1998 Citroen Xantia 1.9td spongy braking!

[avamotor]

Hello FCF members,

I have a minor dilema and hope the past experience of someone out there could advise me of where to proceed next!

I purchased a 1998 Citroen Xantia 1.9 TD knowingly with an hydraulic leak, filled it up with lhm and drove it home. I found the leak in the power steering pipe and had a repair done by Pirtek and plumbed in the new pipe, there didnt appear to any loss of fluid from either union so I covered up the unions with "gaffer tape" to stop and dirt ingress etc.

I wasnt sure how to bleed the power steering system so I just turned it from lock to lock and took it for a run, at which time i noticed poor braking/spongy braking that almost seemd to "grab" and shortly after let go, so currently i nursing the brakes and car.

I got bored today so following the haynes manual, I bled the brakes and the front calipers fluid looked almost brown on bleeding, I used plenty of LHM to ensure good clean green fluid left the clear tubing free of any air bubbles, again took it for a test run and brakes still spongy.

I did read an earlier thread that looked as thought it related to Xantia mark 1's and some business with a bulkhead insulation foam/spring/plastic plug but not sure if this relates to Mark 2's. Am i the only person to experience this or is it a common fault on some Xantia Mark 2's, can someone give me advice on the likely problem please.

Thank you in advance

Garry.

[RichardW]

The spring is fitted to MK2 cars as well, but unlikely to be your problem here I'd have thought - although it may be amplifying the problem. Give the rear brakes a good bleed too - they sometimes need a litre of fluid pulling through to get all the air(*) out. Pulsing brakes is not unknown, and I suspect you will find it needs a new accumulator - how often does the pressure reg tick when the engine is idling? The spring is on the back of the brake pedal and is designed to make the brakes feel more 'normal'. If you remove it, they will resort to Citroens of old - ie very sharp - some like it, some don't. I've never had a problem with the std set up on Xantia brakes in nearly 200k of Xantia-ing.

* lots of gas in the rear brakes is more likely nitrogen from a failed rear anti-sink sphere...

[citronut]

i agree with Richard
air in the brake system,

i have not read the BOL's routine for bleeding hydraulic citroen brakes,

all you need to do with car up on its highest setting and rear wheels removed (car supported properly),
engine running, fit a length of clear tube to one of the bleed valves/kniples into a container, open that kniple and press and hold ( no up down up down up down required )the brake pedel till you get a good flow of citro blood comming out of the tube,
repeat this on the other three kniples,

also if the LHM was brown you might need to empty and the system/tank, clean the tank filters and repill with new LHM,
unless someone had done this but not bled the brakes,

regards malcolm

[DickieG]

If the spring under the brake pedal is still in place the effect is that you apply gentle pressure to the pedal and the brake are applied accordingly but when you press a little harder there is no noticeable increase in braking effort/retardation (as the additional pressure on the pedal is being taken up by compressing the spring/rubber plunger) then once you press sufficiently hard to compress/overcome the spring the brakes suddenly grab to the point of the ABS almost being activated, or in other words non-linear braking action.

Once I discovered this spring malarky the first job I did when buying another Xantia is to replace that spring with a suitable length of 15mm tubing, to me leaving the spring in place verges on being a dangerous defect due to the delay in braking effort between gentle and moderate braking.

[citronut]

the usual fault that causes the brakes to either be fully on or not on at all is air in the system,
and even though the sprung plundger does give less phisical direct presure on the dozour valve i dont ffind it to be dangerous,
as long as the rest of the system is functioning properly

regards malcolm

[avamotor]

Hello again and thank you so far for the advice,

Right then, I have bled the system (front 2 bleed nipples looked very rusty and thought they would sheer off but undid okay) and really concentrated on the back brakes so in total there was 2.5 litres of LHM flushed or should i say bled through and then all bleed nipples tightened up. Took it for a run and still much the same spongy brakes (my car doesnt have ABS so i cant even blame that!!).

I will be swapping the rear discs and pads (when the motor factors have rung to say the parts are in) as the rear side of the disc have he appearence of rust and that not all the surface area is touching the disc, so to ensure my safety for a little while longer its needsto be changed.

So having now bled 2.5 litres of LHM and still have spongy brakes, does it sound like sphere failure the or this "brake pedal spring" thing?

how do I find it, "or Mod it" to test the pedal thing, does anyone have a photo of the possible offending item?

Thank you and please feel free to give me your advice.

Garry

[Xaccers]

Could it be the flexible hoses on the front callipers?
With age they weaken and swell instead of applying full pressure to the callipers.

[DickieG]

even though the sprung plundger does give less phisical direct presure on the dozour valve i dont ffind it to be dangerous,
as long as the rest of the system is functioning properly

Each to their own Malcolm but in a situation where braking effort/retardation needs to be increased from gentle to moderate, anything that causes a delay in the ability to slow a vehicle is dangerous in my books as it reduces the effectiveness of the brakes resulting in longer braking distances not to mention the loss of smoothness in the transition between gentle to moderate braking which in itself means a loss of vehicle stability therefore increasing the demands placed upon tyre grip and so on.

Quite how this spring malarky passed safety tests is beyond me

[DickieG]

I will be swapping the rear discs and pads (when the motor factors have rung to say the parts are in) as the rear side of the disc have he appearence of rust and that not all the surface area is touching the disc, so to ensure my safety for a little while longer its needsto be changed.

Sound like you have corrosion between the rear calpiers and suspension arms causing the calipers to sit at an angle hence the rusty brake surface etc.

So having now bled 2.5 litres of LHM and still have spongy brakes, does it sound like sphere failure the or this "brake pedal spring" thing?

how do I find it, "or Mod it" to test the pedal thing, does anyone have a photo of the possible offending item?

Re sphere's how long is the delay between clicks from the pressure regulator (on the front of the engine) when the engine is running?

To find the spring lift up the brake pedal and about halfway up the pedal arm you will find a black plastic cylinder which presses on the brake valve, the cylinder is removed by twisting it and pulling it towards the front of the car/brake valve. Having removed it from the brake pedal the are two half-moon plastic rings, slide those off and you can then take off the top of the cylinder where you will then find the said spring.

[Xaccers]

If the spring under the brake pedal is still in place the effect is that you apply gentle pressure to the pedal and the brake are applied accordingly but when you press a little harder there is no noticeable increase in braking effort/retardation (as the additional pressure on the pedal is being taken up by compressing the spring/rubber plunger) then once you press sufficiently hard to compress/overcome the spring the brakes suddenly grab to the point of the ABS almost being activated, or in other words non-linear braking action.

I have to say Richard, I've never noticed that in any Xantia with spring, all of them allow smooth and precise application of the brakes.

Now going from a car where the spring has been replaced with a tube into a normal one is dangerous as muscle memory can lead to not pressing the brake pedal enough.
Going back (ie into a car where the spring has been replaced) can end up giving your passengers whiplash

Actually, going from any Xantia into a non-hydraulic car can be scary when you realise how bad conventional brakes can be!

[DickieG]

The problem isn't something you'll experience very often but I did once and if there was any doubt in my mind on the subject it was made up for me there and then, I was following a line of traffic when vehicles ahead started braking gently then for reasons unknown the second vehicle in the line panicked and out-braked the hazard leading to vehicles ahead braking more firmly, as I applied more pressure to the pedal it wasn't matched by additional retardation by the brakes which caused a delay in braking effort leading to me having to use even firmer brakes as a consequence, not pleasant at all and potentially very dangerous in my books as such a delay extends braking distances unexpectedly as it's something beyond the drivers control due to having to compress a pointless spring.

As for the muscle memory thing that's never been a problem for me as I've driven what must now be hundreds of different vehicles and regularly changed vehicles several times every day, as long as brakes respond in a linear fashion I'm happy as I can anticipate and plan for that. Try the brakes on an original Mercedes Sprinter van, on those you can press the pedal completely to the floor, totally normal for those.

[citronut]

i still belive XANT brake as they left the factory do work far in exccess of conventional brakes, and the only time/s i have ever had a problem with XANT brakes is when there has been air in the braking circuit, this cause's there to be no initial braking at all, so when you find any braking it just lock everything up,
as air in the braking system does to all hydraulic citroens,

i also think the spring is so stiff it does not give any actual delay when the rest iof the system is functioning correctly

what you are describing Richard sounds more like the air in the systom syndrom,

regards malcolm

[DickieG]

Definately not air I'm describing Malcolm.

[citronut]

i spoz its a case of each to there own oppinion Richard,
its just the only time in all the years i have worked on and around all models of hydraulic citroens, delay in braking response has always been down to air in the circuit,

regards malcolm

[DickieG]

Take a moment to think about why the spring is there and the mechanics of it's effect, the spring was clearly added to reduce the sharp bite of the brakes in an effort to try and make Xantia's have a more "traditional/mainstream" feel to the brake pedal for those drivers who are unable to moderate the amount of pressure they apply to the brake pedal especially on first acquaintance with a hydraulic Citroen in an effort to increase sales so that drivers were not put off/spooked on a demonstration drive. The spring does not in any way assist the braking system safety wise as it introduces unnecessary moving parts such as the spring itself, the cone shaped rubber plunger that sits within the spring and the moving sides of cylinder shell (top and bottom).

The unfortunate problem the spring introduces is that it it's compression rate is not fully in unison/linear in operation with the opening of the brake valve so that when gentle pressure is applied to the brake pedal very little (if any) compression of the spring takes place so the brake valve starts to open and the vehicle's speed reduces accordingly. Now apply increasingly firmer pressure to the brake pedal and what happens is that a fair degree of that additional brake pedal pressure/energy is now being taken up with compressing the spring instead of opening the brake valve further, so rather than that increased pedal pressure causing the vehicle to increase its rate of braking effort/retardation the vehicle instead continues at its present speed until sufficient pressure is applied to the brake pedal to overcome the spring/rubber plunger and finally open the brake valve as the driver is demanding. There is the delay in brake application.

What I will say here is that in a straightforward emergency stop and most day to day use of the brakes the above effect is very unlikely to be felt, it is only if you experience a situation which demands that braking effort is gradually increased due to a developing hazard will it be noticed as the transition between the stages I describe above is subtle.

I discovered this issue as I go to great lengths to drive as smooth as silk by applying all of the controls/vehicle inputs very gently/gradually to allow time for the suspension to compress to maintain vehicle stability and balance, if one of my passengers, or even worse me as the driver feels a slight loss of smoothness (drivers rarely realise how coarse their driving is as they subconsciously brace themselves in the knowledge of knowing what's coming next) I feel disappointed with myself as driving smoothly is essential for vehicle stability and therefore safety and anything that is unnecessary and disturbs that balance (i.e. this spring) or extends braking distances is something I regard as dangerous.

Trust me here Malcolm the problem I describe is not air in the braking system.