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Another question regarding the bladder on CC forks

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Can you use a needle like you would use to fill a basketball for releasing/filling the inner bladder on the closed cartridge forks? Or is there s special, smaller needle? I'm afraid I may have messed up by using a basketball style needle to bleed out the pressure when I was getting ready to disassemble. Hopefully not!

 

Any help and tips for what to use to fill it would be greatly appreciated as well. I was planning on using a friends Fox shock pump. I'm hoping that it will do the trick.

 

Thanks!

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You needed to use this type needle which has a much smaller profile to barely penetrate the diaphragm inside...

http://slavensracing.com/shop/nitrogen-charging-needle-with-schrader-valve-for-ktm-husaberg/

I suspect you'll need to replace the internal diaphragm as it's unlikely the cartridge will not retain it's pressure when you set it to 17psi. I'm interested to hear who else has do e the same and what their experience was.

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Ya, I also tried a ball-filling needle and it destroyed the silicone/rubber seal. The hypodermic needle which is what's necessary for this type of work, has a tapered hole and a point to "cut" through the silicone seal, leaving a very small hole. When retracted, the hole fills up with silicone on its own.

You will need to replace the silicone seal. Just pull the bladder down a bit and you'll see the piece of white/clear rubber under the hole. Use a screw driver to pop the old seal out and its easy to get the new seal in. I actually bought a sheet of silicone rubber for less then the KTM part and made my own seals.

The needle is available from Race Tech. I also use a loss-less chuck hand pump like slavens does in his video's.

In terms of charging the cartridge:

- Fill cartridge to approx 210cc's of oil

- Pump shaft a few times and wait for bubbles to stop

- Fully collapse bladder

- Install bladder and screw down cap

- Put cartridge in vice at a 70 degree angle so the bleed port is at the highest spot

- Lift bleed port with fingernail for a second to discharge initial air bubbles

- Pressurize bladder 6 - 10PSI

- Push rod through entire stroke once

- Pressurize bladder to 10 PSI

- Push rod through entire stroke again

- Set final pressure (15 - 25psi) depending on application

Do not push the cartridge through the stroke more then 3 times.

Edited by tye1138
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Ya, I also tried a ball-filling needle and it destroyed the silicone/rubber seal. The hypodermic needle which is what's necessary for this type of work, has a tapered hole and a point to "cut" through the silicone seal, leaving a very small hole. When retracted, the hole fills up with silicone on its own.

.

I have been curious how that worked, very cool!

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I do not collapse the bladder.

Also we need to lift the rod about 4 inches and pull down to expel the air under the piston before we install the comp. assembly.

Do this several times and wait for the bubbles to rise to the top.

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Thanks, guys! Looks like I need to replace the silicon seal and get the proper tools to fill the bladder back up. Not too expensive of a mistake, but looks like the bike will be down for repairs for a little while longer.

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I do not collapse the bladder.

Try it sometime… it does change the outcome.

Also we need to lift the rod about 4 inches and pull down to expel the air under the piston before we install the comp. assembly.

Do this several times and wait for the bubbles to rise to the top.

Yep, I forgot to write that, fixed it. ;)

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Never heard of that way , collapsing the bladder

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So, I received my fancy hand pump and needle assembly and am ready to reassemble. Here is what I did per the Slavens Racing video -

- filled the cartidge about 3/4 full with the rod fully extended.

- cycled rod a couple times and then let it sit for about 10 minutes for air bubbles to go away

- collapsed the bladder the best I could (it didn't want to stay collapsed) and inserted/tightened it down.

- put cartridge in vice. Top end of cartridge slightly elevated

- removed the little 2.5mm allen screw and filled the bladder to about 7psi. Oil and a little air came out the 2.5mm screw hole.

- installed the 2.5mm allen head screw and pressurized the bladder up to about 22 psi (my target is 18psi)

- cycled rod 3 times. A little air/oil came out the bleeder valve at the top of the cartridge.

 

According to the video, I should be very close to 18psi because cycling the rod a few times releases a little pressure. But my question is, how do I really know what my pressure is at? Can I insert the needle again and see what the gauge says? And if it is high or low, adjust accordingly? Or is that a no no once you are this far?

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You are likely about to make a 2nd big mistake if you follow the Slavens video. By using the 2.5mm air bleed screw I can almost certainly guarantee you introduced air into the forks and the dampening rod will not fully extend like it should. Many TT members have concluded that the Slavens procedure is flawed, at least in the way he showed in the video. Follow this procedure and as long as your components are on proper working order, it'll be fool proof

1. Take apart the fork and extracting the whole inner cartridge from the outer fork.

2. Take the opportunity to inspect the cartridge and confirm that the rebound piston rod is still extending fully to ensure no internal seals have been compromised

3. Unscrew the inner cartridge fork cap (you'll need a little fork cap removal socket)

4. Slowly pull out the bladder. After removal squeeze the bladder to release the air inside

5. Drain the fork oil from the chamber, and stroke the piston rod to spray out any remaining oil from deep inside the chamber

6. Clean out the inside of the chamber

7. Fill the inner chamber approx 70mm (3 1/2 inches) from the top

8. Stroke the piston rod at least 10 times to force any trapped air towards the top

9. Let the cartridge sit for 10-15 minutes to let the air bubbles at the top of the oil to disperse

10. Take the bladder assembly, and remove the screw closet to the Comp adjuster on the top of the fork cap

11. Using the needle pump available from Slavens or the Powerparts catalog, pump up the bladder with 2PSI, yes just 2 PSI. Be careful not to squeeze the bladder to avoid releasing pressure

12. "Slowly" insert the bladder into the cartridge and apply steady slow pressure as oil overflows from the top. You'll see air bubbles being squeezed out as you do this

13. Fully screw the inner fork cap

14. Insert the needle back into the bladder screw hole and add 25 PSI to the bladder, remove pump and insert screw back in

15. Take the fork in hand, and hold the chamber at a 45 degree angle with the top of the fork facing upwards and the bleeder valve (the one with the little spring) facing upwards

16. Pump the piston rod just 2-3 inches with 5-10 mini strokes to force any air towards the top of the fork and confirm the rod is fully extending nice and smoothly

17. Now, slow and steady, pump the piston rod all the way in (keeping at a 45 degree angle) and hold for 1-2 seconds at the top of the stroke (Air and oil will be released out of the bleeder valve)

18. Repeat step 17 no more than 4 full strokes, 3 is usually enough. Confirm that the piston rod extends smoothly and fully

19. Keeping fork upright, open up the Bladder screw hole and set the bladder pressure to 17.4 PSI (OEM Spec) using the needle pump. Even though you initially set the bladder to 25 PSI, you will notice that the bladder pressure has equalized somewhere in the 15-20 range and setting the pressure to 17.4 is OEM recommended.

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