[foxracing]

Here's the story. Yesterday my friend and I decided to work on his 2007 888 SL ATA, and remove the par piston. We did, successfully. (Only opened the ATA side, didn't touch the damper side.)
Put the fork back together, pump it up to 100psi.
Result is the fork feels nice and plush with the first 130mm of travel, and we never get it more than 160mm.
So, we put the bike upside down, deflate the fork, opened the damperside foot nut, compress the fork, let the air out and seal it up again.
Tried with hands to compress the fork (when there's very low air pressure in sfa chamber), yes ,we can bottom it out.
Pump it up to 100psi, still counldn't get more than 160mm.

Are we missing anything?

some extra info:

We couldn't buttom out the fork originally when the par is still there with correct pressure for enough sag. That's why we decided to remove it.

We put 10ml of suspension fluid into the air chamber for lubrication when reassembling.

Tried search, and read the thread 07 66 sl ata setup information, and the posts of Renegade (Thanks, that helped a lot!!), but it was mainly about 66, which has another air chamber in the RC2 side. But 888 doesn't, so I figure it'll be different.

 

[DHidiot]

The ATA only needs like 4-5 drops of lubricating oil in it without the PAR. 1-2 drops above the piston.

 

[Danimal1]

too much oil in the dampener side

 

[wormvine]

100 psi is a lot. I ran 55psi SFA and 100psi PAR when I had my 66SL and I weigh 190lbs geared up. How much does the rider weigh?

There is no air chamber on the other side on the 888???? Hmmm. I thought there was.

How are you testing thr fork to see how much travel it gets?

 

[DHidiot]

100psi is fine with the PAR removed. You can drain the oil by just getting a valve core remover tool and letting the oil drain out of the bottom shrader valve in the air cart, then dropping a couple drops of fresh oil in, and airing back up. See if that works.

 

[foxracing]

Rider weighs 90kg with gear.
Even on flat land, I can feel a VERY strong ramp up at about 160mm of travel.
Will try to get some oil out.
What about the negative air settings?

 

[essenmeinstuff]

If there is too much oil you should feel a similar ramp up, but to a lesser degree with less or atmospheric air pressure.

 

[kidwoo]

Rider weighs 90kg with gear.
Even on flat land, I can feel a VERY strong ramp up at about 160mm of travel.
Will try to get some oil out.
What about the negative air settings?

Long story short, they made the air chamber too small causing the fork WAY too much ramp up at the end of the stroke.

Letting all that oil out will help but you'll likely never still get full travel. I rode that fork for two years and ended up just dialing down the travel to just over 7 inches. This worked for me and is one of the reasons I got the fork. I wanted to lower the front end of my bike (07 demo 8, slack setting). At 7ish inches of travel, you will get the full range because of the way that travel adjust system works.....dialed down, you only compress the first 7 of the full 8 inches.

But set at the full 200mm, I could never get full travel.

The negative air chamber sets itself. Ideally you should have the piston at full topout when you reassemble it. You can mess with this a litte by moving it about 3/4 of an inch into the travel when you reassemble it. Just don't compress it too much or your fork won't fully extend when you inflate it.

edit: and yeah I took the par piston out almost immediately after getting the thing.

 

[foxracing]

By full topout means the piston touches the black rubber bump, and the rubber bump touches the cap when I reassemble?

 

[kidwoo]

By full topout means the piston touches the black rubber bump, and the rubber bump touches the cap when I reassemble?

Exactly.

 

[foxracing]

Double post... edited... Sorry

 

[foxracing]

With this kind of negative volume setup, do you feel the fork is stiff and hard to compress during the first 2 inches of travel?

 

[wormvine]

With this kind of negative volume setup, do you feel the fork is stiff and hard to compress during the first 2 inches of travel?

No, The whole point of negative air is to keep initial stiction to a minimum.
There is an indention(a dimple) in the cart housing that lets air pass from the main chamber to the negative side. (other side of the main piston). It doesn't matter where you put the piston when you reassemble cause as soon as the piston passes over the indention Air equalizes to both chambers. The indention is fixed and cannot be changed, so the neg chamber volume will always be the same.

That is why when you first air up after a disassemble, you should cycle the fork so that air gets into the negative side. Pressure will decrease a little as it equalizes if you don't.

 

[kidwoo]

No, The whole point of negative air is to keep initial stiction to a minimum.
There is an indention(a dimple) in the cart housing that lets air pass from the main chamber to the negative side. (other side of the main piston). It doesn't matter where you put the piston when you reassemble cause as soon as the piston passes over the indention Air equalizes to both chambers. The indention is fixed and cannot be changed, so the neg chamber volume will always be the same.

Not entirely true in my experience. The negative chamber DOES set itself just fine if you reassemble the cartridge topped out. In an effort to get full travel out of mine at 8in, I tried reassembling the cartridge with the piston about 1/3 of the way into the travel. When doing this it would never reach full extension under rest...or even close. I don't remember offhand what it looks like because it's been a while since I've had it open but I'm pretty sure that neg air setup is a one way valve.....which kind of makes sense.

That is why when you first air up after a disassemble, you should cycle the fork so that air gets into the negative side. Pressure will decrease a little as it equalizes if you don't.

Yup. Foxracing: If your fork is topping out hard after you get it back together, go ride down a staircase or something a few times. The negative air pressure should set itself up after some cycling.

 

[foxracing]

OK. I'm a bit confused....
So in a nut shell, does the position of the piston affect the curve of the air spring after all? I mean, after some use, and in normal condition.

 

[wormvine]

Not entirely true in my experience. The negative chamber DOES set itself just fine if you reassemble the cartridge topped out. In an effort to get full travel out of mine at 8in, I tried reassembling the cartridge with the piston about 1/3 of the way into the travel. When doing this it would never reach full extension under rest...or even close. I don't remember offhand what it looks like because it's been a while since I've had it open but I'm pretty sure that neg air setup is a one way valve.....which kind of makes sense.

I think I understand what would cause that issue. If the piston is past the dimple in the compression stroke, the residual air pressure that is on the negative side might stop the piston from extending towards the dimple. Thus restricting travel. You would have to physically extend the fork till the main piston reached the dimple to equalize chambers.
If you fully extend the piston before assembly, the negative side will have very little pressure till the first compressions and then it will equalize. Soyes, I agree that where you place the piston in relation to the end cap upon assembly can affect the travel if the neg air pressure stops the piston before it extends to the dimple.

But the true proper volume of the negative chamber cannot be adjusted unless you put some grease or foam in it.

 

[wormvine]

OK. I'm a bit confused....
So in a nut shell, does the position of the piston affect the curve of the air spring after all? I mean, after some use, and in normal condition.

No it does not. The volume is fixed by the dimple. But if you assembled the cart with the piston fully compressed, the residual air on the other side of the piston (neg chamber) might stop the piston from extending past the dimple thus never allowing the chambers to equalize and reducing travel.
So the best way to reassemble is to fully extend the piston toward top out. Put it right against the foam top out bumper. Then assemble and pressurize extended. That way when the first compression strokes happen, the piston will pass over the dimple and equalize!

 

[foxracing]

OK, I got it. Finally!! Thanks!!

 

[kidwoo]

Yeah what he said

 

[jsma09]

Hey guys, I know it's a very old post, but I am working on my 2007 888 sl ata and would like to replace all the o-rings. I have deflated both air chambers, disassembled the main chamber but I can't get the PAR piston out of the cartridge.

I tapped with a soft mallet and a plastic the inner cylinder in the cartridge but I'm afraid to damage it I if hit too hard. It doesn't slid out and I haven't been able to see the retaining ring out from the other cartridge end yet.

Any tips?