Hi
I have a 1994 Xantia 2.0 SX
When driving along or when stationary the brake pedal pulses which in turn causes the car to judder when appying the brake gently, sometimes the ABS light will come on too.
The pump is always kicking in and out.
I have undone the 12mm bleed screw 1/4 turn to see if I get a squeel from the regulator but nothing happens!(I thought there may be an air lock) I am thinking there is lack of pressure?
The car is also very quick to do down to the low position when I swicth off and it's taking more time than usual to rise to normal ride height.
Any help at all with this would be great.
I wait in hope!!!
Xantia brake pedal pulsing
Moderator: RichardW
If the pump/regulator is constantly ticking in/out with short time intervals (less than 30 seconds), your accumulator (or central/system) sphere may be flat. It's fairly easy to replace as DIY, provided you have a high quality & heavy duty tool, preferably the sling type tool resembling a large oil-filter removal tool. The accumulator sphere should not cost you more than some £20. (Click the HOME link this site, then click online shop, and search for accumulator sphere for Citroen)
A sphere's life is time dependent, not mileage dependent, since the internal rubber membrane allows the N-gas to diffuse out over time, independent of usage.
Thus if you do'nt have any records of this sphere replaced the last 5 y's or so, it's most likely flat.
BTW : The bleed screw on the regultaor is NOT an air-bleed screw, but a pressure release screw. The hydraulic system (except brakes) bleeds air automatically through return lines to the reservoir. This is necessary because of the above explained diffusing of N-gas, which have to bled out somewhere from the system.
I do'nt think it's your ABS system that makes your brake pedal pulse. It's more likely that the flat accumulator sphere causes the pump/regulator work overtime, when you need to brake, thus giving a pulsating pressure.
The ABS system is truly independent of the hydraulic system, only having valves that BLOCKS your brake pressure, if the ABS sensors senses a wheel blockage during braking. These valves are designed to ALLWAYS give you full available brake pressure, should the ABS system itself fail, thus revealing standard old-fashion non-ABS brakes.
You may simply consider the ABS system as an independent add-on gadget to the brake system.
The intermittent ABS warning light may be an indication of a bad/intermittent connection somewhere in the system (most likely a wheel sensor/cabling/connector), which is provoked by the pulsing/juddering brake action giving vibrations in the whole car body.
Either the problem :
Correct the problem(s) ASAP, any strange brake acting is ALLWAYS utterly unsafe [:0]
A sphere's life is time dependent, not mileage dependent, since the internal rubber membrane allows the N-gas to diffuse out over time, independent of usage.
Thus if you do'nt have any records of this sphere replaced the last 5 y's or so, it's most likely flat.
BTW : The bleed screw on the regultaor is NOT an air-bleed screw, but a pressure release screw. The hydraulic system (except brakes) bleeds air automatically through return lines to the reservoir. This is necessary because of the above explained diffusing of N-gas, which have to bled out somewhere from the system.
I do'nt think it's your ABS system that makes your brake pedal pulse. It's more likely that the flat accumulator sphere causes the pump/regulator work overtime, when you need to brake, thus giving a pulsating pressure.
The ABS system is truly independent of the hydraulic system, only having valves that BLOCKS your brake pressure, if the ABS sensors senses a wheel blockage during braking. These valves are designed to ALLWAYS give you full available brake pressure, should the ABS system itself fail, thus revealing standard old-fashion non-ABS brakes.
You may simply consider the ABS system as an independent add-on gadget to the brake system.
The intermittent ABS warning light may be an indication of a bad/intermittent connection somewhere in the system (most likely a wheel sensor/cabling/connector), which is provoked by the pulsing/juddering brake action giving vibrations in the whole car body.
Either the problem :
Correct the problem(s) ASAP, any strange brake acting is ALLWAYS utterly unsafe [:0]
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
Anders, its the electronics that decide when the valves should be opened obviously, so when a certain and probably before unseen fault occurs causing the valves to open when they should be closed, hey presto no brakes.
Amble over to the bba reman forum where this type of failure has recently occured to a Peugeot 406, this situation was serious enough to get a reply from Peugeot wanting to know what happened.
Dave
Amble over to the bba reman forum where this type of failure has recently occured to a Peugeot 406, this situation was serious enough to get a reply from Peugeot wanting to know what happened.
Dave
Dave -
1) IIRC the ABS valves - on idle ABS - simply leaves the valves in the "normal" brakes state, i.e. any pressure commanded TO the brakes (by the driver activating the pedal) is left through untouched.
This I consider an "open" (idle) ABS valve.
2) When the ABS system senses a wheel blockage, that wheel's (or axle) brake pressure is "blocked", by closing off further pressure to the wheel's (or axle's) brake.
I'm fully aware ther's more to it, since the ABS valve must of course - at the same time - RELEASE the given present brake pressure to that blocked wheel (or axle), releasing the wheel to allow it turn again.
This I consider a "closed" (active) ABS valve.
3) If the ABS system fails (gross failure) in terms of power-loss, broken wires, erratic wheel sensors, the ABS valves are left in the "open" state, resembling a standard non-ABS system.
Are these my simplified terms wrongly interpreted related to given standard of terms in the auto branch [?][?][:I][:I][:o)][:o)]
[?][?][?] You're reporting an erratic ABS-ECU which suddenly by itself - no matter the given wheel rotation - decides to close (activate) the ABS valve, where any brakes pressure is blocked off [?][?][?]
This would be the "HAL2000 syndrome", not considering sensible human needs, which of course is fatal [:0][xx(]
I consider such a system failure, a fatal design void to any given computer/electronics safety design rule, including the CE safety regulations & proofings.
It seems we now also have to consider HAL2000 problems on cars, given the ever increasing use of computing devices in cars [:(!]
This extends stress on faulttracing, since we're used to deal with car electronics in terms as being either "functional" or "dead". A new term must then be considered in electronics as being erratic "thinking".
1) IIRC the ABS valves - on idle ABS - simply leaves the valves in the "normal" brakes state, i.e. any pressure commanded TO the brakes (by the driver activating the pedal) is left through untouched.
This I consider an "open" (idle) ABS valve.
2) When the ABS system senses a wheel blockage, that wheel's (or axle) brake pressure is "blocked", by closing off further pressure to the wheel's (or axle's) brake.
I'm fully aware ther's more to it, since the ABS valve must of course - at the same time - RELEASE the given present brake pressure to that blocked wheel (or axle), releasing the wheel to allow it turn again.
This I consider a "closed" (active) ABS valve.
3) If the ABS system fails (gross failure) in terms of power-loss, broken wires, erratic wheel sensors, the ABS valves are left in the "open" state, resembling a standard non-ABS system.
Are these my simplified terms wrongly interpreted related to given standard of terms in the auto branch [?][?][:I][:I][:o)][:o)]
[?][?][?] You're reporting an erratic ABS-ECU which suddenly by itself - no matter the given wheel rotation - decides to close (activate) the ABS valve, where any brakes pressure is blocked off [?][?][?]
This would be the "HAL2000 syndrome", not considering sensible human needs, which of course is fatal [:0][xx(]
I consider such a system failure, a fatal design void to any given computer/electronics safety design rule, including the CE safety regulations & proofings.
It seems we now also have to consider HAL2000 problems on cars, given the ever increasing use of computing devices in cars [:(!]
This extends stress on faulttracing, since we're used to deal with car electronics in terms as being either "functional" or "dead". A new term must then be considered in electronics as being erratic "thinking".
-
Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
Anders you say in your earlier post,
"These valves are designed to ALLWAYS give you full available brake pressure, should the ABS system itself fail, thus revealing standard old-fashion non-ABS brakes"
This quite clearly is not necessarily the case as per the 406 on the bba reman site, that system failed for whatever reason which lead to no brakes at all.
It doesn't matter what causes it or what component fails even if it is the ECU, after all it is the brain of the entire ABS system, failure is failure, where so ever and how so ever it comes about.
Returning to the original post then it may not be wise to totaly discount any abnormal behaviour of the ABS, I'm sure if a certain fault in the system can cause total failure, its likely that other as yet unknown faults could cause other unwanted anomolies.
Keep an open mind, humans are not perfect by a long chalk and niether are the things that they make.
Dave
"These valves are designed to ALLWAYS give you full available brake pressure, should the ABS system itself fail, thus revealing standard old-fashion non-ABS brakes"
This quite clearly is not necessarily the case as per the 406 on the bba reman site, that system failed for whatever reason which lead to no brakes at all.
It doesn't matter what causes it or what component fails even if it is the ECU, after all it is the brain of the entire ABS system, failure is failure, where so ever and how so ever it comes about.
Returning to the original post then it may not be wise to totaly discount any abnormal behaviour of the ABS, I'm sure if a certain fault in the system can cause total failure, its likely that other as yet unknown faults could cause other unwanted anomolies.
Keep an open mind, humans are not perfect by a long chalk and niether are the things that they make.
Dave
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
A bloke on here a good while back had this now I recall, he said there was dirt in the regulator, can only think it would be fowling the non return ball valve.
You might try Jeremy's re-seating trick by giving the ball a sharp tap with a brass drift.
Drift needs to be 5mm dia. but it may be wise to use a new ball since its being smacked into something alot harder than brass.
http://www.andyspares.com/discussionfor ... PIC_ID=717
Dave
You might try Jeremy's re-seating trick by giving the ball a sharp tap with a brass drift.
Drift needs to be 5mm dia. but it may be wise to use a new ball since its being smacked into something alot harder than brass.
http://www.andyspares.com/discussionfor ... PIC_ID=717
Dave
The re-seating trick worked for me on my BX TD and the cycling time has gone up from 9 secs to something not worth measuring.
It may be helpful to look at the relative pressures here. as far as I know what I say is the same for xantias and BX but your steering may be different if you have the two-outlet pump which separates the steering from the brakes and suspension.
The brakes and suspension are fed from the regulator via the 'safety' valve. This valve provides pressurised LHM for the front brakes and then for the suspension. This is quite definite and the valve only opens to feed the suspension when the light goes out and there is enough pressure for the front brakes. This again is definite as the valve itself operates the light, not a separate pressure switch.
For a long time I experienced the joys of the pressure warning light coming on while driving, particularily when coldish. It was also difficult to get the car to rise but there was no real sign that anything was wrong and once raised the car seemed perfectly alright and the power steering always worked perfectly. After many false starts I found the problem - There is a pressure relief ball valve in the power steering splitter which is controlled by a spring and sits under a plunder. Someone had assembled the valve with the ball and the plunger in the wrong order rendering it almost useless for its intended purpose.
The reason I mention this is that I was driving a car with severely reduced pressure but nothing was apparently wrong and the brakes functioned perfectly. What was happening was that when the pressure dropped the suspension stayed in about the right place due to the height corrector valve having shut and there was sufficient pressure remaining in the accumulator to operate the brakes (even on 9 sec cycling)
Incidentally this car has ABS that works.
From what you are saying the pressure light is not coming on which would suggest that there is adequate pressure. What is strange is the ABS light coming on and goes off again as these things normally need to be reset by turning off the supply once the light has illuminated. The light is only supposed to be a fault indicator and not intended to work when the unit is functioning.
There is another thread running concerning Xantia brakes and he found the problem was air getting into the pump. Have you looked in the reservoir with the engine running to see if there is any air there?
A test of the ABS could be made by withdrawing the operating fuse and seeing if there is any difference in braking performance.
If you have a power steering splitter a test of its function can be made by turning the steering wheel after starting and seeing if the car rises quicker. The steering normally dumps its oil supply when idle and it stops doing this when the valve is closed by turning the wheel, causing the pressure in the system to rise. some of this will find its way into the rest of the system - causing the car to rise quicker.
let us know how you get along.
jeremy
It may be helpful to look at the relative pressures here. as far as I know what I say is the same for xantias and BX but your steering may be different if you have the two-outlet pump which separates the steering from the brakes and suspension.
The brakes and suspension are fed from the regulator via the 'safety' valve. This valve provides pressurised LHM for the front brakes and then for the suspension. This is quite definite and the valve only opens to feed the suspension when the light goes out and there is enough pressure for the front brakes. This again is definite as the valve itself operates the light, not a separate pressure switch.
For a long time I experienced the joys of the pressure warning light coming on while driving, particularily when coldish. It was also difficult to get the car to rise but there was no real sign that anything was wrong and once raised the car seemed perfectly alright and the power steering always worked perfectly. After many false starts I found the problem - There is a pressure relief ball valve in the power steering splitter which is controlled by a spring and sits under a plunder. Someone had assembled the valve with the ball and the plunger in the wrong order rendering it almost useless for its intended purpose.
The reason I mention this is that I was driving a car with severely reduced pressure but nothing was apparently wrong and the brakes functioned perfectly. What was happening was that when the pressure dropped the suspension stayed in about the right place due to the height corrector valve having shut and there was sufficient pressure remaining in the accumulator to operate the brakes (even on 9 sec cycling)
Incidentally this car has ABS that works.
From what you are saying the pressure light is not coming on which would suggest that there is adequate pressure. What is strange is the ABS light coming on and goes off again as these things normally need to be reset by turning off the supply once the light has illuminated. The light is only supposed to be a fault indicator and not intended to work when the unit is functioning.
There is another thread running concerning Xantia brakes and he found the problem was air getting into the pump. Have you looked in the reservoir with the engine running to see if there is any air there?
A test of the ABS could be made by withdrawing the operating fuse and seeing if there is any difference in braking performance.
If you have a power steering splitter a test of its function can be made by turning the steering wheel after starting and seeing if the car rises quicker. The steering normally dumps its oil supply when idle and it stops doing this when the valve is closed by turning the wheel, causing the pressure in the system to rise. some of this will find its way into the rest of the system - causing the car to rise quicker.
let us know how you get along.
jeremy
Hello again chaps,
Just to clarify your points, this ball is something that I will find under the regulator inside the cover held on with allen bolts? and the saftey valve is above the regulator?
I also noticed today that the car has had a height corrector fitted at some time on the rear (before I bought it)I think this because it's shiny. Whold this mean anything?
Sorry for all the questions, I'm going to get stuck in tomorrow to try and sort this out.
Thanks,
Mark
Just to clarify your points, this ball is something that I will find under the regulator inside the cover held on with allen bolts? and the saftey valve is above the regulator?
I also noticed today that the car has had a height corrector fitted at some time on the rear (before I bought it)I think this because it's shiny. Whold this mean anything?
Sorry for all the questions, I'm going to get stuck in tomorrow to try and sort this out.
Thanks,
Mark
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
The ball in the regulator is got at by removing the sphere, then the small plate retaining the ball, one 8mm hex head bolt IIRC.
Safety valve or security valve (same thing) is bolted to the rear of the front subframe above steering rack, don't think you will have any prob's with that, I can't see a way for it to cause pulsing of any kind, its either forced open with pressure or stays closed if there isn't enough pressure and if its closed the warning light will be on.
Is it an early FDV model or 6+2 later (twin output pump) anti sink model.
Dave
Safety valve or security valve (same thing) is bolted to the rear of the front subframe above steering rack, don't think you will have any prob's with that, I can't see a way for it to cause pulsing of any kind, its either forced open with pressure or stays closed if there isn't enough pressure and if its closed the warning light will be on.
Is it an early FDV model or 6+2 later (twin output pump) anti sink model.
Dave
Had an intersting conversation with a knowledgeable and able machanic yesterday over a pint of beer. He's not particularily knowledgeable on Citroen hydraulics but has a problem with a Xantia and ABS brakes. His car is 1994 or so and he says has an electric pump on the ABS system with the ECU sitting on top of it. His problem is that the ABS has failed and the dealer says that the ECU is at fault. I expressed surprise at the presence of the electric pump but my knowledge of these things is confined to BX's.
Is an electric pump fitted to some?
Jeremy
Is an electric pump fitted to some?
Jeremy
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blueboy2001
- Posts: 423
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- Location:
- My Cars:
I'd imagine he's reffering to the ABS valve block which is electrically operated - the ABS ECU sits on top of it (or on the front, depends which way you look at it) and the two connect together via pins on the back of the ABS ECU. Since the LHM is supplied to the valve block under pressure, a pump is not required.
I think he's confused you a little using the term pump to describe the valve block.
I think he's confused you a little using the term pump to describe the valve block.