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Pro Action shim stack, shim shuffling info needed...

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Hello, I just took apart my forks for the first time tonight. I have worked on forks before (seals, springs, and oil) but never any shim work. It’s a 2007 RMZ450 with the showa 47u forks. The suspension was recently revalved and resprung by Pro Action for me (a 160lb B rider riding motocross). Overall the suspension was better after the revalve, but the forks were still beating me up in the braking bumps and smaller chop. It was pretty good in whoops, corners and jumps, but in the smaller stuff it was like a jack hammer. I adjusted the clickers, experimented with oil levels, and even experimented with spring rates, but nothing made it plush through the braking chop. Instead of charging down the track, I was looking for smooth lines and avoiding the rough stuff, which isn’t always the fastest line. I finally decided to see what was in there for shims, and that is where I am at now. I have never worked with shims before, so please understand this is new to me. I will try to describe what I found as best I can. I only mentioned that it was Pro Action because they may have a unique to them valve that might explain if the valving seems very different than a stock valve would use. I will try to post pics of the valves when I get time. The base valve did not look like the stock ones I have seen, it was steel and the compression ports were only .090” in diameter, seemed pretty small to flow much oil. The rebound ports (on the base valve) were .160” diameter with a cross shaped check valve. The mid valve looked more like the pics I have seen of stock valves, so it might be stock, but I’m not positive.

Base valve:

Diam./thickness in mm

16 / .3 (not a shim, a spacer probably?)

30 / 2.4 to 1.3 tapered thickness inside to outside (some sort of tapered base?)

18 / .1 (two of them)

20 / .1

22 / .1

24 / .1

26 / .1

28 / .1

23 / .1 (crossover?)

30 / .1

Valve.

The base valve was pretty easy, the mid valve has a lot more going on.

Mid valve:

Aluminum cup with spring (float?)

11 / .2

10 / .2

9 / .2

8 / 2.0 (a collar? the following 17 and 20mm shims inside hole diameter slips over the collar)

17 / .1

20 / .1 (six of them)

valve

18 / .1 (two of them)

17 / .1

10 / .1 (crossover?)

15 / .1

14 / .1

13 / .1

12 / .1

11 / .1

10.5 / .2

11.4/ .4 (three of these)

12.5/ 2.6 (some sort of base?)

I hope that this all makes sense to you guys that understand this stuff. If anybody has any thing they see that they would try in order to achieve some improved level of absorbing the smaller chop (the elusive “plushness”), I would love to know about it. If this doesn’t work out, my plan B is to ditch all of this and give Race Tech gold valve kits a try. They at least supply shims and tables for general shim stack guidelines to try, instead of taking shots in the dark like I feel like I’m doing here.

Thanks in advance for any help, info, and responses!

Edited by rbreak

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why not just go back to the rep and tell him your feelings and have him work with you on getting it the way you want. pro-action reps usually are happy to work at it until your satisfied.

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why not just go back to the rep and tell him your feelings and have him work with you on getting it the way you want. pro-action reps usually are happy to work at it until your satisfied.

Distance, time, patients, and money. We are a long ways apart, and meeting up with him isn't always convenient. I don't have a lot of spare time to be travelling for hours to deliver my parts, and I don't have the patients to be shipping them off and waiting for them. And if I understand it correctly, re-shimming isn't going to be free, so I would be spending more money as well. I don't blame the rep, he knows his stuff. But being realistic, any revalve from any company is a gamble, you might get lucky and love it, or you might be left wanting more. I'm wanting better from my suspension (I've ridden better, so it's hard to be satisfied if you don't have at least as good as you have felt before), and I'm mechanically inclined so I figured now was a good time to finally learn how to do my own suspension work.

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We can easily improve this setup but we need to know which direction to go, is it bottoming? Is it too soft or too hard? The mid looks good but how much float? Ie how much do the shims lift off the piston face, measured using a feelers gauge each side and should slip in nicely

We can easily improve this setup but we need to know which direction to go, is it bottoming? Is it too soft or too hard? The mid looks good but how much float? Ie how much do the shims lift off the piston face, measured using a feelers gauge each side and should slip in nicely

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We can easily improve this setup but we need to know which direction to go, is it bottoming? Is it too soft or too hard? The mid looks good but how much float? Ie how much do the shims lift off the piston face, measured using a feelers gauge each side and should slip in nicely

The main problem I am having is the jackhammer like harshness on smaller braking bumps and acceleration chop (high speed valving?). The forks transfer the sharp hits straight to my arms and wrists. I am looking for a plusher, more absorbant ride through the smaller, sharp edged choppy bumps. It's not bad on the whoops and jumps (slow speed valving?).

Thanks for the response.

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I have found the soft comp/stiff rebound, on the PA setup shock, to elevate most of the symptoms you are feeling in the forks.

Just my 2 cents.

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To prove if its too stiff in hs you could remove the 28.1 and see how it feels

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To prove if its too stiff in hs you could remove the 28.1 and see how it feels

Do you think removing just one shim is going to make much of a difference? I was considering removing the crossover and making it a single stage stack just to make it more linear in resistance as the fork goes through the stroke. I was thinking this would make it easier to tell what difference the shim changes were making, for a beginner (me) shim shuffler.

I tried meauring the float, but I was trying to hold everything with one hand and measure (using calipers) with the other and it was impossible to get a consistant accurate measurement. I don't have feeler gauges yet, but will get some.

How much does the mid valve affect high speed compression harshness? Should I be looking into that stack? Is it normal to have that little 10.1 crossover in the rebound side of the mid, (I assumed we would want the rebound to be consistant (linear), with no crossovers needed?), or do I have it backwards and that is actually the compression side of the mid? I was thinking the float would only be needed for the compression side, so I assumed the side without the float was the rebound.

What about drilling the tiny .090" (2.3mm) compression ports in the piston, would that help if there is any restriction to flow going through the piston, or is that a terrible idea? I was thinking of opening them up just a little, like to .125" (3.2mm) just to make the shims work a little more.

Sorry for all the questions, I'm trying to learn a lot as fast as I can here, and I am new to this so if any of my ideas are ridiculuos I apologize in advance.

Thanks again for the responses.

Edited by rbreak

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One shim on that stack would make a decent difference, removing the cross over on comp would stiffen it a large amount, so much I think you could not get it soft enough, rebound stacks do have cross overs , cross overs allow low speed responce with hs strenght, think versatile, single stages are hard to tune when they have very few shims , opening up ports is the same as softening the stack, and it may help on hs a little,

Measure the mid when built, or Imo its a waste of time, the torque on the nut can even efffect float to a small degree

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The mid comp has the float, the mid has a huge effect on all damping ranges, one shim here can make the clickers out of range if you go too stiff or soft

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The mid comp has the float, the mid has a huge effect on all damping ranges, one shim here can make the clickers out of range if you go too stiff or soft

Thank you for the fast response. I had been thinking of removing one or more of the 20's in the mid compression stack. Bad idea?

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no that would work, i would be happier suggesting that if i knew the float, large floats in a TC fork can create problems, but it sounds like it might work for you in this case.

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Thanks again, I will try to get a better measurement of the float.

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O.K. I got the feeler gauge set. Being as careful as I can, it looks like there is between .15mm and .2mm of float. It's hard to tell exactly when the shims start bending a little, but I think its safe to say the float is not much beyond .15mm. What do you think, should I pull one or more of the 20's from the mid compression stack? I am planning on removing the 28 from the base valve as well. Thanks.

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Well, I just ran into another dilemma putting the forks back together. If I take out one of the 20 .1mm shims in the compression side of the mid valve, it will increase the float by .1mm. the float is currently .15mm, so that would make it .25mm without the .1 shim. The collar is 1.85mm thick, and it sits in a recessed counterbore in the piston that is 1.0 mm deep, so .85mm sticks out of the counterbore, and the shim stack thickness with 7 shims totals .7mm, leaving the .15mm float. I don't have any other shims to work with, I only have whats in the forks now.

The only solution I can see is either a .1mm deeper counterbore in the piston, or taking .1mm off of the collar width, both permanant changes.

Any thoughts? Am I missing something obvious?

Thanks again for any help.

Edited by rbreak

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