Sticking brake pedal and brakes binding.

[Devon]

I am still running my old E-class S210; a 2001 E200K (auto) estate.

I have had it for 18 years and although it is looking a bit dog-eared nowadays, I am loath to get rid of it. A capacious old bus, it is so useful for many purposes.

In 18 years it has never left me stranded despite having covered dozens of long continental journeys.

However, recently it has developed a brake problem: the brake pedal is failing to return fully and the brakes are binding. This starts after about five minutes use. Initially the pedal functions as normal but after five minutes or so starts to stick and I have to pull it back up with my toe. One morning I found I was unable to move the selector out of “park”. I checked the battery voltage, which was ok (about 12.6v) so I then replaced the brake switch and that cured the selector problem but the sticking brake pedal remains. I have gone through the basic pedal pressure behaviour checks to try to isolate the problem and as far as I can tell the master cylinder and servo function seem ok. The vacuum pipe to the servo is working ok, and disconnecting the plug at the diaphragm position (BAS) sensor made no difference.

But something is holding the brake pedal partially on when it should not be.

Apparently there is a solenoid switch built into the servo unit but I do not know what its function is. Could that be the root of the problem?

Any advice would be greatly appreciated.

 

[00slk]

Lost Kiwi should be along shortly
Possible master cylinder?

 

[Devon]

Lost Kiwi should be along shortly
Possible master cylinder?

Thanks. Yes, I guess it could be although brake pedal behaviour with the engine switched off is as expected: no pedal creep or sticking pedal when pressure is taken off.

 

[onefortheroad]

Bulging flexi hoses, sticking slide pins ,sticking caliper pistons , warped discs ???

 

[bigasotonuk]

Hi
Did the 210 have a brake pedal return spring? worth looking to see if there is one that is snapped or disconnected on the pedal box.

 

[Devon]

Hi
Did the 210 have a brake pedal return spring? worth looking to see if there is one that is snapped or disconnected on the pedal box.

Thanks. Yes there is a brake pedal return spring. I checked it when I replaced the brake pedal switch and it was intact and not broken or stretched.

 

[Devon]

Bulging flexi hoses, sticking slide pins ,sticking caliper pistons , warped discs ???

Thanks. Yes, all possibilities I guess although bulging flexis and warped discs unlikely as it passed the MOT two months ago. I would have thought they would have picked those up??

 

[Uncle Benz]

Never seen it on a w210, but the r170 SLK can suffer a similar problem. The pedal pivots on a plastic shaft (!!!), which can get tight with age and prevent the pedal returning. Certainly worth a look.

 

[Devon]

Never seen it on a w210, but the r170 SLK can suffer a similar problem. The pedal pivots on a plastic shaft (!!!), which can get tight with age and prevent the pedal returning. Certainly worth a look.

Thanks. I'll have a look at that.

 

[joderest]

It does sound like something binding, however, have to ask if in its 18 years it has ever had a brake overhaul, as pistons in callipers could be sticking etc etc etc.

 

[Devon]

It does sound like something binding, however, have to ask if in its 18 years it has ever had a brake overhaul, as pistons in callipers could be sticking etc etc etc.

Thanks. Good point. The brake system is original, with the exception of discs, pads and fluid.so a sticking caliper piston or similar is certainly a possibility however, would that cause the brake pedal to fail to return to its normal position when released?

 

[joderest]

Erm, don't know, but its odd that when engine not running there is no problem, if it were an old car (pre electronics age) I think i would have disconnected the vacuum from servo, blocked it off, and see if issue still there with engine running, if the pedal acts as normal, points to some sort of issue with the servo.

 

[Devon]

Erm, don't know, but its odd that when engine not running there is no problem, if it were an old car (pre electronics age) I think i would have disconnected the vacuum from servo, blocked it off, and see if issue still there with engine running, if the pedal acts as normal, points to some sort of issue with the servo.

Yes it is looking like a problem with the servo unit itself. It seems there are various electrical components (solenoid, release switch, whatever) within the servo,presumably to enable ESP and BAS. Apparently if they go down then the servo unit is finished.

 

[mioba]

If your caliper pistons are binding you would get very hot brakes which would transfer the heat to tyre, is there any heat down there.

 

[Devon]

If your caliper pistons are binding you would get very hot brakes which would transfer the heat to tyre, is there any heat down there.

Thanks.When I apply the brakes and then lift off the pedal they sometimes bind (drag) until I flip the pedal FULLY back up with my toe and then there is no binding.