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Someone with a DUC, please go check it

1205 Views 13 Replies 6 Participants Last post by  BMJ
Could someone please go let the air out of your left leg, push down on your handlebar till you feel the bottom-out bumpers but don't compress them, and measure the travel (use a dab of grease on the stantion if needed)?
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i have two ...

145 and 148mm - when the fork takes a big hit and pushes into the bump stop, these will be roughly either side of 150mm, i guess ...

note that I activated the valve to get the remnant air out whilst gently pushing down on the fork to get the minimum height, and then put in enough air to overcome the negative spring to reach maximum height.

why the request?

First of all, thank you.
I'm playing with a floating piston in the damper and I was pretty sure the insertion depth wasn't right. I was getting 136mm when measuring the same way with a hard stop, rather than feeling the bottom out bumpers. I'm gonna remove the floating piston and assemble the fork like stock and see if my numbers match yours.
Changed the damper back to stock and now it moves 150mm till it touches the bumpers and another 3mm of bumper squish.
I'm trying to figure out if the IFP was too deep or shallow. I just emailed Suspension Experts.
Let us know what you come up with. I have the IFP in my "travis brown" DUC (100mm) and I think the travel reduction bumpers immunize me from your issue (since my fork never compresses that deeply), but knowledge is good.

you have to push the damper rod cpl. into the dampertube when setting the IFP.
For my 4 DUC´s it works best.
What shimming do you use and what kind (wt) of damper oil ??
I use the stock shim setup and 6wt oil. When I use straight 7wt oil the short travel setting is nearly locked out which I don't like.
I thought that when setting the IFP you'd want the damper to be in an extended position. So 44mm is the position the IFP should be at at the end of travel, not the begining? That would explain my results:)
Does anyone have the insertion depth spec for the IFP at the begining of the stroke?
Lelandjt, are you saying the fork is more responsive in climbing mode with a lighter weight oil? Is this only true for the oil in the damper (right leg) itself? I imagine the viscosity of the oil in the left leg would not make a difference. Correct?
Correct. Oil added to the air chamber (left leg) only reduces air volume to make the spring more progressive, weight doesn't matter. The viscosity of the oil in the damper (right leg) affects both compression and rebound damping. 5wt is stock and I've tried up to 10wt.
With 5wt it didn't have as much compression or rebound damping (even with the rebound dial at full slow) as I like.
With 10wt oil it had too much compression damping and in climbing mode was rock solid.
7wt gave the compression and rebound feel I like but in climbing mode the fork was too harsh. It wasn't completely locked out like with 10wt but it had a very high threshold that made even small impacts at low speed too harsh and made climbing mode less versatile (I like to use it on even slight uphills).
Mixing 5 and 7wt equally while running the rebound knob halfway is my current setup.
I weigh 165, ride aggressively on rough trails, run 85psi in the spring, 80 in the damper, and the stock shims.
Kevin told me to insert it 43mm from the bottom of the tube to the inside inset of the IFP. He said that when you finally tighten the top of the damper tube, the space the top cap takes up will push the IFP to approx 40mm from the bottom of the tube. This has worked well for me. No probs since.

I also had clunking against the IFP when I first set it up. My original problem was not getting all the air out of the damper and this allowed it to migrate up into the damper when I charged the IFP. This happened due the small amount of air in the damper compressing.
And this is done with the piston pushed all the way in so that it is touching the IFP? I did what you are saying but with the damper rod in the extended position, up against the top cap.
Oh, I also measured to the outside, taller part of the IFP so there's one mistake.
This is what I did.

Lelandjt said:
And this is done with the piston pushed all the way in so that it is touching the IFP? I did what you are saying but with the damper rod in the extended position, up against the top cap.
Oh, I also measured to the outside, taller part of the IFP so there's one mistake.
I set the height of the IFP first, again measuring from the bottom of the damper tube to the bottom of the inset in the IFP.

Next fill the damper to the top with fluid.

I next cycle the piston head in the fluid with the top loose just to make all the air trapped in the piston head bypass the main shims. When the shims stop burping bubbles I re-top off the damper again with more fluid.

Next thread the top assembly with the damper rod fully extended against the top cap down into the fluid untill the main seal o-ring just touches the rim. At this point check that the IFP hasn't migrated down from the 43mm setting. If it has, push it up slowly while allowing the extra fluid to burp out the top.

Finally, with the IFP set at the 43mm setting and the main seal sitting just on the rim, start screwing in tight. The IFP will migrate down at this point as the main seal head displaces the internal fluid. It should set around the 40mm point when all is said and done.

Inflate to IFP chamber to your favorite psi and carry forward with the final assembly
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Thanks. I'm gonna leave it stock for a couple days cuz I'm riding a lot this week but I'll post when I put the IFP back in.
Oh ya, don't cycle the damper rod at all while there is no pressure in the IFP chamber. With out the psi to seal the o-rings and push it back up, it can suck air past the seals and you have to start all over again!

I also put a small puddle of fluid in the IFP chamber to keep it lubricated on the air side.

Best-O-Luck! It's been well worth it so far for me.
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