Shimming China USD Forks?

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Blender

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Hey, I want to put some shims in my Atomik fury's forks to up the rebound a bit.
Just wondering how I am to go about this? I've done conventional forks before, but USD's are a completely different ball game. I've changed the oil to a lighter grade, etc and I just want them abit more reboundey. Cheers :)
 

my67xr

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it's just a matter of fitting a spacer between the tops and the springs

so undo the tops out of the fork tubes and you'll see a spring directly below the top
inside the spring will be a nut locking the shaft to the top
loosen the nut enough to be able to unscrew to top off the shaft.
now find a 1/2 thick spacer that fits over the shaft and that has a big enough o'd that the spring can seat on it
push the spacer onto the spring to compress it enough to get some thread out the top of the spacer,
screw the top back on tight, you may need to carefully hold the shaft while you do it.
then do up the lock nut again, and screw the top back into the forks tube

give them a few bounces, it should feel more solid now

if it's still not enough then you might be able to try fitting a thicker spacer

here is an exploded view of some forks, it might help you get an idea of what is inside at the top
look at the section to the left
the lock nut is number 19, and the fork top is number 18

 
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my67xr

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the pic is just of some generic forks, so yours will probably be different inside them
i might be able to get a pic of my spare forks if you can't work it out
 

my67xr

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i used some hard plastic/nylon in mine
they are seat spacers from a Falcon, they look sort of like these but are 1/2 or 3/4 " from memory
any falcons use them from XB to XF depending on what seats they have, they go between the runners on the back inner mounting bolts and the floor

these are 1/4" thick



45mm thick
XR-XT SEAT SPACER 45MM

or if you have a plastics supplier or bearing shop close by you could buy a length of nylon rod, teflon rod, urethane etc
coolmodee01 might even be able to hook you up with some ?

 

Blender

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Yeah, I think I have some old spacers out of some other forks in my parts bin, i'll have to see if they'll fit these forks. If not I'll go down to a bearing shop like you said and get some nylon and cut it down to the size required.
 

my67xr

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stoozo

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I thought there is a shim stack that you have to fiddle with/change the configuration of the rebound or compression!!?? Don't break a perfectly good set of forks doing that! Usually on the mtbs was to either run harder springs or progressive springs, I remember fork springs being pretty cheap to get made up....might be a little safer than the shim stack road!

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Blender

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I don't think I know what your talking about Stu, although I don't have much experience or knowledge on forks.

Yea, I don't necessarily want them to be harder, just have stronger rebound (I know that will make them a bit hard)
 
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my67xr

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ok so what exactly is you bike doing ?

is the front end popping back up too quick after hard braking/landing etc
 

stoozo

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Yeah I think progressive springs would be the go then you can retain your high speed and low speed setting and still get more rebound...part number 43 on the above photo I think has the shim stack at the bottom? on other forks I have played with was years ago but that is the damping rod or the thing that controls how the damping works iirc which I probably don't...I think you can over fill your oil a bit to get more rebound too once again iirc...I cant look anything up still on my phone now that is almost out of internet credit....look it up on youtube I'm pretty sure there is a good video on these with forks and changing damping settings in 'non' adjustable forks!!

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stoozo

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Yep, when I hop off the bike, the forks stay down, I have to pull the front break in and pull back for them to come up again, and even then they go down a little still. I thiought Shimming them would fix it?
Yeah that sounds like more than a simple rebound problem mate....permanent sag means something isn't right in those forks!? Maybe oil level is to low you said you changed it...maybe the springs are really weak and they've compressed a bit or something....
 

Blender

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Yeah that sounds like more than a simple rebound problem mate....permanent sag means something isn't right in those forks!? Maybe oil level is to low you said you changed it...maybe the springs are really weak and they've compressed a bit or something....
It used to happen with my 125's old conventional forks, until I shimmed them up, so I figure this should fix it. The stock forks are extremely soft aswell
 

stoozo

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Try find harder springs...say the ones in there would be very soft go for a soft-medium...none of my forks do that they all go back to the top of their travel until I sit on the bike! Yeah hopefully its just shims then. I'm just a bit worried I used to break forks all the time until I worked out the bike shop had nfi what they were doing so I learnt myself...I used to break things all the time. One set of forks I had the plastic shim which controlled rebound used to break constantly, making the forks top out really hard when doing jumps etc...I think it would pay to have a good look at them!

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Blender

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K, so here are the spacers I plan on using:

They're about 15mm long.
Heres where I am at now, Im not to sure what to do next, help meh!! lol
 

Blender

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K, so I decided to change the oil, and I think I put a little more in. They are harder, but they are rebounding more, so I'm happy. Want to try and find some adjustable forks for it though, ones with some more travel preferably.
 

my67xr

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sorry i've been out most of the day today,
if you fitted those spacers in where the red ones currently are that will slightly stiffen the front end,
and it'll probably lift it a bit too, maybe 30mm or so ?

measure how much of the fork stantion tube (bottom chrome tubes) there is showing between the seal and the bottoms of the forks, then once you swap the spacers in, measure it again.

first, take note of how much thread there is above the nut,
as you need to have about the same amount there after you fit the spacers in

to undo the locking nut, hold the nut on top of the fork ends with a spanner and undo the nut
then once the top is off you should be able undo and take the lock nut off
the washer and spacer can then come off and refit your new taller spacer, then the washer and nut
you'll need to compress the springs a bit to get the nut back on
once that's done you can refit the top, and tighten the locking nut again


you could also try some heavier weight fork oil in them too, if you have SAE5 in there now, try some SAE10
 

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