Brake pedal pulsing

ohms · Post by **ohms** » Sun Oct 28, 2007 6:08 pm

Hello chaps, once again trying to sort out the little idiosyncracies of this bloody xantia and would like your opinions.

The brake pedal seems to pulse and squish when pressing hard, this makes for difficult breaking, which isn't very progressive.

Now I've had a poke around at the pedal and the setup seems to be the same as the BX, albeit with what appears to be somesort of springloaded contraption off the back off the pedal contacting the doseur valve. I think it's this that is giving me problems. Why did Citroen bother to change the excellent setup on the BX?

Anyway, how can i get rid of this thing and just have a solid brake pedal feel a la BX?

Thanks chaps

Post by **docchevron** » Sun Oct 28, 2007 6:27 pm

Does the car have ABS?

Cit stuck the poxy plunger on the pedal to give it a longer travel and make it feel more "normal" to drive..
Easy enough to remove and weld a piece of bar in. I know several people that have because the standard setup is, as you have discovered, utter rubbish.

ohms · Post by **ohms** » Sun Oct 28, 2007 7:28 pm

Hi Doc,

yes the car does have ABS, but the pulsing is definitely from that bloody plunger. Haven't had chance to investiagte removing it as yet, but did have a feel around that area. How is it fixed to the pedal, can't feel any nuts or bolts for removal.

thanks

Post by **docchevron** » Sun Oct 28, 2007 7:46 pm

I have no idea at all mate! I think it's a single assembly thats welded to the pedal?
The last one I modded (which was quite some time ago) I just ripped the plunger out with a very large set of mole grips and welded a piece of steel bar straight to the pedal.

jeremy · Post by **jeremy** » Sun Oct 28, 2007 7:53 pm

Is the accumulator flat? Xantias after about 1996 have a twin outlet pump with 6 plungers serving the steering and 2 the suspension and brakes.

To test the accumulator get the car to normal height and let it settle for a couple of minutes. Turn off the engine and sit in the boot. Car should drop a long way and then rise again after about 30 seconds - powered by the accumulator - just like it does with the engine running.

It may be your accumulator is flat and you are feeling the pump pulses. A BX has a single outlet 6 chamber pump.

MULLEY · Post by **MULLEY** » Sun Oct 28, 2007 8:05 pm

You dont mention how fast you are travelling when the pedal is pulsing?? If it pulses as you are travelling slowly i.e. less than 30mph its probably a shagged abs ring on the driveshaft, i had that on a clio one time.

ohms · Post by **ohms** » Sun Oct 28, 2007 9:14 pm

New accumulator sphere fitted and ABS is all fine, it's deffo this plunger. When you brake hard, it takes a while for the plunger to react and when it does it realeases the pressure. Not a very nice trait and doesn't instill faith in the system.

Will have a play about with it tomorrow.

Dickieg · Post by **Dickieg** » Sun Oct 28, 2007 9:21 pm

Two things here, firstly the spring under the pedal. This can be replaced with a short length of 15mm copper pipe or a stack of washers. Reach up behind the brake pedal and you will feel a cylinder, lift the pedal up and twist/lift out the cylinder, then do the above.

The pulsing/squishing or what some might call a 'buzzing' under the pedal may well be due to air being in the rear brake lines, so give them a bleed. Another common indicator of air in the rear brake lines is that the rear of the car lifts slightly when braking rather than falling slightly.

ohms · Post by **ohms** » Mon Oct 29, 2007 3:01 pm

Thanks for the help chaps, have modified the plunger arrangement on the back of the pedal now, so it contacts the dosuer button solid, much better feel, but still getting this pulsing effect.

Just to re-iterate, the car has a new accumulator sphere, is currently running hydraflush and all brakes were bled on Saturday. Tick time is fast at about 20 seconds. Have checked the reservoir and there does seem to be alot of fluid returning to the tank under normal conditions.

Suspect Doseur Valve? Can the doseur valve if leaking badly give this pulsing sensation to the brakes?

Thanks chaps

MULLEY · Post by **MULLEY** » Mon Oct 29, 2007 8:21 pm

See my reply regarding driveshaft???

ken newbold · Post by **ken newbold** » Mon Oct 29, 2007 8:58 pm

Warped brake discs.

Should a bought a BX

jeremy · Post by **jeremy** » Mon Oct 29, 2007 9:17 pm

The spring device under the pedal is apparently easy to remove - there are numerous posts on this subject on Fenchcarforum. I think it just pulls out or something. It will however need to be replaced and I wouldn't think the copper pipe used by some people would be strong enough.

AndersDK · Post by **AndersDK** » Tue Oct 30, 2007 3:06 am

The pulsing Xantia brake pedal is much the same as the rear sinking BX.
Its caused by an internal leaking brake doseur valve.

This pulsing can in rare cases also happen to a BX doseur valve - if the doseur leak is really severe (been there ...)
However the RHD Xantia brake pedal design is really weird. Why did Citroen decide that this version should have a spring fitted and not fitted to LHD versions ?
There is no doubt that if the RHD BX had this spring fitted instead of the solid plunger - the same pulsing pedal would happen on BX'es with a leaking doseur.

The doseur valve have 2 rubber/plastic return hoses leading to the reservoir. Try trace them up, then disconnect at reservoir for a flow check. There should of course ideally be no return flow at all, when brake pedal is not touched and engine idle.
Some dripping is allowable, but fast dripping or flow is a NO-GO.