My 1993 XM 2.1 SD Auto L322 VCV

[Aerodynamica]

Yeh the guy wasn't pleased about them, I'd change them too but no options.

[CitroJim]

My local mob, at the end of my road actually, hate them with a passion but they have the right gear and do a good job...

They know me well and I can see them go pale when I stroll in with wheels. I rarely take a whole car to them as I could almost roll the wheels there...

[russ92xmsed]

We're quite lucky too, there is an ATS round the corner. They are very good.

[Eddie nuff]

Anyway, more constructively: New pair of front boots to cure the slow speed wobble and 70mph vibration has certainly cured the wobble - bit of a twist in the tread. Trouble is that it still vibrated at 70. The tyre place balanced one wheel but the other seems to have a slight out-of-true to it.

Try swapping the fronts and the rears. It won't make an out-of-true wheel right but it may solve the vibration on the steering wheels.

[Aerodynamica]

Cheers, I'm thinking of doing that.

Unrelated development: the fdv valve always gets stuck in the hissing phase and prevents the regulator from cutting out. I've been studying the operation of it for yonks and always reckon the only way lhm flow could be in a leaky state before regulator cut out is if the first slide valve was allowing some of the flow that's all meant to be split 3/4 to regulator and 1/4 to PAS Circuit to return and I could only see one route for this.
If the first valve was slid open a bit as it should when steering pressure is there, the pressure will go through to the second feed for the pas and leak through to the pinion valve that's open to the lhm tank when no steering action is there. This is why isvstops hissing when you turn thevwheel, the pressure is being restored by the closing pinion valveiinstead of the supposedly shut fdv first valve.

[Aerodynamica]

The reason it opens is because steering action causes back pressure in the pas circuit that pushes valve 1 against its spring and opens a normally closed port at the spring end. This open port feeds some of the pump feed to the second fdv valve via calibration jets to the pas circuit thus giving two feeds to the pas and modifying the flow. The modifying leaves less flow for the regulator but normally this is enougte to let it cut out because the pas operating in this state makes up the pressure with its back pressure. The second valve feeds the pas or lhm tank and since the pas circuit pressure helps it stay closed against the lhm tank feed, the pressure all either goes to PAS or regulator in balance of pas demand. Problem is, with valve one open in absence of pas pressure and valve 2 being opened because of the flow fed by one,, the valve 2 lets it open to lhm tank and open pas valve and so most feed pressure is lost. Turn the wheel and valve 2has its spring assisted by the back pressure to copper the lhm return to tank port. Aside from that the hissingmust be the pump flow taking the long winding route through 2 partially open valves and 3 sets of calibration jets all connected to return to tank.
Only 2 things come to mind to cause valve 1 to slide open under feed pressure alone: weak spring or valve bore wear causing it to stick.

[Aerodynamica]

Sorry on mobile here hence blocks of text..
Appears that the failure mode of the fdv in this circumstance is that if valve 1 is prematurely open, it necessarily loses most of the flow as there is no fail safe totthis mode and it becomes a chain reaction.

More evidence for this! I got a g-clamp round the fdv to press in the spring side end cap of valve 1 to assist the spring and at least confirm this valve was open against its spring in the hissing but not steering state. With the engine running and it hissing constantly as usual, one small movement in of the endcap saw it instantly stop hissing and in fact it stayed quiet for several minute with the next hiss being short.

I really think this is the problem, valve 1 spring is weakened and causing thevalve to slide under hp pump flow alone. The fdv springs have no shims to set. Pressures like a regulator.

My experiment! Will be to initially remove the cap from the end and fit a little spring shim of about 2 mm thick ( about hat movement it took with the g clamp) to see if this will restore the action of the thing.

This is all based on the fdv diagrams operating principle from Citroen's workshop manuals. They show that valve 1 shoulder closed all times UNTIL pas steering action ismade.

I'll fit this shim and report back

[Aerodynamica]

Diagrams to follow when I am on laptop

[jonathan_dyane]

Very interesting Graeme, I look forward to hearing the result!

[Aerodynamica]

It never ends with this car! The front passenger seatbelt anchor has come off! Actually just come off I picked up my girlfriend last night at 10 and noticed the belt this morning was twisted, I untangle d it and find the anchor of f, bolt just fallen out. So this seatbelt was a death tap waiting to happen.

So we now have balljoints, rusty patch, parking brake cable and now this to deal with for the impending MOT. Oh forgot to mention an lhm leak from the regulator area. Yay