Fork Seals

[Otis]

On Sunday after a short run of say 5 miles and having met up with some guys it was noticed that my front offside tyre had some moisture streaks on it. Fork seals were mentioned and one chap felt around the lower end and said "yes definitely a weeping fork seal". Another chap said to wipe it all clean and see if it occurs again. Well typically, it hasn't occurred again after circa 60 miles of riding and everything is as clean and dry as a whistle as I write.

My only thought is that on the Sunday I recall hitting a quite depressed manhole cover and felt the forks bottom out; it was quite a jar.. Could it be possible that a significant compression like this could actually force a little oil past the seal or would the consensus be that it is likely that a seal is failing?

Any thoughts/guidance would be appreciated, thank you

[Bryanj]

With correct amount inside nothing should come out on max compression

[taysidedragon]

Just keep a close eye on it. If the seals are leaking there will be a film of oil on the chrome stanchions just above the dust covers. If there is an oil leak on the bottom of the fork sliders it could be coming from the bottom fork bolt. Keep checking.

[Otis]

Many many thanks for those two helpful replies.

I will monitor it closely but its slightly odd that the seepage should have occurred in a one off situation. Perhaps the seals are weak and perishing so whilst it shouldn't happen under max compression, perhaps it did and is a sign that they are going to fail soon.

From the records I have they were replaced 2000 miles ago but that was nearly 20 years ago!!

[taysidedragon]

Was it one leg or both? Worth lifting the dust covers to see what the condition is like underneath.

[Otis]

Yes, in fairness it was just the one leg on the Offside.

[Otis]

Was it one leg or both? Worth lifting the dust covers to see what the condition is like underneath.

Is that possible without dismantling the fork?

[Oddjob]

Yes, dust covers should just pop up.

[Otis]

This is still a bit of a mystery to me. Is there any way of testing the fork performance to see if they are as expected without having to strip down?

[McCabe-Thiele (Ted)]

Might be worth draining the fork oil, measure the volume from each side for comparison.
Check the condition, refill with correct volume of oil.
If fork oil  is badly contaminated, be worth rebuilding them.

[Otis]

Thank you.

Much appreciated advice.

[Bryanj]

With oil in you can push down and see if there is resistance to travel both ways, apart from that no test.
Any leak of liquid is an mot fail, oil mist is allowed

[Oddjob]

Personally when I was an MOT tester I’d most likely have failed it for oil mist, if it was enough to leave a ring I would have wondered how long that had been leaking like that and how much that loss of oil would have degraded the suspension. Saying that, I was a bit of a soft touch back then and I would have just pointed it out and said fix it asap. Depends how bad it looked.

[ST1100]

Personally when I was an MOT tester I’d most likely have failed it for oil mist, if it was enough to leave a ring I would have wondered how long that had been leaking like that and how much that loss of oil would have degraded the suspension.

Well, its progressing...
On my '00 ST both fork seals failed shortly one after another while up in Norway... they do have some nasty roads up there...
So I grew the routine of rinsing down rotors, calipers & pads with brake cleaner twice a day...
By the time we made it back home (Austria) both fork bottoms were FUBAR at the inside/bore... 

[K2-K6]

Personally when I was an MOT tester I’d most likely have failed it for oil mist, if it was enough to leave a ring I would have wondered how long that had been leaking like that and how much that loss of oil would have degraded the suspension.

Well, its progressing...
On my '00 ST both fork seals failed shortly one after another while up in Norway... they do have some nasty roads up there...
So I grew the routine of rinsing down rotors, calipers & pads with brake cleaner twice a day...
By the time we made it back home (Austria) both fork bottoms were FUBAR at the inside/bore... 

They do sometimes just quit after looking and earning fine for many miles. Possibly through rubber ageing at a guess.

Think I'd have tried to make some little towelling catch devices to keep the oil from running down in that situation. A little like those Bjorn Borg era wrist sweat band things.

You'd need to stop yourself getting caught up in the whole headband and "Fame" type leg warmers though 

With MTB forks (up to 40mm stanchion available) its considered reasonable to flip the bike (usually to install wheels after transit in car) and pump the forks a couple of times to keep the fork seals from running dry after storage period.

Difficult on a ST 1100 though