FDV : don't just swap it, overhaul it !

Frequently asked technical questions and common modifications/improvements
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cauchoiskev
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FDV : don't just swap it, overhaul it !

Post by cauchoiskev » Thu Jun 22, 2006 5:08 am

If you swap your faulty/leaky FDV for one from the scrappers, chances are you'll have the same problem or worse within a year or two.

The repair kit is still available and costs about 20 squid in France, maybe a bit more abroad. Expensive for about 10 grams of plastic (although to be honest I was expecting worse). But, when you've done the overhaul,you've got yourself an FDV as good as new ! Well, almost.

Believe me, it is far easier to overhaul an FDV than to put the bloody thing back on the car, which you would have to do if you simply swap it anyway. However, there are a few things you have to be aware of. A French enthousiast has done 3D drawings of all the innards (although I believe he is mistaken on the quantity and posistion of the springs) :

http://www.planete-citroen.com/forum/sh ... hp?t=36437

1) The two filters (one on top, one on the bottom of the FDV) are held in by 5mm allen screws. The bottom filter is inside a metal holder, which itself is sandwiched between two washers with central holes. Here's the state my two filters were in :

Image

Hardly surprising that the steering was intermittent...

2) Once the filters and one washer are out, you need to get the four plugs on the sides out. WARNING ! don't touch this screw :

Image

It regulates the pressure at full lock, and would need special equipment to calibrate.

The plugs are held in by circlips, which look pretty impossible to get out. Here's how you do it :

Image

You just push the plug back against the spring pressure, and then use a small, sharp screwdriver to prise the circlip out. You'll probably think of a more elegant way of doing it, but this worked. You may have to push the plugs inwards to get out the ones on the opposite side.

3) Take the bottom piston out on the opposite side from the filter (left side, where the spring is, as shown below, which is the FDV as seen from the motor)

Image

because, apparently (a French guy says), the other side is not machined, and would scratch the piston. I can't confirm this, but why take a risk ?

4) Now you can get the filter holder out. Underneath it is an unbelievably thin washer (0.2mm) with an unbelievably small hole in the middle :

Image

highly losable, IMO.

5) When it's all apart, wash in petrol. It all looked as good as new, ready for another 300000km ! Buy your kit :

Image

which for some reason contains a double ration of LHM joints. Thanks Mr. Citroën !

Then put it all together again : start with the washers, filters and allen screws. The thicker washer has a conical hole, the wider side :

Image

should be facing you when you put it in.

Then you can put the pistons and springs in and finish with the plugs. You'll have to push them in again to put in the circlips.

6) Now comes the hard bit : putting it back in the car again ! My advice is not to bolt the FDV onto the motor until you've got the HP pipes on (make sure the cable clamps are undone to give some free play). It might be a good idea to take the radiator and even the accu sphere off. As the Citroën workshop manual says, access is "uneasy".

7) Prime the pump, top up the LHM and say hello to sweet, smooth, non -intermittent PAS ! Hurray !

Footnote : there is a common opinion that the FDV was a bodged solution to avoid referencing a new pump. When you take it apart, it looks very carefully designed indeed. It's amazing what clever folk can do with three springs, two pistons and a ball bearing. IMO, this thing will never fail if the LHM is kept clean (unfortunely, few of us have had our BXs from new...) , it will just start leaking as the joints harden. I would also suggest that an FDV will last at least as long as a 6+2 pump.

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Post by jeremy » Thu Jun 22, 2006 7:49 am

Well done Kev - and it works!. I did one for my TD many years ago and I must have made a mistake somewhere as it did not work properly. I didn't pursue it as I had a fault and wasn't sure if it was the FDV or something else and the defective valve was no worse than what it replaced.

The problem I had was getting the thing apart and had to remove rust round the rings with a tool in a Dremel type drill, and then still had great difficulty in removing the caps etc.

Curiously the fault on my car was actually the valve under the plug you mention not to remove. I worked out I probably had a system pressure problem and wanted to re-seat the valve. I thought I could do the job on the car but needed to see what size of brass rod I needed to punch the ball. I took the plug out of the FDV I had taken off the car and found that the bearing support plunger was the wrong side of the ball valve - so I rapidly re-assembled it correctly and my problems were over.

This valve controls the maximum system pressure - and hence the level of power asssistance available for the steering. As Vanny found out without a FDV and incorrect assembly of the pinion valve or its connections - a steering ram can split!

Well done - and thanks for the photos.

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Philip Chidlow
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Post by Philip Chidlow » Thu Jun 22, 2006 7:54 am

Well done indeed. These sort of photo step-by-steps are a well-proven method of giving the inexperienced and confused (count me in!) the confidence to tackle a job.

=D>
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Post by sleepy0905 » Thu Jun 22, 2006 7:56 am

Well done i have done a couple of these now and it makes a big difference the kit is available from citroen part number 95669034 price £24.37 so well worth doing
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Jaba
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Post by Jaba » Thu Jun 22, 2006 8:10 am

Yes this is one worthwhile job - as the results are always apparent.
GSF sell the kit too @ £27.00 (!! more than Cit) p/no N43444A.
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Post by AndersDK » Thu Jun 22, 2006 6:35 pm

Love it when people is getting serious on these issues 8)

Some interesting details from the PR-net listed here.
The prices in Dkr (excl vat) can be used as a price leader for Scandinavian members/readers. Divide by 11 and you have the price in UK£.

BX :
4024.01 - STEERING PRESSURE REGULATOR - Dkr 4448,34 (FDV unit new)
95.534.068 - DISTRIBUTOR FILTER - Dkr 51,05 (kit containing the 2 filters only)
95.669.034 - BALL JOINT KIT - SUSPENSION - Dkr235,45 (repair kit)

XM Mk1/Mk2 & Xantia (early Mk1 only) :
4024.00 - STEERING PRESSURE REGULATOR - Dkr 2493,70 (FDV unit new)
Same 2 kits as above available (though rep kit is not listed for the XM Mk2 & Xantia)

The FDV units are exactly the same for all 4 models involved.
EXCEPT that XM & Xantia units are calibrated differently from the BX units. Hence the different part no's. This calibration is done on the "dont touch this" screw shown on image above.
Its odd that the BX units are almost the double as the XM & Xantia units - only difference being calibration.

My personal experience with 2 FDV units were that only the filters needed replacement. Other bits where perfectly re-usable. A third unit though had a couple of perished O-ring seals - reason for service as it leaked.
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FDV

Post by richjenn » Sat Jul 15, 2006 11:28 pm

Pardon me for being dim, but what does FDV actually stand for?
Excellent tech description - v. impressed.
Cheers
Richard
(Maybe I should buy a Micra after all.............)

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Post by jeremy » Sun Jul 16, 2006 12:30 am

FDV - Flow Divider Valve - which provides a feed for the power steering while allowing the uninterrupted function of the brakes and suspension.

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fdv

Post by richjenn » Sun Jul 16, 2006 12:52 pm

Ahhh!
Of course!
Thanks very much
Richard
Richard
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Adam
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Post by Adam » Wed Aug 02, 2006 9:47 pm

Ok, so where is this located on the engine? Thinking of changing mine as a matter of proventive maintenance.
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Ian_Fearn
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Post by Ian_Fearn » Wed Aug 02, 2006 10:01 pm

Its next to your pressure regulator behind the radiator.
Over and out from me

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Post by jeremy » Wed Aug 02, 2006 10:19 pm

Its the first component after the pump.

If its working I'd leave well alone. They are often blamed as no one really understands how they work but in fact seldom give trouble

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Post by ianselva » Fri Aug 25, 2006 3:57 pm

I have only just joined , in spite of having owned a BX since 1986, (not the same one) , but this looks like maybe the answer to my problem. In the winter especially the assistance on the power steering varies a lot while the engine ( and presumably the hydraulic fluid) is cold, once it all warms up the assistance is back to normal. No problems with the hydraulics in any other area , and I have changed and flushed the fluid with no change.
Does this seem like a symptom of needing to rebuild this valve ?

Cheers

Ian
BX owner since 1986

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cauchoiskev
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Post by cauchoiskev » Sat Aug 26, 2006 9:07 am

Sounds more like your HP pump is on the way out, Ian. When the FDV is dirty, you get problems whatever the temperature is.