RockShox Reba losing negative air pressure – what’s gone wrong…?!

… and how do I fix it (or is it an LBS job?)

I’ve got some ’07 (I think) Reba SL forks that when I got them off here a couple of months back, felt pretty firm. “Must have been a big lad”, I thought, then when I checked the positive / negative air pressure, the positive was fine and there was nowt in the negative. Not a single psi.

I put some in (135psi in both suits my weight) and all was fine, but recently, I’ve noticed that the negative air goes down to practically nothing overnight. Any idea what’s gone pear shaped, and if so, is it something resolvable without a trip to my local friendly shop? I just fear it could cost me as much as I paid for them to fix it.

Also, is there an order in which they should be pumped up? Posi before neg or the other way around?

Cheers in advance.

first try adding mil of 15wt suspension fuild to the chamber (remove valve core and syringe it in there) leave the fork upside down for a bit and inflate the chamber and see if it holds air – dry air seals dont seal.

It could also be the valve core itself that is loose and leaking.

if its not either of the above then your looking at a seal change…

NB, positive chamber first…

Hey there, I’m sad to report I’m having exactly the same problem with my rebas (also SL – 08 I think)

I noticed the problem a few of weeks ago when doing Skyline – after riding the 40 odd km (including far too much climbing!) when I finally got to that lovely descent I couldn’t enjoy it as my forks were all over the shop! The travel just sort of disappeared! I stopped several times (as did my kind friend with the shock pump) to try different pressures, but I either had to run them really hard (50psi in negative) or with reduced and very sketchy travel.

I’ve left them for a few weeks (riding my ss) and just went to see if the problem might have sorted itself out, but it’s worse. They won’t seem to hold any negative air properly. The gauge is reading 70psi but there’s only about two cms of travel showing – and that’s with me pulling it up.

One bike mechanic I know suggested letting all the negative air out (whilst the bike is upside down of course) then leaving it a few mins and pumping it back up to pressure. This did work for me once a while back when I had the same problem (but not as seriously) and it sorted it right out – so it’s worth a try! Unfortunately my forks are past that.

I spoke to my lbs and they said it sounds like a broken seal (which is what my friend who was carrying the shock pump that day also said). Lbs recommended sending them off to TF-tuned, who I’ve heard are excellent.

I don’t know how much it’ll cost but I can let you know when I do. I don’t have much choice than to get them fixed. I, like you, just hope it isn’t going to be a fortune!

Just checked TF Tuned website – they charge £79 for a full service, incl. replacing the seals…

Sounds like you need to reset the pistons, but as The Great Stonk says, if the seals in the chambers are dry it will not help for long.

Basically the process is this:

-inflate pos to a high figure (150 or so)
-empty neg
-empty pos
-repeat 2 or three times

then
-inflate pos to correct figure
-inflate neg to same PSI or slightly (5psi or so) more

Yowch! I’m sure TFT’ll do a brilliant job, but I didn’t pay much more than that for them!

I’m going to have a crack at The Great Stonk’s suggestion before resorting to throwing that at them. Do your forks have the little chart with the rider weight / posi / neg pressures on them? 50psi seems quite low for the negative, AFAIR, it’s the same pressure in both chambers?

retro83 – that sounds do-able to my (non mechanic) mind / hands. I’ll go give it a try. Am I putting too much air in do you think? I’m going off the chart on the fork lower, and it’s 135 – 140psi for my (13 stone odd) lump.

retro83 – that sounds do-able to my (non mechanic) mind / hands. I’ll go give it a try. Am I putting too much air in do you think? I’m going off the chart on the fork lower, and it’s 135 – 140psi for my (13 stone odd) lump.

It’s worth a try, but the seals might already be nackered if they’ve been running dry 🙁

I think I used to use about 115 PSI in my air Revelations and I’m about 14.5 stone 😀

Yeah, it’s not cheap is it! I might give retro’s suggestion a go too – I’m pretty sure the seals are knacked, but it’s worth a try (especially if it’ll save me £80 in the short-term)

Yep, 50psi is very low – I only ran them like that at the end of the Skyline trail as anymore and the travel disappeared. I normally run the neg at about 75psi and the pos at 70psi but then I’m less than 8 stone. I doubt it’s down to how much air you’re putting in… if only it were that simple!