So, I’m building a bike for my son. He’s moving up from 26 to 27.5 wheels and is slowly accumulating parts with his Christmas/Birthday money.

We spotted a pair a secondhand 180mm Lyriks for a good price locally and and have fitted a 150mm debonair air shaft (he’s only 9 yes old/135cm so 180mm of travel turns his bike geometry into Chopper-land). At the same time replaced the seals foam rings etc. We followed the SRAM YouTube video and didn’t have any bits left at the end which is always a good sign.

However, they now need 100psi to have any kind of reasonable resistance. And that pressure ramps up really quickly, maybe only 10 pumps.

What have I done wrong? Clearly I’ve messed up but can’t figure out how.

Is the shock pump chuck actually on properly or Schrader valve blocked so not really putting 100 psi in the fork?

Check you’ve not created a big negative spring in the lowers when you’ve popped them back on after the shaft change, it’s easily done if you compress the air / damper rods fully before you put lowers back on.

You can equalise them by sneaking the end of a zip tie through the seal on each leg… it will be obvious if that’s the problem, you’ll hear a hissing sound.

Thanks both.

@K it’s Def on properly, but I’ll check it’s not blocked 👍

@t0mmm thanks. That definitely could have happened. You mean sneak it past the seal where the stanchion enters the lower?

Correct, you need to go about 1.5cm or so, just to get past the bottom lip of the seal, and don’t put any force through the fork, just let it sit. Obviously, make sure the area is clean to avoid pushing any dirt in!

It’s more common to have to do the same thing to release positive pressure if you don’t drop the lowers very often, although it doesn’t seem to be so much of an issue with the newer seals.

Might also be an excess of grease blocking air going to the negative spring. But deffo try the ziptie first

@t0mmm after much wiggling I still can get a ziptie past the seals. I’ll drop the legs this afternoon and reinstall with the rods fully out.

@honourablegeorge thanks, that’s also a possibility. I was enthusiastic with grease thinking it’d make it slipperier! Hopefully the lower leg reinstall will fix, otherwise I’ll have to take the new air spring back out and clean it. 🙄

If you want to have another go with the zip tie, you need a small one and if you look closely it should have a flat side and round side. Lubricate it then put the flat side on the stanchion and it should slide in.

If the pressure is building after only a few pump strokes the zip tie thing is a red herring but in opening up the fork to work out what’s going on with the air spring you’ll resolve it anyway.

Piston needs a light coating of grease, not fingers full of the stuff! Latest air spring has significantly less friction with the machined bushing.

I run 75 PSI in my 180mm Lyrics. at 150mm I don’t think its unreasonable that I would need to run 100 PSI to get the same sag with less travel. The debonair air shaft requires more PSI anyway to compensate for the larger negative volume so the 2 things combined will lead to much greater pressure required. 10 pumps I cant explain though – unless your pump has a really big volume? I cant work out how you could have assembled the air spring incorrectly to so limit the volume in the air chamber? Have you measured the travel you get? Is it 150mm? Id does sound like could be an issue with your pump or the shock valve…

I’d check it can achieve full travel with no air in. Sounds like possibly grease or oil in the spring (although this doesn’t explain the need for a higher pressure unless you’re working to avoid the bottom out at the shorter travel due to this).

Really appreciate everyone’s advice. Been bonkers at work so haven’t had time to strip them down. I did get a ziptie in there eventually but it didn’t work so I’m guessing it’s overenthusiastic greasing and possibly installing the lowers with the pistons compressed. Either way, going to have a go tomorrow evening and will report back.

Thanks again.

overenthusiastic greasing and possibly installing the lowers with the pistons compressed

Wont be either of those things. Vacuum does get trapped in the lowers and sucks the forks down a tiny bit but it wont cause the quick ramp up of pressure you are seeing. Grease is also a red herring unless you packed an entire tub of the stuff into the positive air chamber leaving no space for air.

My money still on valve, pump or just not being used to the increased pressure you need with less travel and the new air spring.

Check how much travel you get with the fork inflated to 100 psi. Is it 150mm as expected…if so how does it feel?