Suspension Parts..What are their functions

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#1
OK.. I'm ignorant. Can anyone tell me the basic functions of the different parts of a fork and shock. I know the spring carries the weight while allowing movement of the wheels and the hydraulic actions absorb excess energy. That is about the limit of my knowledge.
How does a valve work? What changes when you adjust one. Are there more than one in each? What do the shims do? How?

Thanks,

Jerry



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Old guy who putts around on a '00 WR400F behind the KX_kid
 

JTT

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#2
OK, let me give this a try. I'm not even close to an expert (but am learning). First the shock and fork are slightly different, but the principals are similar.

Picture a piston on the end of a shaft, now that shaft is in cylinder filled with fluid. The piston has holes in it that pass oil from above the piston to below and below to above as the piston moves through the fluid (if it didn't there would be a hydraulic lock adn the shaft could not move).

Now the damping effect is created by the resistance of the fluid moving through these holes in the piston. The smaller the holes, the greater the resistance. Similar to passing a cupped hand through water or an open hand. In a crude system this is what you've got to control damping.

For our purposes though, we need to better control that fluid flow to give greater control of movement. Shims (thin little washers) are stacked on the top and bottom of the piston, covering the holes, or ports.

Now you must imagine this piston having 8 holes. The shims on the top cover 4 of these holes completely, the remaining 4 holes are covered by the shims on the bottom of the piston, but exposing the other 4. So, on each side there are 4 holes covered and 4 holes exposed.

Now move the piston upwards (as if the shock is compressing). The oil is displaced from above the piston and forced to flow to below. The shims are restricting this movement, but because they are thin, they deflect allowing the fluid to pass by.

On rebound, you will see the same effect takes place only in reverse, wit fluid travelling through the other set of 4 holes, past the shims and into the upper side.

This piston and shim arrangement is the "active" valving that you will hear referred to in this forum. Active in that it is moving through the oil, as opposed to being stationary and having oil flow through it.

...starting to make any sense?

Now, I going to throw another peice of the puzzle your way. Go back to when we compressed the shock. As the piston is moving upwards through the oil, the shaft that is pushing it is also filling the lower chamber of the cylinder. If the cylinder is sealed, then you again have a hydraulic lock situation as the internal area that the fluid occupies has now been deminished by the additional area of the shaft. (like putting an ice cube in your drink, that level in the glass rises).

So we have to do something with this displaced fluid. A second valve is provided, in a similar fashion to the one I just described above, only this one is stationary (ie: passive). This displaced fluid is passed through this valve arrangment and controlled in a similar manner (with stacked shims).

I hope I haven't made this any more compex than it has to be, but here's another curve...

In addition to the fluid that is passing through these valve assemblies, builders have given the oil an additional "out". Bypass holes or bleed are usually provided to allow a percentage of the fluid flow to bypass this valving arrangment. For simplification (if that word can even be used at this time :p ) I will not get into different types of bleed too in depth.

Remember our piston on the shaft? Make the shaft hollow and provide holes in shaft, above and below the piston so that some oil can flow past valve freely. Now we install a restriction between those two holes and into that restriction we install a tapered needle that can be threaded into and out of the restriction hole, thereby allowing us to control how much fluid travels through our "bypass". Voila! this is your clicker! (rebound that is anyways).

Do a similar bypass in your "passive" valve. You now have your compression clicker.

I am sorry for the length of this post, but I hope you understand my ramblings. If anyone has any additional items to add, or corrections to make, please do.

DBD, if you ever get the opportunity to see inside a shock or forks, take a close look and try to trace the flow of the fluid. It makes much more sense when you can see it in your hands.

Hope this helps!

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JTT
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MACE

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#3
JTT, thanks for taking the time to type this all up. Word to the wise, save a copy on your HD. Okie's storage space is finite and you may want to use this again.

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MACE

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Hey ho, let's go... Hey ho, let's go-o-o-o!
 
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#4
JTT,

Thanks, Great explaination. I have the basics now. I guess I'll have to find some junk shocks to disassemble as training aids. My curiosity is peaked!

Do you know any sources for detailed engineering information on fluid flow calculations, piston size etc.

Does anyone modify their own valving by changing the shims or enlarging the holes?

I may want to modify the valving on my new wr400f. Its a little stiff.


Jerry

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Old guy who putts around on a '00 WR400F behind the KX_kid

[This message has been edited by dirtbikedad (edited 04-16-2001).]
 

JTT

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#6
DBD glad it was of help. Skip the "junk shock" thing, your forks are going to need an overhaul very soon anyways (to wash out all that "break in" trash). Good chance to see the real thing!

Stick around here, you can learn a huge amount. There's some pretty smart cookies in here, including some who like to stir the pot once in a while...eh, Mace? :D

As far as doing mods yourself, you can do some experimenting, but for maximum performance gains, it seems best to stick with the pros. Guys like Jer have been studying and doing this stuff so long we'll never catch up! If you just want the "right" setup, get someone like Jer to do it for you, if you want to learn, experiment, them get the work of a pro, then experiment some more. It's far cheaper to have a pro do it for you the first time and forget about it, but then again education is never cheap!

Mace...thanks for the comment, and saving it might not be a bad idea...

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JTT
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yardpro

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#8
that was an excellent explanation!!!
dirtbikedad
Race tech (sorry jeremy, i still think you're the man, and would recomend your company soely to do the work) puts out a video that shows you how to dissasemble, change valves, and reassemble both forks and shocks. it is a step by step. the actual dissasembly, and reassembly is pretty easy, the fine tuning, however is pretty complex. if you're just wanting to tinker around, try getting your hands on these videos. they're provided when you but thier gold valve kit. but there are lots of them floating around. Just be careful, little mistakes can have major consequences, and you have to keep everything "spottlessly clean"
or just send them to MXTECH and be worry free.;)