Installing lowers on Lyriks and getting a vacuum - help!!

[Nautonier]

I got my Vorsprung Luftkappe and tried installing it today. Everything went smoothly and as per Steve's excellent instructions until I went to pump the fork up and equalise etc. The forks are stuck down, somehow air is getting trapped in the lowers and sucking them down. Even at 100psi they won't extend to the full 170mm. There is no 'top out' as Steve describes as they are nowhere near maximum travel. I tried the cable tie method to 'burp' air out of the lowers and it didn't work.

I also tried undoing the bottom bolts again and that released the air in the lowers. The problem was that the air shaft wasn't full extended, so the only way I could get it to extend again was to pump it up while the lower bolts were detached. It seems like the air shaft gets sucked back up the stanchion, so the only way to attach the lower bolt is to compress the lowers onto the uppers, which then creates the vacuum that sucks them down.

When I initially inserted the air shaft back into the stanchions, I made sure the shaft was fully extended and didn't attempt to push it in. It may have gone in a bit when I pushed the lowers on to make the bolts line up with the shafts.

The forks have just had a full service and were working perfectly before I took them apart. Since pumping up the air chamber while the forks had the lower bolts off I'm getting closer to 170mm travel and the Luftkappe seems to be working well, but I can still pull the stanchions much further out of the lowers.

Has anyone had this issue of the air shaft sucking back and the subsequent vacuum in the lowers reducing travel before? Am I good to ride or do I need to take them apart again? Or am I missing something really obvious and looking at a one way trip to the f@*kwits thread? I know the way the Luftkappe works is to create negative air pressure, but that should only be after it equalises. Initially, as per Steve's video, it should be topping out hard at the absolute end of its travel, which, I would guess is even more than 170mm as the top-out bumper has been removed (I can pull the stanchions out to about 180mm).

 

[moman]

Have you tried forcing the chambers to equalise by pulling firmly on the crown arch while putting your foot on the bolt up axle? You should hear a small fsssst and any air trapped below the luftkappe should be pulled into the positive chamber.

I’ve done this when I had lost about 10mm of travel to get rid of that trapped air in the air shaft chamber.

How much travel have you lost?

 

[mark22]

Sounds like the small oring under the Laftkappe is not present or not sealing.

Pull out the schrader valve to make it easier to remove the piston and shaft.

 

[JTmofo]

I'd also check that the equalization port isn't full of grease.
Can happen if you go too heavy on the slicko at the piston head.

Sent from my SM-G955F using Tapatalk

 

[Nautonier]

Thanks for the replies, I got it sorted. I was going off the Vorsprung video only, there are some additional (and crucial) notes on their website that I missed. In particular this:

NOTE: Make sure the Luftkappe piston is close to or touching the*sealheadwhen you reinstall the*sealhead. If it's pushed a long way into the stanchion before the*sealhead*is reinstalled, you can trap too much air in the negative chamber, which will result in your fork "sucking down" even when pressurised as it is not able to extend far enough to equalise pressures between positive and negative chambers.

Note: ensure footbolts are done up with the fork fully extended. If they're done up with it partly or completely compressed, the fork will suck down into its travel.

Although Steve's video explains everything really well, the problem area is where he says "and refer to the Rockshox manual for this part..." That's where I got lost and stupidly took the top cap off the air spring, so when I reinstalled the piston and air shaft, it wasn't pushing against anything, so must have worked its way in enough to create a vacuum when I was installing the shaft bolts.

I found a thread on MTBR where so many people made the same mistake I did. On the plus side, I've now got the lower leg service/air shaft assembly thing down pat. Second time I did it I reckon it took me less than 10 mins all up. Luftkappe is working beautifully now and my Lyriks no longer have the nasty top out they always had.

 

[Nautonier]

Have you tried forcing the chambers to equalise by pulling firmly on the crown arch while putting your foot on the bolt up axle? You should hear a small fsssst and any air trapped below the luftkappe should be pulled into the positive chamber.

I’ve done this when I had lost about 10mm of travel to get rid of that trapped air in the air shaft chamber.

How much travel have you lost?

I did try that, but no joy. I had lost about 35mm travel.