zx front brake imbalance...

[RussellF97]

1995 ZX 1.9D Hatch; Bendix calipers, non-ABS. Brake fluid changed last year.

Unfortunately, 'Old Clanky' has failed her test on front brake imbalance - 33% would you believe! Road testing, I can lock up the front n/s but the front o/s won't lock up even on a wet road.
So far, checked for free movement of the pistons and caliper sliders - OK. The pad wear is a bit uneven though; i.e., the pads one side of the disc are worn more than t'other side - although not excessively.
I'll try a new set of pads, but because the system is split diagonally, I have a horrible feeling that the master cylinder may be the culprit 'cos there was also imbalance on the rear brakes as well - but only 9%. Does anyone concur with this diagnosis... or have any other thoughts..?

[Peter.N.]

It sounds as though the caliper is stuck on the sliding part. I can't remember exactly what the brakes are like on there but if they only have one piston the caliper has to be able to slide in order to apply the other pad and they often seize. If this is so you will have to remove the slide bolts and see if you can free it off.

Peter

[RussellF97]

The first thing I did was to check both the pistons and caliper sliders were moving freely. Everything at the wheels seems to be OK, which then made me start thinking back to what makes the pistons move.
The Bendix calipers have some weird locking bar arrangement to keep the pads in place. The bar goes rusty quite happily but I've cleaned everything up and the pads don't stick, which is why I keep coming back to the m/cyl.
Thankfully, they aren't too expensive...

[Peter.N.]

The only other thing I can think then of is a partially collapsed brake hose. I can't think that it would be the master cylinder unless it has one front brake and one rear on each section, but I don't think they do now.

Peter

[RussellF97]

The Haynes book says the system is split diagonally front/rear. I might go out shortly and do some fast reversing to see of the o/s/r brake works better than the n/s/r which may confirm - or otherwise.
That'll be fun...

[Gibbo2286]

I'm with Peter on this, sounds like an internally collapsed brake hose, or even one that's squashed flat by poor fitting.

I assume that the piston is self adjusting properly.

[RussellF97]

Thanks for your thoughts on this gents. That's two against one so I'll go with the majority!
There was an advisory on the front brake hoses, so if the new pads don't cure the problem, I'll fit a couple of new hoses.
Thankfully, over here you get two months to sort out any problems rather than two weeks. Much less stressful..!

[RussellF97]

After fitting a new set of pads, the brakes were 100% better, but still locking up on the ns.
Before I had got that far though, I'd realised the problem was with the os caliper. I must have been feeling particularly butch t'other day when I checked the sliders and piston movement 'cos the piston was a darn sight harder to push back this time. Also, when pressing the pedal to put the pads in contact with the disc (quite important before driving off), the caliper creaked.
I'd looked up ZX brake probs on another forum and someone on there mentioned that creaking front brakes was a sign that the calipers were past their best.
Anyway, a new caliper is en route along with a set of brake hoses so hopefully by the end of next week it should have a set of healthy front brakes and be fit to pass the ct.

Thanks for all your thoughts on the problem folks, much appreciated.

[white exec]

It's amazing how little of a movement 'workout' brake caliper pistons get, so maybe not surprising the odd one goes sticky, creaky or seizes up. The most exercise they get are probably when pads get replaced.

Even worse, I suppose, if standard hygroscopic fluid is never changed - which must be the case for most vehicles. Who ever does this - except LHM users!?

[Peter.N.]

I keep an oil can labelled 'brake fluid' and that's what it contains. If before doing anything else if you lift the edge of the piston seal and pump as much in as you can get you will find that with a bit of a work out it will free off nicely.

Peter