I have just bought a second 95 xantia. When you touch the brake pedal lightly you can feel a high frequency vibration through your foot for the first few seconds of braking. The accumilator sphere has just been replaced recently as it was ticking badly, but as I have just bought the car I cannot remember whether the vibration was there before the sphere was replaced.
I know this vibration isn't normal as I have not encountered this before and I have covered 250K pleasurable miles in my other xantia. I seem to have encountered most other problems but not this .
Any ideas anyone?
Thanks
John
high frequency vibration on the brake pedal
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johntheshop
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Known causes for the Xantia brake pedal pulsating :
1) Air in the hydraulics : Citaerobics. Note that "air" could be N-gas from a slowly leaking rear suspension sphere. This would be indicated if Citaerobics cures the problem first off - then re-appears a couple of days later. the sphere can leak for months before it actually goes flat.
2) Weak spring device between pedal and brake valve. This device was incorporated on Xantia models to make the hydraulic Citroen brakes feel like a "normal" car.
3) Flat accumulator sphere.
4) Defective brake valve.
1) Air in the hydraulics : Citaerobics. Note that "air" could be N-gas from a slowly leaking rear suspension sphere. This would be indicated if Citaerobics cures the problem first off - then re-appears a couple of days later. the sphere can leak for months before it actually goes flat.
2) Weak spring device between pedal and brake valve. This device was incorporated on Xantia models to make the hydraulic Citroen brakes feel like a "normal" car.
3) Flat accumulator sphere.
4) Defective brake valve.
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Dave Burns
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Had this on my car on leaving the testing station last time round, tester had given the pedal a hell of a pounding during test, it lasted for a couple of weeks or so in which time I had got a new valve ready to shove in, but it stopped doing it so the valve is not going in yet, no point until a permenant fault occurs with it.
Anders, this vibrating is not the usual pulsing that is so common with cits, imagine putting your foot on an electric shaver while its switched on, that sort of vibration.
Dave
Anders, this vibrating is not the usual pulsing that is so common with cits, imagine putting your foot on an electric shaver while its switched on, that sort of vibration.
Dave
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johntheshop
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Dave,
Good discription. It feels like your foot is on an electric shaver. No sound just vibration. It just lasts a second and doesn't seem to affect the braking of the car. It is annoying, plus as it is the missus car it would be good to know if this will develop (quickly or slowly to a failure. As you have experienced the same it must be a common fault and probably hydraulic related rather than mechanical i.e not pads vibrating or bedding in. When I go home tonight I will try the brake when stationary to see if it still vibrates or just when it is on the move. if it is when stationary it must be hydraulic. Maybe the accumilator wasn't bled properly when it was put in and some air is in the system. However that doesn't explain your why your vibration occured after MOT and then went away. Hope mine goes away!
Thanks for all of the responces so far.
John
Good discription. It feels like your foot is on an electric shaver. No sound just vibration. It just lasts a second and doesn't seem to affect the braking of the car. It is annoying, plus as it is the missus car it would be good to know if this will develop (quickly or slowly to a failure. As you have experienced the same it must be a common fault and probably hydraulic related rather than mechanical i.e not pads vibrating or bedding in. When I go home tonight I will try the brake when stationary to see if it still vibrates or just when it is on the move. if it is when stationary it must be hydraulic. Maybe the accumilator wasn't bled properly when it was put in and some air is in the system. However that doesn't explain your why your vibration occured after MOT and then went away. Hope mine goes away!
Thanks for all of the responces so far.
John
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Dave Burns
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John, when mine did it, it would do so whenever the brakes were applied, be it moving, stationary or even stationary with the engine off providing there was still plenty of stored pressure, that to my mind had doseur valve nailed as the source.
I found that by pressing the pedal slowly I could use it without making it vibrate most of the time, but the faster I applied the brakes the more sever the vibration would be, meaning greater amplitude rather than frequency.
Why such high force on the pedal should have caused it and why it ceased after a while is not something I can explain, that bugs me.
Anders, as John says you can't hear it, only feel it.
Dave
I found that by pressing the pedal slowly I could use it without making it vibrate most of the time, but the faster I applied the brakes the more sever the vibration would be, meaning greater amplitude rather than frequency.
Why such high force on the pedal should have caused it and why it ceased after a while is not something I can explain, that bugs me.
Anders, as John says you can't hear it, only feel it.
Dave
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johntheshop
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Guys,
Well isn't that just typical, I was just getting somewhere and its only gone and dissapeared on me. went to do some investigation tonight and the vibration is no more.
The valve seems the likely source ( or perhaps trapped gas as it has just dissapeared) so should it return I will tackle that first. Thanks for all your help it has been very helpful advise. As the vibration had gone I changed my glow plugs instead (They did need to be done honest! plus estenders does nothing for me these days!). Worked out a way to change glow plug number 4 in about 15 minutes. I am going to post it now just incase the method is of use to anyone .
Thanks again guys.
John
Well isn't that just typical, I was just getting somewhere and its only gone and dissapeared on me. went to do some investigation tonight and the vibration is no more.
The valve seems the likely source ( or perhaps trapped gas as it has just dissapeared) so should it return I will tackle that first. Thanks for all your help it has been very helpful advise. As the vibration had gone I changed my glow plugs instead (They did need to be done honest! plus estenders does nothing for me these days!). Worked out a way to change glow plug number 4 in about 15 minutes. I am going to post it now just incase the method is of use to anyone .
Thanks again guys.
John
I belive the problem may be cured by bleeding the brakes.
Over time when pads wear down - the longer caliper piston travel is automatically compensated by more fluid in the caliper cavity - fluid that is supplied from the brake lines.
Any air/gas resting at the onset of the brake lines will then over time slowly move out the caliper cavities - and it will then first have to pass thru the brake doseur valve - with a possibility to be trapped here.
Such air/gas is not vented by Citaerobics - as there is no fluid movement in the brakelines. But the Citaerobics must be done first to avoid any air/gas resting here finds its way into the brake lines.
I was puzzled by the problem of keep getting air/gas into the rear brakes circuit of my CX - untill I understood that the rear suspension in fact had quite some air/gas trapped.
That was when I had a strange feeling of the brake pedal "bouncing" at a slow rate during braking.
Believe me - but from your descriptions I now recall the same strange buzzing feel on the brake pedal from the CX.
I think I cured it by Citaerobics - and THEN did a thorough bleeding of the brakes.
Over time when pads wear down - the longer caliper piston travel is automatically compensated by more fluid in the caliper cavity - fluid that is supplied from the brake lines.
Any air/gas resting at the onset of the brake lines will then over time slowly move out the caliper cavities - and it will then first have to pass thru the brake doseur valve - with a possibility to be trapped here.
Such air/gas is not vented by Citaerobics - as there is no fluid movement in the brakelines. But the Citaerobics must be done first to avoid any air/gas resting here finds its way into the brake lines.
I was puzzled by the problem of keep getting air/gas into the rear brakes circuit of my CX - untill I understood that the rear suspension in fact had quite some air/gas trapped.
That was when I had a strange feeling of the brake pedal "bouncing" at a slow rate during braking.
Believe me - but from your descriptions I now recall the same strange buzzing feel on the brake pedal from the CX.
I think I cured it by Citaerobics - and THEN did a thorough bleeding of the brakes.
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DoubleChevron
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Hi Guys,
it's just air in the brakes. A small amount of air that is (my CX is actually doing it at the moment as I was smart enough to run the reseviour dry [:o)] ).
Just give the brakes a good bleed and it should settle down. BTW: Larger amounts of air in the front brake circuit will show as a time delay between you pressing the brake button, and the brakes actually engaging.
Should anything special be done to bleed ABS equipped cars ???
thanks
Shane.
it's just air in the brakes. A small amount of air that is (my CX is actually doing it at the moment as I was smart enough to run the reseviour dry [:o)] ).
Just give the brakes a good bleed and it should settle down. BTW: Larger amounts of air in the front brake circuit will show as a time delay between you pressing the brake button, and the brakes actually engaging.
Should anything special be done to bleed ABS equipped cars ???
thanks
Shane.
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ghostrider
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I think Anders is probably right, I certainly had it with several of my Cxs and nearly always there was a sphere going flat, my current Xantia does it some times but you need a really light touch on the pedal to make it happen, Bxs much the same, it never seems to affect the braking, so I have to say I've largely ignored it until I've needed to bleed the brakes or change a sphere, which seems to cure it
Pete
Pete
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Dave Burns
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Well I don't agree with the air theory, for several reasons, 1, this came on suddenly as I said during the mot test, on the drive to the testing station the brakes (and rest of the car) were fine with no such vibrating or whatever.
When I got in the car to drive back home the pedal was vibrating on its first application straight after the test on their forcourt, so where did the air suddenly come from if that was the cause, 2, my cars are maintained by myself to a high standard as far as servicing and its mechanincal systems go (not quite so concerned with the cosmetics), the hydraulic system gets particular attention and becuse it does can say that there was no air present, no braking delay and no other symtoms associated with air in any part of the hydraulic system.
3, this vibrating eventually ceased as suddenly as it started, yet no air has been manually removed by me nor had it been attempted, since I was of the opinion that it was not the cause, so again if it was air in the brakes causing the pedal to vibrate, how did it get out without the brakes having to be bled.
As said before, this came about by fierce application of the brakes during the mot test, maybe causing components of the valve to operate beyond their normal operating position, perhaps encountering less clean or previously unwiped (by the seals) surfaces that may affect the sealing efficiency of the seals, which at high mileages will have some wear on them anyway.
But whatever it was I don't buy the air theory, all to easy to put the hydraulic systems foibles down to air getting in (when in a properly maintained and healthy car it can't get in anyway) thats too convenient a reason for me in this case given my particular set of circumstances.
And yes I know the spheres have diaphragms that are pourous to nitrogen, but these minute quantities will be vented during everyday use of the car.
Dave
When I got in the car to drive back home the pedal was vibrating on its first application straight after the test on their forcourt, so where did the air suddenly come from if that was the cause, 2, my cars are maintained by myself to a high standard as far as servicing and its mechanincal systems go (not quite so concerned with the cosmetics), the hydraulic system gets particular attention and becuse it does can say that there was no air present, no braking delay and no other symtoms associated with air in any part of the hydraulic system.
3, this vibrating eventually ceased as suddenly as it started, yet no air has been manually removed by me nor had it been attempted, since I was of the opinion that it was not the cause, so again if it was air in the brakes causing the pedal to vibrate, how did it get out without the brakes having to be bled.
As said before, this came about by fierce application of the brakes during the mot test, maybe causing components of the valve to operate beyond their normal operating position, perhaps encountering less clean or previously unwiped (by the seals) surfaces that may affect the sealing efficiency of the seals, which at high mileages will have some wear on them anyway.
But whatever it was I don't buy the air theory, all to easy to put the hydraulic systems foibles down to air getting in (when in a properly maintained and healthy car it can't get in anyway) thats too convenient a reason for me in this case given my particular set of circumstances.
And yes I know the spheres have diaphragms that are pourous to nitrogen, but these minute quantities will be vented during everyday use of the car.
Dave
Ok Dave -
So much for air then [:)]
I take it you deam the same route for any N-gas.
The hydraulic Citroen brake pedal (compensator or doseur) valve has an internal mechanical stop - which prevents the pistons & springs being compressed beyond working limits. You never reach this limit during normal braking with a functional system - as you then would be in very uncomfortable contact with the windscreen.
If this mechanical limit was not built in - the weak springs between the pistons would instantly crumble - and misplace the pistons on pedal release.
But during testing with car at standstill the mechanical limit will always be reached by hard footpressure.
The brake valve does not contain any seals working off the system pressure - only for sealing against leaks to the outside world.
The exception to this rule is the rear brakes circuit in the valve - which has a tephlone/rubber seal combination - very similar to the BX front struts inner cylinder seal.
This seal is used for the piston responsible for the hysteresis in the rear brakes pressure at onset of braking - to make the rear brakes start braking a fraction more powerfull at onset of braking - causing the rear to dip a bit for equalising the brake forces over the car body.
If this seal starts leaking - you have the "famous" 1.generation suspension rearsink problem - draining the rear suspension.
But the piston working on this seal can never be displaced any more than usaul - because of the mechanical endstop in the valve - and the weak springs between pistons pushing against this rear brake piston at the end of the row of pistons & springs.
It should be noted that any LHM under pressure used by the brakes always means a flow thru the brake valve - in amounts according to the cavity filled in the calipers for the pistons to move.
Even the smallest amount of air/N-gas in the brake valve would cause the pistons to oscillate - at any rate according to the physical properties and the actual amount & location of this air inside the valve.
It's a known problem from industrial hydraulics systems with regulating valves ....
A drawing is always better than loads of text/words.
Unfortunately this drawing is shown upside down on the website it's found.
The pedal end of the valve is at LHS on drawing :
http://citroeny.cz/servis/xmser/brzdovy_valec.gif
So much for air then [:)]
I take it you deam the same route for any N-gas.
The hydraulic Citroen brake pedal (compensator or doseur) valve has an internal mechanical stop - which prevents the pistons & springs being compressed beyond working limits. You never reach this limit during normal braking with a functional system - as you then would be in very uncomfortable contact with the windscreen.
If this mechanical limit was not built in - the weak springs between the pistons would instantly crumble - and misplace the pistons on pedal release.
But during testing with car at standstill the mechanical limit will always be reached by hard footpressure.
The brake valve does not contain any seals working off the system pressure - only for sealing against leaks to the outside world.
The exception to this rule is the rear brakes circuit in the valve - which has a tephlone/rubber seal combination - very similar to the BX front struts inner cylinder seal.
This seal is used for the piston responsible for the hysteresis in the rear brakes pressure at onset of braking - to make the rear brakes start braking a fraction more powerfull at onset of braking - causing the rear to dip a bit for equalising the brake forces over the car body.
If this seal starts leaking - you have the "famous" 1.generation suspension rearsink problem - draining the rear suspension.
But the piston working on this seal can never be displaced any more than usaul - because of the mechanical endstop in the valve - and the weak springs between pistons pushing against this rear brake piston at the end of the row of pistons & springs.
It should be noted that any LHM under pressure used by the brakes always means a flow thru the brake valve - in amounts according to the cavity filled in the calipers for the pistons to move.
Even the smallest amount of air/N-gas in the brake valve would cause the pistons to oscillate - at any rate according to the physical properties and the actual amount & location of this air inside the valve.
It's a known problem from industrial hydraulics systems with regulating valves ....
A drawing is always better than loads of text/words.
Unfortunately this drawing is shown upside down on the website it's found.
The pedal end of the valve is at LHS on drawing :
http://citroeny.cz/servis/xmser/brzdovy_valec.gif
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Dave Burns
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- x 2
Anders, I bow to your superior knowledge, Large slice of humble pie to go please[:I]
Thanks for posting the doseur valve drawing, much clearer than the one I've been gorping at, I've studied it intensly and have come to the conclusion that you are right, I can't see a reason for it other than gas getting in, I can see several areas of the valve where gas might produce this exact result.
Of course any gas escaping from the rear sphere's and the anti sink sphere is very likely to make the brake valve its first port of call, I totaly overlooked this fact. I was thinking more in terms of the front brakes, regular citaerobics is a must, not just at times of service.
Looking at how the valve works with regard to the pressure reduction feature for the rear brakes, you simply have to admire how thoughtful the designers were, allowing the rear brakes to work at such initial high pressure, then to instantly reduce it to a safe level when the vehicles mass is transfered forwards and away from the rear suspension during heavy braking.
Dave
Thanks for posting the doseur valve drawing, much clearer than the one I've been gorping at, I've studied it intensly and have come to the conclusion that you are right, I can't see a reason for it other than gas getting in, I can see several areas of the valve where gas might produce this exact result.
Of course any gas escaping from the rear sphere's and the anti sink sphere is very likely to make the brake valve its first port of call, I totaly overlooked this fact. I was thinking more in terms of the front brakes, regular citaerobics is a must, not just at times of service.
Looking at how the valve works with regard to the pressure reduction feature for the rear brakes, you simply have to admire how thoughtful the designers were, allowing the rear brakes to work at such initial high pressure, then to instantly reduce it to a safe level when the vehicles mass is transfered forwards and away from the rear suspension during heavy braking.
Dave