I've been talking about this for a while but today it took a turn for the worse - with identifiable symptoms.
Previously when sitting stationary with the engine running the pedal would slowly sink towards the floor but not all the way to the floor - now it goes all the way to a solid stop. But there are still 'brakes' at that point. Worse though, it now does it on the move - with a specific habit.
When I go in lightly on the first part of the pedal travel it's fine. Push a little bit further and the pedal is heading for the floor and actual braking effect is being lost. Only at the far end is there solid braking again.
This smacks of master cylinder failure - agreed?
There is one other oddity that may or may not be connected. A week or so back I got a bit of an improvement after forcing the wheels to lock and invoke the ABS. As I was doing that the pedal went for the floor (typical ABS) and the ABS pump made a zinging noise which I'd never heard an ABS pump make before but in truth I've probably not heard another ABS pump - only the noises associated with the actual locking/unlocking of wheels.
Since then (and not before) I've had a few instances of a 'zinging' kind of noise that reminds me of the ABS pump always during cornering, very brief and not provokable. It did that this evening when I had to go back out in it but not once during the 65 miles of 'long pedal' in the afternoon. It sounds like when something rotating is rubbing against a spring - that kind of zingy zizzy sound. Rear brakes are the obvious thought but when I previously mentioned the long pedal (when stationary) someone here (Supercharged IIRC) urged me to check out the rear brakes. Which I did, replaced both cylinders and everything went back together without problems.
The two aren't necessarily connected.... and, there's nothing at all (especially) from the pedal to suggest that there's bits loose/breaking up/etc within the drums. At the front the calipers are all good - worked on them earlier in the year.
Will get a chance (hopefully) tomorrow to check some obvious stuff but does the pedal as I describe it sound like a failing master cylinder to you guys?
In case it matters, mine is the JD7 system with HydraBoost on a 1999 C2500 5.7 Suburban.
Previously when sitting stationary with the engine running the pedal would slowly sink towards the floor but not all the way to the floor - now it goes all the way to a solid stop. But there are still 'brakes' at that point. Worse though, it now does it on the move - with a specific habit.
When I go in lightly on the first part of the pedal travel it's fine. Push a little bit further and the pedal is heading for the floor and actual braking effect is being lost. Only at the far end is there solid braking again.
This smacks of master cylinder failure - agreed?
There is one other oddity that may or may not be connected. A week or so back I got a bit of an improvement after forcing the wheels to lock and invoke the ABS. As I was doing that the pedal went for the floor (typical ABS) and the ABS pump made a zinging noise which I'd never heard an ABS pump make before but in truth I've probably not heard another ABS pump - only the noises associated with the actual locking/unlocking of wheels.
Since then (and not before) I've had a few instances of a 'zinging' kind of noise that reminds me of the ABS pump always during cornering, very brief and not provokable. It did that this evening when I had to go back out in it but not once during the 65 miles of 'long pedal' in the afternoon. It sounds like when something rotating is rubbing against a spring - that kind of zingy zizzy sound. Rear brakes are the obvious thought but when I previously mentioned the long pedal (when stationary) someone here (Supercharged IIRC) urged me to check out the rear brakes. Which I did, replaced both cylinders and everything went back together without problems.
The two aren't necessarily connected.... and, there's nothing at all (especially) from the pedal to suggest that there's bits loose/breaking up/etc within the drums. At the front the calipers are all good - worked on them earlier in the year.
Will get a chance (hopefully) tomorrow to check some obvious stuff but does the pedal as I describe it sound like a failing master cylinder to you guys?
In case it matters, mine is the JD7 system with HydraBoost on a 1999 C2500 5.7 Suburban.
