[Udi]

EDIT - Done and done. New pics, page six! (or post #83)

I don't think this has ever been discussed yet, so here it is - has anyone tinkered with the stack yet?

I've had a quick look at the damper, and basically the bottom of the MC damper comes off (and that bottom houses both the LSC port adjuster, and floodgate mechanism). After removal, inside the main MC unit (a little way up) is the shimstack. There appears to be a hex head to perhaps unscrew it but it looked too deep to access with a normal socket wrench.

Running a fair amount of LSC (~5 clicks) with the floodgate (blowoff point) backed all the way off, the fork still wants to spike on high speed braking bumps - which I suspect is very likely to the fact that AFTER the nice easy blowoff, the oil has to pass through the "blackbox speedstack" too. IMO that makes the floodgate adjuster somewhat redundant, as the whole point is so that compression damping can regress after a certain speed threshold.

It wouldn't hurt to can the shimstack all together imo, or at least shim it much more lightly - and i'd like to hear about it if anyone has given it a shot (performance results would be nice too)

Thanks, Udi

 

[KnightChild]

?? The shimstack will be reducing the spike.
The spike may be occuring because you are running too many shims (as you have said) as well as the bypass-valve way too open.
This makes it feel plush at slower stuff (mind you brake dive will be a problem too) but as soon as you hit a square-edged hit at high speed it's forced to go through the shimstack.
My advice is to:
Less 1 (or 2 at max) shims - take the smaller ones off, and close the bypass off as much as possible so that it feels quite stiff (it will brake dive less, and absorb bumps better this way.)

 

[Udi]

You have no understanding of how the motion-control damper works, nor did you do a very good job of reading my original post.

This is nothing like a conventional compression damper where LSC is ported and oil will blow through a surrounding HSC shimstack simultaneously as oil speed increases. The "speedstack" is seperate and oil has to pass through the LSC and blowoff mechanism before it passes through the stack.

I'm not really looking for advice on what to do, i'm wanting to know how to do it. Looking for replies from anyone who has a method on accessing/removing the speedstack which is recessed quite deep.

 

[vitox]

you got any pictures of that?

i was toying around with a boxxer wc and was a bit puzzled by how the adjusters worked and also with how linear it felt in the mid travel, are you also noticing this?

 

[CBJ]

Dosn't Tim Flooks advertise he does shim stack adjustment? I remember talking to a RS tech who mentions something about SID shims could be used but I am not sure at all.

 

[vitox]

Dosn't Tim Flooks advertise he does shim stack adjustment? I remember talking to a RS tech who mentions something about SID shims could be used but I am not sure at all.

ooh that could be interesting, maybe not too much for udi as he wants to decrease the damping, but did you happen to hear if it was pure or c3 shims he mentioned (got some c3's i could open)

 

[CBJ]

Don't know.

 

[A.P]

You want your fork without the blackbox speedstack? Get a boxxer race. They are the same fork, motion control, rebound, low speed compression, floodgate......but without the speedstack.

The older races were crappy, but these look to be pretty good. I have a hydracoil team and the internal high speed compression adjuster is such a pain in the ass to adjust, I really wouldnt do it anyway.

 

[teaguers]

The Race does not have the floodgate, or at least it doesn't adjust.

 

[A.P]

RockShox Boxxer Race Suspension Forks feature external rebound and low-speed compression adjustment.

* External rebound and low-speed compression adjustment
* New Motion Control damping with external Floodgate
* 32mm EA70 straight wall aluminum stanchions low-friction coating
* Upper crown allows direct stem mounting (stem not included)
* New aluminum control knobs


...straight from qbp...

 

[davep]

Does your fork still spike if you open the LSC a bit more? I am thinking that maybe the high speed stack is passing the oil just fine, but the LSC (which is not shimmed, and is just a variable orifice) might be causing cavitation and blocking the flow.

In a traditional set up, the LSC and HSC are in parallel. When the oil velocity gets to a certain point, the LSC port is hydraulically locked, but it does not matter, as the oil can (and does) pass through the HSC. Due to the parrallel nature of this set up, the oil can go through either path, un affected by the other path.

If I understand the Mo Co damper, it seems like the LSC and HSC are set up in series. So all oil must go through BOTH dampers. If your LSC orifice is 'to small', it does not matter how much oil the HSC can pass, as they are in the same path. Which ever one has the most restriction, will dictate the maximum flow.

So if you open the LSC gate, and the spiking goes away, then the LSC is at fault. If you open the LSC and the spiking remains, then the HSC stack is not opening enough, and a re-shim is in order.

Sorry i cannot tell you how to get at the stack as i do not own this fork...

post some pics

 

[toodles]

davep - you've hit the nail on the head there I reckon. Is there a way to increase the LSC without starving the HSC circuit though? That would be handy.

 

[davep]

No idea about the shapes and sizes or holes we are talking about, nor the oil velocity, but some orifice shaping might help a little.
I have seen pics of standard shimmed comp heads where someone shaped all of the ports in the head into smooth funnel type shapes. Dont change the opening size, just round off and smooth any corners to decreace the turbulance. This would have not effect at low oil velocities, but at high velocities, the LSC might be able to pass more oil.

 

[peachy]

davep,

what u said is EXACTLY how i understand the MoCo. didn't make too much sense to me that it has a "blow off" (gate) since all the oil basically goes into the LSC first.... then to the HSC. so it seems to me that his spiking may also be from the LSC (5 clicks ...out of 6).

a blow-off (gate) to me is if that opening enlarges or another hole opens up when u hit something hard enough. i'm no expert but it seems to be that having them in series makes no sense.

Udi, how did u remove the bottom piece of the MoCo... just unscrew?

 

[Cave Dweller]

Udi, how did u remove the bottom piece of the MoCo... just unscrew?

There is an allen screw at the bottom on the side of the MCU stack, about 2 inchs up from the bottom, i think you unscrew that and it comes apart.

a blow-off (gate) to me is if that opening enlarges or another hole opens up when u hit something hard enough. i'm no expert but it seems to be that having them in series makes no sense.
[/IMG]

It does do that. The black plastic bit is a stiff spring. When you hit something hard enough the other 2 ports are opened that are under the disc show.

you've hit the nail on the head there I reckon. Is there a way to increase the LSC without starving the HSC circuit though? That would be handy.

You mean trying to increase the platform but still be able to take small and big hits?

The blow off is controlled by the orifice size, but also controlled by the plastic MCU spring which is basically a really,really stiff spring that holds the 2nd,3rd and a bit of the 1st LSC port closed.

To really change things you will need to try and modify the plastic MCU spring i suspect, if you stiffen the plastic spring and open the port a little you will get more oil flowing through the lsc port but the blow off will be higher and will thus provide more pedaling platform effect i suspect. If you soften the MCU spring i suspect the fork would become more plush and wallow, like a marzocchi fork.

I could be way off the mark though

 

[Udi]

A.P - race has no adjustable floodgate (my good friend toodles actually OWNS the fork). Team and WC have the gate and the speedstack.

vitox - will get some pics next time I open the fork. having too much fun riding it at the moment (don't let the thread get you wrong, the fork rocks)

CBJ - TFtuned indeed does work on the speedstack. I have ridden an 06 team that was TF'd however (speedstack tune + bushing size/polish), and must say while it felt great, it didn't feel any more great than a stock boxxer team.

peachy - the silver part on pic 17b turns to cover the port that is open (controlled by the blue comp knob), obviously. The bottom section comes off with a 2mm allen key and one screw as cave dweller pointed out. But how does the floodgate/blowoff work? Simple.

At lower oil speeds (ie LSC), the oil simply moves through the port. At higher oil speeds, the actual part that has the ports on it can move UP and AWAY from the silver plate, exposing the existing ports as well as two others that are hidden by the silver part, initiating blowoff. The part with the ports on it effectively has a hard spring on top of it, in the form of the long plastic cylinder with holes in it (the trademark motion control part, bright red in a pike, black in a boxxer).

But how does the floodgate adjust this? The floodgate adjusts how far up the silver part can move WITH the ported part. Because if the silver part moves up with the ported part, blowoff can't happen, as the ports will still be covered. At a low floodgate setting (easy to blowoff) the silver part cannot move very far up at all. At a high floodgate setting (harder to blowoff) the silver part will move up a fair way with the ported part before it stops. With the floodgate fully closed, the silver part will not stop at all (ie lockout, no blowoff). The small amount of movement will just be from the black plastic "spring" compressing a little. So essentially, the floodgate + spring IS your high speed shimstack that allows blowoff, leading me to still believe the "blackbox speedstack" is a little redundant and probably doesn't do a whole lot.

A quick thanks to thaflyinfatman on here for helping explain this to me.
Post edited to aid any future readers.

 

[peachy]

awesome post! that's very informative. I'm removing my MoCo and re-read this. That'll make me understand this much better for sure. Anyone seen a cross section of the MoCo unit?

ok, i gave it some more thought... the main plastic piece w/ holes all over it can actually move up and down independent of the silver piece (silver-piece that contains the LSC hole). this silver piece has some holes unseen during normal operation. the more the main plastic piece slides up the more exposed these hidden ports are... higher oil flow = blow-off.

what's the purpose of the horizontal holes seen on 17a? or is that what makes the main plastic compress and expose the ports.

 

[Udi]

what's the purpose of the horizontal holes seen on 17a? or is that what makes the main plastic compress and expose the ports.

Bingo.
Those holes just help the plastic act as a (very hard) spring.

The silver piece has no holes, the holes are in the black piece just under it (the black piece moves up and down with the "spring"). There is one port fully open in image 17b, the silver piece rotates (with your compression adjuster) to open and close that port different amounts.

There are 2 more ports hidden under the silver piece to assist with blowoff once the two parts seperate, but only one port is used for LSC adjustment (the one in the pic).

 

[thaflyinfatman]

Does your fork still spike if you open the LSC a bit more? I am thinking that maybe the high speed stack is passing the oil just fine, but the LSC (which is not shimmed, and is just a variable orifice) might be causing cavitation and blocking the flow.

In a traditional set up, the LSC and HSC are in parallel. When the oil velocity gets to a certain point, the LSC port is hydraulically locked, but it does not matter, as the oil can (and does) pass through the HSC. Due to the parrallel nature of this set up, the oil can go through either path, un affected by the other path.

If I understand the Mo Co damper, it seems like the LSC and HSC are set up in series. So all oil must go through BOTH dampers. If your LSC orifice is 'to small', it does not matter how much oil the HSC can pass, as they are in the same path. Which ever one has the most restriction, will dictate the maximum flow.

So if you open the LSC gate, and the spiking goes away, then the LSC is at fault. If you open the LSC and the spiking remains, then the HSC stack is not opening enough, and a re-shim is in order.

Sorry i cannot tell you how to get at the stack as i do not own this fork...

post some pics

Ok I don't think you or Udi are quite on the right track here WRT tuning around the problem - the dampers ARE in series, but the thing is that the initial LSC is actually a variable aperture valve (as Udi explained) so in theory it should just "blow off" after a certain point. Given that you need to maintain a certain oil pressure differential in order to blow it off, however, it will only uncover the 2nd and 3rd ports enough to let the pressure drop (as oil moves through the ports obviously) before it begins to shut those ports off again. In essence, it achieves the same thing as a shimmed damper, only in a more complex and less easily adjustable way (since with the floodgate you can dictate where the ports begin to "open" but you can't dictate how MUCH they'll be uncovered, since obviously the gap between the silver plate and the piston will be pretty small and thus make a difference to the damping effects).

Now given that the LSC doesn't just hydraulic lock and thus open the parallel HSC circuit, but the whole LSC thing disappears and becomes the HSC (so you effectively have the same HSC regardless of your LSC setting, once the plate has separated from the piston at all, which is good I suppose), I don't think turning down the LSC is going to solve any problems. Instead what I would recommend is pulling out the HSC shim stack and using only say a single, large OD, thin shim (I don't know how many they have to begin with, but I'm guessing 3-4 based on Manitou forks), if anything at all. In addition to, or in place of this, I'd suggest running a slightly lighter oil and cranking up the LSC to suit. This will reduce the amount of HSC through the primary circuit as well as obviously reducing the effect that the secondary circuit (shim stacks) have. I believe there is also a bleed port out the side of the compression tube in order to prevent the HSC shims also increasing the LSC, which is effectively a secondary damper that acts the same as a conventional ported-LSC/parallel shimmed HSC damper. I think this is pretty pointless and a pretty crappy way of trying to advertise "more damping control" really, but whatever.

So in short, try any combinations and permutations of the following:
- Thinner oil, more LSC, adjust floodgate to suit
- Removing the smaller diameter shims from the top (back) of the stack

 

[vitox]

say ffman, you think when the ports uncover on the bottom of the MoCo unit, they stay open long enough? or that it allows enough oil flow? maybe the harshness is related to that?

 

[Cave Dweller]

Don't forget that changing the oil is going to effect your rebound as well.

You guys do realise that by removing the black box stack that you are turning it into a boxxer race MCU? I have ridden both and the team/world cup is much better at controlling high speed impacts, which is what it is there for.

Udi, here is a pic i have. You should be able to unscrew the nuts on the speed stack to get to the shims, provided they didn't loctite everything together (possible)



I still reckon playing with the stack won't effect the LSC much. You need to modify the blow off spring rate somehow, if you want to lighten it (like you do) a dremel would probably work, just enlarge the holes. I wouldn't do it to my $200 MCU stack though

 

[bjanga]

A bit off topic here, but it seems to me that the shimstack is not redundant, it allows for a harsher high speed compression stroke, instead of an effectively undampened one. I do not know why you would want compression damping AFTER you have activated the LSC blowoff, but I am no WC racer either

 

[Cave Dweller]

A bit off topic here, but it seems to me that the shimstack is not redundant, it allows for a harsher high speed compression stroke, instead of an effectively undampened one. I do not know why you would want compression damping AFTER you have activated the LSC blowoff, but I am no WC racer either

To give you some pedalling platform, activated by a spring rather then air pressure.

I cant understand why people are all so confused about this

The speedstack is a standard shimmed disc setup to stop the fork packing down in high speed hits. Its not adjustable in the boxxer (it is in the new totem, gate does not equal high speed compression control). The bottom disc is just there to stop the fork bobbing around.

Its very, very similar to the dorado tpc+ system in some ways.



You had a floating piston (fixxed orifice size, not adjustable like boxxer) on the bottom that was spring loaded (little spring, very soft, internally adjustable) and covered a hole on the shaft (analogy the 2 covered holes on the boxxer), when the force was great enough it was lifted off the hole and fluid flowed into where the shim stack was. Once past the shim stack it pushed against the floating spring plunger.

Main differance is the boxxer has an air chamber at the top and uses a bit of an air spring instead of the spring loaded bladder the dorado had, and the other main differance is the black MCU spring controlling the LSC is alot stiffer then the little dorado spring. Other differance is the boxxer LSC orrifice size is adjustable, the dorado was basically fixxed unless you changed around the piston to a custom item

 

[peachy]

I'm finding it hard to visualize that the main plastic tube w/ holes on it compresses to reveal some ports.

i wonder why the Totem would have this HSC and the Boxxer would not.

 

[Cave Dweller]

I'm finding it hard to visualize that the main plastic tube w/ holes on it compresses to reveal some ports.

Well, it does. We are only talking about it compressing 5mm or so btw, not 8inchs like a normal spring

i wonder why the Totem would have this HSC and the Boxxer would not.

Totem is a new fork, thats why.

I would say next years boxxer will have the new damping system "mission control", or at least the WC will. They need to space things out to make more money out of it.

I bet if you look at rennies or hills WC boxxer they would have the new controls.

 

[thaflyinfatman]

Don't forget that changing the oil is going to effect your rebound as well.

You guys do realise that by removing the black box stack that you are turning it into a boxxer race MCU? I have ridden both and the team/world cup is much better at controlling high speed impacts, which is what it is there for.

No, it still has the adjustable floodgate, which makes a world of difference.

 

[thaflyinfatman]

say ffman, you think when the ports uncover on the bottom of the MoCo unit, they stay open long enough? or that it allows enough oil flow? maybe the harshness is related to that?

Well, in principle it's no worse than shim-stacks (except for a less controllable/re-tunable damper curve in that regard), and it's self-governing in the way it opens/closes based on the oil pressure (same as shim stacks do). With the floodgate adjuster, you should pretty easily be able to get the setup you need. Provided the covered ports are sufficiently large that the actual PORT size isn't the restricting factor, there shouldn't be much of a problem.

I still seriously cannot see the point of having another damper IN SERIES though. The only reason I'd buy a Team over a Race is for the floodgate adjuster, not because the shim stacks offer any practical advantage (having tried both, the Teams actually felt harsher, which was a bit arse-about IMO).

 

[peachy]

so X1 and X2 moves at the same time due to oil pressure? O stays in place depending on the gate's setting. the more gate (+) the more flexible the spring is inside allowing it to move w/ X1 & X2.

Udi, going back to your original question... what part is too deep for a regular socket wrench? when u pull the bottom piece (X2) u're left w/ what's shown in the cut-out right (ABCDE). how far down does that threaded part goes (B)? that's what holding the resistance of the gate? i have a socket that was meant for a spark plugs and it's made of a cheap thin tube w/ the end pressed to a hex shape. i wonder if something like that can fit inside. it's about 3" long. is there a way to access it from the other end (top)?

 

[bjanga]

I still seriously cannot see the point of having another damper IN SERIES though.

to stop the fork packing down in high speed hits.

I guess it makes sense. I would want my fork to be super responsive to hits that are blowing off the LSC threshold though.

I guess you could run slower rebound compared to a fork without the stack.

 

[thaflyinfatman]

I guess it makes sense. I would want my fork to be super responsive to hits that are blowing off the LSC threshold though.

I guess you could run slower rebound compared to a fork without the stack.

Fair call on the slower rebound, however the LSC threshold thing already provides some modicum of HSC damping as I explained above, and IMO it's that which (at least in an ideal situation) should be used to achieve the desired compression damping.

 

[bjanga]

so X1 and X2 moves at the same time due to oil pressure?

Peachy, I know little about boxxers or about damping, but I believe that X1 (shimstack?) does not move at all, however a larger impact will allow oil to move freely through X1.


flyinfatman, I agree that the stack seems redundant, and it makes sense that the stack will make the fork ride more harshly.

so basically, there are a number of things going on here:

- port size for low speed compression damping

- oil pressure levels necessary to move X2 (and O)

- pressure level necessary to force oil through the shim stack

also (I assume that the X2 LSC blowoff happens before the X1 shims allow oil flow), it appears that multiple hard hits are necessary to allow the oil to flow freely through the damper

interesting

 

[peachy]

oh shoot! my X1 is actually suppose to point to the black plastic part... and it's just an accident that it's also pointing at the shims. my bad.

 

[bjanga]

I see. That is the interesting part about this fork, the LSC blowoff port (apparently?) changes size depending on how stiff "A" and X1 are. X2 should move more easily than "A" to prevent cavitation and spiking (A is what you intended X1 to be).

As I understand it, the answer to you question is no, "O" compresses slower than X1.

 

[Cave Dweller]

Crickey! You guys are loosing the plot.

X1 is the mcu spring
X2 is bolted via an allen key to the black MCU spring (part X1), they move together, you can consider them the same part.

A is attached to 0, they are the same part

B,C,D and E are a rigid peice.

I can't beleive it has come to me drawing this in paint.



Low speed hit / pedalling
Depending on the setting of the 0 in relation to x2 (ie how much of the one port is uncovered), some oil flows backwards and forwards under low speed oscialtions, not really enough to bring into play the black box shim stack, it works like a ported damper.

When the pressure reaches a certain point in the bottom of the fork it will push against x2/x1 (the spring) and "blow off". If it didn't you would get hydraulic lock (ie 2000 marzocchi compression carts). This point is totally dependant on the MCU spring stiffness and how much of the port is open.

High speed hit
Oil pressure increase, can't get through the uncovered holes (x2 and 0), pushes part X1/X2 up opening the remaining ports on X2. Oil rushes into the chamber, it is slowed by the black box shim stack, the energy is disapainted by the shims bending. The fork doesn't pack down.

If you do not have the black box shim stack the oil will just rush into the chamber with its velocity uncontrolled.

Further, there is a mini air chamber at the top which adds a bit of ramp up at max compression.

The only part of the MCU that moves up and down is X1 and X2, and they move together as they are attached. Got it???

 

[Shepherdwong]

Thanks Cave Dweller, so if I'm to understand you and the previous posts correctly the floodgate adjustment isn't a threshold adjustment(how much of a hit is required to open up the additional ports). But an adjustment of how much dampening there is once the low speed dampening is blown off?

 

[thaflyinfatman]

Thanks Cave Dweller, so if I'm to understand you and the previous posts correctly the floodgate adjustment isn't a threshold adjustment(how much of a hit is required to open up the additional ports). But an adjustment of how much dampening there is once the low speed dampening is blown off?

No, it's both. Think of it like the preload on a spring (if you were preloading it by say 50% of its available travel that is) - it takes a certain amount of force to overcome the preload (or pressure threshold in this case), but once you've overcome it, you have to maintain that base pressure/preload force as well as the additional pressure/force created by the friction effects of the damper. The friction effects (for a given volumetric flow rate) are (non-linearly) proportional to the size of the opening the flow has to pass through. The size of the opening is dependent on the difference in the pressure required to reach the threshold point, and the gauge pressure across the ports. Therefore, the floodgate knob adjusts both the threshold point AND the amount of HSC you're getting.

 

[davep]

Awesome CD..nice drawing Haaaaa.

You know, all you guys with the questions.......just pop open the fork and take a look/play around a little. It will become clear what i sgoing on.

 

[Shepherdwong]

No, it's both. Think of it like the preload on a spring (if you were preloading it by say 50% of its available travel that is) - it takes a certain amount of force to overcome the preload (or pressure threshold in this case), but once you've overcome it, you have to maintain that base pressure/preload force as well as the additional pressure/force created by the friction effects of the damper. The friction effects (for a given volumetric flow rate) are (non-linearly) proportional to the size of the opening the flow has to pass through. The size of the opening is dependent on the difference in the pressure required to reach the threshold point, and the gauge pressure across the ports. Therefore, the floodgate knob adjusts both the threshold point AND the amount of HSC you're getting.

Thanks! That's how I thought it should work, I just got confused because in previous posts it sounded like the floodgate adjusted only how much of the additional ports could be opened up. That makes more sense.:biggrin:

 

[thaflyinfatman]

If you do not have the black box shim stack the oil will just rush into the chamber with its velocity uncontrolled.

Yeah except for the whole damper-before-the-shim-stack thing...

 

[Bicyclist]

Alright, so sorry for being a little slow.

In dumb people terms, what does the floodgate do? Adjust how much force it takes to go to the HSC circuit as well as adjusting the HSC at the same time?

Sorry...