Just failed the MOT on binding front brakes.
It's only done 80 miles since renewing the disks and pads. The job seemed to go well, and I had a high degree of (seemingly misplaced) confidence in it. From the start since the job, the brakes have been extremely powerful and even. Car was undrivable before that due to disintegrating disk from pad gone down to the metal, which was the point at which I acquired it cheap!
I noticed the car didn't seem to coast without slowing down rather more than I expected, but put this down to not being used to its characteristics. I think the binding has worsened though.
Since it failed this morning I've failed to free the binding despite repeated removal of the pads and exercising of the pistons by winding them in and out.
Checking old posts, I tried penetrating oil on the handbrake lever side, but it made no difference. It all looks clean and well greased in there, and the lever moves nicely, moving the piston in and out. The piston sides were like an unblemished mirror, although I haven't removed it entirely, not wishing to have to bleed the brakes at this stage unless unavoidable.
One wheel seems reasonably free running (moves easily with one hand turning the disk, but stiffly). The other needs two hands to turn it, and obviously isn't right. Despite taking care to line up the slot in the piston with the stud on the pad when fitting, I noticed that the stud on the new pad was nearly flattened, and there were corresponding dents in the piston face. At least one of these I remember seeing when I first did the job, and they are both rusty, not fresh looking. This makes me wonder if pad studs riding up out of the grooves onto the piston faces is a common problem or design weakness?
Anyway, since the stud is redundant on the outboard pad I swapped them over, taking even more care not to misalign with the slots, and bringing the self adjust on the brake pedal up gently. No difference whatsoever.[:(!]
I removed the handbrake cables from the levers to rule out handbrake adjustment.
I have 6 days in which to fix this before the re-test, but I'm stumped.
Haynes gives no information about the caliper, referring you to the instructions that come with reconditioning kits. Which begs the essential Q, 'is it the caliper(s), bearing in mind the binding seems consistently worse on one side? Any help much appreciated.[:)]
Neil T (who has just borrowed his kids glass painting kit to re-orange the failed indicator bulbs! Whatever happened to orange lenses? Victims of fashion and accountants we are [:(!][}:)])
Xantia binding front brakes.
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AndersDK
- Posts: 6060
- Joined: 21 Feb 2003, 04:56
- x 1
Neil -
The stud/peg on the pads should line up with the groove (if found : the double groove) on the piston.
I've never read about owner's experience with this becoming misaligned during use.
The peg on the pads locks piston against turning - when handbrake are applied/adjusted - since the internal handbrake mechanism is a threaded rod moving inside the piston.
Have you bled the calipers ? (important !)
Another point may be to check for Brake (pedal) master valve failure :
If the valve leaks - it will constantly apply some pressure to the pads. This requires disassembly of the brake line - engine idle - (or as long as the acc sphere still have pressure when engine stopped) -
brake pedal NOT touched.
Any such faulty pressure would be fairly equal both sides.
If you're still unsure the pistons may bind - it's perfectly allright to let them work out a bit (pads removed) - then grease their surface with silicone/brake grease.
The pistons MUST be screwed in (clockwise) - NEVER pressed in - because of above mentioned threaded handbrake rod mechanism.
The adjuster nuts on handbrake cables must NEVER be used to adjust handbrake force - they have only 1 purpose : to adjust for cable slack/equalling when cable fitted first time.
In wiev of short prep. time for MOT - keep posting - I'm sure the rest of the gang here will add/correct to my ideas.
CORRECTION :
Above suggested test on brake master valve leak does not need a brake line disassembly.
It would be possible to see the pistons very slowly moving out when pads removed.
The stud/peg on the pads should line up with the groove (if found : the double groove) on the piston.
I've never read about owner's experience with this becoming misaligned during use.
The peg on the pads locks piston against turning - when handbrake are applied/adjusted - since the internal handbrake mechanism is a threaded rod moving inside the piston.
Have you bled the calipers ? (important !)
Another point may be to check for Brake (pedal) master valve failure :
If the valve leaks - it will constantly apply some pressure to the pads. This requires disassembly of the brake line - engine idle - (or as long as the acc sphere still have pressure when engine stopped) -
brake pedal NOT touched.
Any such faulty pressure would be fairly equal both sides.
If you're still unsure the pistons may bind - it's perfectly allright to let them work out a bit (pads removed) - then grease their surface with silicone/brake grease.
The pistons MUST be screwed in (clockwise) - NEVER pressed in - because of above mentioned threaded handbrake rod mechanism.
The adjuster nuts on handbrake cables must NEVER be used to adjust handbrake force - they have only 1 purpose : to adjust for cable slack/equalling when cable fitted first time.
In wiev of short prep. time for MOT - keep posting - I'm sure the rest of the gang here will add/correct to my ideas.
CORRECTION :
Above suggested test on brake master valve leak does not need a brake line disassembly.
It would be possible to see the pistons very slowly moving out when pads removed.
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RichardW
- Forum Treasurer
- Posts: 12442
- Joined: 07 Aug 2002, 17:12
- x 1431
Neil,
Have you checked the caliper is 'floating' properly on its slides?
Also are you sure it's the brakes? I had a wheel bearing in mine that was tight - the car never seemed to 'roll' as I owuld have expected it to, but I just ignored it. Then the bearing got noisy so I had it changed - the car then rolled as you would expect it to, and was much faster[:D]. Worth a spin of the wheel with the pads out just to check!
Otherwise looks like you're going to have to change the caliper[:(].
Richard
Have you checked the caliper is 'floating' properly on its slides?
Also are you sure it's the brakes? I had a wheel bearing in mine that was tight - the car never seemed to 'roll' as I owuld have expected it to, but I just ignored it. Then the bearing got noisy so I had it changed - the car then rolled as you would expect it to, and was much faster[:D]. Worth a spin of the wheel with the pads out just to check!
Otherwise looks like you're going to have to change the caliper[:(].
Richard
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Homer
- Posts: 1503
- Joined: 26 Feb 2003, 10:52
- x 16
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jeremy
- Posts: 3959
- Joined: 20 Oct 2002, 16:00
- x 2
As Anders says "Is there any air in the system"
Citroen brakes being powered don't go spongy in there is air in the system, but in fact just fail to release properly. this is because the brake valve isn't a pump with assistance as in a normal system but simply a valve admitting already pressurised fluid to the rest of the circuit.
So - air in system, open valve - high pressure fluid passes valve, compresses air and applies brakes - so far - so good.
release brake, shut valve, fluid and highly compressed air trapped - brake stays on!
Jeremy
Citroen brakes being powered don't go spongy in there is air in the system, but in fact just fail to release properly. this is because the brake valve isn't a pump with assistance as in a normal system but simply a valve admitting already pressurised fluid to the rest of the circuit.
So - air in system, open valve - high pressure fluid passes valve, compresses air and applies brakes - so far - so good.
release brake, shut valve, fluid and highly compressed air trapped - brake stays on!
Jeremy
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Neil T
- Posts: 21
- Joined: 19 Jul 2003, 03:06
Thanks for the replies.
I'm half way through replacing the LHM which looked more brown than green. By my calculations it was about 12K overdue. It seemed logical to do this before adding new LHM to old just to bleed the brakes. Rain stopped play today, but if tomorrow is OK I hope to complete this and bleed the front brakes as suggested to see if this makes any difference. If not I'll have the worst piston right out to examine for corrosion sticking.
Haynes mentioned that when opening the bleed valve a whole turn after having lowered the suspension, that there should be a hissing noise as fluid is returned to the reservoir. There was no sound of any kind, and the total amount of fluid emptied was 3.25 litres indicating to me that there is either 2.15 litres of sludge left in the system, or the reservoir level was down by this much!? I know that the level was down because on the high setting test the yellow disk was below the marks on the sight glass, but could that acount for this much? Does this sound like a normal LHM drain amount, or not?
I still feel somewhat disturbed to have followed a text book procedure for fitting new pads, and yet have managed to shave off half a brake pad stud, and no one has experienced this? I mean it isn't difficult to get one of the 4 wide gaps in the piston to line up with the stud when folding the caliper back, so that it doesn't catch, right? Given that the piston faces have already received prior bruising, and I'm 99% certain this car has never been DIY'd before, only garage maintained, and dealership exclusively up to 60K, I have to suspect this is a known vulnerability.
Any further thoughts appreciated as I feel I'm going through the motions a bit. I'll report back on what tomorrow resolves, or not.
Many thanks.
I'm half way through replacing the LHM which looked more brown than green. By my calculations it was about 12K overdue. It seemed logical to do this before adding new LHM to old just to bleed the brakes. Rain stopped play today, but if tomorrow is OK I hope to complete this and bleed the front brakes as suggested to see if this makes any difference. If not I'll have the worst piston right out to examine for corrosion sticking.
Haynes mentioned that when opening the bleed valve a whole turn after having lowered the suspension, that there should be a hissing noise as fluid is returned to the reservoir. There was no sound of any kind, and the total amount of fluid emptied was 3.25 litres indicating to me that there is either 2.15 litres of sludge left in the system, or the reservoir level was down by this much!? I know that the level was down because on the high setting test the yellow disk was below the marks on the sight glass, but could that acount for this much? Does this sound like a normal LHM drain amount, or not?
I still feel somewhat disturbed to have followed a text book procedure for fitting new pads, and yet have managed to shave off half a brake pad stud, and no one has experienced this? I mean it isn't difficult to get one of the 4 wide gaps in the piston to line up with the stud when folding the caliper back, so that it doesn't catch, right? Given that the piston faces have already received prior bruising, and I'm 99% certain this car has never been DIY'd before, only garage maintained, and dealership exclusively up to 60K, I have to suspect this is a known vulnerability.
Any further thoughts appreciated as I feel I'm going through the motions a bit. I'll report back on what tomorrow resolves, or not.
Many thanks.
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- x 2
A couple of thoughts, a family member had a fiesta a good few years back, this crate developed sticking front brakes and was getting progressively worse, so I decided to strip the calipers down and see what was going on and fit new seals on the rebuild.
Well it soon became apparent what the trouble was, the square section piston seal had swollen up and had got hold of the piston so tight that it wouldn't retract by the tiny amount required and the brakes dragged, the swollen seal was so big that the new one would almost fit inside it.
This shouldn't happen with LHM seals running in pure LHM, but has anyone konwn otherwise, if however the LHM has been contaminated then its on the cards I suppose.
Moving on to the possibility of air causing the brake to drag, this is a non starter, pressure is pressure wether it be hydraulic or pneumatic, and if the valve lets hydraulic pressure return on release of the pedal as it should, then it will also do the same if there were air present.
The doseur valve will not close off the ports to the calipers, they must remain open to any returning fluid to allow for expansion of same so not possible to trap air in the pipes this way.
One thing that can cause some pressure to remain in the caliper is the flexible hose, if this is breaking up internaly.
Locked in pressure is easily tested for by simply loosening the bleed screw, LHM should not squirt out but should only run out.
Dave
Well it soon became apparent what the trouble was, the square section piston seal had swollen up and had got hold of the piston so tight that it wouldn't retract by the tiny amount required and the brakes dragged, the swollen seal was so big that the new one would almost fit inside it.
This shouldn't happen with LHM seals running in pure LHM, but has anyone konwn otherwise, if however the LHM has been contaminated then its on the cards I suppose.
Moving on to the possibility of air causing the brake to drag, this is a non starter, pressure is pressure wether it be hydraulic or pneumatic, and if the valve lets hydraulic pressure return on release of the pedal as it should, then it will also do the same if there were air present.
The doseur valve will not close off the ports to the calipers, they must remain open to any returning fluid to allow for expansion of same so not possible to trap air in the pipes this way.
One thing that can cause some pressure to remain in the caliper is the flexible hose, if this is breaking up internaly.
Locked in pressure is easily tested for by simply loosening the bleed screw, LHM should not squirt out but should only run out.
Dave
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thatorangething
- Posts: 5
- Joined: 19 Jul 2003, 11:11
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Neil T
- Posts: 21
- Joined: 19 Jul 2003, 03:06
It's sorted! [:D][:D]
In the end it was those grotty pins at the bottom of the caliper sticking. To tell the truth I hadn't stopped to analyse how the centering worked, and it didn't occur to me that the top half of the slider would be a nice smooth greased cylinder with protective rubber gaiter, and the bottom would be a steel pin through a spring clip facing the full force of the weather, salt spray etc coming straight at it unprotected! Well that's my excuse anyway, he says trying not to look too stupid! [;)]
Once I cleaned them and the clips up, also wire brushing the cups in the casting that hold the end of the pads, and applying copper grease to all moving bits, the sticking vanished.
I'm now wondering how often these pins will need unsticking since there is nothing to protect them from getting in the same state apart from a smear of copper grease. This has to be the number one contender for sticking calipers I would have thought. Oh well, at least its an easy no cost job once you've sussed it.
I did check the doser valve before making this discovery though, using the engine running with pads out method to see if the piston drifted out. It didn't. Isn't brake bleeding fantastic on these machines? [:)] Just undo the nipple a quarter and watch the constant stream turn from crud to nice clear green. [:p]
I could get to like planet Citroen [;)]
In the end it was those grotty pins at the bottom of the caliper sticking. To tell the truth I hadn't stopped to analyse how the centering worked, and it didn't occur to me that the top half of the slider would be a nice smooth greased cylinder with protective rubber gaiter, and the bottom would be a steel pin through a spring clip facing the full force of the weather, salt spray etc coming straight at it unprotected! Well that's my excuse anyway, he says trying not to look too stupid! [;)]
Once I cleaned them and the clips up, also wire brushing the cups in the casting that hold the end of the pads, and applying copper grease to all moving bits, the sticking vanished.
I'm now wondering how often these pins will need unsticking since there is nothing to protect them from getting in the same state apart from a smear of copper grease. This has to be the number one contender for sticking calipers I would have thought. Oh well, at least its an easy no cost job once you've sussed it.
I did check the doser valve before making this discovery though, using the engine running with pads out method to see if the piston drifted out. It didn't. Isn't brake bleeding fantastic on these machines? [:)] Just undo the nipple a quarter and watch the constant stream turn from crud to nice clear green. [:p]
I could get to like planet Citroen [;)]
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AndersDK
- Posts: 6060
- Joined: 21 Feb 2003, 04:56
- x 1
Neil -
As a rule of thumb -
I allways do a general brake service - all 4 wheels - once a year.
Generally late autumn - ensuring brakes are working at their best - once icy roads becomes a daily nuisance - at the same time shifting over to winter tyres.
This ensures catching beginning-to-stick pistons - and judging how often my driving habits needs replacing of pads/discs.
I allways stock a complete set of pads/discs/caliper service bits - not to get stuck in parts shortage.
(having had the same car type : BX - for 10y's now)
As a rule of thumb -
I allways do a general brake service - all 4 wheels - once a year.
Generally late autumn - ensuring brakes are working at their best - once icy roads becomes a daily nuisance - at the same time shifting over to winter tyres.
This ensures catching beginning-to-stick pistons - and judging how often my driving habits needs replacing of pads/discs.
I allways stock a complete set of pads/discs/caliper service bits - not to get stuck in parts shortage.
(having had the same car type : BX - for 10y's now)
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Neil T
- Posts: 21
- Joined: 19 Jul 2003, 03:06
Anders wrote:
As a rule of thumb -
I allways do a general brake service - all 4 wheels - once a year.
Sounds like good advice with these machines, even though we don't get 'proper' winters in Milton Keynes in the south of England the way I imagine you do in Denmark.
It passed the re-test today, so thanks again everyone for your invaluable help.[:)]
As a rule of thumb -
I allways do a general brake service - all 4 wheels - once a year.
Sounds like good advice with these machines, even though we don't get 'proper' winters in Milton Keynes in the south of England the way I imagine you do in Denmark.
It passed the re-test today, so thanks again everyone for your invaluable help.[:)]
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AndersDK
- Posts: 6060
- Joined: 21 Feb 2003, 04:56
- x 1
Ah - well
It's not that bad here in DK either Neil [:D]
We use to call it wet/cool summer - in wintertime.
- and warm/dry winter - in summertime.
The problem is the sudden onset of ice - some 1-3 deg C below 0 - usually in the beginning of november.
The season where all panel beaters are happy guys [:D][:D]
- and insurance companies are issuing warnings on upcoming rate raises [:(][:(]
Later we have the usual : some snow at times & loads of salt [:(!]
It's not that bad here in DK either Neil [:D]
We use to call it wet/cool summer - in wintertime.
- and warm/dry winter - in summertime.
The problem is the sudden onset of ice - some 1-3 deg C below 0 - usually in the beginning of november.
The season where all panel beaters are happy guys [:D][:D]
- and insurance companies are issuing warnings on upcoming rate raises [:(][:(]
Later we have the usual : some snow at times & loads of salt [:(!]
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Neil T
- Posts: 21
- Joined: 19 Jul 2003, 03:06
Anders wrote:
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Later we have the usual : some snow at times & loads of salt <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Yes, we get a lot of salt too, even when there is no frost.[:(!] I always imagine Scandinavian drivers know how to drive on ice and compacted snow, but in England, we can turn a few inches of snow into a holocaust on the roads! I practiced sliding on snow early on, and you never forget, once you've learned. Lost the back end on the old Carlton going at my usual sedate pace round an unusually greasy island recently, and found myself on full reverse lock, throttle off without thinking about it. Then realised that I had never slid in this car in the 11 years I've had it. This Xantia is my first front wheel drive car though so I'll have to try to remember a different procedure! Still, with a heat wave forecast for next week here, I should have plenty of time to get used to it. [^]
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Later we have the usual : some snow at times & loads of salt <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Yes, we get a lot of salt too, even when there is no frost.[:(!] I always imagine Scandinavian drivers know how to drive on ice and compacted snow, but in England, we can turn a few inches of snow into a holocaust on the roads! I practiced sliding on snow early on, and you never forget, once you've learned. Lost the back end on the old Carlton going at my usual sedate pace round an unusually greasy island recently, and found myself on full reverse lock, throttle off without thinking about it. Then realised that I had never slid in this car in the 11 years I've had it. This Xantia is my first front wheel drive car though so I'll have to try to remember a different procedure! Still, with a heat wave forecast for next week here, I should have plenty of time to get used to it. [^]