Hi Guys, I posted a couple of weeks ago about my hamfisted attempts ro rebuild a FDV.
The problem is getting worse so I have pretty much resigned myself to buying a new valve, however I would like to be positive this is my problem. The symtoms are as follows:
The car, since I got it in Easter, has had poor brakes, which need a harder push than normal. Calipers are good and new discs and pads made little difference. Also, the steering has always been heavier than other BX's I have driven, and now it is starting to lose assistance on some corners, and sometimes having a 'sticky' feel. Generally the hydraulics on the car seem fit however, it does not drop too quickly, and goes up nicely, which I feel rules out the brake valve and pump. The problem is worse when the car is cold.
I would appreciate comments on whether this sounds like the FDV.
Cheers,
Flow distributor valve diagnosis
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jonathan_dyane
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uhn113x
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Hi Jonathan
Brake problem does not sound like FDV, unless the system never reaches cutout pressure, but the steering problem does.
You have probably figured out how the FDV works, but here is a resume:
When system is in 'normal' (cutout) mode, the return from the PR that dumps the pump output into the reservoir goes via the FDV in case any is needed for steering.
When system cuts in, a proportion of the line pressure is taken from the FDV for steering.
Anders or others may expand on this.
Probably worth cleaning filters in FDV for a start.
Brake problem does not sound like FDV, unless the system never reaches cutout pressure, but the steering problem does.
You have probably figured out how the FDV works, but here is a resume:
When system is in 'normal' (cutout) mode, the return from the PR that dumps the pump output into the reservoir goes via the FDV in case any is needed for steering.
When system cuts in, a proportion of the line pressure is taken from the FDV for steering.
Anders or others may expand on this.
Probably worth cleaning filters in FDV for a start.
I'd still be inclined to check out other issues. The fact that everything seems to be tougher than usual to operate makes me suspicious, especially given the sequence in which things should be "dropped out" by the safety valve (suspension first).
There are other possibilities: for example, leaks in the reservoir-to-pump feed, sucking in air which then plays havoc with both pressure and general hydraulic function.
I'll have a read of the previous post and see if anything else suggests itself. In the meanwhile,
(i) Is the accumulator new or recently tested?
(2) is the pump "knocking" at all?
There are other possibilities: for example, leaks in the reservoir-to-pump feed, sucking in air which then plays havoc with both pressure and general hydraulic function.
I'll have a read of the previous post and see if anything else suggests itself. In the meanwhile,
(i) Is the accumulator new or recently tested?
(2) is the pump "knocking" at all?
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jonathan_dyane
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Hi Mike and DLM
Hmm, the perplexing thing is the suspension seems spot on; it rises quickly and the ride is fine. One strut is sticky, which means the front tends not to drop unless the car is left for a few days, and will then rise in a series of lurches, but this is not affecting ride.
The system does reach cut out pressure fine (I can hear the PR), and the accumulator sphere is recentish and cut in time seems reasonable (although sometimes it seems to speed up for little reason). The pump does not knock, and the fact that it rises well suggests to me that it is healthy. I will check the feed pipe tomorrow.
To attempt to further clarify, the problem is far worse when the car is cold (it was dreadful this morning and took about 6 miles to become bearable) and I *think* it is worse when I am braking and turning at the same time. (now that does suggest low pressure to me).
When I first got the car the steering was 'universally' heavier than other BXs I have driven, but this was not unpleasant and made the car feel less nervous at speed than BXs often feel - I assumed at the time that this was a characteristic of the 'hotter' BX, both of the other ones I have driven were naturally asperated diesels. I now realise at the time that this was a fault and not design. The brakes require an excessive push; far greater than the other BXs. This one does have ABS [which has now thrown a wobbler too
light is on], but I don't think this is simply a different feel to the pedal, an unexpectedly heavy pedal pressure is needed although the brakes do *work* OK.
Mike - I don't really want to clean the FDV filters right now because that will mean removing the unit from the car and partially dismantling it, and if I make a pigs ear of it the car will be immobilised. I shall renew the LHM and clean the reservoir filters over the next couple of days tho. The service record says this was done very recently, but I should no better than to trust that...
Cheers,
Hmm, the perplexing thing is the suspension seems spot on; it rises quickly and the ride is fine. One strut is sticky, which means the front tends not to drop unless the car is left for a few days, and will then rise in a series of lurches, but this is not affecting ride.
The system does reach cut out pressure fine (I can hear the PR), and the accumulator sphere is recentish and cut in time seems reasonable (although sometimes it seems to speed up for little reason). The pump does not knock, and the fact that it rises well suggests to me that it is healthy. I will check the feed pipe tomorrow.
To attempt to further clarify, the problem is far worse when the car is cold (it was dreadful this morning and took about 6 miles to become bearable) and I *think* it is worse when I am braking and turning at the same time. (now that does suggest low pressure to me).
When I first got the car the steering was 'universally' heavier than other BXs I have driven, but this was not unpleasant and made the car feel less nervous at speed than BXs often feel - I assumed at the time that this was a characteristic of the 'hotter' BX, both of the other ones I have driven were naturally asperated diesels. I now realise at the time that this was a fault and not design. The brakes require an excessive push; far greater than the other BXs. This one does have ABS [which has now thrown a wobbler too
light is on], but I don't think this is simply a different feel to the pedal, an unexpectedly heavy pedal pressure is needed although the brakes do *work* OK.Mike - I don't really want to clean the FDV filters right now because that will mean removing the unit from the car and partially dismantling it, and if I make a pigs ear of it the car will be immobilised. I shall renew the LHM and clean the reservoir filters over the next couple of days tho. The service record says this was done very recently, but I should no better than to trust that...
Cheers,
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jonathan_dyane
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I had a BX that was displaying symptoms like this, heavy steering, sometimes intermittently from one corner to the next, but always worse the colder the weather. It always pumped up quickly so I dismissed the idea that it could be the hydraulic pump.
I eventually took it to Pleiades who tested the pump, said the output was very low and replaced it. This totally cured the problem, I owned the car for another 4 years after this and the heavy steering never came back.
Pleiades said that people often assume that if the car rises ok the pump must be fine, but raising the car actually puts very little stress on the pump, its powering the PAS that really tests it. Hence the first sign of a knackered pump on BX's is usually problems with the power steering.
Nick
I eventually took it to Pleiades who tested the pump, said the output was very low and replaced it. This totally cured the problem, I owned the car for another 4 years after this and the heavy steering never came back.
Pleiades said that people often assume that if the car rises ok the pump must be fine, but raising the car actually puts very little stress on the pump, its powering the PAS that really tests it. Hence the first sign of a knackered pump on BX's is usually problems with the power steering.
Nick
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jonathan_dyane
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This squares with what was happening on a previous BX before retiring it - OK most of the time, but it rose somewhat sluggishly, and steered VERY stiffly especially soon after startup. It was even worse in the cold. For whatever reason, I couldn't stop this particular pump rattling, and I suspect it may have been at least one cylinder down.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jonathan_dyane</i>
Can you remember if the pressure regulator behaved normally when the car was in this condition?
I may check out the scrapyards for a s/h pump.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
As far as I remember it behaved normally apart from the heavy steering. It always did 'click' a lot, even after the pump change, but I think that was down to a worn doseur valve, the back end always sunk quite quickly after switching off.
The history of this particular car was that it had had numerous previous owners, who all polished the bodywork and serviced the engine perfectly, but none of them had ever bothered to do any work on the hydraulics. I think when I bought it at 7 years old with about 110k on the clock it was still running on its original set of spheres and LHM. I did get it very cheap (£1000, in 1996 when BX diesels still fetched around £2500) but the hydraulics were the worst I'd ever seen. The LHM was black, and the engine had to be revved to make the brakes work! I flushed the hydraulics out, fitted all new spheres filled with fresh LHM and it was fine until a year or two later when the heavy steering problem began.
Can you remember if the pressure regulator behaved normally when the car was in this condition?
I may check out the scrapyards for a s/h pump.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
As far as I remember it behaved normally apart from the heavy steering. It always did 'click' a lot, even after the pump change, but I think that was down to a worn doseur valve, the back end always sunk quite quickly after switching off.
The history of this particular car was that it had had numerous previous owners, who all polished the bodywork and serviced the engine perfectly, but none of them had ever bothered to do any work on the hydraulics. I think when I bought it at 7 years old with about 110k on the clock it was still running on its original set of spheres and LHM. I did get it very cheap (£1000, in 1996 when BX diesels still fetched around £2500) but the hydraulics were the worst I'd ever seen. The LHM was black, and the engine had to be revved to make the brakes work! I flushed the hydraulics out, fitted all new spheres filled with fresh LHM and it was fine until a year or two later when the heavy steering problem began.
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jonathan_dyane
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Hi,
I have been thinking, and I don't think it can be the pump; if it were the PR would not cut out, and/or the brakes would be ok *some* of the time.
The pinion valve could not affect the brakes, unless there was a massive internal leakage in which case the PR would not cut out due to the internal leakage.
Could the PR be cutting in too early?
I am going to replace the LHM with hydraincage and see what happens...
Cheers for the suggestions,
I have been thinking, and I don't think it can be the pump; if it were the PR would not cut out, and/or the brakes would be ok *some* of the time.
The pinion valve could not affect the brakes, unless there was a massive internal leakage in which case the PR would not cut out due to the internal leakage.
Could the PR be cutting in too early?
I am going to replace the LHM with hydraincage and see what happens...
Cheers for the suggestions,
There are two factors to consider really; pressure and flow rate.
What Pleiades told me was that the brakes and suspension need good pressure to work normally, whilst flow rate was less important to them.
Conversely the PAS needs a good flow rate, but pressure is less important to it.
When HP pumps wear they are apparantly still often capable of providing good pressure (so the brakes & suspension are still fine) but the flow rate becomes poorer ( so the PAS suffers).
This doesn't really explain your brake problem though...
Certainly its well worth trying the hydraflush before assuming its anything more serious.
Nick
What Pleiades told me was that the brakes and suspension need good pressure to work normally, whilst flow rate was less important to them.
Conversely the PAS needs a good flow rate, but pressure is less important to it.
When HP pumps wear they are apparantly still often capable of providing good pressure (so the brakes & suspension are still fine) but the flow rate becomes poorer ( so the PAS suffers).
This doesn't really explain your brake problem though...
Certainly its well worth trying the hydraflush before assuming its anything more serious.
Nick
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uhn113x
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1982 GSA Pallas - on road April - September.
1997 ZX 1.9D Dimension. - x 1
Jonathan
I'm with Nick on this. If, say, you disabled two cylinders of the pump, on startup it only has to charge the accumulator and pump the suspension up from whereever it has sunk to. This does not require a lot of volume, and if the pump could still supply sufficient pressure, you would not notice the difference.
However, the amount of flow needed for steering would probably not be met.
I'm with Nick on this. If, say, you disabled two cylinders of the pump, on startup it only has to charge the accumulator and pump the suspension up from whereever it has sunk to. This does not require a lot of volume, and if the pump could still supply sufficient pressure, you would not notice the difference.
However, the amount of flow needed for steering would probably not be met.
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jonathan_dyane
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Nick and Mike, good points regarding the pump; I had not thought about it in those terms. I am starting to consider that I may have two seperate problems...
I shall change to hydraflush and bleed it through to the calipers to see what happens. I have a suspicion that this might improve the steering but not the brakes; we shall see!
Cheers,
I shall change to hydraflush and bleed it through to the calipers to see what happens. I have a suspicion that this might improve the steering but not the brakes; we shall see!
Cheers,
If the light soes out properly you shauld have sufficient pressure for the brakes! I speak from some experience as I had FDV problems and the light would come on indicating low pressure. This had no noticeable effect on the brakes but I would stop until it had gone off again (or rev the engine or if stationary, turn the wheel)
Are you sure the brakes themselves are ok - ie front calipers sliding properly etc. Is the handbrake exceptionally strong? - it should be - and the car should manage to pass the MOT footbrake requirement (0.5g) on the handbrake alone!
jeremy
Are you sure the brakes themselves are ok - ie front calipers sliding properly etc. Is the handbrake exceptionally strong? - it should be - and the car should manage to pass the MOT footbrake requirement (0.5g) on the handbrake alone!
jeremy