must be were the moon is

[citronut]

L reg TD XANT hatch sinker


continuous pulsing brake pedal if you press with normal pressure even when stationary,
press hard and pulsing stops,

i thought air in the brake circuit, but after lengthy bleeding it still does it,

fitted a re/con pump from Martin about a year ago,

if you gently press the pedal you can here continuous flow of fluid/whoooooshing,

can a worn out dosour valve cause such a fault,

car has over 200k on the clock

[Mandrake]

ABS fault ? Pull the ABS fuse to rule that out...

Flat accumulator sphere ? (but I assume you've checked that already)

Could it be an air leak into the pump causing a lot of air to get into the system ? Bleeding wouldn't help if more air kept getting pumped into the main high pressure system in sufficient quantities.

Chris (cc101) was having problems with pulsing/grabbing brakes before he did his tank pipe mod: http://www.frenchcarforum.co.uk/forum/v ... =3&t=44923" onclick="window.open(this.href);return false;

It's a few minutes work to splice in a clear section of hose at the tank on the line going to the pump to see if there is any unusual amount of air being drawn into the pump, ideally there shouldn't be any. (Although it could also be an air leak at the pump end that wouldn't show up in this test)

If both those are ok the doseur is about the only other thing I can think of but I haven't experienced it myself...the only time I've felt a pulsing brake pedal has been air in the system.

[citronut]

ABS fault ? Pull the ABS fuse to rule that out...

cant find the ABS fuse as it dont have ABS

Flat accumulator sphere ? (but I assume you've checked that already)

new one already fitted

Could it be an air leak into the pump causing a lot of air to get into the system

re/con pump fitted about a year back from Martn

If both those are ok the doseur is about the only other thing I can think of but I haven't experienced it myself...the only time I've felt a pulsing brake pedal has been air in the system.

likewise

[addo]

I had this when the rear spheres were going flat.

As I also observed when overhauling the doseur, these are not a "forever" part anymore; wear was visible - not to the point of lipping, but appreciable effects to the shuttle bore.

[Mandrake]

I had this when the rear spheres were going flat.

Yep, I've seen the same symptoms (oscillation of the brake pedal when pressed part way even when the car isn't moving) when the anti-sink sphere was punctured, dumping loads of nitrogen into the brake lines. Bleeding the brakes only helped for a week or so as more nitrogen kept being released by the sphere. This car is not anti-sink though, and I'm assuming that the rear spheres have been checked already Malcolm ?

[Mandrake]

Could it be an air leak into the pump causing a lot of air to get into the system

re/con pump fitted about a year back from Martn

You misunderstand Malcolm. I'm not saying that there is an air leak physically at the pump (although that can happen too) I'm suggesting the air bubbles are coming from the reservoir tank and being sucked into the pump from there. I believe this happens a lot more often than people think.

That's why I suggested connecting a loop of clear hose (say a foot long) in between the hydraulic tank and the front pipe going to the pump to watch for any bubbles going from the tank to the pump. You might be surprised by what you see whizzing by. Given that you've checked pretty much every thing else that could cause it I'd almost put money on this.

[addo]

I've just had tea, but all this talk of dosa is making me hungry.

You might be surprised by what you see whizzing by.

Then again, this makes me think of colonic irrigation and suddenly I'm not so hungry!

[Old-Guy]

Removing the VSX's LHM tank 'header' to clean the filters last week reminded me of a fundamental weakness in the design. Being at the highest point of the low pressure side of the hydraulic system and above the level in the LHM tank, all the pipe connections onto the header unit are under negative pressure at times, and:

• all those pipes have gone hard with age on every Xantia,
  the HP pump has to suck it's supply up-hill out of the tank,
  any restriction by a dirty filter (and it's very fine) will increase the 'vacuum' (negative pressure)
  a fine stream of air can be sucked in through cracks (or less than perfect joints) that won't weep LHM .

Logically, being at the point of greatest suction, the HP pump feed-pipe's joint onto the header unit is the most likely source air bleeding into the LHM flow - at the worst possible part of the system!
I made sure that every clip went back on in exactly its original position and that the pump uptake pipe in particular was pushed hard against the flare in the header stub as I closed the clip.

If there are symptoms of low system pressure, particularly at low engine revs, another candidate that I didn't notice being mentioned is the auxiliary belt condition and tension - it doesn't have to be squealing to be slipping, particularly as the usual garage 'cure' is a good squirt of WD40.

[citronut]

Could it be an air leak into the pump causing a lot of air to get into the system

re/con pump fitted about a year back from Martn

You misunderstand Malcolm. I'm not saying that there is an air leak physically at the pump

yes Simon i did miss read your reply, thanks

front and rear of the car have plenty of free movement, and it ride very smooth,

the pulsing is very sever on normal braking pressure