pulsing brake pedal

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higgy
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pulsing brake pedal

Postby higgy » Tue Apr 23, 2002 3:34 am

the car is a 94 xantia td when the car has warmed up there is a pulsing sensation through the brake pedal when pressed hard.this gets worse the more the brakes are used.There are no problems with the suspension or power steering.this problem occurs when the car is stationary so it is not warped discs. any help please
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Dave Burns
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Postby Dave Burns » Tue Apr 23, 2002 4:28 am

More than likely a flat accumulator sphere, you could be feeling the output pulses from the pump, often refered to as hydraulic hammering.
Is the regulator cutting in and out at a high rate, clicking sound.
A well worn brake doseur valve might also produce similar symptoms.
Dave
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nick
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Postby nick » Wed Apr 24, 2002 12:54 am

This seems to be quite a common problem on Xantias, and main dealers apparently often tell people its not a fault and nothing can be done about it !!
However, mine did this when I first bought the car and replacing the accumulator sphere seemed to cure it, as Dave has suggested.
regards,
Nick
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higgy
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Postby higgy » Wed Apr 24, 2002 10:43 pm

Thanks for the help I will try a new accumulator sphere at the weekend
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higgy
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Postby higgy » Sun Jun 02, 2002 2:57 am

I have eventually got round to changing the accumulator shpere this weekend. It's made no difference to the pulsing problem with the brake pedal, anybody got any ideas?
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nick
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Postby nick » Sun Jun 02, 2002 3:57 am

I can't exactly remember what the timescale was with my Xantia between the spheres being replaced and the pedal pulsing stopping!, it may not have been immediate, so it may not actually have been the cause.
However, replacing spheres is the only hydraulic work I have ever had to do on my car and I know it had the fault before the sphere change, but it doesnt have it now. (nearly two years later) It could have been pure coincidence and it stopped on its own.
I have also heard of the brake doseur valve being blamed for this problem, so that would certainly be worth investigating if it persists.
Nick
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Dave Burns
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Postby Dave Burns » Sun Jun 02, 2002 3:44 pm

With the new sphere you can more or less be sure the high pressure delivery is constant.
A 94 model might have a seperate power steering circuit or a flow distributor, look at the pump, if there are two steel pipes coming from it the steering is seperate from the rest of the system.
Now there is a new accumulator sphere fitted, at what frequency (how often) is the regulator ticking, assuming the regulator is ok, a high cut in rate with a new sphere would suggest rapid pressure loss due to internal leakage.
You could disconnect the return pipes from the various components at the reservoir, look for pulsing in any of these, with and without the brakes applied.

At what sort of frequency does the pulsing occur, is it always the same or does it increase or decrease, especialy with engine speed.
Whats the condition of the LHM (is it still green) and filters.
From the suspensions lowest position to normal at tickover, how long does it take.
Does your car have anti lock brakes, I noticed a pulsing at times on car's that I test drove that had anti lock.
looks like we are looking for a worn component somewhere in the hydraulic system, the more info you can supply the better.
Dave
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alan s
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Postby alan s » Sun Jun 02, 2002 5:20 pm

Don't want to sound like the villiage idiot here, <img src=icon_smile_clown.gif border=0 align=middle>but does the car have ABS by any chance? And if so, is the ABS system working correctly or alternatively is there one wheel wanting to lock up?<img src=icon_smile_blackeye.gif border=0 align=middle>
Alan S
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higgy
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Postby higgy » Tue Jun 04, 2002 3:18 pm

Thanks for the replys,I'll have to investigate further. The car doesn't have ABS so that rules that out as the cause. Can anyone tell me which return pipes are which?
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higgy
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Postby higgy » Sun Jul 07, 2002 2:01 am

Finally solved it. A blockage in the regulator, have now filled the system with flush and all seems fine.
Thanks everybody for your suggestions.
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