Mysterious Fork Leak - Any Ideas Please

[Bill Alexander]

Since I completely rebuilt my 78 GS1000 about 6 years ago I have had to replace a fork seal on 2 or 3 occasions. The seals have spontaneously started leaking oil for no apparent reason at random intervals. I have ruled out the obvious suspects. The inner tube chrome is in good condition – the only pitting is way above the area the seal runs (and I did consider and finally rule out the possibility that the forks were being compressed far enough for the seals to reach the pitted area – NOT happening). Also I have used both OEM and aftermarket seals – the original was OEM and failed maybe within 2 yrs. I actually seem to have had the best results with a “Pyramid” brand seal I installed about 2 and ½ years ago.


It has just sprung a leak again and this time I am starting to identify a pattern (maybe). Firstly, the problem seems to always be the right hand leg (I don't think I have replaced the lh side since the rebuild). The other part of the pattern is strange and I can not figure out an explanation. The leak always seems to start after the bike has sat unused for a prolonged period (for me that means 2-3 weeks). On every occasion I have noticed the oil running down the fork leg on my return after a break from riding it – it has been my daily ride for most of the last 5 years. On a couple of occasions it occurred on my return from summer vacations (so only a couple of weeks max of no use) and that had made me theorize that it may have been related to heat - maybe pressurising the system ?? - but I have never been able to figure out a sound explanation to confirm that theory.


This year 2 things have happened that have made me wonder more about it …... firstly, I had the bike parked up a couple of weeks over this summer vacation and right on cue there was the leak as soon as I set out first ride back. I was a bit busy at the time so I just cleaned up the oil and decided to put up with it until I had a chance to fix the seal – however (and this was not the case previously), once I was back in daily routine the oil stopped and for the past few months all has been fine. Secondly, last month I retired the GS as my daily ride and it has once again sat for a month unused. The other day I was walking past it and noticed an oil mark on the ground under the rh fork leg. Its autumn here now so I don't think there is any heat related issue but I am totally mystified as to what is going on.


Anyone got any ideas ?. Additional information that you may need to know (could mean nothing too ???) – whenever it has occurred the bike has been on its center stand, front wheel off the ground. When I say it has been ridden daily, that is not quite literal, there have been times it could have sat for 4-5 days maybe even a week and shown no sign of a leak. Seems like it takes at least a week but probably less than 2 – I am only going by memory.


Even though it has been replaced as my daily ride (mixed emotions about that but since the new bike is a GSX1400, which puts a smile on my face every ride, I am not totally heart broken) I intend to keep the GS. I have had it 28 yrs and as money and time allows I intend to give it another thorough tidy up and look after it as it deserves. I would therefore like to get to the bottom of this issue and stop the leak from happening.


I am baffled by it and would appreciate any insight anyone has. I acknowledge that my observations may be irrelevant and the leaks occurrence after sitting totally coincidental but maybe not …....

[hillsy]

Do your forks have bushes in them between the stanchions and the lowers? I know the later GS's do and they need replacing to bring back the rigidity in the fork.

If you do not have these, then it's possible the RHS fork lower is worn and the fork upper "moves about" inside the leg which in turn elongates or ovals out the seal.

[Bill Alexander]

Thanks Hillsy
I see where you are coming from. There is no bush in my tubes. I have looked at diagrams in my manual and see what you mean in one of the later model set ups. I won't rule out that there is wear and it gives sufficent lateral movemet to elongate the seal but I have just been out and given the forks it a pretty hard twist and shake but I can't get any lateral movement. Also what would be a reason for it taking a while to manifest ?

[Cyrano]

The leak always seems to start after the bike has sat unused for a prolonged period (for me that means 2-3 weeks).

This /\/\/\

Mine used to go after sitting through a winter (4 - 6 months) but I wouldn't have thought that 2 - 3 weeks would do it.

[mrbill5491]

No inner bushings for the forks? That sounds odd to me. What does the slider tube of the forks slide on in the lower leg? Are you using air pressure in your forks?

I get 4-5 years if not more out of a set of fork seals. One thing I do is wipe the fork tubes down once I get in from a ride.

[Bill Alexander]

Mr Bill
Thanks for the input

No inner bushings for the forks? That sounds odd to me. What does the slider tube of the forks slide on in the lower leg? Are you using air pressure in your forks?

Nope (unless we are not using the same terminology here) no bushings. As far as I can tell from the diagrams and what I see in my spare set of forks the slider tube slides directly in the fork leg - no bush. There is quite a large bearing surface and lots of oil about to lubricate so unless the forks are run dry of oil or the oil is full of grit the risk of wear is pretty low (I would think). In my manual, which covers 1978-81, it appears that only one model in 1980 (the GS1000GT) had the bush arrangement in it ????

I do pressurise the forks and I have a regulator on my compressor to make sure the pressure is right and even. On one of the previous occasions that it leaked I let the air out but it didn't seem to stop the oil !!!!

I get 4-5 years if not more out of a set of fork seals. One thing I do is wipe the fork tubes down once I get in from a ride.

Yes, I would expect at least that and I think the lh side has been good for 6 years (memory fails - I may have change the left seal on one occasion just in case - not sure).

Thanks

[Agemax]

I do pressurise the forks and I have a regulator on my compressor to make sure the pressure is right and even.

Using an air compressor to set the air pressure in the forks seems a bit wrong. most of us use a bicycle pump or a proper mini hand pump specially for fork leg pressures. Are you sure you are not over pressurising the legs? what air pressure do you run in them?

[Bill Alexander]

I do pressurise the forks and I have a regulator on my compressor to make sure the pressure is right and even.

Using an air compressor to set the air pressure in the forks seems a bit wrong. most of us use a bicycle pump or a proper mini hand pump specially for fork leg pressures. Are you sure you are not over pressurising the legs? what air pressure do you run in them?

Yeah, I probably shouldn't have said that . It is true that the book says not to use a compressor but my compressor has a good regulator which can be set to the required 80kpa and I have checked the calibration of the gauge on occasion. I find it a good way to get evenness and accuracy - it is such a small volume of air required that even the volume taken by a gauge can drop the pressure a couple of psi. Anyway, I am pretty confident I have never over pressurised them and if I had I would have expected the leakage to show up within days rather than a year or two later.

[GregT]

Bill - it's the seals drying out between usages IMO. Some fork oils are more prone to it than others. I've struck it with racebikes which sit for long periods between use. Air assist doesn't help, less instances with straight springing.
Two things you can do.
Increase the pressure of the garter springs in the seal. If you pull a garter spring, you can see where the ends meet and are screwed one into the other. There will be a pointed end and an open end, cut about 1 - 1.5mm off the open end and rejoin. Fiddley as the first time you do it but it can be done.
Second, add a teaspoon of a teflon base grease to the fork oil. Besides easing the action, it helps prevent the seals drying out. ATF has the same effect.

[Bill Alexander]

Thanks Greg,
Good tips esp about tightening the spring - might have a go at that.

Seem to remember having trouble finding a "fork" oil at one point and don't remember what I used. I used the last of what I had last time and stupidly didn't keep the bottle as a sample. Are you saying to use all ATF or just as an additive ?

[GregT]

Use a good quality one for a start. In NZ we don't have a particularly wide choice but the Maxis brand seems quite good. Anything sold as having anti foaming agents helps too. I'd just use atf as an additive.
If you know a suspension guru local to you - dirt or roadrace - ask them for a recommendation as to fork oil. They're dealing with this stuff daily so should know what's good locally. If they ask you what centistoke rating you want, just look blank and say it's heavy and slow....
Personally, the biggest problem I have with GS1000 forks is an owner who does seals often due to his habit of pulling wheelies (on track of course....)