bleeding brakes xantia

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Mandrake
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Re: bleeding brakes xantia

Post by Mandrake »

Gregg1100 wrote:Hello All,
Can I ask why one would want to return aerated LHM to the tank. You wouldn`t do that with normal hydraulic systems--you wouldn`t get the system bled properly. When I get to have to do my Xantia brake bleed, the old LHM will be discarded. May cost a bit more, but no air or crud left in the system.
Greg
There is no harm in pouring "aerated" LHM back into the resoviour tank (as long as it is clean) - one of the jobs of the resoviour tank is to allow "air" to escape into the atmosphere as it bubbles out of spheres gradually etc. (This is what makes the suspension a self bleeding system....)

The pump takes its input from near the bottom of the tank _inside_ one of the filter towers and any air bubbles in the main tank area where you pour oil in can't pass through the very fine filter guaze due to the surface tension of the air bubbles.

Anyway if you're concerned about it (and I wouldn't be) why not let the collected "aerated" LHM stand in a jar for a few minutes to allow the bubbles to escape before pouring it back in ? :)

If by "normal hydraulic systems" you mean alcohol based brake systems in other cars, a reason why you might not reintroduce "aerated" fluid in that case is because brake fluid is hygroscopic and will absorb any moisture that happened to be in the air. (LHM does not)

Regards,
Simon
Last edited by Mandrake on 18 May 2006, 20:59, edited 1 time in total.
Simon

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Re: Mark 2 xantia pulsing breaks

Post by Mandrake »

jgra1 wrote:but the car still feels the same :( and now it tends stay down at the back.. if you put it on high and then on normal it lowers to correct height, but doesnt come up from down? - i can live with this..
This is nothing to do with air in the brake lines... its something to do with the movement of the height corrector linkage at the rear, as I think was discussed in another thread. Most likely the linkage is a bit corroded and slightly seized.
so, the main symptons, :

the brakes still feel odd, the pedal pulses, the brake control valve hisses as it pressurises and depressurises, the front dives a lot, there is a small chance the hydraulic pump may have a leak but I need to confirm this..
The brake control valve hissing (more of a slurping noise) when you release it after pressing it hard is normal. Pedal pulsing is not normal though.

First of all you want to confirm that its not being caused by a misbehaving ABS system - simply find and unplug the ABS computer fuse and go for a drive and see if it still pulses the pedal. (If you got the right fuse the ABS warning light should be on continously on the dash)

If it no longer pulses you know you have an ABS problem like an intermitant sensor wire - I had a problem with the front right sensor on mine which made the brakes behave strangely at low speeds around 10Km/hr - sometimes pulsing/chattering the brake pedal when pulling up to a stop.

Occasionally the ABS warning light would come on while driving too. After I fixed it I havn't had any more occurances of the chattering brake pedal at low speeds.

If you still get the pedal pulsing, you know the ABS is not to blame, so put the fuse back in.

One thing that you could try which worked for someone else (see near the bottom of the thread "terrible xantia brakes" which talked about the pedal spring) was to simply run the car until pressurized, turn off the engine, and sit there fully depressing and releasing the brake pedal until all the stored pressure is used up. (This can take a LOT of depressions, approx 50, you know when the pressure is gone when the pedal starts to go limp)

We still don't understand how this worked, but we suspect he had an air bubble trapped in the brake control valve itself which was difficult to dislodge.

As for the nose dive - are you sure its the front diving, or is it the rear lifting ? If its the rear lifting it means the rear brakes are not biting as well as they should (pad/disc surfaces, or pistons that need freeing) while if the front dives excessively it could mean the FRONT brakes are not biting as well as they should.
Could it be the pump isnt outputting enough, Shall i take it off and renew seals?

Could it be the brake control valve?

there seems to be no air in system,

the accumulator is new
Well if you didnt find any air in the system at all, the seals in the pump are probably ok. If they weren't it would be allowing air into the system, (for seals on the suction side) or causing an obvious oil leak. (For seals on the pressure output side)

Regards,
Simon
Simon

1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White

2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
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Post by jgra1 »

Simon, and all, thanks..

No ABS on this car.

Sorry I shouldn't have mentioned the rear not rising as I can fix that seperately and its not really part of discussion.

I can confirm there is something wrong with the brake as both of my other xantias dont pulse/dive etc

The front dives.. Cant say whether back rises at time of writing. (I am not overly worried about this tho, the suspension is VERY soft and supple and it may just be that the other cars are firmer and wont allow this effect)

The slurping noise happens when you leave your foot on the pedal and keep it there - what ever causes this loss (and increase) of pressure and noise is 100% what causing the brakes to pulse (it is the same thing so to speak)
The brakes are very strong, passed they're test recently. Very happy that the car slows down quickly. its just that all the pressure acts and slows car down, then the pressure drops slightly, you press pedal harder, it builds and (sometimes) locks the wheel, this repeats..

I dont believe the idiot spring can cause this, honestly....
will try the de-pressure method you mentioned.
John
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Post by jgra1 »

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Post by Mandrake »

Try bleeding the pressure with the brake pedal first, (it's just an off chance that it might do some good) and failing that try removing the spring... its an easy mod if you have a suitable size of tubing handy, and easy to undo if you don't like the result.

Most people who have tried it notice an improved ability to finely control and modulate the braking with the spring removed. (Although it can sometimes take a bit of getting used to for those that didn't grow up with DS/GS/CX/BX brakes)

Regards,
Simon
Simon

1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White

2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
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Post by DaveW »

There are 'how to' pics here for removing the spring from the connector.

http://www.aussiefrogs.com/forum/showth ... tia+brakes

Dave.
Xantia Forte 1.8i, 16v X reg.(09/2000) 93K, aircon
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