xantia 1.8 i 1999 BRAKE PROBLEM

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jgra1
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xantia 1.8 i 1999 BRAKE PROBLEM

Post by jgra1 »

Folks, I have still a braking issue with my xantia.

The brakes lock on with lots of power, then the pressure drops, builds, and the process repeats. Bearable in the dry, suicidal in the wet!

I have changed front accumulator as per advice on this board. This fixed the suspension pressurising 'click' from being every 3 seconds to every 20-25.

But the brakes remain the same. The idiot spring is still there, but I am 100% this is not anything to do with this problem.

finally, tonight i depressed the brake pedal, and held it down. There was a hissing sound, which stayed for a few seconds, then, it went, came back, went etc. Seems very coincidental with the symptoms I described above?
Any thoughts?

John
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Post by Mandrake »

I know you don't want to hear this, but try doing the brake pedal spring mod, and then test it out again. It's a 10 minute job, and 100% reversable if you don't like the result.

And if it doesn't help your problem you get to say "I told you so". What more could you ask for. :lol:

Seriously though, my Dad's car had this pulsing effect with the spring in place too. Something about how the spring unit works upsets the natural feedback mechanism of the brake doseur valve - it has a "reaction piston" which uses the brake pressure to apply a force back on the drivers foot which is proportional to the brake pressure, thus giving you your proportional control and feedback.

The trouble with the spring is not so much that there is a spring there, but the way its implemented - there is also a rubber cone snubber inside the spring that provides a progressive change in the spring rate beyond a certain point, plus you have large amounts of sliding friction in the (unlubricated, non-precision) plastic shells themselves, and I think binding and breakout friction of the plastic shells is the real culprit in upsetting the proportional control.

If that is the case the brake spring mod works not so much because it eliminates the spring, but because it prevents the plastic shells from sliding over each other anymore, preventing this erratic binding friction while moving.

By the way hissing is normal when you release the brake from having pressed it hard, and because of the decoupling of the spring unit the doseur valve may in fact be moving back when the pedal is not.

Regards,
Simon
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Post by Kowalski »

This sounds like either air the brake system or a flat accumulator sphere. Accumulator spheres cost something around £20 and can be easilly fitted.

Our Mandrake hated the spring in the canister in his car, so he took it out and tends to recommend everybody else does the same ;) Personally I disagree, I don't have a problem with the spring under either of my two brake pedals so I'm leaving them alone.
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Post by Mandrake »

It's not just my car Kowalski, I've seen the mod done on two others as well, and observed the before and after characteristics, and I only did the mod in the first place after both me and my Dad (longtime Citroen drivers) were both very unimpressed by the charactersistics of the Xantia brakes, and then discovered DoubleChevron's post about it.

It wasn't a matter of finding his post first and then deciding I didn't like the brakes...I was already very unhappy with the brakes without being aware of the existance of the spring canister, and searching for information about it was what lead me to the GSF forum in the first place.

I'm glad that you don't have any problems with the brakes, but please don't assume that nobody else does... :) Let's not restart the "terrible Xantia brakes" thread, I merely point it out as a possible culprit, as it seems that people still don't fully appreciate the effects of the plastic canister...which are not as simple as it appears. (It's not "just" a spring)

I would also remind that in the original discussion about it the reaction to the mod was overwhelmingly positive with only a small percentage of "dissenters" most of whom did not even try it :wink:

By the way, if you recheck his original post you'll see he's already replaced the accumulator, so that rules out a major possible culprit.

Bleeding air from the brakes is a good suggestion though, which I forgot about in my initial response, so definately bleed the front and rear brakes thoroughly as well.

Regards,
Simon
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Post by jgra1 »

guys guys common ! :lol:

i am looking forward to removing the spring.. i remember driving a bx years ago and thinking i liked / preferred the press the button brakes much better than this ;)

but, yes acc sphere reaplced aout 4 weeks ago by me..


bleeding first..

doubt anymore that the Hyd pump is failing...
but, what ever the brake activates, (I will re read thwe above posts later) could this unit be the problem?
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Post by Mandrake »

jgra1 wrote:guys guys common ! :lol:

i am looking forward to removing the spring.. i remember driving a bx years ago and thinking i liked / preferred the press the button brakes much better than this ;)
Me too, after being used to the GS and CX brakes. The feel of the Xantia brakes is basically the same as the GS/CX/BX brakes after the spring is removed. Possibly even a bit more sensitive.
doubt anymore that the Hyd pump is failing...
but, what ever the brake activates, (I will re read thwe above posts later) could this unit be the problem?
It's not clear what "unit" you're refering to ?

If you mean the hydraulic pump, then no, I don't think a weak pump would account for the symptoms because a good accumulator sphere can give at least 10 full depressions of the brake without the pump even running at all, so a weak pump is not going to give variations in braking with a single pedal press when you have a good accumulator sphere.

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 Sturdybloke »

I can also speak from experience of having performed the brake mod. Although the Xantia was the first Citroen that I have owned or driven when I was driving home with the car I couldent seem to get to grips with the brake pedal. It seemed to be, well, bouncing back if you can understand what I mean. After the brakes of a MK 3 Ford Escort the Citroen brakes felt like pushing a brick through a puddle of mud. After I performed the mod I could actually stop the car without resorting to throwing a anchor out of the window. Some people can put up with the spring as Kowalski proves because it clearly dont bother him, but as its one of the simplest improvements to do to a Xantia its worth you trying it out as Mandrake points out.
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Post by jeremy »

Air in the hydraulics will cause all amnner of problems - noyt least of all as the close fitting valves and pistons used in the hydraulic system rely on surface tension and the viscosity of the LHM so basically separate the air from the LHM.

Air can only get in on the input side of the pump which basically is the hose from the reservoir to the pump. This can become porous or sufer from bad joints - usually with the reservoir - and should be examined carefully. If you look in the reservoir you may be able to see some evidence of air when the engine is running. Green milky fluid is a sure sign, other bubbling may be especially if it is vigorous.
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Post by citronut »

if you have got all or nothing braking it is most definatly air in the system,when the AC sphere looses its gas it dumps it into the system, it is nothing to do with the enersher spring under the pedel
regards malcolm
jgra1
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Post by jgra1 »

thankyou everyone :)
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