|
Can anyone help with this....the car is an auto and when stationary in traffic the brake pedal will very ocassionally sink slowly to the floor.....the brakes still hold it and it doesn't creep at all but very disconcerting. It never ever happens while moving....and recently passed MoT with no problems. My first thought was maybe a sticking caliper overheating but a complete checkover showed no signs of that at all, replaced hoses and fluid anyway though.....no sign at all of any fluid loss....next was servo, no sign of any problem there...did all normal checks as per manual. I suppose my next move will be to replace the master cylinder but reluctant to, especially because whilst moving there has never been any sign of the problem at all, which simply doesn't make sense to me!! I'm a little in the dark about abs in general and can't help suspecting it, although it works fine, no light has ever come on and I have checked and cleaned all electrical connections. Any suggestions would be very welcome indeed....I hate replacing parts just in case but its beginning to look that way!!
Edited by Pugugly on 01/06/2009 at 19:58
|
Sounds like the master cylinder, and either the bore is worn or the seals. 96 car? 14 years old??
Had the problem on my Honda after I bled the brakes through. I hate to pump the pedal to do this, preferring to use a bleeding kit off the tyre, but one of the few cars I can not make it fit is a Honda. Pumping past the normal stroke can "wash out" the seals.
It will not show a leak as the piston will slowly travel down the bore, pushing fluid out behind, which goes past again when pedal is released.
|
|
You will need to check your model but some Auto's have an electric vacuum pump that kicks in at low revs to maintain a vacuum when engine braking is very low. Regards Peter
|
|
It it is going right to the floor and you have no leaks, it must be the master cylinder. When you are moving your not keeping your foot on the brake long enough for it to happen.
Edited by Peter.N. on 01/06/2009 at 18:16
|
|
I suppose so, yes....I suspect the master cylinder but no problem on the MoT brake test either....just hoping to be convinced before I chamge it!
|
|
Just thought I'd post to say that I finally solved the problem!! I couldn't bring myself to change the master cylinder because as well as the cost and the work involved I didn't really think it was the problem...it only ever happened when stationary and the brakes always worked even when the pedal sank.....It suddenly occurred to me that it might be something to do with the handbrake so I took off and stripped both rear calipers...one was fine but the other took some getting apart and the piston was badly corroded....I found a decent one at a breakers (for£10!) rebuilt it...put it all back together....problem gone completely...that was a month ago.....has been fine since! I'm guessing that the piston was sticking sometimes and using the handbrake freed it allowing the pedal to sink?
|
You may still have a master cylinder problem. The pedal to the floor is classic symptoms of fluid getting past the worn rubbers. Probably the fluid is hydroscopic and by changing the caliper and re-bleeding you've improved the quality of the fluid in the system. The siezed caliper alone would only allow the pedal to go down so far - as you have a split braking system - the pedal would only go down half way. Your pedal went to the floor which indicates a.) BOTH systems were leaking or b.) Master cylinder seals leaking. For what it costs and yours and others safety you really should replace the master cylinder seals as a minimum precaution although at this vehicles age I'd SUGGEST a master cylinder replacement.
Robin the Technician
|
|
Thanks for the reply but one of the first things I did was replace the fluid....still no problems since the caliper was replaced though! The problem I've always had about replacing the cylinder was that even when the pedal sank the brakes still worked fine....even though the pedal was most of the way to the floor you could still hold the car quite normally when you revved it.....thats the bit I could never understand?? That said, I finally found a new cylinder at a reasonable price and replaced it yesterday....but no signs of any problem when I removed the old one..ie no fluid between cylinder and servo...anyway thanks for comments and one way or another its sorted!!
|
|
|
