c class front brake fault

[mrmagoobird]

Hi, My car; C Class 1.8 Classic 2004, has developed a brake fault and I can't find the cause. Front Brakes are sticking on when the car gets warm. Has anyone else had this problem or knows the cause please let me know.

 

[Ellsy Tanners]

Hello and welcome, ive seen this on a- class's and its turned out to be the callipers.

Do the wheels lock or just very stiff to turn wheel?

 

[roofless]

is it free when cold then after a few miles start to lock on more & more then be ok when it cools

 

[mrmagoobird]

Yes that is exactly what it is doing, on the front only.

 

[mrmagoobird]

No, the wheels lock after a few miles but are ok from cold

 

[television]

This is an odd fault, the master cylinder normally allows for the backing off of the pistons, if both are sticking on this lets the calipers off the hook

 

[roofless]

i had this years ago but with a ford changed the master cyl but still the same so changed the servo & that did the job

 

[mrmagoobird]

I actually feel that this may have been a fault from new, I have had the car 10 months and it looks as if someone has been messing with the brakes previously. It started on O/S first and then N/S started playing up. Rob

 

[mrmagoobird]

Yeh my thoughts are with the servo.

 

[roofless]

the next time try to release the vacuum pressure & see if it frees the brakes ?

 

[television]

Something not right here, the vacuum is only an assistance to the master cylinder.

The tank holds the vacuum, and the one way valve only stops the air escaping back to the engine. If it was leaking that would not affect it, if the pedal is right up, then no fluid is pressurized as the master cylinder is open to the top up tank. the pedal does need to be checked to be sure that it is returning to the correct position with the hole lined up with the tank

 

[roofless]

it's a strange one if i remember i released fluid from the bleed nipple & it would let me drive for a bit but that would not help in finding the fault thats why i think it might give a clue as when i had the fault the pedal would get harder as i drove ?

 

[television]

it's a strange one if i remember i released fluid from the bleed nipple & it would let me drive for a bit but that would not help in finding the fault thats why i think it might give a clue as when i had the fault the pedal would get harder as i drove ?

Thats interesting as one must have free play in the pedal often ½ inch

 

[roofless]

it might be the mechanism inside the servo sticking & not letting the piston return in the master cyl ?

 

[television]

it might be the mechanism inside the servo sticking & not letting the piston return in the master cyl ?

yes agreed, but your clue on the free play should answer that, that was the best bit of info to check

 

[roofless]

a few causes for servo fauls on here http://www.sunbeamtiger.co.uk/tech tips/brake.htm

 

[ernieh]

Master Cylinder?

I wonder if somebody has been 'at' the master cylinder on this car? I once had a car brought in with all the brakes fried. It transpired that the owner had 'reconditioned' the master cylinder and fitted one of the seals wrongly so that the pressure in the system wouldn't bleed off. In fact, the only way he could get the car to move was by bleeding off the pressure by opening one of the unions.

Ernie

 

[television]

I wonder if somebody has been 'at' the master cylinder on this car? I once had a car brought in with all the brakes fried. It transpired that the owner had 'reconditioned' the master cylinder and fitted one of the seals wrongly so that the pressure in the system wouldn't bleed off. In fact, the only way he could get the car to move was by bleeding off the pressure by opening one of the unions.

Ernie

You never know ernieh, but with roofless's post on the clearance should answer that.
When the brake is off the hole in the piston in the master cylinder is inline with the tank so there cannot be any pressure in the system, unless the piston is not returning fully and all mrmagoobird has to do is to get hold of the pedal after a drive and check

 

[Cole@MBS]

Common as muck with the 203, front calipers seizing, changed a few of them in me time!!

 

[wireman]

I have also seen this fault or at least something like it since it was the rear brakes jamming, both the master cylinder and servo were replaced and the fault cleared.

My suspicions were that the servo booster was not fully returning to its proper rest position and in not doing so was holding the master cylinder slightly pushed forwards hence blocking of the "snifter holes" (Bosch name for the ports in the side of the master cylinder) and not allowing fluid to return to the reservoir resulting in a closed system which when the calipers etc warm up the expansion of the fluid makes the brakes bind harder as the heat increases.

Some installations have an adjustment of free play in the pedal assembly (push rod) and if this small amount of lost motion is reduced by wear and tear the same fault symptoms can occur.

The control valve within the booster may be at fault by leaking and aplying slight pressure to the master cylinder. Unfortunately this valve is bang in the middle of the booster and there is little that can be done about it short of a replacement booster.