Return pipe from rear suspension cylinder - what does it do?

[KevR]

May seem like a daft question. In fact it may BE a daft question, but there you go.
There are two return pipes on each rear cylinder. I noticed a bit of oily dampness around one side cylinder yesterday (an hour before setting off on a 1000 mile roundtrip back to Blighty...) so investigated. OF the two pipes, one is clear plastic and obviously the return to the reservoir. This is in good nick. The other is black plastic and has been rubbed through on the swinging arm. I've spliced it with a bit of hose but in the process realised that all this pipe does is poke into the rear axle tube/swing arm pivot. So what's it for? A breather of some sort? In which case why's it leaking LHM (if indeed it is - perhaps the LHM is coming from elsewhere...). One day I'll have to get my head round exactly how the whole system actually works!

[docchevron]

it is a breather yes, the cylinder is designed to leak a bit past the seal hence the return pipe to the octopus, the breather is simply to kwwp the pressure in the boot atmospheric. If it's leaking ALOT then it may be showing you the cylinder is passing more fluid than it should, although there is always a little LHM in them, if it doesn't pass fluid in to the axle tube now it's repaired I shouldn't worry about it

[mat_fenwick]

Just to add a couple of things to that - a couple of years ago I noticed the breather pipe had worn through in the same way, but didn't do anything as it was "just a breather". Early this year I noticed that the strut was passing quite a lot of fluid - i.e. the bellows actually had LHM/rusty water pooling in them. On stripping it down the piston had corrosion on allowing LHM past the cylinder seal. I suspect the water which cause the corrosion came in through the failed breather tube.

There are two seals in the cylinder wall - the first lets a bit of LHM past to keep itself lubricated. Any that does come past is (should be!) prevented from entering the bellows by the second seal, and instead goes back to the reservoir.

I've had a pushrod snap once, and what happened was that the piston came out a little more to take up the slack. No problems in normal driving, but if I put it on high the piston would come out past the first seal and the return pipe suddenly saw full system pressure and blew off!. For some time I was suffering from an intermittant LHM leak, and a return pipe that kept seemingly getting snagged on things and pulling out...

[KevR]

OK, thanks guys - I understand now! There didn't seem to be much LHM lurking in the area, just enough to dampen things a little and collect dust and crud, but I'll keep an eye on it. I've got as spare nearly new cylinder so if necessary I'll change it later.

[citronut]

one of the plastic pipes is a vent and the other is a seepage return back to the tank,
all the while the cylinder is holding its presure there wont be mich at all running through that pipe,