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one less car
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523 Posts
Discussion Starter · #1 ·
or there's something wrong with it. in adjusting the neg air i noticed the stanchions rose about .5in. this happened several times after letting the fork set a few minutes, and even starting with no air in either chamber. that normal? thx
 

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singletrack mind
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65 Posts
yeah it seems normal

you're probably raising the negative air level above that of the positive, which will cause the lowers to rise and reduce your available travel.

you should set positive first and then set the negative to a pressure slightly lower than the positive. how much lower is, i think, a matter or personal preference.

some people set the negative higher than the positive on purpose, claiming a plush feel, or to reduce the axle to crown length of the fork (sacrificing some travel)
 

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one less car
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523 Posts
Discussion Starter · #3 ·
well, atleast it's nothing to worry about. thx. thing is, the first time i noticed this, the pos was higher, and on pressurizing the neg about 30psi was lost between refills, and i can't see that much either escaping when removing the hose, or that much in said hose
 

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singletrack mind
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65 Posts
well, apparently the negative air is a very small chamber (you notice how quickly it pumps up compared with the positive), so i think it's not infeasible.

i'm going to pump a wee bit in myself today, so i'll let you know how much the pump takes out on mine, but i'm guessing that when you add what's lost attaching the pump to a slight loss of pressure over time 30psi is quite reasonable.

anyway, i'm no suspension expert, so i could be assways....
 

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I run higher negative pressure myself. Had to learn the hard way.

I thought I had it nailed with my first Revelation with negative lower than positive, but had a nagging doubt about the small bump response. I got a Push modified Revelation on a new bike and negative less than positive really didn't work. Took me ages to figure out and once I did I haven't looked back.

Setting negative pressures can be a bit fiddly to be entirely accurate, because the fork sucks down (altering the chamber volume). If the fork action is sticky and it doesn't suck down, you can end up with a misleading pressure reading.

Sometimes the valve cores are not entirely tight and this is the most likely cause of pressure loss. Tighten the valve cores if you have any doubts about pressure loss, but the previous reply that negative pressure varies significantly on re-attaching the pump is 100% true - the negative chamber is very small.

One thing you can do to check the actual pressure is this. On re-attaching the pump, wind the adapter on only as far as needed to make a seal to the outside world and before the adapter presses in the pin of the schrader valve. In this state, you can pre-pressurise the hose with a couple of pump strokes (there should be no leaks and the pressure should build very rapidly). When the pressure is close to where you expect the chamber pressure to be, fully wind home the adapter and the gauge reading will settle, showing a more accurate indication of the actual pressure remaining in the chamber - less air moves across the valve because of the pre-pressurisation and this alos prevents you getting a spurt of oil out of the valve and into your shock pump.

before you get a pressure reading from
 
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