Brake Pedal Goes Hard(Intermittent)

[jonew]

2001 2.3 galaxy..

Had issues where every now and then the brake pedal would go hard causing all 4 wheels to bind,switch off ignition n pump pedal, hold, start engine n pedal drops as it should which fixes the issue.

Ive removed servo pipe and it appears ok, I can hear the valve moving if I blow through it etc..

Any other suggestions as money is limited and I do have some tech knowledge, servo works as it should..im lost where else to look?????

[jonew]

Anyone?.

[insanitybeard]

Servo issues don't usually cause binding brakes, are ALL wheels definitely binding when the fault occurs? Servo faults are usually due to vacuum loss resulting in a loss of braking assistance, not binding!

Edited April 30, 2014 by insanitybeard

[chromedome]

Master cylinder maybe.

[insanitybeard]

The other possibility is that the servo itself is defective, if the unit itself isn't allowing the air that enters (on one side of the diaphragm when you apply the brakes) the unit to vent when you release the pedal you could end up with a brakes stuck on scenario. If it is the servo the complete unit will require replacement, it's not a serviceable item. Alternatively, as Chromedome says above, if the master cylinder is not returning properly or releasing pressure when you release the brake pedal it could cause a similar problem. Is the brake fluid clean? Debris in the system can cause problems.

[jonew]

Thank you for the replies, ive had the rear brakes apart and replaced pads.. all is free.. feels like the rear brakes are binding but my wife claims lack of power when it happens yet its not happened to me.

Ive noticed that in the morning the pedal is extremely soft and hardens the longer I drive, its not happened over the last few days though.

When it does happen like I say I can pump turn car off, pump pedal til hard, hold n restart car which rectifys fault.. until the next time

[insanitybeard]

When you say lack of power, I take it you mean that the engine is lacking power, not the brakes? Also, the 'soft' pedal in the morning, do you mean abnormally soft or just the normal brake pedal feel (with servo assistance) which then goes hard in a not normal way (i.e, how the pedal feels without servo assistance)? What condition is the brake fluid in?

[jonew]

Softer than normal I guess, brake fluid quality does look poor.. my wife says its a struggle to hit 50mph and keep to it.

Basically we parked up n after time we went back to the car and drove off but it felt like the handbrake was on, on driving home we could see smoke from rear wheels. I removed wheels to see pads down to metal n then changed them. Sliders free, handbrake free etc. I thought pistons out to max causing this hard pedal/binding.. after replacing it was fine n now this intermittent issue.

I will change brake fluid but im drawn to vacuum side because of the intermittent hard pedal and lack of power??

[jonew]

Just to add, when doing the servo test. It takes 3-4 pumps to harden then will drop on start up as it should.. idle fluctuates ever so slightly when pedal hardens, when brakes bind I can still turn wheels by hand at a push.

[insanitybeard]

It's a strange one, servo faults usually tend to be the reverse of what you describe- a hard pedal due to loss of vacuum and lack of braking assistance. As a test, my suggestion would be to try to reproduce the fault whilst static, and then pull the vacuum pipe off of the servo with the engine still running (be VERY careful as you do this not to get tangled or burned!), either at the servo or vacuum pump end- you will need to plug the pipe or vacuum pump connection (depending on which end you disconnect) quickly as you do this, and then see A) If the engine runs better as a result and B ) If the brakes then free up and stop binding, which will involve getting some wheels off of the ground, though be warned if you do this with the ignition still on it's likely to put the ABS warning lamp on. Obviously with the vacuum supply disconnected then the brake pedal will go hard and not feel normal but it may help diagnose the fault.

Edited May 1, 2014 by insanitybeard

[jonew]

Thank you..

Was thinking the exact same thing, after removing the vacuum pipe whilst static the fault disappeared for approx 3 days.

I can hear the valve moving if I blow/suck through the pipe, can't see any holes..

 

Ive forget to check if the pipe has collapsed during the fault though.. I just dont want to put a servo on it if its not going to cure it.

[insanitybeard]

If you can get a substitute pipe readily and cheaply enough then it's probably worth trying that first, simply because it's much easier and cheaper to change than the servo! From the symptoms you describe though, I'd be surprised if the pipe is at fault.