O ring sizes, FDV valve

[Stickyfinger]

Need to know the O Ring sizes in my newly acquired sinker Xantia FDV valve..... I understand "the O Rings" are the same as those used in the BX and XM .... (but the XM are a different shape/design and the BX is the same but is calibrated differently so are not direct substitutes)

My plan is to dissemble and clean/refit prior to taking off the H-Pump and Regulator valves for rebuild at Pleiades (if required/does not solve a "slow pulse when braking)

[aerodynamica]

Hi Alasdair, are you meaning the 4x O-rings for the FDV end caps? Or the pipe seals for the 5x pipes connected through the FDV? If it is the 4x cap O rings these only really seal against LHM oozing out. I am fairly certain any performance issues with the hydraulic system are caused by other aspects and not the common LHM leaks to the outside.

I'm certain the FDV of the XM is the same as the FDV of the early Xantia and that the BX one is different (different setting to the PAS ram top out pressure). At least on the early BXs. the original FDV was painted green on BXs and painted black on XMs and Xantias. I think it was black on later BXs but not sure if this corresponds to any change in the spec for the BX one.

Any problem on an LHM car braking is unlikely to be the FDV. Brakes get their pressure from the main accumulator and from the rear suspension pressure separately.

FDV main problem in my experience is low system pressure caused by the FDV sinking the pressure from the pump before it gets to the pressure regulator. No amount of cleaning the LHM tank filters/ new pump belt/ accumulator sphere/ or new LHM changes it. The main cause of FDV faults is the spring inside the first of the two slide valves gets tired and slides partly open sinking the inlet pressure off the HP pump before the regulator affecting the whole system. Second main fault is the little nylon filter fitted in the pipe inlet of the FDV deteriorates and its debris gets stuck in the first FDV slide valve.

If you get pulsing when turning the steering then it is caused by the HP pump either having a failed piston or drawing in air. Had this on a BX and XM.

Buzzing at the brake pedal and/or delayed brakes is air in the brake circuit. If it buzzes on initial contact pressing the brake pedal then it is the front brakes' circuit. If you get a sudden drop of the rear suspension a delay after pressing the brake when driving, then likely rear brake circuit has air trapped in it.

Red STOP light coming on often with the engine at idle is low pressure. Caused by different things but if it is 'cured' by the steering being turned and similarly, if slow raising of the suspension is helped by turning the steering (and holding it against the resistance) then it's certainly the FDV valve as the cause. This never occurs on non FDV cars, DS/CX/GS and anti sink XM & Xant

Many years ago I've been there on a MK1 BX and on 2x XMs!

[CitroJim]

To add to this a little Graeme, the pump on Alasdair's Sinker is very, very noisy when pressurising and goes fairly quiet when the pressure regulator cuts out. It sounds like a machine gun and is unnaturally loud.

The the duration of the pump pressurising cycle is quite short, almost that of the 'tick rate'.

The 'tick rate' is very short (5 seconds or so) and initially I suggested the accumulator sphere was flat - as that might account for the pulsing brakes and fast tick but on test the sphere shows 50 bars.

The suspension rises and falls very rapidly and is in good order; the car rides very well. All corner spheres appear good,.

When I initially had the car running after its 10-year slumber, the steering felt very lumpy to me but Alasdair says this is now OK.

Brakes have been filly bled. Next time I see Alasdair and the car I'll go armed with my in-line pressure tester and check mainline hydraulic pressure and the regular cut-in and cut-out pressures...

The more I think about it the more I think the pressure regulator may not be 100% happy.

Cleaning the FDV filters won't hurt.

Having had a Sinker for a long while, one thing Alasdair's sinker does not do is hiss. Mine used to hiss like an angry snake!!!

[aerodynamica]

Hiya Jim, I see it's had a good looking over, I think if the pump is really noisy like that it's likely very worn.

I had a spare but gave it away with my last sinker when I had it and the refurbished pump on the car disintegrated on the new owner when he went on a euro trip to Germany... I think those pumps suffer from excess endfloat when they're worn.

Pressure regulator might need reshimmed and/or replacement springs.

Great that another sinker lives!

[aerodynamica]

Just thinking also if it is not making that hissing noise that may be a good sign that the FDV is quite 'tight'.

You can test that it works by 'making' it hiss by very slightly turning the steering wheel and holding it while the regulator cuts in. It should hiss during this. Even for a short duration. That shows that the built up pressure in the PAS ram is moving the first valve in the FDV and that the pump pressure build at the regulator is pushing against it. If it's still silent and the steering still feels off, then the FDV's first slide valve might be sticking. Often lumps of rubber fragments jam it. The LHM pipe seal is often the culprit.

[CitroJim]

Excellent Graeme, much appreciated I think that's given Alasdair a few more pointers...

Indeed, all good Sinkers should hiss!!!

Between us we'll get it sorted

[CitroJim]

Just to add, Alasdair has a spare pump on his sphere tester... I built it using a Sinker pump and pressure regulator with the FDV port. So also, in theory, a spare regulator too.

Only problem is, the pump may be off a petrol engine and they may have a different pulley diameter to that needed for the diesel engine.

[Stickyfinger]

The 1.9td and 1.8 petrols have different numbers Jim, so almost 100% not swappable.

[CitroJim]

The 1.9td and 1.8 petrols have different numbers Jim, so almost 100% not swappable.

Measure the pulleys Alasdair as I don't know for sure the provenance of your sphere tester pump

I do know you can't swap the pulley over...

[Stickyfinger]

The 1.9td and 1.8 petrols have different numbers Jim, so almost 100% not swappable.

Measure the pulleys Alasdair as I don't know for sure the provenance of your sphere tester pump

I do know you can't swap the pulley over...

Diameter ?....distance from the body ?.... or are the mounts/body casting not totally different anyway ?

[xantia_v6]

for TU/TUD/XU/XUD engines, I think it is just pulley diameter, as the diesel typically operates at lower RPM. There are also variants with V-belt pulleys or different offsets for earlier engine types.

[aerodynamica]

Yea I thought it was only the pulley diameter that was different. I think you can remove the pulley from the pump body but that you must take the flange/ pully housing with it. I think there are thin shims that can be added to help if you have pulley endfloat. The chap at Plieades used to mix and match Xantia pump parts. He did the best with mine but in the end I swapped another pulley assembly on to the rebuilt pump body to get the best result. It might have been a lucky combination though with trial and error. I had 3 pumps to play with at the time.

[CitroJim]

Mix 'n' match on later (anti-sink) Xantia pumps could be a nightmare Graeme! There were so many subtle variations

Even if the pulleys are a bit different, the on on your sphere tester might be worth a try on a temporary basis just as a test to eliminate a pump fault...