Note: these diagnostic procedures will apply to pretty much any Rockshox dual air fork including Reba, Reba 29er and Revelation forks.
Issue: fork stuck down or not returning to full travel
There are a number of potential causes:
- neg air pressure greater than pos air pressure;
- too much stiction in the fork caused by lack of air piston lube or splash lube;
- damper fluid leaking past rebound rod seal into fork lowers;
- leaking air piston seal allowing positive air pressure into the negative air chamber;
- leaking positive air spring schrader valve or top cap.
Diagnostic procedure:
- let all air pressure out of neg side - does the fork return to having full travel? If yes, neg pressure too high (but may be OK to get small bump compliance - ie. sometimes with particular pressure/travel combos you need to loose a bit of total travel to arrive at a plush setup);
- increase air pressure in pos side (say 100psi) with no pressure in neg side - does the fork length increase? If yes, then you may have excess stiction in the fork (lack of air piston lube or splash lube in the outers) or you may have a leaking air piston o-ring;
- cycle fork with 100 psi pos and no neg pressure - is there now any pressure in neg side? If yes, then you have a leaking air piston o-ring. If no, see if there is a leak at the positive air spring schrader valve or top cap by painting a water and detergent mix around the top cap and schrader valve and see if there are any air bubbles. To fix see if the top cap is tight, replace the valve or the top cap o-ring.
If the answer to all three questions is "no" then damping fluid in the damping leg has leaked into the fork lowers and the rebound rod seal (possibly just an o-ring) needs replacing. Get an o-ring kit or full service kit
Issue: fork not achieving full travel
There are three potential causes:
- too much pressure in the positive chamber;
- too much pressure in the positive and negative chamber;
- damper fluid leaking past rebound rod seal into fork lowers.
Diagnostic procedure:
- let all air pressure out of the positive and negative air chambers - can you compress the fork all the way down?
If the answer is YES, then you're running too much pressure in the positive chamber. Set your positive pressure to achieve the desired amount of sag .
If the answer is NO, then damping fluid has leaked into the lowers past the rebound rod seal. You can't compress damping fluid so this is stopping the forks achieving full travel.