93 Xantia VSX Brake Problem

AndersDK · Unread post by **AndersDK** » 27 Apr 2003, 04:55

Alex :
With the knowledge you clearly have demonstrated on Hydraulic Citroens, I simply think we're talking each own directions on same issue [:)][:)]
Of course you have some LHM in returns, but UNpressurised, or as I took it : "air cavity" - a somewhat missleading expression.
What I really meant was, that when the controlling elements are letting out any excess pressure in returns, this pressure goes into a NON-pressure cavity, giving a spray-jet action. This produces a sort of oil/air mixture emulsion, flowing out the returns at the reservoir, giving quite some air in the reservoir.
I've seen this on all BX'es & CX'es I've owned and serviced.
It was a swedish owner that had an "impossible" air problem in a BX, and after longish & troublesome faulttracing, he finally - by pure coincidence - came over a crack in the reservoir filter.
Replacing the filter instantly reverted the poor BX back to normal & comfortable drive.
On the other hand Alex - if you can contribute further on this "air-in-return" issue, I'm dead sure that we're quite a few who'll listen very carefully with stiff ears to you. First time I actually saw this air/oil emulsion in the reservoir, I was puzzled, since I'm clearly aware that air in ANY hydraulic system is UNwanted (from my air-force duty time).
Years ago I even took my time to service my scrap car's engines, for a test start up, solely to investigate this issue. But when this air/emulsion was seen on all cars, and also on later species I bought, I considered it a perfectly normal condition.
What's your opinion on this topic Alex [?][:p]

alexx · Unread post by **alexx** » 27 Apr 2003, 17:00

Anders, although I suppose there are no other members interested in this "bubble in return pipes" issue, so we are just wasting the bandwidth here, let me think.
Of course, I believe that you have seen bubbles in LHM tanks of various cars, but I don't think it's really perfectly normal, at least not in greater quantity. Sure, when the car came from the factory, air was in all hydraulic elements and pipes. Then, it gradually drifted to tank from the system through return pipes, so there were bubbles for some time. But, if there are bubbles in return pipes all the time, it means that the air is coming from somewhere, it can't arise from nothing. It can be sucked in before the pump, or it can come from some sphere leaking nitrogen. I don't see other way for air to come into system, because, strictly speaking, all other parts of it are under the pressure, even return pipes. Just it's only up to about 0.05 bar there - it is a hydrostatic pressure, because the tank is at higher position than all other elements.
Maybe I'm wrong, this is just a theory, so maybe I overlooked something here.
Anyway, this hydropneumatic system is in fact very simple, but there's still enough room for so many different problems. Air suspension on Phaeton, for example, is much more complicated (hundreds of sensors, valves etc). I'm really considering buying some ordinary car instead of Xantia.

Dave Burns · Unread post by **Dave Burns** » 27 Apr 2003, 17:51

Stuart, returning fluid is just dropped into the reservoir IIRC and doesn't go in through a submerged pipe, so any air bubbles coming in will stay on the surface, also the intake is low down in the tank so there shouldn't be any air down there to recirculate.
I'd be looking for air being pulled in by the pump.
Dave

AndersDK · Unread post by **AndersDK** » 27 Apr 2003, 22:13

Alex -
You're in fact comfirming my thoughts -
Some (seemingly common) problem must exist on the pump allowed to take in air in some way.
My best guess is, that this problem would be common on older species, with rotten or simply leaking pump intake hose (stiffened rubber), or simply cracks in the reservoir's plastic manifold.
Or - as you mention - leaking spheres. The N-gas slowly diffusing out could go on for considerably longish time, since when it escapes to 0-0.05 bar pressure it expands a lot.
Anyway - not riscing more waste of bandwidth - I'm satisfied.
Tx Alex.

stuartb · Unread post by **stuartb** » 28 Apr 2003, 00:12

Hi All,
I've fitted the new accumulator sphere and bled the brakes (having exercised the suspension system several times). What a difference - the brakes work immediately and powerfully (back to how it should be).
Many thanks to all for the help - I'm sure it's not the last time I'll need it!
Cheers,
Stuart.

akojic · Unread post by **akojic** » 28 Apr 2003, 04:44

Glad that you solved brakes problem. Having the new acumulator sphere fitted and brakes working correctly, period between ticking of acumulator sphere is increased, isn't it?

stuartb · Unread post by **stuartb** » 28 Apr 2003, 15:27

Akojic: I thought I had cured the problem, but this morning the delay in braking was back!
The LHM returning to the reservoir is still very foamy, so I think I'll try the feed pipe from the reservoir to the pump next because I suspect it may have a slight leak allowing air to be drawn in to the system.
At least the period between ticking has now increased from around 15 seconds to well over 2 minutes, so it obviously needed that new accumulator sphere!
Cheers,
Stuart.

stuartb · Unread post by **stuartb** » 09 May 2003, 21:22

Well, I found the source of the air leak. It turned out to be a leak around the flange of the hydraulic pump.
System (including brakes) was bled successfully and the brakes now work better than they ever did since I've had the car.
I also carried out the brake pedal spring modification and that made a massive difference to the feel of the brake pedal. It now feels like I can "stand the car on it's nose" easily but with enough feel not to do so accidentally!
Thanks to all of you for your help and advice - I hope I can help someone else out in the future (I like to give something back if I can).
Cheers,
Stuart
'93 Xantia TD VSX - 107000 miles)