Hi guys I recently bought a pair of revs that were 150mm . I installed a new airshaft yesterday at 120mm and after putting them together the forks won’t show 120mm of travel measured at the stanchion unless I put in around 100 psi . I need them roughly around 80 psi and when I lower the pressure the forks sink back to approx 110mm of travel. Any ideas ? Thanks

They’re sucking down due to air migrating to the wrong chamber I believe.

I’d do lower leg service and use just enough grease to lube them & not so much as to clog them. You can skimp with minimal grease in the airshaft and add 1cc of oil in the top once assembled.

It’s a common issue, others swear by a shoving a cable tie down the side of the fork seal to release the trapped air, but I think this may be a short term fix

I’m sure others will be along with other ideas as it’s plagued many of us at one time or another.

It’s a feature. If you want them to rest unsagged at 120 you’ll need a longer shaft or one of the new debonair seal heads which makes the fork sit higher in its travel.

Or if it’s sucking down severely then the chambers haven’t equalised and you’ll need to cycle the fork incrementally as you repressurise.

Which model of airshaft did you fit? The newest ones (with the deeper piston head and a red foot nut on the end of the shaft) have a bigger negative air spring volume and would require more positive air pressure, though 20 more psi does sound like a lot.

If its the previous model airshaft (thin seal head and silver foot nut on the end of the shaft), it could be the negative and positive air chambers have not been equalised. This can be fixed by cycling the forks up and down with a bit of pressure in the positive chamber.

It could also be that there is grease covering the internal ‘dimple’ on the inside of the fork leg – this allows air between the positive and negative air chambers. If there is too much grease it won’t allow air to cross over.

Without wanting to teach you to suck eggs, have you set the sag correctly? See this SRAM video, particularly the bit around 0:50 about equalising pressures.

Hi guys thanks for the help. I took the air cap completely off and pulled up on the lowers and heard a huge suckey noise . Pumped them back up and all seems normal. Yes it is the newer air shaft. I think maybe I might have been a little bit too liberal with the grease maybe on the seal head ? Hopefully this is a cure and I don’t have to strip them down again.