Xantia - air in rear brakes

alexx · Post by **alexx** » 18 Aug 2004, 23:05

I have a problem with this since I bought the car about half a year ago. It's a Xantia mkII, '98. Upon braking, rear end of the car rises several cm, then after about a second, when rear brakes start grabbing, it dives back. It can also be checked by depressurizing the system on the regulator, which disables the front brakes, but rear remain operative until you press the pedal 20-30 times and exhaust the pressure in the antisink sphere (of course, with every press on the pedal, braking force is lower)
After bleeding the brakes, feeling on the pedal is much better, like in BX, and there's no rising of rear end of the car. Unfortunately, within about a week, air gradually enters the rear circuit again. Bleeded the brakes 2 times so far, with the same result. With air in rear brakes, stopping ability of the car is much lower first second, until rear brakes start working, and the feeling on the pedal is odd.
Checked LHM tank, but there are no bubbles indicating that the pump is sucking air. All spheres were checked in the meantime, rear corner spheres and accumulator sphere were regassed, other were still good, ABS seems to be working well and everything else seems to be in perfect order.
I presume that this is caused by the nitrogen slowly escaping from the antisink sphere (after 6 years still at 40 bar) and going to doser valve. But - front circuit is connected to accu sphere in a similar fashion and there are no problems with it.
Any similar experiences or thoughts about this?

stephen burch · Post by **stephen burch** » 19 Aug 2004, 03:05

It would be interesting to know if anyone has had a similar problem with a pre '95 model (no anti-sink).

alexx · Post by **alexx** » 19 Aug 2004, 04:03

Well, my BX (without anti-sink and ABS) didn't have this problem

oilyspanner · Post by **oilyspanner** » 19 Aug 2004, 13:37

my Bx was doing a similar thing when I had a pinhole in the low pressure feed to the hp pump, sucking in small bubbles and making lhm mousse, the tiny bubbles then got together to make bigger ones.
Stewart

ItDontGo · Post by **ItDontGo** » 19 Aug 2004, 15:42

It could be something to do with the split calipers. I have seen air slowly getting into the rear brakes on a few BXs and a Xantia.

tomsheppard · Post by **tomsheppard** » 19 Aug 2004, 16:12

I'd second that. There seems to be an issue if you strip a rear caliper. Does anybody have a source for the internal O ring?