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There has been lots of sound advice given here, but here,s my six penneth. What retracts a brake piston a few microns after the brake has been let off, and allows the disc to spin freely, is the piston seal. When hydraulic pressure is applied, the seal 'drags' on the smooth caliper bore, and distorts slightly. It's a bit like stretching a rubber band sideways. Once the hydraulic pressure is released, the rubber retutrns to its natural shape pulling the piston back a tad as it does so. I have come across this fault a few times, and it can only be rectified by removing the pistons and seals, cleaning all the gunge out which can make the piston stick, (and there will be plenty) and rebuilding, preferably with new seals. Or a new caliper1The piston only needs to move back slightly to release the brake. The odd thing here is that the piston will feel perfectly free when pushing it back by hand, but stiff enough to prevent the seal doing the job. This is easier said than done with some calipers, as the dust seals can be impossible to remove to get the pistons out. I reckon everything else has been done, so it stands agood chance of curing it, I hope so. Mike
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What does the garage say to 1 side getting hotter than the other?
Are they considering replacing caliper under warranty? or have they better ideas yet?
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Have the garage had it on some brake testing rollers, like the ones used for MOT's? That will show you whether the brakes are binding or not.
Yes, and they say they didn't find anything wrong. But is it it possible, if a pad is rubbing on one side of a disc as seems to be the case here, for there to be enough friction to cause noticeable heating without this showing up on the rolling road?
I did have one other case of sticking Bendix brakes not caused by the sliders. The pad backplates on these calipers fit like a jigsaw with dovetailed ends into the brake carrier, retained at one end by a wedge to facilitate pad removal. I found that a set of well known branded pattern pads were not a sufficiently free fit in the carrier and were binding at the dovetail ends, giving sticking brakes
Could this problem affect either pad on a single-piston caliper, or only the one on the inner (piston) side?
What retracts a brake piston a few microns after the brake has been let off, and allows the disc to spin freely, is the piston seal...
I was thinking that since it's just the pad on the outer side that's rubbing, which I believe is the pad that isn't attached to the piston, then I can rule out causes related to piston movement & hydraulics. If I've got this wrong I'll be happy to be put right!
The car's going back to the garage tomorrow for another look.
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I think I would look at other poss reasons for this,As no fault found on caliper,would look at possible brake pipe flexi fault,ie nothing to say pipe has not collapsed internally holding the pads on/apart from that I can only think faulty wheel bearing transfering heat through hub and nothing wrong with calliper
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Steve
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I was thinking that since it's just the pad on the outer side that's rubbing, which I believe is the pad that isn't attached to the piston, then I can rule out causes related to piston movement & hydraulics. If I've got this wrong I'll be happy to be put right!
It's only the piston retracting that gives any free play at all, at either side. The free play should then be equalised by the sliding pins, so both sides have enough and the same. If the pins are stiff, then the free play will be mostly on the piston side, quite rightly stated, but if there is insufficient retraction of the piston for both sides to have enough free play, the piston side will be the first to get it, is because of frictional losses in the sliders, so the floating side will rub. It's difficult to explain here, I hope it makes sense! Mike
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It was indeed the outboard pad which was sticking due to a lack of freedom at the pad backplate dovetailed ends. It's easy to see how Newton's Third Law applies to the sliders in terms of actuating the outboard pad, but if you study the whole caliper and carrier assembly carefully, you can see that the pads have to move in the carrier when the brakes are applied, and also have to move back again.
I would put my money on a lack of freedom at the pad backplate ends where they dovetail into the carrier.
659.
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>>I would put my money on a lack of freedom at the pad backplate ends where they dovetail into the carrier.
Highly poss 659,but that would wear pad at hub side assuming rest of pad is free
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Steve
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>>but if there is insufficient retraction of the piston for both sides to have enough free play, the piston side will be the first to get it,
No if piston is retracting as it should then the drag factor will be on float side ie sliders if they dont work as should/causing the other pad to stick in place.
as long as the piston is working correctly,pad on that piston will retract.the calliper on piston side is fixed to rear of hub/float side is only connected via the sliders so if they fail then pad drag will occur...If they are found to be working properly and both pads are free of disc(excluding disc runout ) this often occurs without any problems,
Need to look at other problems as mentioned
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Steve
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I can't quite understand your comments.
A simple but revealing experiment: Assuming pads are partly worn, retract piston and fully assemble caliper with both pads as far away from the disk as is possible. Arrange for the pad to disk gaps to be about equal.
Now get someone to slowly press the brake pedal whilst you watch all the free movement being taken up. The movement of the pad backplate ends relative to the carrier will be very obvious.
659.
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Quick update: the car's currently at the garage. When I took it in, the head man said they get a lot of problems with ZX front brakes, with the single-piston caliper design not working so well as the car gets older. He said the only thing that causes the outer pad to rub is the caliper not sliding correctly, and that since the operation of the caliper itself has already been checked, the next thing to look at is where the caliper is mounted to the hub. He said these are sometimes not aligned correctly and that this can cause the caliper not to slide freely. Make any sense? I await their call.
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The garage have phoned to say they still can't find anything wrong. Their next suggestion is to try a new master cylinder, in case a faulty valve is causing the problem. That doesn't seem to fit with my observation that only the outer pad seemed to be rubbing. They say I was mistaken if I thought I could see daylight between the inner pad and the disc, as the gap is never big enough for this to be the case. Comments on that are welcome!
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Fitting a new master cylinder to overcome stiction in one service brake (only) is ridiculous. The daylight obsevation is quite valid - I've seen it too with disks and pads in good running condition.
I reiterate my earlier comments - try my experiment and you will see why free movement between the ends of the pad backplates and the carrier is so vital for the proper functioning of this design of caliper.
659.
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Fitting a new master cylinder to overcome stiction in one service brake (only) is ridiculous. The daylight obsevation is quite valid - I've seen it too with disks and pads in good running condition.
I agree with 659.
Cheers
DP
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ive just read the 11.17 post and yes the caliper holding brackets do bend with zealus use of screwdrivers to push pistons back and this will indeed cause the sticking pad,if i was the garage i would be changing this £10 part before a £150+ master watsname........
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I agrre too with 659. It's rubbish. Ask then to name the valve in the master cylinder which could cause one pad or piston to stick. This will allow you to judge whether or not there is any theory or reason behind this suggestion, other than their bonus and your cash. I have come across the actuator rod which connects the pedal to the master cylinder to have no free play, so that the master cylinder piston will not fully retract , and not uncovering the ports, so as the fluid heats up and expands naturally with breaking, the brakes apply as the fluid cannot get back to the cylinder. With a diagonal split I suppose one front and the other back may come on first., but doubt this is the problem here. ask them!
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Sorry to post again, another call from the garage. They took the car out for a test drive for 10 mins then checked the temperature of both front wheels with a digital thermometer and they say they were the same. Which doesn't seem to fit with my own observations based on feeling the wheel nuts after numerous journeys. The mechanic I spoke to had owned a few ZXs and said they're known for the brakes getting hot and occasional fade. (I've read elsewhere of people fitting Berlingo ventilated discs & calipers to ZXs to improve braking.)
Basically they're saying they haven't been able to reproduce the fault or find any mechanical problem. They're not ruling out that there is a problem that intermittently causes binding and consequent overheating during use. They believe they've ruled out the caliper as the cause. I want to re-check my observation of clearance between inner pad & disc before spending money on hydraulics.
Fitting a new master cylinder to overcome stiction in one service brake (only) is ridiculous.
Their explanation was that the master cylinder has a valve that can produce a fault affecting only one braking circuit. I don't know enough to evaluate this.
The daylight obsevation is quite valid - I've seen it too with disks and pads in good running condition
Thanks for the information and for your vote of confidence in my powers of observation! I was beginning to doubt what I thought I'd seen.
I reiterate my earlier comments - try my experiment and you will see why free movement between the ends of the pad backplates and the carrier is so vital for the proper functioning of this design of caliper.
I have resisted fiddling so far because I don't want someone who doesn't know what they're doing (i.e. me) fiddling with my brakes, and because the work is supposed to be under guarantee. But I'm inclined to believe you. I don't think the garage are going to do any more, so I suppose I've nothing to lose by trying filing the pad backplates. I've never fiddled with brakes but I have the Haynes manual, are there any pitfalls I should know about?
Thanks everyone for your helpful and informative comments, much appreciated.
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Thanks for your kind words.
If you file the pad backplates, bear in mind that you will be removing an absolutely minute amount of metal - little more than the thickness of the paint. It's really the burr on one side which is caused by the stamping process which needs to come off. Don't under any circumstances remove a significant amount of metal and make sure you use high temeperature copper loaded anti-seize compound (never ordinary grease) at the very ends of the pad backplates. Keep this compound well away from the friction surfaces.
My feelings are that the garage have themselves temporarily "cured" this problem simply by removing and refitting the pads, but unless you take action, the fault will come back.
One final point. Before you start, make sure you know exactly how the pads, wedge and anti-rattle springs are fitted. Make a diagram or use a camera. The pads are handed, although they look very similar and it's easy to get it wrong.
659.
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Yes, to avoid the trauma that 'deep diver' has had over the weekend (read the threads) if you need to push the caliper piston back to get the pads out, undo the bleed nipple to let the the fluid escape, don't force it back though the hydraulics into the master cylinder. Good luck.
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>I don't think the garageare going to do any more, so I suppose I've nothing to lose by trying filing the pad backplates. I've never fiddled with brakes but I have the Haynes manual, are there any pitfalls I should know about?
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If you try and file the Pad backplates, you'll remove as most pads have is an Anti-squeal material bonded to the plates, this contacts the piston and caliper.
If you follow the manual you should have no problem.
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>>If you try and file the Pad backplates, you'll remove as most pads have is an Anti-squeal material bonded to the plates, this contacts the piston and caliper.
Shouldnt need to unless pads are wrong thickness/not correct pads for car!
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Steve
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>>If you try and file the Pad backplates, you'll remove as most pads have is an Anti-squeal material bonded to the plates, this contacts the piston and caliper.
Shouldnt need to unless pads are wrong thickness/not correct pads for car! -- Steve
Steve,
Read my replies again, they are in reply to the above threads.
I am not suggesting the pads be filed, as you say they should not be touched.
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autumnboy,Fair comment,But would think any garage worth there name should have sorted this problem out much quicker than they have.
also tend to agree with comment about the wheel bearing CV joint,I also suggested wheel bearing some posts ago
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Steve
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>>next thing to look at is where the caliper is mounted to the hub. He said these are sometimes not aligned correctly and that this can cause the caliper not to slide freely. Make any sense?
No,its secured ,no way of adjusting its mounting..its a precise fit with bolts,ie once fitted its secure/unless they did not tighten the bolts correctly,I dont think oldmans comments were totally correct but severe force on calliper could missalign it but it would have to be severe force
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Steve
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seen it done but to be fair it was a 106 not a zx......(with 2 different people and two different cars i might add) a tool was placed to push the piston back but because the piston was semi seized the holding bracket twisted,everything bolts back but the non piston loaded pad sits at a slight angle and jams within days/weeks
its only an observation mind........
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Quick update: the car's currently at the garage. When I took it in, the head man said they get a lot of problems with ZX front brakes, with the single-piston caliper design not working so well as the car gets older. He said the only thing that causes the outer pad to rub is the caliper not sliding correctly, and that since the operation of the caliper itself has already been checked, the next thing to look at is where the caliper is mounted to the hub. He said these are sometimes not aligned correctly and that this can cause the caliper not to slide freely. Make any sense? I await their call.
Mine has done 172k with no problems in ten years although mine are vented disc's.
If there was a problem with the Master Cyl. you would have more than one brake getting hot, also they a dual system.
If you say its the wheel nuts that feel hotter than the other side, then this suggests the hub bearing or CV joint is the cause rather than the brakes.
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