Xantia strange brake pedal behavour

[Dommo]

Hello everyone

My Activa recently passed it's MOT, however failed initially on a poor foot brake. It turns out it just needed some weight in the boot as I've read about on here before.

My question is that the foot brake often feels like it comes on and goes off again, rather like brakes that need bleeding, however I have bled them before and there is no improvement.

So far I have done the brake pedal mod, changed ALL 10 spheres for new Amtex, bled the brakes, cleaned up the corrosion on the rear calipers and ensured pads were well lubricated.

Can anyone see anything I have missed? Does the Doseur valve ever fail? Could it be this?

Thanks all. Dom.

[xantia_v6]

What brand of brake pads are fitted? Some pads, (especially "performance" brands) are just too hard and slippery to work well.
OE Citroen pads, or Mintex or Ferodo seem to work well in my experience.

[Dommo]

I know the rears are OE spec but the fronts I have no idea, whatever were fitted by the previous owner. I've had good experiences on my 1.9TD with Pagid pads from euro car parts, and I've also used OE Citroen pads which worked nicely as well but they are horrendous for brake dust.

Good suggestion on the pads though, might be my next port of call if nothing else works.

Thank you.

[myglaren]

If it is of any help then Pagid pads were fitted to my C5 at the last MOT and although some have mentioned concerns about them I have found them to be perfectly OK.

[Old-Guy]

Been there!
IMHO, your original diagnosis of 'air' in the hydraulic symptom was correct. 'Surging' brakes is a fairly common Xantia problem that has been much, and at times hotly, debated on this forum over the years, with various members, me included, seeking advice. The general consensus seems to be that the cause is 'gas' in the hydraulic system. Bleeding can effect a temporary cure, but the problem returns.

My logical analysis
The hydraulic system is self-bleeding apart from the brake lines which dead-end at the callipers; you have bled those but the problem has returned.
There are only two possible sources of gas in the system:-
1. Nitrogen leaking from a failing sphere. You have replaced all spheres, and it's improbable, but not impossible, that you have installed a defective new one.
2. Air from the atmosphere. The hydraulic system is under positive pressure through-out, except for the supply from the hydraulic reservoir to the pump. The HP pump sucks fluid up from the reservoir, the flow through the filter

The cure
The one part of the hydraulic system that you haven't tackled is that supply, which consists of two parts, the reservoir 'head' unit and the pipe from the top of it down to the pump.
Have you cleaned BOTH tank filters? Wash in petrol, using a soft toothbrush with a long handle to very gently clean the mesh (it will have become brittle and fragile with age). This won't fix the underlying problem, but will improve the flow to the pump and thus decrease the negative pressure and thus the tendency for air to leak in.
The highest point in the suction system, and thus the point of lowest static pressure, is the joint where the 'rubber' supply hose fits onto the stub of the plastic reservoir head. In my experience, the hose, which can't easily be replaced (NFP), gets slightly stretched widthways by being pulled off over the 'olive' in order to remove the filters for cleaning, and having become hard with age has lost its elasticity and become slightly loose. The 'trick' is to push it firmly in against the swell of the 'olive' - trimming a few mm off the end of the pipe if it butts up against the moulded bend - before re-tightening the clip just enough to hold the pipe firmly in place. If in doubt, wash the end of the pipe and the exposed part of the stub with brake cleaner and apply some silicone sealer.around the joint - looks a bit messy but better than air being sucked in.

I had this happen to me twice in the 11 years we had our Xantia. During our first year of ownership (should that be guardianship?), when a failed sphere (O/S/R) prompted a full hydraulic service (spheres, drain and clean reservoir, bleed out all the old LHM). Took me ages to find the probable cause. Second time around was some years later after I had overhauled the rear brakes (calliper corrosion, new bolts, discs and pads, clean filter and change LHM). This time around, I immediately went for the suction hose, refitted it more carefully (didn't need silicone) - surging brakes cured!

For the benefit of others, and my curiosity, could you let us know how you get on?

[Dommo]

Thank you for that in depth reply Guy. I should have mentioned that the steering is currently quite heavy at idle which made me assume the tank filters need attending to. And funnily enough, the only reason I haven't yet done that job is to make sure I didn't disturb the feed pipe!

I will get that seen to hopefully this weekend and with a bit of luck that will be the cure! Will it need a brake bleed again afterwards, my guess is it will?

Thanks again Guy.

[Old-Guy]

I will get that seen to hopefully this weekend and with a bit of luck that will be the cure! Will it need a brake bleed again afterwards, my guess is it will?

I think you're probably right. But I'd wait and see if the brakes still 'surge'. If you've changed the LHM fairly recently (and bled the brakes thoroughly to purge the lines of all that old yellow stuff), then what you get out should be clean, clear, bright green LHM that can go straight back in the reservoir.

I 'invested' in a proper pair of hose-clip pliers some years ago (about £17 IIRC). They make removing/replacing the 'proper' hose clips sooo easy; Click off, click on. Thus it's easy to remove the reservoir to empty it thoroughly and wipe it clean inside with kitchen roll (good quality, you don't want to leave little bits of paper inside). I know lots of people throw the OEM clips away and use screw-up hose clips instead - I don't like them, too easy to over-tighten and crush the plastic stubs. The proper jobs are the correct diameter to exert exactly the designed pressure.

If you need some let me know (and what colour code), I can probably find a few salvaged from a scrapper.

[Stewart(oily)]

I have found that it takes a lot to bleed the rears, I generally keep going until a good half a litre has come out, re your stiff steering, have you tried lubricating the universal joint on the column ? mine was stiff and making me think dire thoughts about HP pumps and filters, I can lubricate mine through the drivers side wheelarch with the suspension raised using a half inch paintbrush, a mix of diesel and grease seemed to get to the places it was needed.

[elma]

When I bleed mine I purge the tainted LHM into a container then use a long hose from the bleed nipple to the reservoir. I leave the each brake for about 5 mins bleeding itself back to the LHM tank in this manner. Overkill? Probably but it works well.

Brake pedal doing as you describe says air or warped discs to me. I'm guessing that the discs are ok if you've cleaned the rear callipers so just mentioning it in case you didn't. Xantias are terrible for wearing the front discs unevenly.

[c.morewood]

I've taken to leaving my Xantia on low overnight with the front higher than the rear..it seems to purge a lot of air out of the system resulting in a smooth brake pedal, it doesn't vibrate (fart) when pressed and the ride is much better. I tried the shortened LHM return, that helped a bit, but not as much as leaving her down overnight.

[Dommo]

Right then chaps, slow reply here I'm afraid but I've been doing a bit more than just messing with brakes, have swapped over the front ram for a good unit from my old Activa, literally had 6 months of use. While I was there I drained and cleaned the LHM tank, not particularly dirty, and nor were the filters. They weren't 'clean' but they certainly weren't particularly dirty either.

With the feed pipe to the pump, can't say as I've ever seen a pipe like this before



It could be standard procedure for early cars but certainly my '99 Activa and '97 1.9TD and 2.1TD weren't like this. It's handy though because replacement of that hose costs a pittance and is very easy, unlike on my 1.9 where I had to change the whole lot due to a split in the pipe - and I was chasing an air leak so replaced it out of completeness.

I can't say what the brakes are like yet as it's still going to be in bits for a good few days while I tend to an LHM leak around the back of the car, but I'll keep you posted.

Stewart I will try lubing up the steering UJ, not something I've tackled yet though.

Cheers all.

[c.morewood]

"I will try lubing up the steering UJ, not something I've tackled yet though."
A handful of grease on a gloved hand should be sufficient. It seems to work its way into the U.J.

[Dommo]

"I will try lubing up the steering UJ, not something I've tackled yet though."
A handful of grease on a gloved hand should be sufficient. It seems to work its way into the U.J.

Thanks Chris. Has anyone ever bothered to fit a gaiter over UJ? Seems like it would need one just as much as any other joint with a gaiter would. Any thoughts on the subject?

Cheers.

[c.morewood]

Last time I was going to try a plastic bag, tied with cable ties, but its probably a bit warm there for plastic. I do it once a year when changing summer to winter tyres.

[Old-Guy]

I've had/worked-on three '95 1.9TDs, '98 2.0i, '98 2.1TD - all had the 'usual' one-piece moulded hose. The arrangement in the photo is much better - The moulded plastic elbow looks very familiar, just like the ones in a mixed bag of fuel fittings that I bought a few years ago. I think this might be a thoroughly professional modification, that all Xantia owners should take note of. Any chance of some photos of the rest of the replacement please Dommo, so that others can copy the design?