C180 Brake assist problems

[Stuart Disley]

Hi
Having problems with the brake assist, Brakes work ok but not as well as they used to, pads are ok and had fluid changed. no difference.
I think they went after breaking constantly coming down about a 3 mile hill.
Garage said if still under grauntee they would change the servo. but this would cost about 800 euro's, it was not a servicable item and recomend to leave it as it was. I feel sure that there must be something else that it could be and would apprecite any ideas as to what the problem might be,
Last time I had a broplem the garage put in new bits, which did not need replacing.
thanks.

 

[type49]

Brake assist only operates in emergency, panic braking. Your description does not sound like you have a brake assist problem.

 

[lackofgrip]

was the new fluid the same dot type?

 

[television]

Has someone fitted incorrect pads, this could be a good reason for them to require a higher pressure on the pedal.

 

[Stuart Disley]

Thanks very much for the replys,
Brake pads are still the originals, and fluid was done at the Mercedes garage ,so I would hope that they used the correct fluid, I know when
it happened we were on hols in Austria, (great drive from Ireland).and at first i thought it might be my imatgnation, but last MOT showed breaking on all wheels still perfect, but the pedal pressure needed had increased.
At first you hardly had to touch the pedal where as now you have quite a lot of movement in the pedal and not the same strong break feel, though they still work well (incl abs etc) if you need them.
On the bright side,drove to Switzerland last year and going back again this summer,brillant....would recomend it.
again thanks

 

[anyweb]

I think they went after breaking constantly coming down about a 3 mile hill.

consider replacing your brake pads and discs to be sure to be sure
also, verify that your brake fluid resevoirs (front/back) are both at the MAX level, if not, you may have a broken pipe.

cheers
anyweb

 

[oigle]

Thanks very much for the replys,
Brake pads are still the originals, and fluid was done at the Mercedes garage ,so I would hope that they used the correct fluid, I know when
it happened we were on hols in Austria, (great drive from Ireland).and at first i thought it might be my imatgnation, but last MOT showed breaking on all wheels still perfect, but the pedal pressure needed had increased.
At first you hardly had to touch the pedal where as now you have quite a lot of movement in the pedal and not the same strong break feel, though they still work well (incl abs etc) if you need them.
On the bright side,drove to Switzerland last year and going back again this summer,brillant....would recomend it.
again thanks

Sounds to me that you have a failure in the brake booster. This can be as a result of the booster itself failing or the vacuum not being produced. If you have a petrol vehicle, this is generated by the manifold vacuum - if a diesel, it is generated by a pump on the back of the alternator. There could also be a vacuum leak somewhere (pipe off or something similar)
The fact you have good braking, albeit with increased pressures, would indicate the pads and discs are working reasonably OK. The pads can glaze from heat though and may be at fault.

 

[wireman]

Since your fault appeared after prolonged braking it sounds like de-glazing the disks may help you, Use some moderetly fine abrasive paper and remove the shine off the disks. If there is any major rippling, scoring or a built up rusty edges (at the periphery or centre) to the disk replace them.
Constant braking to hold your speed down can cause over heating of the disks and pads, the roadcraft (police drivers manual, get it from most good book shops) recomended method of keeping your speed appropriate is to brake to the required speed and then use a lower gear to maintain that speed using engine braking, this process should be undertaken in good time such that you are not changing down after you should do. Engine braking should not be used to reduce speed since undue wear will occur to the engine and transmission and they are not as easy (or cheap) to repair as the service brakes.
When the fluid was changed was the correct bleeding sequence followed?
If not there may be a very small quantity of air trapped in the master cylinder which may be the source of your increased travel. I have made this mistake.
I think its both rears first and then front left then right but you had better check this.
If the servo is completely dead you will have to push realy hard to get any brakes at all. Reduced vacuum will reduce the amount assitance the servo provides.

 

[wireman]

PS
There is a non return valve in the servos vac pipe if this goes leaky the servo can get a small amount of petrol in it every time you stop the engine, the servo diaphragm will get tired and cease to work if this happens.
To check the valve operate the pedal a few times with the engine stopped you should feel through the pedal that some thing has changed (usualy a firmer feel) after a couple of brake applications.

 

[Stuart Disley]

Thankyou all for your help, I will go investigating