Xantia brakes

Unread post by **aerodynamica** » 07 Oct 2011, 18:06

I have been getting the full house of problems with the brakes.

Initially, the car showed the classic signs of trapped air in the brakes: scary delay in action and the tail lifting up once the front brakes finally bite. I bled the living hell out of them and all was good.

Next, I get occasional grab on the front as though one side is braking later than the other - say 2 out of 5 brake tries then cures itself.

Next, a sensation that the brakes are underpowered at times until more pedal pressure is given (this one might just be me as I'm used to the CX's brand of hydropneumatic brakes...)

And next, the old binding brakes problem - not had this on a car for years but it seems that it affects it on the fronts - always cures itself but there's a marked difference in the car's driving with it binding - feels 'crashy' over bumps, there's a sensation of pull to the near side and a definite cyclic twitching to the steering wheel (also can be felt to an extent through the gearstick ) and at low speeds there's deffo a side-to-side wobbling towards the rear. Thought tyre? but the fronts are new. It's definitely the front I feel the wobble from (when it does it) and I feel this too, is something to do with the brakes.

The binding is surely not the 'XM sticking pivot bush' thing with the pedal-to-doseur valve linkage is it? If I manually lift the brake pedal up it is loose to lift.

Now after a few weeks' running from the extensive brake bleeding, the brakes are developing a bit of a delay again! Is air getting in? Is it possible the HP pump is sucking in air and pumping air into the hydraulics?

Any previous experience on this?

Separate (I think) is an occasional locking up of the steering! Just on occasion, at low speeds less than 20mph, a lock change to the steering causes a sudden jamming of the action. it's unnerving. It never loses PAS though - just a sudden, short 'stuck' to the steering that doesn't reappear for days.

Any help gratefully received!

Graeme

Diabolical · Unread post by **Diabolical** » 07 Oct 2011, 18:19

Graeme

Does the car have ABS? faulty sensor/ABS ECU can cause delay in braking. Just a thought.

David

citronut · Unread post by **citronut** » 07 Oct 2011, 18:36

are the tank filters clean, pump belt tight ??????

how quick does she rise from fully down on first start up in a day,

regards malcolm

Unread post by **CitroJim** » 07 Oct 2011, 19:04

Hi Graeme,

She's keeping you busy! You sure it's not a cunningly disguised Activa you have there

Binding: Most likely the handbrake cables; they have a nasty habit of splitting the outer sheaths in the guide rings, then letting water ina dn then binding...

Then old XM bogey of sticky pivots on the dosuer can't happen on a Xantia.

Delay: yes, air most likely. Air can get in on the suction pipe to the pump or, as you noticed, yours has a lot of side play and it may be getting in via the driveshaft bearing...

You may also have a rupturing sphere that dumping nitrogen bubbles into the system or air is getting in somewhere else.

A good test is to look in the top of the LHM reservoir with the engine running. If there's a nice frothy head on the LHM then you have air... The surface of the LHM should be reasonably calm and not too bubbly...

As a test, the main suction pipe between the reservoir and the pump can be replaced by a length of clear hose to see if there is any bubbly in there...

ABS faults will normally cause the brakes to prematurely release at slow speed rather than causing a delay...

A re-bleed of the rears will show if there is any amout of air getting in... It's usually the rears that suffer most...

Unread post by **aerodynamica** » 07 Oct 2011, 21:12

Thanks all, The car rises up quickly from lowest, Tank filters cleaned in petrol and then compressed air 5 weeks ago, new LHM, pump belt replaced 3 weeks ago and retightened 4 days in. So I think those can be discounted?

It does have ABS, I did wonder about that being a possible cause. It doesn't do anything alarming yet but at times I feel the brakes are a little under powered (funnily enough, at speeds of less than 30)

The handbrake does bite pretty low and holds very well - couldn't be over adjusted could it? Trouble is, the binding is occasional..

I'll rebleed the brakes as it (should

) cost nothing. Maybe give the abs rings a mild brushing with the wire brush?

What about this steering issue?

I noticed that the car makes the FDV hiss noise a LOT when you start up from cold but less (hardly at all) when it's heated up. Last 2 days it's hardly been doing it at all.. wonder what's changed.Has anyone figured out yet what the FDV is doing at the 'hiss phase' of its 4 states? Extensive study of the BX workshop manuals left this unanswered though i did learn a lot about how the thing works.

Anyway, thanks again.

citronut · Unread post by **citronut** » 08 Oct 2011, 09:37

i wonder if she is sucking air in somewere along the line, between tank and pump?????

regards malcolm

DickieG · Unread post by **DickieG** » 08 Oct 2011, 09:54

I'd say the brake delay issue is possibly down to the spring under the pedal, lift up the pedal and you'll find a black plastic cylinder fitted to the back of the pedal, remove it by pulling it towards the front of the car, then pull apart the two plastic collars, remove the spring and replace with a piece of 15mm domestic plumbing pipe cut to the appropriate length, that will give you CX style brakes.

The problem with the spring is that when you apply moderate braking a fair degree of the pressure on the pedal is taken up with compressing the spring and 'wastes' pedal pressure, the result is a non linear braking action/application.

For the steering issue is the stiffness there at certain points of the steering? I'm wondering whether the column UJ is becoming stiff.

Diabolical · Unread post by **Diabolical** » 08 Oct 2011, 19:23

DickieG wrote:I'd say the brake delay issue is possibly down to the spring under the pedal, lift up the pedal and you'll find a black plastic cylinder fitted to the back of the pedal, remove it by pulling it towards the front of the car, then pull apart the two plastic collars, remove the spring and replace with a piece of 15mm domestic plumbing pipe cut to the appropriate length, that will give you CX style brakes.

The problem with the spring is that when you apply moderate braking a fair degree of the pressure on the pedal is taken up with compressing the spring and 'wastes' pedal pressure, the result is a non linear braking action/application.

Dickie

Why, Why have I and nobody else thought of that, almost guaranteed what it is.
It's dangerous in my opinion removed mine after following the tip from yourself.

Unread post by **Dommo** » 08 Oct 2011, 19:58

Diabolical wrote:
DickieG wrote:I'd say the brake delay issue is possibly down to the spring under the pedal, lift up the pedal and you'll find a black plastic cylinder fitted to the back of the pedal, remove it by pulling it towards the front of the car, then pull apart the two plastic collars, remove the spring and replace with a piece of 15mm domestic plumbing pipe cut to the appropriate length, that will give you CX style brakes.

The problem with the spring is that when you apply moderate braking a fair degree of the pressure on the pedal is taken up with compressing the spring and 'wastes' pedal pressure, the result is a non linear braking action/application.
Dickie

Why, Why have I and nobody else thought of that, almost guaranteed what it is.
It's dangerous in my opinion removed mine after following the tip from yourself.

I've asked my brother to get me something to replace this spring, I'd like to try a 'proper' citroen brake pedal

Unread post by **aerodynamica** » 08 Oct 2011, 20:46

Well today the brakes were fine... Even, instant and no pull to the side. Odd.

But you're all right: I think it's all in my mind! I was over to see the stored CX today and started it up to keep it alive, moved it to keep the tyres' shape and found the brakes to be ludicrously Citroëny! Pedal like a brick. I think the Xantia's brake pedal with its extra spring is simply affecting my 'Citro-sensitivity' that's all.. I'm tempted to swap the spring for a rigid copper strut as suggested. Just to keep things consistent you know..

Anyway,

i wonder if she is sucking air in somewere along the line, between tank and pump?????

regards malcolm

It's possible Malcolm, I think I will be adding a clear pipe to the HP pump suction to keep tabs on its performance.

Anyway, a NEW problem has arisen...... do I start a new thread? Nah. too many threads of my Xantia makes the FCF a dull forum (?)

Well it seems there is that wobble observed at slow pace 15mph, it's like having a twisted tyre tread but I haven't spotted this on the treads so far. The front trues are new (May) and I'd think they'd be OK. The rears are old but certainly the wobble feels like it's from the front.

Wonder what is the problem - are there any Xantia-notorious issues that cause this effect or do I just keep investigating..

Unread post by **myglaren** » 08 Oct 2011, 21:16

Swap wheels front to rear and see if there is any change.
Swap wheels in turn with the spare.
If it is a wheel or tyre problem that should show up the one in question.

citronut · Unread post by **citronut** » 09 Oct 2011, 09:58

or maybe slightly warpped front brake disc/s,

regards malcolm

Unread post by **Estately** » 09 Oct 2011, 12:18

If you notice this on a smooth road surface giving a little feedback through the steering wheel and disappearing above say 15-20 mph with no appreciable wheel wobble at higher speeds then I would put it down to a wheel rim being very slightly out of true in some way.

One of my rims does this and is kept for the spare, we have spun it with and without a tyre and cannot identify any visible fault but it will always give the wobble having had different tyres fitted and before and after new front discs.

I always use michelins and run with tyre pressures on the high side, torque the wheel bolts up to 90Nms and find it more noticeable as the tyre wears but they all wear reasonably evenly.

As for the binding brakes, have you cleared the brake dust etc from the moving parts, worked the pistons in and out, checked that the the front calipers slide freely and applied copper slip between the back of the pad and the piston and maybe sparingly to the edge of the pad where it is guided by the caliper.
The handbrake cables can also be "copper slipped" where they pass through the guide rings, messy but protects the outer sheath.

Regards.