Coming from 7 years of riding vanilla's I was expecting a bit of faff, but this is ridiculous.
I set the - and + as per the guide on the leg and I get nothing like enough sag. Drop the pressures, I get the sag, but only something like 110mm travel. They loose about 30psi from each chamber over 2 weeks.
Has anyone got a foolproof way of setting these bastard forks up that is pretty straightforward for a simple soul ?
1) they dont lose 30psi from the chamber, thats just air from the spring entering the pump hose when you screw it on to check, expanding the volume available and reducing overall pressure.
2) Sag is usually about 20% of travel isnt it? So Id put in the pos air until you get the sag you want (or a little less) then match it with neg.
Remember the addition of neg sometimes pulls the fork a little bit further into it's travel. In which case dont use so much neg.
Stoner is correct. 🙂
In addition, do it like this:
When resetting air pressures, let the -ve air OUT first!
Then adjust the +ve air, then reset the -ve to the same amount as the +ve.
You can use more +ve air, but you run the risk of dragging the fork down into it's travel, so I never botther
Set sag to around 20-25% of fork travel. Ignore the printed RS pressures!!
The last 10-15mm of travel will rarely be used, but they WILL go if you hit them hard enough.
I also switched from Vanillas to Rev RLTs, and the Rev is in every way a better fork: Stiffer, better damped, better sprung, more supple.
🙂
feel free to miss the bin and chuck them my way 😀
Stoner and Peter, pretty much covered both the issues, have a look at the setup guide to for rebound and compression twiddling 😀
http://locotuning.co.uk/tech-info.html
loco, can you have a look at another thread for me please...wait there, will go and get the link
Actually they might be losing pressure, my 08 Revs lose pressure from the negative chamber, sometimes over the course of a ride all pressure is lost. I took them apart and there is a scratch inside the little aluminium bit that holds the O ring with a bit of swarf coming off, when they fitted the O ring they must have scratched the aluminium. I replaced the o ring and removed the swarf and they now lose about 20psi over a week which is better but not great. Never been impressed with RS quality though they are better since SRAM bought them.
If you are binning them I'll take them though!
following on from this thread:
http://www.singletrackworld.com/forum/topic/dual-air-u-turn-service-what-am-i-doing-wrong
I ordered a new upper assembly anyway from TFT - whcih also had the holes in the pos spring valve unit. So later found this thread
http://www.singletrackworld.com/forum/topic/rockshox-revelation-2010-u-turn-service-advice
Mates forks are running fine, but still concerned that the internals were not the same as for the manual.
any ideas?
bigjim when there's an air leak, it usually goes to the other side of the spring. Thats what happened to my mates uturn revs. I replaced all the orings with a service pack and it's been fine.
When the air in the spring moves across from pos to neg or vice versa, you can either get loss of travel, easily used, or full travel but stiffer spring. Im guessing the air can move both ways intermittently causing all sorts of shennanigans 🙂
Last version of the Uturn system, if it works leave it, for further details drop me a mail.
cheers Loco. So it was a late (undocumented) variant to uturn before they went to two stage travel?
Yes just for 2010 (i think) may have been fitted to some late 2009 models when they ran out of the older Uturn assemblies. 😕
magic. ta.
When the air in the spring moves across from pos to neg or vice versa, you can either get loss of travel, easily used, or full travel but stiffer spring. Im guessing the air can move both ways intermittently causing all sorts of shennanigans
IME you only get air moving from +ve to -ve
Why?
Well, if you don't use the forks at all, they'll both just equalize!
And if you DO use it, you cannot compress the -ve spring, only the +ve as the fork compresses. To compress the -ve you'd have to EXTEND the fork past the stop.
Compressing the fork raises pressure in the +ve spring, and then some air transfers to the -ve if there's a leak, resulting in a higher -ve pressure, dragging the fork down. The only symptom of this leak is the fork dragging down
🙂
Actually they might be losing pressure, my 08 Revs lose pressure from the negative chamber, sometimes over the course of a ride all pressure is lost. I took them apart and there is a scratch inside the little aluminium bit that holds the O ring with a bit of swarf coming off, when they fitted the O ring they must have scratched the aluminium. I replaced the o ring and removed the swarf and they now lose about 20psi over a week which is better but not great. Never been impressed with RS quality though they are better since SRAM bought them.
These things happen. I hd some Rebas like that. Did you not send them back under warranty? I did and got a new pair..... 🙂
Replacement air tubes are available on their own too, main thing is to be carful and use something as soft as possible to push the upper assembly out of the tube when servicing
Lowey, I have 2 sets on my bikes (one on my 5 spot and one on my Cotic Soul), both work great, if you want pop round and we can have a fiddle with them.
I don't use the sag as an indicator by the way, I use the pressures off the back of the leg and tweak from there.
understood PP.
Odd characteristic of my mates then that the travel was lost but the compression was still firm.
Stoner, yeah good point. What I [i]think[/i] happens is that you don't get an actual difference in pressures as the fork travel reduces, they just stay equal and the -ve chamber gets bigger due to more air in it as the fork dorps, if you see what I mean? So the spring/compression feels the same in isolation, but the fork gradually drops as air transferres each time you hit a bump/raise +ve pressure
When mine did it I didn't notice until I stopped and looked at the fork! 🙂
So the spring/compression feels the same in isolation, but the fork gradually drops as air transferres each time you hit a bump/raise +ve pressureWhen mine did it I didn't notice until I stopped and looked at the fork!
now that sounds like it might be right!
bigjim when there's an air leak, it usually goes to the other side of the spring. Thats what happened to my mates uturn revs. I replaced all the orings with a service pack and it's been fine.
No this scartch was in the seal at the bottom of the neg chamber, so it must just go into the lower leg. I didn't send them back as they were OK at first, it seems to gradually get worse as the o ring wears, guess less pressure is pushing the o ring into the scratch so air can get out more easily, pumping them up and oil leaks etc didn't seem too unusual from other people's experiences, plus having owned lots of RS forks since 1997, I'm used to them not working properly!
aha.
As others have said ignore the RS pressure guides: absolute bollox!
Always make sure you have slightly more +ve than -ve pressure else the travel is pulled down.
Pressure setting is a faff as setting +ve affects -ve and vice versa.
Once it's right it's good though.
I have two sets and they both very slowly loose a bit from +ve to -ve....
Thanks for the help guys.. food for thought.
So is it right then that you pump up your forks to the desired PSI, but when you reconnect the pump, the pressure drops as it fills the tube on the shock pump ? I never realised that, but now you point it out its obvious.
So you cant merely connect the shock pump to check pressure... as doing so will always drop pressure.
**** me this is a faff. Anyone wanna swap for some FOX 36 Vans ?
So you cant merely connect the shock pump to check pressure... as doing so will always drop pressure.
Yes! 🙂
Set pressure.
Go ride.
If it's not right, adjust as I said in my 1st post up there.
Don't connect the pump to check!
I've not touched mine in 3-4 months 🙂
Thanks very much guys. This is why STW is ace!
Loco... whats your current lead in on servicing my the way ?
Can one of you suspension guru's please explain Motion Control to me as I cant find anything on the Sram website.
What is it and is it adjustable.
Thanks.
compression damping innit.
Yep - it's the gold dial on the top right of the fork. It sets the sensitivity of the lockout - the larger blue dial mounted underneath the gold motion control threshold.
It basically chokes the compression, but is only activated when the blue dial is turned.
Right, er... its attached to a remote on the bar which I thought just locked the fork out. Does this blue dial affect how the fork compresses then or is it purely for lockout ?
I know I know,.... I'm too stupid to own this fork etc.etc.
Ah! The blue dial and the bar remote are one and the same thing.
Does the blue dial have a small gold knobbly dial on top?
Yeah it either locks it out when fully closed, or you can set it to reduce the amount of oil flow through the damper to stop it blowing through it's travel so quick.
Motion Control is a compression dampner that is basically a big plastic spring. With the blue dial untensioned the valve is fully open, tensioned it is closed and the pedal platform is engaged. The plastic spring the outside of the unit gets compressed with big hits and valve is bypassed the gate or threshold adjuster sets how easily this bypass ocurs. Where the blue dail sits in it's rotation does effect the compression (it sets how much the valve is open) but only one of the poploc units allow's you to set this at a given place. There is a whole range of new mo-co's coming out with new tricks.