BX Rear struts parts

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tomsheppard
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BX Rear struts parts

Post by tomsheppard »

I don't think that the rear struts are repairable, due to Citroen not listing seal kits.
(Tell me if I'm wrong!)
Those with estates are beginning to find this a problem, because they are of a different size, 37mm as opposed to 35.
I have been given a used strut which has a seal within. I'm considering having a batch made.
If anybody has an off the shelf number (Likely one of our Antipodean correspondents) for a suitable seal, I'd like it
and if anyone would be interested in getting seals made please let me know.
Thanks.
NiSk
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Post by NiSk »

All of the BX rear cylinders I've replaced (quite a few in days gone by) have suffered from terminal exterior corrosion - but that could be due to the enormous amounts of salt they put on the roads over here in the winter.
//NiSk
alan s
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Post by alan s »

I think you're correct about there not being a kit as such for these. I was a bit sus about one of mine a while back & I had no joy sourcing kits either but mine seemed to reseat itself.
I haven't done a BX rear cylinder but we did have a CX one let go in a big way a few of years back and I'm pretty sure they're very similar.
In that case we found very little if any wear on the teflon "O" ring but the damage caused to the rubber one. This was caused through "white rust" growing inside the lower end of the cylinder due to lack of use of the vehicle whilst it was parked on a concrete floor. The rubber O ring simply got scored due to its abrasive acion of the verdigrease (sp?) on the O ring. As the car was about 90 klms from home at the time, we couldn't wait for parts to arrive from wherever so went to the nearest bearing shop & bought an O ring suitable for use with engine oil & used that as a "get home" solution. It was still in there & working when the car was written off about 5 years and 100K klms or more later.
Alan S
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Post by tomsheppard »

As far as I know, the strut body doesn't seem to be corroded, the Rubber O ring seems to be the secondary seal. The teflon one appears to be the primary one which, if sound, prevents a constant leakback to the reservoir. As I am seeing fluid flow in the rearmost return pipe, the rubber one is doing its job but the teflon one is not.
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Post by prm »

Teflon back-up rings are normally fitted to dynamic hydraulic cylinders to centralise the ram section within the main cylinder due to tight machining tolerances. Although they would appear to offer some sealing properties sealing properties, there usually fitted to provide a back-up face for the main O ring and a wiper action on the low pressure return stroke. I'm sure I can match and source theses both estate and hatch. They should be BS4518 spec. Just need all measurement details on rams and cylinders, plus old ring to match hardness. Any spec sheets on LHM, to get a material compatibility.
tomsheppard
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Post by tomsheppard »

Normally I'd agree with you Peter (Cos I don't see how it seals either!) but the construction of the ram is such that the O ring surrounds the piston after the port for operational return fluid and seals the fluid in the cylinder (I get none in the bellows so that works) and the teflon ring is before it, so the LHM is supposed to be excluded from this area, I'd have thought. Certainly a duff Teflon ring in a front strut is a slightly different animal, working as you suggest. I'm mystified!
prm
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Post by prm »

Certainly got me thinking Tom.
Possibly with the rears -- the suspension return stroke is the greater pressure, where the fronts are on compression. Teflon seals as you know have very limited expansion chararaistics. Sometimes this O/teflon ring application is reversed on high impact cylinders to avoid rapid O ring expansion and wear, where the Teflon acts as a pressure buffer.
Only ever changed one rear and I must admit didn't take a lot of noticed on internal workings.
Will have a look at hydraulic circuitry and let you know.
alan s
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Post by alan s »

buggaya, now you've got me thinking.
I wonder if in the case of our CX if the white rust unseated the teflon ring and when we removed, cleaned up and refitted it simply reseated itself? Also if I'm not mistaken (been a few years remember) doesn't the return outlet sit between the teflon and the rubber rings?
Alan S[;)]
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Post by tomsheppard »

Yes Alan. Clearly the furry hat keeps the brain at optimum operating temperature. This is just my point. The order is sphere, fluid, teflon, RETURN PORT, O ring.
As for the assertion that teflon has limited expansion characteristics, this is true but it is dimensionally unstable, being easily compressible. Does the fluid pressure squeeze the teflon into a very tight (but sliding) grip on the ram piston?
prm
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Post by prm »

Tom -- The Teflon seal can-do, has it got any curved properties to induce expansion --cup seal, or parallel in construction. Any firing pressure holes under the ram seal?
I should have stripped that one apart and had a look--sorry.
After thinking about it. Painfull some times !!
Most hydraulic cylinders are steel in construction. But Citroen have fitted ali ones. I wonder if they found teflon was a more suitable material. Might have some problem in sourcing those off-the-shelf. unless its a std. metric size. Might be able to find stock tube and then machine. I know we will needing those seals at some time.
R
Peter
alan s
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Post by alan s »

The ones on the CX were such a loose fit they could almost be described as "flapping" around in the cylinder; I couldn't believe they'd hold any liquid even without pressure.
Alan S
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Post by tomsheppard »

Agreed they do seem to be loose, but with 100 bars of pressure behind them I would reckon that they would soon be squashed up a bit! I wondered as Peter has about the profile but those in the front strut are not handed and I don't think these are either. I don't know if the recess for it in the cylinder is ramped but I doubt that, too. Wish we knew a Citroen development engineer!
alan s
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Post by alan s »

Just to add to the mystery, the front teflon seals are the same size as the rears on a CX and we swapped them around with no ill-effects.
Alan S
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Post by tomsheppard »

! The CX must have a piston about 20mm in diameter then?
alan s
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Post by alan s »

Can't remember back that far, but I can remember getting a call from the son, having a car in the process of being stripped and being able to get to the front but not rear cylinders and noting they were the same size.
As it turned outy, he couldn't get here & I couldn't get up to him and he saw the local bearing place who supplied the new rubber O ring that fixed it.
Alan S
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