Hydraulic System Priming

BX Tech talk
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nige!
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Post by nige! »

Way2go wrote:
jeremy wrote:The pressure needed to compress the spheres and possibly raise the car is less that required for safe operation - so the safety valve does its job and turns the light on. As the system does its job the pressure rises and the light goes out.
This statement cannot be right according to the laws of physics (Newton's 3rd law etc).

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New to this forum, am impressed quoting laws of physiscs to a post.. makes my posts seem at best uninformed! :oops:
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Way2go
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Post by Way2go »

mnde wrote:I would say it is quite normal for the STOP light to come on for a few seconds when moving the lever from lowest position to high. Mine does it, and the LHM reservoir is, if anything, overfull.
Mark.
I agree that if the car is dropped first to it's lowest (ie onto it's bump stops) then this would be seen as usual on rising. I had however interpreted the poster's 'low' as the 'normal' position where the system is already pressurised and he is taking it to the next level up; I still don't think the light should come on during this transition.
mnde wrote: It's the same as if you're starting the car after it has lain stationary for a week. There's no hydraulic pressure, then the STOP lamp extinguishes as the car is rising when full pressure has been reached.
Mark.
Totally agree but it's not the same if he's going from 'normal' upwards' if the car is already sitting at normal ride height. Perhaps Windy Miller will clarify for us what he is terming 'low'?
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jonathan_dyane
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Post by jonathan_dyane »

Aerodynamica wrote:My stop light also comes on with the car running and having just moved the height control up - it is a common BX characteristic but it is not correct operation and I'm thinking the cause is the FDV since that device is present in the BX and not in Eg. CX, GSA etc that I've had that never displayed this characteristic. Also my first sheddy BX didn't do this either and it was non-PAS.

When I first got the BX the light would come on after moving the lever and it took an age to go out - replacing the accumulator helped but it'll still come on with raising the height with the engine idling.
My current BX does this (although it does have a dodgy accumulator which seems to need the ball reseating; the STOP light also comes on after a few minutes at tickover, and also occasionally when driving :-( ), as did my previous one.

Think carefully before diving into the FDV, although often blamed for dodgy steering and other hydraulic maladities, I don't think it ever particularly wears out, weak pumps and dodgy accumulators are more usually the source of difficulty IMHO. That said, its filters will clog if the LHM is neglected.
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Windy Miller
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Post by Windy Miller »

Thanks for all the posts.

Just to clarify, the STOP light comes on when moving the height control from the bottom position up to the top (i.e. when performing areobics). Having read your posts it seems to me that it may be that the accumulator sphere has insufficient reserve to maintain system pressure when asked to raise the car once the suspension has been depressurised and has to wait for the pump to build it up again.

The tick time on my car is sub 10 sec. although you can hear the accumulator depressurising when you undo the 12mm bolt on the PR so it can't be absolutely flat. I previously thought that the short tick time was caused by either the ball valve in the PR needing reseating or a leaky brake doseur (the back end of the car drops under braking).

Anyhow it seems that I'm not alone with the STOP light symptom so I guess it will be OK to leave until the Hydraflush has done its job when I'll try and overhaul the Doseur and PR.

Cheers, Ian
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Post by Brian »

(the back end of the car drops under braking).

Ahh, this can be caused when nitrogen or air finds it's way into the LHM.

Give all the 4 corners a good bounce, to see if a sphere has gone hard.

Carry out some areobics, and see if you can bleed out any air.

Then try the brakes again to see if the back of the car still drops.

Could be a leaking accumulator sphere.
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Way2go
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Post by Way2go »

Windy Miller wrote:Just to clarify, the STOP light comes on when moving the height control from the bottom position up to the top
Ah, then that is to be expected as the security valve is telling you the truth after you have temporarily depressurised the system! :wink:
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jeremy
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Post by jeremy »

To test the accumulator - set the car to normal height - run the engine for a couple of minutes to let it all settle, then turn off the engine and sit in the boot. The back should drop a long way - then rise again after about 30 seconds powered by the accumulator. If it doesn't - change the accumulator.

It'll do the same powered by the engine if you want to see what should happen.
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