Strange Front Height Corrector Behaviour

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steelcityuk
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Strange Front Height Corrector Behaviour

Post by steelcityuk »

After putting all the rear bits back together I took the car out for a spin on Friday night. It still seemed to have strange things going on at the front. So I thought I'd remove and strip the front HC to see if there was gunk in it or if it was rusty or I'd rebuilt it incorrectly.
I found nothing amiss so I cleaned up a spare I had in the shed, ultrasonically cleaned it, thoroughly lubricated all parts and rebuilt it. Once back on the car and bled through I tried the usual sitting on the boot lip and front slam panel tests. The rear was excellent, nice and supple, dips a few inches when you sit on the boot lip then starts to rise after several seconds, getting off if does the same in reverse.
But the front still isn't right, as soon as you sit on the slam panel the front jumps up and as soon as you get off it drops so fast it over corrects. I've never come across this behaviour before, I thought the HCs included dampers that stopped this behaviour so what is going off?

An ideas please I'm baffled.

Steve.
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Post by CitroJim »

Steve, is this a late XM with antisink valves and a 6+2 pump? I ask as the symptoms are very reminiscent of the valves closing due to low hydraulic pressure at times of high demand and then reopening again as the pressure recovers.

If it is an antisink, then the pump or pressure regulator may need some skilled attention.

Also, force hard mode by removing the Hydractive ECU fuse and see if the same symptoms occur. It might be caused by leaky electrovalves but normally they give themselves away with a very fast tick rate.
Jim

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Post by citronut »

you have put it back together in the right order :wink:, and conected the pipes the right way round???? :shock:


did you take any picy's of the procedings by any chance,


regards malcolm
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Post by steelcityuk »

Hi Jim,

No it isn't, it's the 2.1 SED, single outlet pump with FDV and switching to sports mode does make the suspension hard as opposed to changing the parameters. It couldn't be the hydractive block doing this could it? I don't see how myself but I'm out of ideas. Or could the very hissy FDV have a hand in it? I'll do the tests in hard mode and report back. Do Hydractive 1 systems have leaky electrovalves?

Hi Malcolm,

I'm pretty sure it's back in the right order, to make sure I checked diagrams and user posted photos such as this.
Image

I think that if the pipes were the wrong way round then it would react in the opposite way to normal. I only took two photos of the strip down because I've done several before without problems.

I'd love for somebody to point out my mistake so I could get it sorted out.

Thanks all.

Steve.
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Post by steelcityuk »

To add to the cars strange behaviour the rear rises up and then settles again just before coming to a standstill. I'm sure the ABS is releasing the rear brakes then re-applying them again. There's no ABS light on after the initial self test. I can't get my Lexia to work with the SED so hopefully I'll get time to check the rear rotors this weekend to check that they are clean and OK. Maybe all that grit blasting caused it.
Steve
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Post by kenhall1202 »

Hi Steve,

This may be a long shot but having taken a height corrector to bits for the first time recentlyI'm wondering if it would help to pre-fill the end chambers of the HC with LHM before fitting. This LHM being moved one way or another through the restriction in the plastic insert is what I believe provides the damping of the slide valve. If the HC is installed 'dry' then the full damping effect will only be seen when the end chambers have filled with LHM and expelled the air through the leak off line. Presumably in normal operation the end chambers will receive the continuous slow leakage of high pressure LHM past each end of the slide valve and will take a finite (unknown) length of time to fill.

Ken
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steelcityuk
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Post by steelcityuk »

Hi Ken,

I hadn't thought about that, the ones I've stripped down before have just worked straight off.

On Friday I bled the ABS block and the brakes again, I'm not sure if this has had much effect. Saturday I managed to read the fault codes from the ABS and Hydractive ECUs. Two permanent faults were logged for the rear ABS sensors - speed information inconsistent, that tallys with the behaviour of the car when stopping. Sunday was a good run into the Peak District, the car was comfy but the rear brakes are still releasing for a split second before coming back on again.

So tonight I decided to remove a rear hub and take a look thinking it would be full of grit or metal particles.

This is what I found-
Image

Image

Nothing obvious so I just cleaned everything up with brake cleaner, removed any corrosion and rebuilt. Next side tomorrow perhaps.

Steve.
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Post by citronut »

the first picy you have both the calliper bolts missing completly :shock: :lol: :wink:


regards malcolm
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Post by kenhall1202 »

Hi Steve,

Soon after I bought my 2.1TD in 2001 the ABS light came on and the selling dealer (Telfords Carlisle) 'fixed' it under warranty by replacing a rear sensor. However the fault quickly reappeared and on checking myself I found that the ABS loom running along the inside of a sill had been snapped and repaired in the past by simply twisting together the wire ends and applying tape ie a bodge. Soldering the broken connections and applying heat shrink insulation has given a durable repair with no further ABS lights, apart from those due to failed front sensors.

Ken
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Post by steelcityuk »

I wondered what the 2 holes were for!

Once I've checked the other sides rotor I'll be checking connections if that doesn't fix it.

Steve.
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