Brakes coming on!

Ages ago i had problem with O/S/F caliper sticking on. Bought new caliper, did umpteen miles, no problems.
I am very light on brakes, and 1st time they were used in anger resulted in brakes coming on progressively [not just O/S/F], all four! Pedal gets harder and harder!
Problem has not gone away? If left for twenty minutes they return to normal? Please any ideas?
I am thinking; Vacuum pump? Servo? Master cylinder?
Very limited budget [aren't we all?], four kids, mortgage, one income! Can't afford to chase problem around, your help gratefully received!

My advice would be to change the brake fluid. Especially if you didn't change it in the past years. Use only new fluid from a sealed bottle.

Sounds like your brake flexi hoses are partially blocked/collapsed internally they will allow fluid through under brake pedal pressure but will not allow the fluid to return once pressure is released.

stig said:

Sounds like your brake flexi hoses are partially blocked/collapsed internally they will allow fluid through under brake pedal pressure but will not allow the fluid to return once pressure is released.

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had that recently in a Ford (pause to shudder ...) where the front flex hoses passed though steel locating clamps on the struts. The symptom was brakes would go ON, but took ages (many minutes or hours) to go off.

The locating clamps had rusted inside, and the rust was building up and CRUSHING the brake hoses. Fluid could squeeze through under pedal pressure, but could not get back, so the brakes jammed on.

Thanks for all your input. Have already renewed flexi hoses! Have ordered servo valve, am starting with cheapest option 1st! Will keep you posted.

Update on brake problem.
Checked servo operation, replaced valve. Still got brakes sticking on! However after initial sticking, ie 10miles and there on! Leave for 20mins and everything seems normal! Am going for new fluid and master cylinder next!

Check this before you spend any more money.

Park the car somewhere, and jack up a front wheel.
Spin the wheel to see if it's brake is free or not.
Start the engine and apply the footbrake hard on and off a dozen times.

Now leap out and slacken any brake pipe union to the raised wheel. If there's a spurt of fluid followed by the wheel freeing off you now KNOW you have a hydraulic pressure retention problem.

This is usually caused by no clearance on the pedal (through servo) to master cylinder, stopping the master cylinder from fully returning.

This loss of clearance might be due to the servo not returning fully fro some reason. Has anything been changed, damaged, deranged?

CharlesY

Thanks CharlesY!
The 1st sign of anything untoward was at Longleat. When holding on the footbrake on slight incline, pedal went right to floor! Pumped pedal back up and all seemed OK until O/S/F caliper stuck! You have the story since then.
Thanks again for your help, will do test as you recommend. Regards Guy.

DISCOGUY said:

Thanks CharlesY!
The 1st sign of anything untoward was at Longleat. When holding on the footbrake on slight incline, pedal went right to floor! Pumped pedal back up and all seemed OK until O/S/F caliper stuck! You have the story since then.
Thanks again for your help, will do test as you recommend. Regards Guy.

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Excellent .... if the pedal went right to the floor and you are not losing LOTS of brake fluid, the fault MUST lie in the master cylinder seal(s).

I suspect the rear nearside brake may also have stuck some, as the brakes will be split that way I think.

Do not rule out that there may be TWO unrelated faults, (1) the master cylinder letting the seals go down THROUGH the fluid (very serious - don't drive till sorted) and (2) a sticking front O/S caliper.

I think from this latest description that pressure retention could still be the problem, but possibly it's just one half of the split system at fault. This would let the pedal collapse nearly to the floor, leave some brakes, and scare your pants off, all at once.

CharlesY

CharlesY', yes deffo 2 seperate probs! Caliper now A1! Pedal problem seperate issue! What you say makes perfect sense!
Pedal has only hit the deck this once! Has never lost any fluid! Have already got master cylinder on order. Many thanks, will keep you posted

Great news, but wouldn't it be nice to find out why the pedal collapsed?

I think you must hold the master cylinder inner seals as prime suspects, and that being so, could you trust them again?

New master cylinder seems like a great plan.

Then strip the old one, and fit a seal kit, and flog it on Ebay!

CharlesY

Brakes sticking update!!! After extensive road test!
All is A1! Master Cylinder [£22-EBAY] and brake fluid has fixed problem!! Also did servo valve but i think that was OK.
Caliper also replaced but that was different problem.
Many thanks to you that have helped!!