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Are the stated oil volumes for RS forks completely wrong? I've got the technical manual and it states the Motion Control bit of my Revelations (2012 Dual Air RCT3) needs 134ml 5wt fluid. This seems to be wrong - I've rebuilt my forks with this amount and they hydraulically lock at around 60% through the travel. I've taken (very non-scientifically) a 'bit' out and they work fine - get full travel and lockouts/compression all working as it should. I estimate I've used 110ml.
Am I doing something wrong? Is the service manual wrong? Something wrong with the forks?
The exact same thing happened when servicing my old Pikes, but they were old and they had a Franken-damper inside so I didn't think too much of it - I just rode with the reduced oil volume and all was well.
Did you fully cycle the forks several times when draining the oil? I've found that a good quantity can get held in the compression circuit which doesn't get released until you have cycled the fork a few times. In fact, last time I did my forks, in a hurry, I managed to squirt large quantities of fork oil all over the conservatory!
Yeah, I'm pretty certain I got all but the last few drops of oil out. By 'compression circuit', you just mean the MoCo?
Yep... the MoCo... and you compressed the fork while upside down a few times to get all the oil out?
If so, then I have no idea... I did a set of Rebas not long ago and the RS oil levels were spot on.. as were the Revs I did a month ago...
You're actually refilling the damper? Not just adding the leg lube on the damper side?
Never had a problem with oil volumes stated for my Reba's or a mates Revelations....
foureyes - Member
You're actually refilling the damper? Not just adding the leg lube on the damper side?
Sure you're not just doing this?
If the oil is going in the right place, maybe there is a problem with the fork.
On a slightly different topic. I have the manual for my Reba SL's as want to do an oil change and states 2 different cwt oils to use. Do people use the same oil or do I need to but 2 different oils. Have loads of 5 in the cupboard.....
^^ damping oil as lower lubrication is ok, just use a bit more of it.
OP, as 110ml feels OK but 134 doesn't, it sounds your oil is a bit too heavy - even though it may say 5wt on the label. Personally I wouldn't use thicker oil (although using less of it) but it'll be ok TBH.
Yes, I'm putting the oil in the right place! Refilling the damper from the top end, I was only fiddling [i]because[/i] of this hydraulic locking.
I don't think it's to do with the viscosity. Prior to messing about with the fluids - I.e. with the damping set from the factory, with no air in the forks I could open the Motion Control right up and there was a very definite bottom out with about an inch of travel remaining. It wasn't just an increase in compression damping (as you would expect from higher viscosity fluid), it was a sudden stop. I don't think this was the case from brand new though.
The problem with running slightly too little fluid in the damper side is that I'm sure I've lost the hydraulic bottom out resistance.
Just a thought, but how are you measuring your oil? When I had to service mine, I was a div and used scales that can measure liquid volume, not thinking that 100ml of fork oil would weigh more than 100ml of water. Took me a while to work out why I couldn't fit what I thought was the correct amount of oil in the fork!
It's easy to tell if you have enough oil: just put the compression damper in with it locked out. it there is enough oil to cover the ports at the bottom you'll struggle to get it in with it locked out. if it goes in fine then the oil level is too low.
take the motion control out, measure the distance between the 2 O rings, then -15mm.
So if the distance is 100mm -15mm makes it 85mm
85mm should be the distance from the top of the fork to top of the oil in the leg. (make sure you measure from below the treads where the Oring sits and that sorts out the correct oil level. 😀
A bit of a late response but thanks for the advice MTB Rob - although it's still not quite right, your method gave the same results as using the quote oil volume of 134ml (I.e. hydraulic locking). Not quite sure what I'm doing wrong - have sent an email to Fisher's but any other advice welcome.
Adam 1330 - I'm measuring the oil volume with a syringe (but that's a good thought anyway!).
Glenh - Interesting idea but is that right? As MTB Rob says, the oil volume has to be slightly [i]higher[/i] than the bottom of the MoCo? I think this is correct - the bottom part of the motion control unit has to be sitting in at least a bit of oil otherwise the lockout won't engage for the first part of the travel.
the bottom of the moco needs to be sitting ON the oil, not submerged in it. With the lockout applied this will resist the oil when the slightest movement in the fork occurs. If its submerged IN oil its too much.
I used this method (oil level = bottom of comp damper) to service some Lyriks when I didnt have a syringe and it worked perfectly, and Ive seen it recommended as a way of setting oil levels.
the bottom of the moco needs to be sitting ON the oil, not submerged in it. With the lockout applied this will resist the oil when the slightest movement in the fork occurs. If its submerged IN oil its too much.I used this method (oil level = bottom of comp damper) to service some Lyriks when I didnt have a syringe and it worked perfectly, and Ive seen it recommended as a way of setting oil levels.
You sure? SRAM Tech recommend the oil covers just above the LSC compression port. On the later forks the 193ml they require takes it to that point measuring down from the top.
Glenh - Interesting idea but is that right? As MTB Rob says, the oil volume has to be slightly higher than the bottom of the MoCo? I think this is correct - the bottom part of the motion control unit has to be sitting in at least a bit of oil otherwise the lockout won't engage for the first part of the travel.
Yes, that's my point. If you try and put it in with it locked out and it won't go in, you can be sure you don't have too little oil, no matter if the volume you put in is less than RS says you need.
Obviously that doesn't stop you having too much but if you put in enough so that it only just covers the bottom of the moco compression damper (ie. it still goes [i]most[/i] of the way in while locked out), then you've got it right.
Make sure to cycle the fork gently a bit first though, to make sure the oil is properly on both sides of the rebound damper at the bottom of the stanchion.
You sure? SRAM Tech recommend the oil covers just above the LSC compression port. On the later forks the 193ml they require takes it to that point measuring down from the top.
That was my understanding too, although I can't find this information in any of the service manuals. Any ideas where you got that from?
Using MTB Rob's technique means the oil sits just above the compression port - as I said, this method leads to hydraulic locking.
I have had another thought - they're 150mm forks but I've got them set at 140mm. Last time I did the damper service I didn't bother taking the lowers off. This shouldn't cause any problems if I was using absolute values for the oil volumes but using MTB Rob's technique I'd need to use the O-ring to O-ring length minus a bit MORE than 15mm (to account for the fact that the fork is already part way into its travel).
Turns out I [i]was[/i] doing something wrong. I'm not sure exactly what, but I stripped the forks down and took all the oil out, replaced it with 134ml as RS suggest in their tech manuals and it's all working properly. I guess there must have been some residual oil in the system.
Anyway, the oil does cover the compression port as stated above.