Rock hard brakes after driving some time
Discussion
I have a strange and slightly unnerving problem in my cars braking system as suddenly the brake pedal goes very hard,so this is how i can re-produce it
"cruise at 70mph for say 10 minutes but without ever touching the brakes (happens only on a motorway) then when you need to slow down and press the brakes ,the pedal is rock hard!, the only way to release it is to lightly tap the pedal a few times and then it becomes normal, this is very unerving, but the funny part is that as long as you used the brake now and then to slow down it works fine and this issue wont happen ,this happens only when you cruise without using the brakes for a few mins and then it becomes rock hard"
The local indie could not fix it and does not understand on how to recreate it either but worse still the main dealer was the same
Anyone has any idea as to what the problem is or faced something similar and if so how to rectify it?
Possibly a sticking calliper causing the pads to drag on the disc, heating the fluid up and causing it to expand? Although I confess I don’t know why tapping the pedal would fix this. I’m just guessing, I’ve heard of sticking callipers on bikes causing the fluid to heat and expand, resulting in the brakes suddenly being applied.
GreenV8S said:
The symptoms suggest you have a faulty servo which is not holding vacuum. There are various potential causes of that within the servo, but this is a complex component and not the sort of thing you should expect to diagnose and fix - just replace the whole unit.
^^^^ Wot 'e said.Having said that, make, model and year will help as not all cars use engine vacuum servos these days.
E-bmw said:
GreenV8S said:
The symptoms suggest you have a faulty servo which is not holding vacuum. There are various potential causes of that within the servo, but this is a complex component and not the sort of thing you should expect to diagnose and fix - just replace the whole unit.
^^^^ Wot 'e said.Having said that, make, model and year will help as not all cars use engine vacuum servos these days.
tr7v8 said:
E-bmw said:
GreenV8S said:
The symptoms suggest you have a faulty servo which is not holding vacuum. There are various potential causes of that within the servo, but this is a complex component and not the sort of thing you should expect to diagnose and fix - just replace the whole unit.
^^^^ Wot 'e said.Having said that, make, model and year will help as not all cars use engine vacuum servos these days.
Edited by TwinKam on Monday 3rd February 09:58
TwinKam said:
tr7v8 said:
E-bmw said:
GreenV8S said:
The symptoms suggest you have a faulty servo which is not holding vacuum. There are various potential causes of that within the servo, but this is a complex component and not the sort of thing you should expect to diagnose and fix - just replace the whole unit.
^^^^ Wot 'e said.Having said that, make, model and year will help as not all cars use engine vacuum servos these days.
I agree with others on something about the car loosing vacuum boost somehow - confirm the pedal is hard at the top of travel - not the bottom, I have once driven for a good 2 hours without touching the brakes, then I needed to slow for a roundabout. Pedal sank nearly to the floor as the pads were pushed up to the discs. I needed new pants.
Peanut Gallery said:
I agree with others on something about the car loosing vacuum boost somehow - confirm the pedal is hard at the top of travel - not the bottom, I have once driven for a good 2 hours without touching the brakes, then I needed to slow for a roundabout. Pedal sank nearly to the floor as the pads were pushed up to the discs. I needed new pants.
you would need to have a serious warped disc or bearing failure scenario for the pads to be pushed that far away from the disc in the first place.Before you go changing your servo or looking at the vacuum pump if it has one, there is probably a small plastic one way valve which is pushed through a rubber grommet into the servo body. If that has failed then the servo won't hold vacuum. You can take it off and try blowing though it. You should only be able to blow one way.
Do you know the name of the valve that you mentioned?
btw: I had changed the discs as well as the calipers sometimeback,as well as stuck a secondhand servo, stil no improvement
witko999 said:
Before you go changing your servo or looking at the vacuum pump if it has one, there is probably a small plastic one way valve which is pushed through a rubber grommet into the servo body. If that has failed then the servo won't hold vacuum. You can take it off and try blowing though it. You should only be able to blow one way.
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