Xantia 1.9TD Brake Judder and Hissing Hydraulics

[CitroJim]

I've been working on the old TD today, partly getting it ready for its busy towing season in a few weeks time and to investigate bad braking reported by SWMBO. These days I rarely drive it so it came as a shock just how bad the brakes were. I put it down to worn-out pads so today I've given it a good brake service.

The problem is that the brakes are juddering but not in the usual way. On reasonably normal application they judder and this judder can be quite distinctly felt through the pedal, almost as if the ABS is coming in but it's not regular like if it was ABS. It is best described as a rough, uneven judder, the sort you'd get if the discs were really, really rough and uneven. Like if they were really badly rusty after being unused for years.

So, I put new pads in and checked the front discs. Nice and shiny and as far as I can see, not distorted although I have not checked them for run-out with a DTI. I bled all four brakes but only got a little air out of one rear.

It has improved it but not by much. I'm thinking it may be hydraulic in origin as there are other symptoms that point to weaknesses in the hydraulics.

The regulator tick rate has got shorter recently. In fact it never ticks (never has in my ownership) but hisses for a while and they does not hiss. This hiss followed by no hiss is occurring about every 15 seconds now.

The car drops very rapidly when it is stopped, it will sink fully in 15 or 20 minutes and starts to sink almost immediately it is switched off. Perviously it would stay up for a good hour. This car is an early non-antisink model.

It is not the accumulator as I swapped this recently trying to chase this short hissing cycling. In fact Xac is running the old one on his 2.1. On initial strart the STOP light goes out quickly and the car rises very rapidly. Each corner is nice and soft and doing citarobics the speed from low to high and down again is really quite rapid.

The Brake Doseur makes a squelchy hissing sound when the brakes are applied but does not appear to be leaking. The ABS is working normally (in that the lamp behaves normally) and there is no loss of LHM anywhere. I did notice that the regulator went into a long hiss when I was bleeding the brakes as if the system was having trouble keeping up with the pressure demand and this I think is why the brakes feel so strange, the system is unable to keep up with the pressure demand but having said that, the suspension does not drop noticeably under braking and nor does the feel of the power steering change.

Am I looking for a complex problem here when it's just slightly warped discs? Grateful any thoughts on this one. Its got me

[slim123]

Jim, in my humble experience, I cant ever recall the hydraulics causing brake judder, I think that as you say in the end of your post that you are looking for a complex problem when it could only be warped discs. I think that it will be!!

Try driving down the road, dip the clutch then pull the handbrake lever up gently, if the discs are warped, you will feel the judder through the handbrake lever.

Regards.
Slim.

[AndersDK]

Defo with Slim here. Brake judder caused by hydraulics weakness would be in those instances you have a completely flat acc sphere and the pump cycle (i.e. pressure variations) can be directly felt in the pedal.

The same would happen if something internal to the hydraulics have a huge leak back. An example could be a defective doseaur valve, though I dont think its been tried on a Xantia yet. I have exactly this symptom on my running BX, where a huge constant leak flow is seen from the doseur valve.

One sure indication would follow the above problems : a very short ticking interval, i.e. a defacto constantly working pressure regulator.

As Slim points out the handbrake is completely mechanical with no influence from the hydraulics it will tell you immediately if the discs are warped - or if dirt/rust between disc and hub has warped the fitment of the disc.

[jeremy]

Short tick, rapid stop light going out . . . - try the sit-in-the boot test for the accumulator - it costs nothing and you keep your hands clean.

[CitroJim]

Thanks one and all for bringing me back to reality and stopping the chase of red herrings

Anders, I'll see how much LHM is returning from the Doseur, it's pretty easy to do on these

The judder is mechanical in origin as I can feel it through the handbrake and see the steering wheel shake a little so GSF will be enjoying yet another order from me very shortly for some new discs (they asked me if I was a garage the other day )

This hissing rather than ticking of the regulator is really bothering me. It is very loud and I could hear it driving through town with the window open today

The accumulator passes the sit in the boot test Jeremy (if done immediately after a stop) and as this is sinking Xantia (a very early one) with the single outlet pump I'd expect it to put the STOP lamp out in fairly quick time (around 5 seconds). It takes a good 20 seconds to rise from fully down and a few more seconds before the PAS starts working. I changed the accumulator not long ago in an attempt to discover why its tick (or hiss) interval is short. Furthermore, if I open the bleed valve, there is a healthy rush of LHM back to the reservior for a fair while. Would a flat accumulator show up by not causing a healthy rush back? In fact the only time I have ever heard a distinct click from the regulator is when the bleed valve is opened and the rush of LHM stops.

Please correct me if I'm guilty of muddled thinking here but as I understand on these sinking systems, the FDV and Security Valve will give priority to the brakes, followed by the suspension and finally the PAS. As the PAS is always working and the STOP light never comes on then is it reasonable to conclude that there is adequate pressure available at all times? As I say, under braking I never experience anything untoward happening in the PAS or suspension department. In fact all works beautifully except for the hissing which, as I say, it has done from the day I first took ownership of it.

To define the hiss a little more: It hisses continually for a good 20 or so seconds after startup until pressure has built. It will then go silent for perhaps 10 or 15 seconds and then hiss again briefly for say 2 or 3 seconds followed by silence for maybe 10 or 15 seconds again and repeat ad infinitum in a similar vein. If you set it to high it'll hiss until it is aloft and then hiss a few times very quickly before settling out to a short hiss followed by a 10 or 15 second gap.

What is making this hissing noise? I'm thinking it may be the ball in the regulator not seating well but I've never had the courage to try a re-seat. Also, I note there is a weep of LHM from the pressure regulator body. Not a leak exactly, just damp. Cracked maybe? A bad union seal but then I would have expected a leak The hiss seems to originate around the regulator and the feed pipe to the pump looks good and does not seem to be drawing air.

All this has been thrown into rather sharper focus since I've had a late Hydractive anti-sink Xantia that has a regulator tick measured in hours it seems. I once knew no better

Would another regulator be a good idea to try?

[philhoward]

I've never had to do the re-seating trick, but sounds like it might be beneficial in your case. I've been tempted a couple of times where i've had a "hissing" car, but the cars in question died or got sold on before then..

I reckon a return line check would be first; if that shows nothing sinister, then take the plunge and try a re-seat.

I'm guessing (having only ever had Anti-sink Xantias) that yours is basically a BX hydraulically - so the normal BX fixes will apply..and i doubt there's anything mysterious about BX's now after this time through all the knowledge here!

[jeremy]

I hadn't appreciated that this was a non-anti-sink Xantia - and thought the judder might be pump pulses from the 2 pistons of a later type pump.

LHM can escape from the accumulator in 3 ways - onwards, down the centre piston or back the way it came - ie via the non-return valve.

If the car lifts at all with the engine off then the accumulator must have some capacity - as the fluid to raise the car will be quite considerable to raise the car is considerable.

I ran my BX for a while with a faulty FDV until I eventually traced it. The pressure relief valve was assembled incorrectly and the thing would not supply sufficient pressure to the rest of the system and the safety valve would put the warning light on. At all times the PAS worked perfectly so the FDV wasn't prioritizing the rest of the circuit then. The safety valve should prioritize the brakes but they work at a lower pressure than the suspension.

Re-seating the regulator non-return valve is very easy and on a BX TD it can be done in situ with no real problems (and those beat removing the regulator which is a pig due to the close proximity of the radiator and other components which mean that some of the pipes have to be undone about half a flat at a time)

As other posters have said - the handbrake can be used for checking if the vibration comes from the brake discs etc.