Confusing problem with Xantia hydraulics

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stuartb
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Joined: 20 Feb 2003, 15:12

Confusing problem with Xantia hydraulics

Post by stuartb » 02 Sep 2003, 15:57

Just when I thought I understood the hydraulics, something happens to make me realise how little I really know[xx(]!
For some time, My '93 Xantia 1.9TD VSX has been dropping to the floor within an hour and the time between regulator clicks
has been averaging 20 seconds (despite a new accumulator sphere). I've been meaning to take
a proper look at it but haven't had the time.
However, 2 days ago, I discovered LHM on the ground beneath the HP pump (6 piston, single output).
When I checked, the through bolts holding the pump together didn't seem particulary tight.
I tightened them up and the leak is now a bit better although it is still leaking a bit.
It's also drawing air in through the same leak and there is quite a lot of frothing in the LHM tank.
The bizarre and puzzling thing is that now the car isn't on the floor even after parking overnight and the
time between regulator clicks is now averaging 2 minutes!
If it wasn't for the problems that the air in the system is causing to the steering and brakes, I'd just leave it like that[:D]!
Does anyone have any ideas why this leak would cause this sort of 'improvement'?
Obviously, I'll have to sort out the pump, but I'm confused[?]!
Thanks,
Stuart.
'93 Xantia 1.9TD VSX - 120,000 miles.

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AndersDK
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Confusing problem with Xantia hydraulics

Post by AndersDK » 02 Sep 2003, 23:29

Stuart -
What you have seen is a leaking pump - before tightening the pump body bolt.
This leak has allowed the pressure in the system to leak back thru the pump - no doubt. And was the cause for the fast sinking.
If you experience problems with air in the system - it can only get into the system one way :
On the pump's suction side - which is the largest diameter rubber hose on the reservoir.
This hose may be rotten with surface cracks - or rubber has hardened - no longer a tight fit on pump/reservoir studs. You won't see any leaks from this hose - it's under constant vacuum from pump's suction.

alexx
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Confusing problem with Xantia hydraulics

Post by alexx » 03 Sep 2003, 00:37

... except, of course, when the engine is off.

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AndersDK
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Confusing problem with Xantia hydraulics

Post by AndersDK » 03 Sep 2003, 00:48

... then it wil be under slight pressure from the gravity of the LHM.

stuartb
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Confusing problem with Xantia hydraulics

Post by stuartb » 03 Sep 2003, 02:57

Anders and Alexx - Thanks for the replies. Unfortunately, there is still a leak. It's actually leaking from the flange on the pump (only with the engine off though!). Despite this, the suspension is still staying up longer than it was before!
I'm still confused.

Dave Burns
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Confusing problem with Xantia hydraulics

Post by Dave Burns » 03 Sep 2003, 03:36

If your pump has been sucking large amounts of air in then the LHM being pumped into the system will have been intensly airated, this air will go through the tiny gaps in the valves very quickly, where as the LHM can only squeeze through at a much lower rate, so tightening the pump body up reduced the amount of air getting in and so there was much less airated LHM getting into the system.
Dave

alexx
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Confusing problem with Xantia hydraulics

Post by alexx » 03 Sep 2003, 12:33

I agree with Dave. Anders, leaking pump can't be the reason for fast sinking, because there's a security valve and a non-return valve (in regulator) between suspension and the pump.

jeremy
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Confusing problem with Xantia hydraulics

Post by jeremy » 03 Sep 2003, 13:25

But the non-return valve itself frequently leaks and causes rapid regulator ticking. It is easily repairable by tapping it smartly with a brass rod.
Get rid of your air problem, run it for a few days and then see how often its ticking.
jeremy

stuartb
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Confusing problem with Xantia hydraulics

Post by stuartb » 03 Sep 2003, 14:55

Thanks to all for the ideas, but the point is that the fast sinking and frequent ticking problems *went away* when the pump *started* leaking!
Stuart

jeremy
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Confusing problem with Xantia hydraulics

Post by jeremy » 03 Sep 2003, 15:46

I think what is hapening is that the air in the fluid is acting to increase the apparent capacity of the accumulator and other spheres by in effect rendering the LHM compressible.
Bet the car feels soft and rolls a lot?
jeremy

stuartb
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Confusing problem with Xantia hydraulics

Post by stuartb » 03 Sep 2003, 17:35

Jeremy - No, if anything the ride is a bit hard. I've certainly not noticed any rolling!
The biggest problems are that the steering is incredibly heavy most of the time and there's a very slight delay between pressing the brake pedal and the brakes actually applying!

RichardW
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Confusing problem with Xantia hydraulics

Post by RichardW » 03 Sep 2003, 17:56

Did you put new LHM in? This is well known to change the behaviour of the hydraulics for about 3 days, then all is back to normal.....
Richard
Oh, and brake delay and heavy steering indicates that the pump is shot (providing it's primed poperly, and there's enough LHM)

jeremy
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Confusing problem with Xantia hydraulics

Post by jeremy » 03 Sep 2003, 18:03

Brake delay is probably a result of the air meaning that it takes a little time for the small fluid flow from the brake valve to establish operating pressure at the calipers. the brakes probably don't release properly as well.
Sounds as though your pump fault is affecting the steering section of the pump which isn't working very well. This should I thing be the 4 piston part of the pump and if the oil leak is minor than I think you need another pump.
The rest of the steering mechanism should bleed itself when operated and in particular when turned from side to side and I would have thought a rack pinion valve problem was too much of a co-incidence. In any event the usal problems affect one side only or are leaks.
Hard suspension sounds like its failing to reach its proper height.
jeremy

Dave Burns
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Confusing problem with Xantia hydraulics

Post by Dave Burns » 04 Sep 2003, 02:20

Stuart doesn't mention the low pressure warning light so either it doesn't work or the pump is at least generating the minimum specified hydraulic pressure.
I think you ought to take a look at the flow distributor since you are getting heavy steering, but then again don't, or at least not untill you have rectified the pump problem if indeed one still exists.
No point in troubleshooting elsewhere when you know where the main problem allready lies.
Dave

stuartb
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Confusing problem with Xantia hydraulics

Post by stuartb » 04 Sep 2003, 04:55

Thanks for all the replies.
Unfortunately, when I came to leave work today, I was greeted by the sight of my Cit sitting in a big puddle of "green blood". This was the first time the "stop" light has come on (apart from at first starting up). I guess the pump has finally given up completely! (No suspension/brakes/power steering at all).
I'm just trying to decide whether to replace the pump or just sell the car for spares!
Stuart