Rev dual airs losing travel – what to check ?

Hello,

Have a set of Dual air Revs (2012) and have noticed that over a week or 2 the amount of stanchion showing decreases (measured).

I set them up with about 85psi +ve and 75psi -ve. It’s as if the two air chambers are equalising or something.

No change in performance as such, but 5-10mm less travel after a few rides & releasing the pressure from the -ve chamber restores the lost travel.

Interestingly I have another bike with the same model fork and year but I leave that for weeks between rides and nothing changes – probably only check the pressures twice a year.

So can anyone advise exactly what to check.

Change the air seals is best thing to do really, due a service by now if you haven’t done one, not worth the faff of stripping and cleaning for them to work ok for a week or two and then start doing it again and necessitate another strip and rebuild.

Had this with mine too, would be interested in an answer.
Edit, thanks for the reply.

leak between pos and neg chanbers or out of seal head most liekly cause, worn seals to blame.
or

air valve cores leaking.

The chambers are different sizes so you’ll get a bigger pressure drop when attaching the shock pump on neg chamber so bear this in mind to when checking pressures

Mmmm – they may be 2012 MY (bought them new last December) but I’ve only been using them since April this year so don’t really want to pay out for a full service after just 6 months use.

Did a ‘lower service’ after about 3 months – cleaned foam rings, lowers etc. but those things don’t affect the air spring.

I’m thinking if the -ve chamber valve is leaking then that would lower the pressure and travel would increase so could do with homing in on the ‘air seals’ – can you get service kits for just those parts ?

Maybe return to seller for a warranty inspection then if under 12 months and have had minimal use, we do pattern seals kits too if you wnat to just replace air seals.

This is called “suckdown” and it happens to 99% of dual air revs, there are many threads on it: see below for two to start but a Google reveals more.

http://singletrackworld.com/forum/topic/rs-rev-dual-air-strange-going-ons-advice-needed

http://singletrackworld.com/forum/topic/dual-air-revs-my-thoughts

In a nutshell when you pump up the negative, pump it up just until you start to see suckdown occur (use the o ring to spot a small movement) – the chambers are balanced at this point.

10mm is too much though with 10psi less in the neg chamber, as stated in OP, shouldn’t be any pressure transfer between chambers, I’d expect 2 to 3mm approx when both chambers balanced at 100psi each.

Thank you for the info – LoCo understands the problem. I plan to strip them down, check and service the air spring.

There appear to be 2 kits available for this (2012 dual air MoCo DNA)

Basic – RS part number 00.4315.032.180

Full – 11.4015.550.000, think fishers call it R5550000.

The latter looks favourite as it also includes the foam seal for the air springs ?

I’ve got that P600 red grease stuff or is 15W oil alone or Red Rum better for the air spring ??

10mm is too much though with 10psi less in the neg chamber, as stated in OP, shouldn’t be any pressure transfer between chambers, I’d expect 2 to 3mm approx when both chambers balanced at 100psi each.

Yeah, you could be right.

However personally, I run mine with 80psi in the + and 50 in the –

This gives about 3mm suckdown, if I run 70 PSI in the negative (20 psi more, 10 psi less than +) I get easily over 10mm suckdown.

Full kit includes foam ring for main air piston. grease ok, little bit of oil in air chambers ( very little) will help things too