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Usual desperate cry for help from first time suspension tweaker....

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Just redid my shim stack (06 RM250, Showa twin chamber) to try to alleviate mid stroke harshness (removed one 20.10 mid valve shim, as appeared the recommended fix on TT RM threads). My local RaceTech dealer told me I would need to replace my (lower?) damper seals, as 'these would have been damaged during dissassembly'.

The thing is, these seals are at the end of the damper rod, which is still together with the inner chamber, so I can't see how this would have been damaged, as I didn't dissassemble the damper rod, only unscrewed the compression valve from the inner chamber (or whatever you call the piece it screws into). I can't see how the seal would have been damaged by exposed threads etc.

So, do I need to remove the damper rod and replace the seal or not? If so, why? And um how?

I'm very proud of myself for giving this a go, but quite scared as well (have made sure compression valve retainer nut has plenty of loctite.....gulp....anything else?). I just can't afford to pay a suspension guy - racing motocross costs enough as it is.

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The seal can get damaged by the threads on the damper rod when removing the damper rod from the cartridge. When I remove the damper rod from the cartridge, I always wrap the threads with some teflon tape to prevent the threads from cutting the seal.

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Thanks MX. I guess my problem is I don't have names for all the components. In my mind, the 'damper rod' is the rod that slides in and out of the inner chamber (the 'cartridge/?) which is at the other end from which you screw the compression valve into (the device with the short spring and all the shims). And my guess is the 'damper rod seal' sits in the bottom of the cartridge, through which the damper rod slides in and out of. This would make sense, as it holds the inner chamber oil in. And I didn't remove this 'damper rod' (and I define it) from the inner chamber. And you would need some special long tube spanner to undo the retaining nut for this?

So what I don't get is how (if at all) the damper rod seal could be damaged. Or do the damper rod and the compression valve interact, in a way that could damage the damper rod seal when removing just the compression valve? The 10mm nut on the end of the compression stack covers all its threads, and I can't see any seal among the shims and things I took off over this thread. Or is there one there? (but why?)

So the question is, where is the seal that's prone to damage, and would I have likely damaged it or not doing as described above?

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How did you adjust the midvalve without taking it out of the cartridge?

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Well....the forum guys said the fix is remove one of the two 20.10 shims from the midvalve, so when I removed the shim stack from the compression valve, I just looked for two 20.10's, and removed one of them, and put all shims (and piston) back in order of removal (and put the 10mm nut back on with loctite).

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Are you talking about the stack that is visible as soon as you take off the top cap? That is your basevalve

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Are you talking about the stack that is visible as soon as you take off the top cap? That is your basevalve

I am thinking this is what the original poster meant as well. It would be extremely difficult, if not impossible to change the valving on the midvalve without removing the damper rod from the cartridge.

So if that is the case, then your inner chamber seal should be fine.

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I'm starting to see now.....there's.....shims on the....'base valve' (the thing underneath the top cap with the short spring on it)....AND on the....end of the damper rod (the 'mid valve stack'?) - is that right?

Hmmmm. In which case, I should probably put back the 20.10 in the base valve (yes?)....and work out how to remove the midvalve (long 10mm tube spanner to reach into the cartridge?).

I'm sure they have their reasons, but wish could access an exploded parts diagram for the complete fork.

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Here is a schematic for you:

ff%20comp.jpg

From the figure above (this is of a set of KYB forks, however, they nearly resemble SHOWA forks as far as general components go), #5 is the base valve assembly. The damper rod is #4. At the top of the rod, you can see the midvalve assembly.

So yes you are correct that the base valve is the center cap thing at the top of the fork, and the midvalve at the top of the damper rod.

To revalve the midvalve do this:

wrap a few wraps of teflon tape around the threads at the bottom of the rod and lightly coat it with fork oil, fork seal grease, etc. Push the damper rod from the bottom out through the top of the cartridge. You will likely have some peening on the midvalve nut if the forks have not been revalved before. Remove the peening and then go from there on your valving. As far as assembly just work backwards (be sure to keep the teflon tape on the threads so you don't damage the seal at the bottom of the cartridge.

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I can't say thank you enough for this info - I've since gone in and dissassembled the actual mid valve, and removed a 20.10 shim from each, and carefully reassembled it with teflon tape. I know you're 'supposed' to change the seal regularly, but will just hope the seal stayed good (or not a good idea?).

Could I ask one more qu - what effect do you think leaving out the originally-removed 20.10 shim from the base valve would be? (what does the base valve do?).

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the cart seals do go but I have only replaced one set in 10 years so don't go thinking you need to replace them , they often last as long as the bike

you could leave out the 20 on the base , it doesn't do much damping compared to the rest of the base valve

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