to push the caliper pistons out. When the brakes are released, hysteresis in the caliper piston seals pull the pistons back slightly and that small amount of fluid has to return to the master cylinder reservoir. There will be a small return hole in the master cylinder reservoir. If that gets blocked then the caliper pistons are not able to retract after the brake pedal is released, leading to the brakes binding. If the return hole can be identified it's simply a case of poking the hole with a wire to ensure it's clear.

 

[DrNick]

Brake pipes can collapse internally, trapping pressure and keeping the brakes on. Doesn’t explain the flashing brake lights though, and unlikely to affect all 4 corners unless there is a common pipe.

 

[Don22]

^Thats a point, forgot the motorcyclist behind me that day said the brake lights were triggering on and off. Don't think the lights have come on and off since- or at least not at night (as thats the only way I can see the reflection of the brake light in the back screen to know).

Discs though are defo warped and under minimum thickness, the fronts that is. Suspect the rears maybe much the same. Will inspect over next few days more.

Previous owner seemed to think the brakes looked after themselves, that's the impression he gave; as well as thinking a leaking injector wasn't an issue you needed to be concerned about! Luckily I freed up the injector, cleaned and resealed it with a new seal without issues, other than having to run the car for about 2 months with WD40 soaking in the injector hole, to eventually free it off, so I could get the injector out finally. Took about 2 months of soaking to free up. Think the previous owner was a mixture of looking after the car and also maybe neglecting it in some respects. I.e 'This car is very easy on brakes and they need little maintenance' !! Don't think I know a car that is 'easy on brakes' and needs little maintenance! Brakes work hard, especially stopping a brick of a car like this and also with its decent sort of performance! Time for new discs and brakes all round I think.

 

[mersum1es]

When the brakes are applied, a small amount of brake fluid moves out of the master cylinder to push the caliper pistons out. When the brakes are released, hysteresis in the caliper piston seals pull the pistons back slightly and that small amount of fluid has to return to the master cylinder reservoir. There will be a small return hole in the master cylinder reservoir. If that gets blocked then the caliper pistons are not able to retract after the brake pedal is released, leading to the brakes binding. If the return hole can be identified it's simply a case of poking the hole with a wire to ensure it's clear.

Good but SBC 'master cylinder' is not directly connected to brake circuit (unless in emergency mode). It is purely pump and solenoid valve actuated.