rebas not getting full travel

xixang

I'm having a problem with my reba sl's in that I'm not getting full travel.

If I remove all the air from pos and neg chambers by removing most of the air then compressing again with the valves depressed the lowers reach right to the crown, save around 5mm headroom.

Then when I put any air into the pos chamber the forks extend as expected but the I cannot get the lowers anywhere near the crown - I'm talking 30mm away with 20psi! Once the pos is up to pressure (say 100psi) there is 130mm of exposed stantion, so taking off the 5mm "headroom" this would give a theoretical 125mm travel (on 115mm fork!). As I can only get to 30mm from crown with VERY low pressure I'm realistically only getting 100mm travel (with me so far?).

If I then let the air out again (without compressing the forks) I'm still stuck with a 30mm gap, unless I further compress the forks whilst depressing the valve to get all the air out again.

The forks are obviously getting "full travel" at first but as soon as air is introduced I'm stuck at 100mm travel.

Whats going on? Am I missing something obvious?

tia

supersonic

What year Reba, and what travel are they set at?

When the positive and negative pressures are equal, how much exposed stanchion? Do you ever bottom out on the trail?

It seems to me you are measuring the negative travel too and adding it to the positive.

xixang

2007 reba sl's set to 115mm (no spacers)

when 100psi in pos and 0 in neg there's 130mm stantion exposed

when 100 in both pos and neg theres 110mm exposed but max compression travel is 80mm (to 30mm exposed) plus 20mm neg travel - 100mm total

never had more travel than to 30mm from crown mark (total 100mm assuming 130mm is top out). Even with zero pressure both sides its the same. Can only get 100+ travel (to crown, as near as damn it) if I compress forks whilst depressing the valves (pos then neg), which releases a little more air (or maybe creates a vacuum?)

hth

supersonic

I have the same fork. The air spring is more progressive than recent versions, and takes a big whack to bottom, even when running a lot of sag.

The travel is 115mm, plus or minus about 5mm as the negative chamber was never designed to be more than 10psi away from the positive pressure. The 130mm is a red herring really as is the fork fully topped out ie no negative spring.

I would open the fork up and make sure there is not excessive oil in the pos air chamber causing even more ramp up. Levels can be got from SRAM tech. (infact may be an idea to service it at this stage).

Then try again, maybe with 90psi in each chamber. Measure the sag in mm.

Given the forks will depress fully it shows that there is not a leaky damper.

having tried a more recent Reba I can report it is a btter ride, less progressive.

xixang

oils are right as I serviced the forks on Sunday and I've not ridden them in anger since. I thought my servicing/rebuilding might sort the travel issues I initially had. anyway,

tried with 90 in both

exposed stantion off the bike is 110mm (so 20mm sucked down)

travel is to 25mm from crown, and thats really pushing it hard, so.....

110-25=85mm travel with 20mm sag is 105mm

Maybe the other 10mm or so will only come in a really hard knock!

Does this sound about right?

ps - thanks for all the input so far

supersonic

You don't add the sag back into the equation - you are coming up 25mm short of full travel however you look at it. I asume the damper is not spiking...

So I'd go even lower 80 and 80. 20mm of sag is fairly low anyway.

Thatsaid the last10mm of travel is very hard to achieve.

diy

I have the same fork too, I can't get my head round the problem, doesn't sound like there is a problem to me. Seems to be more about setup?

I actually run mine with 20% sag.

I assume you are setting +ve first and then -ve?

If the forks suck down too easily, it could be a problems with seals in the air chamber or lack of oil in their +ve chamber?

xixang

setting pos first then neg. May try 80/80 when I go out later for a spin, even though guide says 110+ for my weight.

Thing is regardless of pressure I cannot get more that 100mm of travel no matter what I do except when I do the empty chambers, then compress and empty some more. Then forks travel right to crown. Once air is in then they stop 25mm-30mm from crown and stay like that until air released, compressed and released again.

Fine after rebuild until air added, then I can only achieve 100mm travel unless I squeeze all the air out. normal deflate doesn't give back full travel.

maybe i just live with it and accept the last 10-15mm are only acheivable under a really heavy bang :?

supersonic

It is very similar with mine, maybe the last 10mm. I am not sure whether RS travel claims include the bottom out bumper. My 115 Reba behaves like a newer 100 Reba.

xixang

ok - update time

80psi in both chambers and same story re travel (tried 70 as well). Only difference is fork is obviously more active/responsive

80+ve/0-ve 130mm stantion exposed

80+ve/80-ve 110mm stantion exposed (off the bike); 90mm on the bike so is that 40mm or 20mm sag? (130 total less 90 seated or 110 seated less 90 seated?)

at max compression 25mm stantion exposed

so...110-25=85mm +ve travel with 20mm(?) -ve travel/; 105mm total with 10mm reserved for extreme hits.

sound about right?

but, in answer to DIY the forks start to suck down around 40-50psi and at 80psi 20mm has been sucked. Too much? Oil is right as I only added the right about (off sram site) on sunday. Seals gone maybe? Time for a "pro" service?

Other than that I think its time to just live with it - or get a new fork....

thanks again guys, as you've gathered I'm a bit of a novice with modern forks - last set I had were elastometers (quadras?) many many years ago