Help me understand my monarch RT3 rebound shim stack.- Mtbr.com
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  1. #1
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    Help me understand my monarch RT3 rebound shim stack.

    I'm still learning about shock shimming. I think I mostly understand single stacks for forks and I can get them doing what I want. On the shock side, still a little in the dark.

    So I have a ML tune RT3 monarch with the debonair can.

    On the rebound piston face, it has a preloaded stack. I get that. Then it has a spacer stack that seems excessive, then another preloaded stack with a plate with cutouts.

    I dont understand how the top cutout plate and second shimstack come into play. Im guessing its a higher speed stack, but it appears fluid would have to push through the shimstack on the face plate, then go around the spacer stack through the center and come out the top? Not sure whats happening on the second stack or how approach even tuning this thing.

    I know what I like in compression. I basically just minimize preload on the stack, eliminate the lockout, and it magically works 10x better than stock. I can do coarse tuning from there to get LSC in check. I think I need to do the same for the rebound stack, but with 2 circuits and the weird plate on top I'm not visualizing how to attack this thing!

    The shock feels like it relies heavily on the needle freebleed, and chokes bad when closed. Tons of HSR, minimal LSR. I believe this is what RS is calling "rapid recovery" which feels like uncontrolled movement to me.

    Id appreciate any tips on tuning strategies for a shock circuit! For now, I removed the preload ring on the lower stack that touches the rebound piston face, so its just a basic 3 shim stack with no preload at all.

  2. #2
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    The top cutout plate is the check valve to stop oil flowing through the LSR on compression. You will see the sides of the piston arbor is flat so oil can flow in to the lsr circuit, out in to that gap between the shims and flats, the exits in to that plate and opens the shims. It has very little effect on damping, but you can remove the preload ring let it open easier and respond quicker, reducing lag in direction changes.

    So the shims against the main piston are the only ones you need to worry about. You are right they rely on the freebleed a lot as most stock dampers do, so you may need to rebuild it a few times, adding and removing shims until you have a comfortable rebound speed at around 4-6 clicks out from closed.

    Replacing a preloaded stack takes a little more trial and error as it is hard to predict where you will end up once you remove the preload. Was it a very soft stack with a lot of preload? In which case you will need extra shims, or if it was quite firm with a small amount of preload you migh tfind just removing the ring shims gets close to a good spot right away
    www.thesuspensionlab.nz
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  3. #3
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    Dammit, I should have measured the big shims. I think they were 0.15mm, and theres two of them. Face shim and top shim match.

    But the preload ring is 0.30mm, and the centering shim is 0.11mm, so I guess thats a lot of preload? The top stack preload ring is only 0.20mm.

    So I changed the preload stack from 0.15, (0.30 preload ring with a 0.11 center) 0.15 into: 0.15, 0.15, 0.11, with the 0.11 being smaller in diameter.

    This is a light tune. I'm almost positive its way too light now. I'll probably have to steal shims out of my other dead monarch to redo the face shim stack.

    So just leave the top preloaded stack alone? It sounds like its acting more like a check valve then.

  4. #4
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    Yeah 0.2 is a lot of preload! That will be very soft now. If you canít get enough Thicker shims, look to see if there is something you can use as a larger clamp shim eg if you can move the check valve down to sit directly against the stack, whatever is the last shim is the pivot so if you get a 12 or 13mm shim Thatís a good way to increase the damping

  5. #5
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    Is the RT3 lock circuit any different than a normal lockout? Its not a unique bypassing circuit, right? I didnt see anything to indicate otherwise.

    If thats the case, I should be scavenging a compression shim and switching it over to the rebound face anyway. The compression on this thing isnt bad, but its never been fantastic either.

  6. #6
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    Basically the main shim stack determines the lockout strength. Most of the oil is going through the large orifice in the shaft and opens a poppet valve which is controlled by the blue lever. When the pressure on that valve is too high the shims will open, but that doesn't really happen in open mode unless you have a very soft shim stack.

    You really need a double piston to separate the lockout from compression damping. (or 2 circuits if you have a piggyback shock eg 11-6)
    www.thesuspensionlab.nz
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  7. #7
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    Check out the main Monarch tuning thread. There is a ton of info there. Many people have tried different things.

    On the rebound side the stock approach is quite good. Donít touch the LSR stack, just add more 0.15mm shims to main rebound stack to match your weight.

    On the compression side I like exactly same things as you and went to fully linear stack - it made the shock really good.

    https://forums.mtbr.com/shocks-suspe...l#post14195107

  8. #8
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    I thought there was one! Thank you!

    Reducing rebound preload hasnt worked out for people? Hmm.

    I reshimmed it again, and my damn shock pump blew a seal! I have another one coming, but it could be a while. I'm stuck at home and mostly bored at this point.

  9. #9
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    Quote Originally Posted by One Pivot View Post
    Reducing rebound preload hasnt worked out for people? Hmm.
    The preload is needed to make the RapidRecovery to work. Some quite knowledgeable people spent lots of time to tweak the the rebound, but in the end it was not worth it.

    I must say that rebound is just working after I changed the tune from L to H+.

    BTW, I suggest you to modify the IFP adapter if you haven't already. The stock one is very unreliable, you can never be sure how much pressure is left in the IFP when you remove it. And the small o-ring could be easily damaged as well. The mod is described here:

    https://forums.mtbr.com/shocks-suspe...l#post13343476

  10. #10
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    Quote Originally Posted by One Pivot View Post
    I thought there was one! Thank you!

    Reducing rebound preload hasnt worked out for people? Hmm.

    I reshimmed it again, and my damn shock pump blew a seal! I have another one coming, but it could be a while. I'm stuck at home and mostly bored at this point.
    In a lot of cases, if you remove the preload you do need to add a substantial amount of stiffness to make up for it. If they didn't like the linear tune I would guess they didn't add enough shims.

    This is the punishing part of shim tuning, you really do need to rebuild your shock at least half a dozen times to really find a result....and don't just change 1 shim, you want to double the shims, then double it again until it is clearly too hard and then come back from there. You will end up with a much narrower range of adjustment so the valving needs to be more refined to get it working well, a firm tune like the factory one has a wider range of OK adjustment

    The factory "rapid recovery" tunes actually create a very progressive tune instead of the supposed digressive curve that they claim, which is not ideal
    www.thesuspensionlab.nz
    Suspension servicing & tuning in Rotorua, NZ/Vorsprung Elite Tuning Centre/Insta @thesuspensionlab

  11. #11
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    The idea behind rapid recovery is to lessen rebound at deep stroke, right? To rapidly bounce back. It feels a little uncontrolled sometimes. Judging by how preloaded the stack was, it does seem to just let loose once it pops open. I want a smoother transition.

    I don't mind a little bit of packing out back. Nothing crazy, but if it needs to slightly pack to maintain damping control, I'll take it.

    I can tell this is going to take a while. No shock pump until Tuesday now. Doh!

  12. #12
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    There are two rebound circuits. One is heavily preloaded and opens only when the shock is deeply compressed (i.e. the rebound force is big). It flows a lot of oil though when open, so the shock can extend quickly. The other circuit is very lightly preloaded, so it is open most of the time, but it has a limited throughput (that can further reduced by external adjuster).

    So, the shock can be in two modes when rebounding: when it was only lightly compressed, the forces are small and the main rebound circuit is closed, so the external adjuster determines how fast the shock expands. You want to open the rebound so that it is not packing up on small shatter - it must no be too slow.

    Then the shock is heavily compressed and expands both circuits are open and shock expands rapidly until the pressure drops and it goes back to mode one. If you feel that the bike wants to kick you out of saddle when you are riding on track with bigger and slower bumps where the shock is almost fully compressed, it means that the total flow of oil through both circuits is too much. You cannot close the external adjuster because that would throw off the small bump compliance. Instead you must make the HSR stack stiffer so it flows less oil when open.

    You said that you have ML tune shock - I suppose it means M rebound tune? If you are heavier rider then it is too weak - you need higher tune. Experience from Monarch tuning thread shows that Rockshox has developed good rebound tunes - I suggest to try them out before experimenting. You only need 19x0.15mm shims to go from L to M to H. If you are really heavy rider like me (100kg), add one more shim.

  13. #13
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    Quote Originally Posted by One Pivot View Post
    The idea behind rapid recovery is to lessen rebound at deep stroke, right? To rapidly bounce back. It feels a little uncontrolled sometimes. Judging by how preloaded the stack was, it does seem to just let loose once it pops open. I want a smoother transition.

    I don't mind a little bit of packing out back. Nothing crazy, but if it needs to slightly pack to maintain damping control, I'll take it.

    I can tell this is going to take a while. No shock pump until Tuesday now. Doh!
    The idea yes, in reality no. Even with the light tunes the shim stack barely opens so the damping rate keeps increasing with speed most of the time. Which is why most people run them at the more open end.

    It will feel uncontrolled on big hits just from the lack of low speed damping ie too much free bleed. I see this often in data where the shock feels too fast at the top but doesn't peak very high at all when coming out of deep compressions. A linear tune flattens out the curve to have more control in the middle while still returning fast enough from the end of travel.

    Oh yeah what pressure are you running?
    www.thesuspensionlab.nz
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  14. #14
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    300psi in the IFP... 255psi in the db can. Im using maxima 3wt instead of RS 7 wt, so 14cst instead of 22ish cst.

    I redid the stack again and put it back to stock on the rebound side. I moved the ring shim up to the very top of the comp stack. It had a huge .4mm ring shim with a .10mm centering shim. I added a .20mm clamp shim between the whole thing to essentially make it 0.10mm of preload, on the top of the whole stack. So basically no preload, just a linear stack.

    Lockout is gone. I think comp damping is too light, or the thin fluid just has too much freebleed.

    However, small bump is significantly better. I can steamroll a curb and its just gone. Thats cool, but I could use more compression!

    I need to order shims. Ugh. This is quite a process! Probably need to order slightly thicker damper fluid, its still cool here and we're going into hotass summer.

  15. #15
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    Quote Originally Posted by One Pivot View Post
    I need to order shims. Ugh. This is quite a process! Probably need to order slightly thicker damper fluid, its still cool here and we're going into hotass summer.
    Welcome to shim tuning! It takes a lot of trial and error, especially without a dyno. At 255 psi if you remove the rebound preload you will need to add several 0.15mm shims. I canít remember exact numbers but it will be at least 4. Just adding 1 wonít do it

    Thicker oil should help with your low speed support, in open mode the shims only affect very high speeds.

    I suggest teknik Motorsport in Australia for shims, especially 9mm ones. Re suspension is another good one in ĎMurica. Depends what restrictions you have! Get Mostly 0.15 and A few 0.2mm ones at least

  16. #16
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    I put the preload stack back on the rebound side. I think I need to leave the preloaded rebound side on there, and simply add another shim.

    I wanted to mute the lock, but its completely gone and doing nothing. I think my HS stack is acting sort of like a check plate. No real damping, just blowing open. I either need to put the preload back on, or go waaay thicker.

    MX tune has shims for about a buck. Ill just order a bunch I suppose.

  17. #17
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    Yeah preload has a huge effect, 0.05 is minimal but .1mm bumps the damping up a lot and .2 is huge. So if you want that lockout mode you will need to do some fine tuning there to get the balance right.

  18. #18
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    Quote Originally Posted by One Pivot View Post
    300psi in the IFP... 255psi in the db can.
    With such pressure I recommend you to put 4 19x0.15 shims on top of ring shim on rebound side. M tune has 2. H has 3. I'm running 195psi with Debonair can and I have 4 shims.

    Another source for shims is Revalving Shims

    It seems that all the required shims are stock at the moment.

    Quote Originally Posted by One Pivot View Post
    However, small bump is significantly better. I can steamroll a curb and its just gone. Thats cool, but I could use more compression!
    If you like to try linear stack you need some thicker shims. My main compression stack is 4x22x0.25mm + 1x19x0.15mm.

  19. #19
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    Hmm, just to be clear you're suggesting more rebound shims on TOP of the ring shim? So piston-(shim, ring, center, shim), and then more shims on top? This creates an increase in preload, correct? I believe im at 4 19mm rebound shims total, including the preload sandwich.

    I was hoping I could wing it and get lucky with my comp stack. I didnt expect it to be so preloaded. I think mine ended up 3x22x0.15 plus a 22x.10, so I basically have no damping at all it seems. Yours is many times stiffer than mine! Which makes sense, considering how wide open my lock is now.

    Im good with getting rid of the lockout. I actually never use it. Its more of a gauge I suppose. In general with fork tuning, I've found that once the lock out is firm but not actually locked, my damping is going to be in the ball park. Wide open when locked means I screwed up the stack! This was extremely apparent when I tuned my xfusion RL2 forks, they wont place nice with a lock.

  20. #20
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    Quote Originally Posted by One Pivot View Post
    Hmm, just to be clear you're suggesting more rebound shims on TOP of the ring shim? So piston-(shim, ring, center, shim), and then more shims on top?
    Exactly. The whole point of this is to be able to open the external adjuster more, so that the shock is not packing up on small stuff. And at the same time increase the rebound damping after deep compression so that bike is not kicking you OTB.

    Quote Originally Posted by One Pivot View Post
    This creates an increase in preload, correct?
    Yes. I added chart to compare them - orange is M and blue is H+ that I suggest. (don't look at the numbers - they are not correct. Only shape of curves and relation to each other matter).

    Quote Originally Posted by One Pivot View Post
    I believe im at 4 19mm rebound shims total, including the preload sandwich.
    This means that you have M tune.

    Rockshox sells three tunes: L, M and H. L is one 19 + ring/center + one 19. M adds one more 19mm shim on top of ring/center and H adds one more.

    I recommend go beyond that and add fourth shim on top. This is the tune that I'm using at 100kg and 195 psi.

    Quote Originally Posted by One Pivot View Post
    I was hoping I could wing it and get lucky with my comp stack. I didnt expect it to be so preloaded. I think mine ended up 3x22x0.15 plus a 22x.10, so I basically have no damping at all it seems. Yours is many times stiffer than mine! Which makes sense, considering how wide open my lock is now.

    Im good with getting rid of the lockout. I actually never use it. Its more of a gauge I suppose. In general with fork tuning, I've found that once the lock out is firm but not actually locked, my damping is going to be in the ball park. Wide open when locked means I screwed up the stack! This was extremely apparent when I tuned my xfusion RL2 forks, they wont place nice with a lock.
    Yes, if you remove preload you need to add many thick shims to get the overall compression back to the zone where you started. I promise you will like it

    The overall design of the Monarch compression side is stupid. Basically the main stack stays closed 99% of the time and only opens in case of biggest hits. This is needed to make the lockout work. So the nice piston and elaborate shimstack are not used most of the time at all. All oil flows through the center channel and then through simple two shim stack on the LSR plate.

    By going full linear, you will take the main stack and piston into real use.
    Attached Thumbnails Attached Thumbnails Help me understand my monarch RT3 rebound shim stack.-rebound.png  


  21. #21
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    I used your comp stack. 4x 22x0.25's and a 19x.15 on the comp stack, no preload. Maybe a hair firm but I need to hit a real trail first. added 2 19x0.15's to the rebound stack and that fixed that.

    Now would be a great time to ditch the debonair can. I think this shock would actually work best with a linear stack and normal can. The debonair is trying to hide the preload while keeping the lockout. No need for that.

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