hydraulic woes continue

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citroen7
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Post by citroen7 » Tue Sep 12, 2006 9:14 am

Spent most of saturday under the car playing around stripped the linkage down and cleaned it up it was actually quite free so while i was at it i changed the height corrector with one that seemed to have better movement, put it all back together and the back end went up a lot smoother but it would only go up the once unless you turned the wheel to full right lock.
yesterday driving to work same as before down on the stops after 3 miles but this time no brakes! so last night i decided to change the accumulator and bleed the back brakes but as both my bleed screws are shot i disconnected the supply pipe and got my son to pump the brake pedel and it took a while to get any fluid out i thought it would have flown out ,so this makes me think the brake compensator valve must the scource of my woes
any thoughts chaps as i am now getting desperate as mot is 6pm thursday,

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Post by jeremy » Tue Sep 12, 2006 10:15 am

Firstly the rear brakes are fed from the rear suspension circuit - and so when the car is jacked up there is little or no pressure in the rear circuit. Brakes must be bled with a load on the rear suspension - and the simplest way is to raise the car fully which opens the height corrector and means that full system pressure is available. BE CAREFUL - the rest of the suspension may move and make the car unstable on its supports.

Is the pressure warning light working correctly? I don't think it is as it should be on long before the brakes fail. It is wired for checking purposes with the engine oil pressure light - which also activates the coolant level warning light - so they came on when the engine starts then that source of power goes when the oil pressure builds up. The hydraulic warning light should remain on until the accumulator has charged and the safety valve which operates it directly opens and allows high pressure to the front brakes. It then opens further and puts off the light and feeds the front and rear suspension circuits.

If pressure fails it operates the other way - shutting off the suspension first and putting on the light - and saving the remaining accumulator pressure and pump output for the brakes.

So the hydraulic light should stay on for 20 seconds or more while the thing charges, and go out at the same time roughly as the suspenson rises. (generally a little before) The light should also come on if the rear suspension sinks.

The light is operated directly by the safety valve which is situated at the back corner of the front subframe (follow the pipe fron the regulator under the engine) and has an electrical lead going to it. It sounds to me as though someone has removed this lead to disguise the faults.

Incidentally your problems sound to me very much like the FDV problems that I had.

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Post by citroen7 » Tue Sep 12, 2006 10:33 am

have just been out and had a play on start up the car rises quite quickly and you get a good hiss and click from the pressure regulator then i put my foot on the brake and the rear sinks slowly turn the steering wheel to full right lock and the suspension comes back up if you leave the wheel on full lock and then press the brake pedal plenty of brakes and the suspension stays up
i did bleed the rear brakes under pressure which was why i thought it strange that only a dribble came out.
Jeremy i will go ang check the wiring for the light now as i have not seen it on for a day or two

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Post by jeremy » Tue Sep 12, 2006 12:02 pm

The reason I say FDV is that its purpose is to provide power for the steering. It provides a continuous bleed which when there is no pressure on the steering wheel, simply returns to the reservoir. Turn the steering and the appropriate valve shuts, causing a rapid rise in pressure in the supply line, which is then communicated to the FDV which then provides more high pressure for the steering at the expense of the rest of the system.

This operation will also generally increase the pressure in the system - which can then reach other parts - and cause the car to rise etc.

In my case one of the problems was with the system pressure valve in the FDV (wrongly assembled) but I had other problems with one I dismantled which caused the same symptoms.

The wrongly assembled valve was not a proper one painted green - but a different one - painted black - and without the usual nylon filters but pressed in steel cones with holes. It actually looks a better device than the standard one and I have retained it.

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Post by citroen7 » Tue Sep 12, 2006 12:22 pm

the fdv i rebuilt was a black one which i put on the car a few years ago the green one is in the cupboard in bits ... The more i think and read about this i am convinced the fdv is at fault i have a complete fdv and pressure regulator i the spares box which came of a car that was working i think tonight i will change the whole unit and see where we end up . i checked the wiring and it is ok also the stop light comes on when starting but goes out almost imediatley , i think that all this mess is purely down to lack of flow through the system, if this does not work i am snookered as mot needs to be cancelled today to get a free one but that could be weeks away and they will not issue another exemption certificate to cover me

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Post by cauchoiskev » Tue Sep 12, 2006 12:41 pm

Stinker of a problem, citroen7 :(. Have you had a look at your leakage returns ?

Just pull the hoses off at the reservoir one by one (not the two big ones on the right), this could give you precious info on the source of your problem. The third hose from the right is the brake leakage return. Take it off, and see what comes out with and without somebody's foot on the brakes (or a stick will do). Normally, there should only be drops, at most.

Considering that you have changed the pump three times, it's fair to say that it's not likely to be the problem. The FDV is a possible cause, but you have rebuilt it. I take it you didn't have these symptoms straight after the rebuild?

The height corrector linkages work, and, in any case, these can't affect the braking. So, IMO, the problem is major leakage, somewhere in the system. I would still bet on the brake valve, but it could be the height corrector or something else. The quickest way to find out (5 minutes) : pull those hoses off !

By the way, my FDV was black, but had the plastic filters !

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Post by citroen7 » Tue Sep 12, 2006 1:02 pm

the only difference after rebuilding the fdv is that the stop light does not flicker on and of going over bumps but i still cant get my head around the fact that the pump is not being taken off demand by the pressure regulator which leads me back to flow of lhm which leads to fdv.
i will probably only have time to do either fdv or brake valve tonight the question is which?

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Post by citroen7 » Tue Sep 12, 2006 10:33 pm

right chaps just 4 hrs spent in the garage and deceided to replace the fdv and pressure regulator in one so rad out and away we go, on stripping down i was amazed at the amount of air in the system so all rebuilt rad back in etc and guess what ? NO f****** change
However after some fiddling the suspension did come up but the pump is still not hissing and clicking as it should so i spent 20 mins doing citroarobics all be it i had to have the steering on full right lock i then took her out for a run and the rear stayed up and the brakes were awesome.
so now i am happy with the brakes i will try and bluff through the mot failing that i have a viewing of a 19tgd auto tomorrow night that has t&t but a cracked screen and is up for £150 ,watch this space as they say!!

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Post by jeremy » Tue Sep 12, 2006 11:01 pm

If you've got air in the system check the hose from the reservoir to the pump. It may have gone porous or its ends may be leaking.

If necessary for diagnostic purposes it can be replaced by a clean section of garden hose.

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Post by citroen7 » Wed Sep 13, 2006 12:13 pm

ive changed that pipe not so long ago, but after my major tidy up over the summer i have a coil of industrial clear plastic pipe that i found in the bottom of the boot of the gti so i think i will try it and see.
I was dropping the kids to their school this morning and the ride is ok but not perfect it looks as if i need to check the ride height,before the mot but the stop light is now flickering sgain when you go over bumps but the back end is not sinking to the stops anymore so some progress i just hope the tester does not see the stop light come on when he is doing the brakes or maybe that wire might just fall of on the way to the centre!!?

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Post by cauchoiskev » Wed Sep 13, 2006 4:32 pm

The fact that pressure regulator is not clicking means that the available supply of LHM is more or less equal to the total system leakage. This is why you have to turn the steering to full lock to get the suspension up : that diverts a bit more LHM from the PAS to the rest of the system.

This also explains why the STOP light flickers when you go over a bump : the height correctors open and need a surplus of LHM. Same thing for the back going down under braking.

So the problem is either an insufficient supply of LHM or major system leakage. If you look at your leakage returns at the reservoir, and there are no significant flows, then you will know for sure that the problem is on the supply side.

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Post by jeremy » Wed Sep 13, 2006 5:03 pm

Kev

1. Height correctors are built so that there is a delay before anything happens. This is why nothing happens for about 1/2 minute when the control is moved and is the reason why if you are foolish enough to play with the height control and raise the car fully you are always left like a lemon with it on full height when the traffic moves off. I believe early DS did not have this feature but its been used ever since.

2. Turning the steering wheel cuts off the bleed to the steering - and the consequent rise in pressure is communicated to the pinion valve, and the supply to the rest of the car is restricted. This does seem to produce a rise in pressure in the remainder of the system. This is controlled by the FDV.

The regulator settings are: Cut out 170 bar
Cut - in 145 bar (both with a tolerance of 5 bar.)

The safety valve isolates at a minimum pressure of 80 bar and supplys the suspension at a minimum of 100 bar. This means that the light will go out at about 100 bar, and below that all the available pressure is available for the brakes. The suspension will only sink when enough LHM has leaked away (some through operation of the height corrector) as initially the height correctors will shut and keep the car at normal height.

Air can produce very strange problems - as amongst other things it will pass through the valves when LHM won't

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Post by cauchoiskev » Wed Sep 13, 2006 6:19 pm

Jeremy,

I totally agree that air intake could indeed cause all sorts of problems (although my gut feeling is that these would be more "unrepeatable" than citroen7's). The FDV disfunctioning could also be the problem, but he has both rebuilt one and then changed it.

However, I don't agree that there is a delay built into the height correctors. If you play around with a height corrector piston, the effect is instantaneous. What there is is hysterisis, which comes from the free play between the command rod and the lever which pushes the height corrector. This means that small bumps do not provoke correction, but a big enough bump will indeed activate the corrector and make the suspension rise up - albeit temporarily.

I have to say that I've looked and looked again at the innards of the FDV, and I still don't understand why more pressure is available to the pressure regulator at full lock (as the excess should go to the reservoir) but there you go : there is !

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Post by jeremy » Wed Sep 13, 2006 8:23 pm

I think the delay part of the height corrector is the collection of discs with small holes.

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Post by citroen7 » Wed Sep 13, 2006 8:41 pm

cauchoiskev, i think you have shown me the light at the end of the tunnel as to the reason the pressure regulator is not cutting in and out ,its too late to start mucking now but tomorrow after mot will have a play and look at pipes and connections as having fitted 4 different pumps it has to be something else .
if the old girl does fail tomorrow i think i will buy the meteor and this will give me time to work out what is wrong , i did have a look at the brake compensator valve last night thinking it would not do any harm to bleed it but i could not find the bleed nipple so i assume it is underneath it which case i would need ET fingers to get at it ! By the way has anyone changed one before as it looks a pig of a job?