Air in shocks?

pits · World Chat Champion Joined: 22 Apr 2008 Karma :

Seem to have an issue with my forks on my Duke, and I have no idea how or what is happening, but I think I am getting air in my shocks, or something is wrong with them.

At the moment I have no damping on my suspension, you try and compress the forks, nothing happens, they just don't move if you push down on them.

Now I believe they are filling the left over void with air, or something is mega wrong with my rebound on them, but it did this last week, and when I undid the top caps, a lot of air shot out of one, which leads me to believe there is air getting in.

Is this possible? I am guessing that it would be getting in through the lower dust seals? They are the Showa units, non adjustable.

If I am honest I have no idea Mr. Green

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Should be a bit of air in there. Acts as a spring. When lightly compressed and with the valve released that air will come out.

Have they suddenly stopped moving?

All the best

Keith
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Pete. · Super Spammer Joined: 22 Aug 2006 Karma :

Many forks are air filled, they'll usually have a valve on them for adjusting/re-filling.

If they are not moving at all that won't be because of air in them because the air would compress allowing the fork to move.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy

pits · World Chat Champion Joined: 22 Apr 2008 Karma :

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

I would suggest this is actually a damper problem, possibly a screwed shim stack not letting oil through on the compression stroke so when you accelerate the forks extend to their full length but cannot compress again.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Which bike is it?

As Pete says, the air would still compress. If the air is really building up then I would suspect it is a symptom rather than a cause. Are the forks extending fully? If rebound damping was somehow blocked then the forks wouldn't return to full length properly and that would probably pressurise the air.

But that is VERY much a guess without knowing the forks and having a look at how that set work.

All the best

Keith
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Pete. · Super Spammer Joined: 22 Aug 2006 Karma :

I'm with Sickpup it sounds like there's no oil passing on compression. What has caused this to start to happen? Have you had the seals done or any other work?
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy

pits · World Chat Champion Joined: 22 Apr 2008 Karma :

That is what I thought, air can be compressed.

shocks were working properly, I put cable ties on them took it out for a ride, and I was getting decent travel on the front, now the front is up at the top and they just wont go back down, if I push them.

Had no work done to them, the seals aren't leaking fluid, there is oil in the forks as well.

Bike is a 2000 Ducati 750SSIE with the non adjustable Showa front end.

Sickpup, I see what you are saying, but I don't think you're right, I need to consult a trainee mechanic who has only touched one set of shocks in his life Laughing

This last bit is a joke, anyone wondering, read the GT550 air shocks thread, rather amusing.

Pete. · Super Spammer Joined: 22 Aug 2006 Karma :

If you drain the oil they will have a lovely bit of bounce Very Happy

____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

The only time I have seen this before was a set of GSXR600 upside down forks where someone had bent the damper rod while changing the forks seals.

That or the shim stack thing I mentioned earlier.

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

As this problem intrigues me heres a picture from Showa of what the inside of your fork probably looks like...

https://www.showa1.com/en/product/motorcycle/img/detail_shock_touritsu.jpg

Which may give you an idea of what could go wrong, not much.

pits · World Chat Champion Joined: 22 Apr 2008 Karma :

Well, I have left it and checked it this morning and I have some suspension back.

What I can see in my mind is that there is a build up of pressure in the forks, and it can't go anywhere quick enough to be removed, but that pressure can drain over night.

I have no idea really, I mean there is no oil on the shiny bits, and when they have been left or had the top caps removed, they work again, and I haven't had any work or dicking about with them until now, time for a garage me thinks Crying or Very sad

pits · World Chat Champion Joined: 22 Apr 2008 Karma :

Got the bike back now from having a few jobs done, found nothing wrong with the forks, but rebuilt them.

Reckoned the oil was too heavy at 10w, still not sure on that diagnosis as it had been fine sine April when I bought it then went from riding lovely to instant riding like a big bag of crap.

New seals, and the oil replaced with 5w, which I think may be a bit too thin, the bike rides lovely, but the arse end is really stiff now which is fine, but the front is murdering my wrists and you can feel every single bump in the whole road, might try dropping 2psi of pressure out of the front tyre and the rear, but because I weigh nothing I don't think I am putting enough weight on the bike for the thinner oil, may take it back and see if I can back to 10w depending how it continues to ride, at the moment, I don't like it.

That said, I appear to be having no problems on the front end, road around 150 miles over the course of Friday and Saturday, all different roads, even some really bad country back roads and all seems good.

Again, just not sure on this oil in the front end, would dropping the tyre pressures help? It is just to stiff for me on the front that I am not as confident in going as low as I used to as I can feel every bump, it feels more stable and doesn't feel like it wants to chuck me off like it did before, but it feels similar as you feel every little stone on the road, and as I said it also destroys my wrists now, still happy though.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

5W oil is thinner and should give a softer ride, with you feeling less bumps. Thicker 10W oil would hammer your wrists even more.

Is the preload on the forks adjustable? If so try running a bit less preload.

Simple terms, the springs control how far the suspension moves while the damping controls how quickly it moves.

All the best

Keith
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