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  1. #51
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    This is a modification to a Marzocchi 55 TST2 fork damper cartridge. This modification converts the lock-out to a low speed compression adjustment and adds a high-speed compression shim stack.

    (For a bleed only proceedure, see here: TST2 Bleed alternative w/pics )

    It all started with an MTBR post asking for help on how to set up a Mazocchi 55 TST2 fork...And turned into a complete damper modification.

    The problem I was having was high speed spiking. With the help of Flyag1 (he cracked open his damper cartridge and set me the pics) we were able to figure out that the damping was a port orifice design. The port orifice being the source of the high speed spiking. But from Flyag1's pics I also noticed something else; a blanked off potential compression piston.

    This compression piston was simply blanked off with just some thick washers. I speculated that we could replace the washers with a shim stack with the lock-out orifice acting as an adjustable bypass port. Sounds great, but modifying my new 3 year warranteed fork on some pics and guesswork was pretty racy for me. Then I got the dreaded hydro-locking damper cartridge - a week before Sea Otter (I was entered to race). And Marzocchi Tech Department replied to my post with confirmation of our guesses and additional great info, to give me the confidence I needed.

    I knew I had to crack open the cartridge to be able to run the fork for Sea Otter. I figured, if I'm in there I may as well give the damper mod a shot. I had my spacer ready, shims ready, beers ready...


    Here is how it went down:

    1) Pry up the lock out with a flat blade screw driver - it is held in by the friction of an O-ring.



    2) Remove the plastic bits and keep them in order



    3) Use a 22mm ground down socket and unscrew the top of the damping cartridge from the fork crown.

    This next part is NOT part of the Marzocchi recommended damper bleed proceedure - but I was able to do the whole modification and bleed without removing the damping cartridge.

    4) Push the fork to bottom (air and spring removed from spring side) while making sure that the damping cart is still extended out of the fork.

    5) Unscrew cart top. I used an old tube to friction hold the outside of the cart to keep it from spinning. It was tough and required a beer for courage. lol.

    6) After loosening carefully pull compression damper straight out.


    fixxxer0 provided a correction:
    its a 27mm socket you need to grind down, not a 22mm as stated in the picture below



    7) Remove bottom bolt from damper shaft. More beer for courage. Marzocchi Tech Department advised to heat the bolt as there is loc-tite on the threads - and I don't think I could have gotten the bolt off without doing so. Again, I used my old tube to hold the damper.



    8) Bye bye thick unflexing washers. Hello flexy goodness shims and spacer! Welcome speed sensitive damping!
    Right now it is a pyramid stack 17mm, 16mm, 16mm, 15mm, 13mm. All (I think) .010 thick except for the 13mm which is .005 thick. 18mm scraped the side of the cartridge. (all 8mm ID)

    The spacer is an aluminum chainring bolt spacer.




    9) Measure oil level in the damper at full extension. Flyag1 came up with measurement of 110mm from the top - it is dead-on! This will give an oil level just above the piston/shim for proper operation.

    10-x) Reverse rest of proceedure to put back together.

    Success = beer.


    RIDING RESULTS:

    Damping was controlled and felt as normal (pre-mod) with trail riding at wide-open. Then I stuffed the front wheel straight into the boneyards at speed; the smaller stuff was simply erased, 3" or larger squared rock stills had some feedback, but it was controlled and not spiked feedback (and could be related to spring ramp-up). It did make my rear shock seem less plush - not a technical issue just a feel issue. End of DH rock run, my hands were not killing me as they were prior to the mod. I did still have some arm pump, but that is expected on that particular trail.

    Drops and jumps seemed to go just a bit deeper into travel, (spring rate or less HSC?) but the ramp up of the air spring still gave that lovely landing-on-a-couch feel, and covered any mistakes.

    Lock-out is now a compression adjustment. Full lock out is firm compression (port orifice is off and piston/shim is active) that makes the fork only move about an inch under stand and pedal situations (2 inches max when stand and mash is tired and sloppy). The cool part this this retains 80% of the lock out benefits, but the travel remains well controlled and active - still eating up small and large features. I will never have to worry if I am locked or not on a downhill, as it is still perfectly rideable on "full lock".

    So am I happy? Hell yes! It is now the fork I thought I bought and wanted. I love that I can also easily modify to shim stack to shape the compression to my riding.

    I am using a quarter turn compression setting to give an nice controlled and efficient feel on XCish and flowy trails - it also helps with dive. (just a quarter turn gives me full shim stack only compression)

    MAINTENANCE RESULTS:

    After a couple of 20+ mile rides, 40-50 runs on the Sea Otter dual slalom course that included uncountable jumps and drops all is working fine (it should). And I am glad to say the damper has not hydro-locked. I should also note it only takes about 10-15 minutes to get to shim stack now.

    Start modding!!

    Thanks again to Flyag1 and Marzocchi Tech Department. They helped me to make a good fork great.

    P

  2. #52
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    Quote Originally Posted by Stevo the Devo
    Hey Bronze, The travel adjuster works great if you perform a very simple, quick fix that Renegade posted to stop it winding down. It is actually a purely mechanical system that doesn't change performance in any way except travel; I like it a lot. Maybe not too late to grab that second fork... Cheers, Steve
    Cool, do you know what forks this damper is in? The ATA is a bit too much fork. I was looking at the Marzocchi XC 600 '08 at Jenson. The travel adjuster fix, is that for ATA2?

  3. #53
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    Quote Originally Posted by thebronze
    Cool, do you know what forks this damper is in? The ATA is a bit too much fork. I was looking at the Marzocchi XC 600 '08 at Jenson. The travel adjuster fix, is that for ATA2?
    The fix works for ata or ata2 forks so take your pick!

  4. #54
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    A few update as I finished the mod last night.

    1. You do not need a strap wrench to open the TST cartridge. Remove the cartridge and you'll find wrench flats on the bottom of the cart. You can then put your socket on top and your box wrench(13mm?) to crack it open.
    2. Same goes for the piston. I believe it was a 10 or12mm but keep the socket on the top and wrench on the bottom and it will come loose. I did not need to heat anything up to break the loctite.
    3. The 17mm OD shim is a bit too small and leaves the ports exposed. This will create more free bleed and less LSC. I recommend an 18mm OD shim #1.
    4. The xc600 TST2 can be upgraded to 140mm travel by removing a 20mm spacer below the spring on the pumping rod.

    I have not had a chance to ride it but i'm really excited to rip into it.

  5. #55
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    Quote Originally Posted by thebronze
    A few update as I finished the mod last night.

    ...

    I have not had a chance to ride it but i'm really excited to rip into it.
    Nice one! Thanks for the tips.

    Let us know how it rides.

    P

  6. #56
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    I should be getting my 55 tst2 tomorrow. After dumping over $500 on a Fox fork and still wanting the Marzocchi feel my old fork had, I couldn't resist $250.

    I have a question for the few of you who have experience with this mod. Will this shim-stack mod prevent the hydro-locking issue these forks are known for?

    I would like to just buy anything I need now and get the fork reliable before it goes on the bike. Then maybe some tuning here and there.

  7. #57
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    Good stuff!!!!

    After reading thought this thread I must say the 55 TST2 fork looks like it can be a very inviting. These can be found pretty darn cheap and once you get rid of the washers and add the shim stack you will have a decent performing fork without spending a fortune. Once the mod is done, (I'm thinking this was metioned) the damper is works exactly like the the TPC which we all know is a very reliable and well performing damper.

    I also like the fact that a RC3 cartridge could be installed at a later time.

    I'm looking for a replacement for my 06 Vanilla RC2. I'm looking for more bottom out control and with the air preload I think it would help.

    I have a few questions.

    This may be silly, but does this fork have adjustable rebound? I could find anything in this thread that mentioned it. If it doesn't have an adjustable rebound, can the rebound pistion be shimmed?
    Last edited by spacoli; 01-17-2009 at 03:56 PM.
    I can fix it............... my dad has an awesome set of tools

  8. #58
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    Quote Originally Posted by cesper
    I should be getting my 55 tst2 tomorrow. After dumping over $500 on a Fox fork and still wanting the Marzocchi feel my old fork had, I couldn't resist $250.

    I have a question for the few of you who have experience with this mod. Will this shim-stack mod prevent the hydro-locking issue these forks are known for?

    I would like to just buy anything I need now and get the fork reliable before it goes on the bike. Then maybe some tuning here and there.
    Hey Cesper,
    Unfortunately the mod will not fix the hydro-lock problem, it can only be fixed by replacing the damper (or at least the bottom end cap) with the newer design. I would recommend contacting marz USA (or Marz Tech Dept on these forums) to arrange for a replacement under warranty before you do the mod. Cheers, Steve

  9. #59
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    Hey spacoli, it does have adjustable rebound.

  10. #60
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    Good Call, Steve-O. I think I'm just gonna get the parts from Marzocchi and do everything at once. I know that if I put the fork on now, I'll just keep saying "one more ride" until it's too late.

    I'm really hoping I can get this thing to feel like my '04 Z1. Man, I should never have sold that thing

  11. #61
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    Quote Originally Posted by cesper
    I'm really hoping I can get this thing to feel like my '04 Z1. Man, I should never have sold that thing
    I still have one, mint condition, qr axle though. I'm hoping for the same results. Can anyone compare the two?
    I can fix it............... my dad has an awesome set of tools

  12. #62
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    Quote Originally Posted by Stevo the Devo
    Hey spacoli, it does have adjustable rebound.
    Nice, thanks Steve. Hey I have been reading some of your posts, looks like you have a handle on this stuff. Can the rebound piston be tuned with shims?
    Last edited by spacoli; 01-17-2009 at 06:30 PM.
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  13. #63
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    Quote Originally Posted by spacoli
    Nice, thanks Steve. Hey I have been reading some of your posts, looks like you have a handle on this stuff. Can the rebound piston be tuned with shims?
    Hey Spacoli,
    Firstly, I won't claim to be any suspension guru, I know quite a bit about this particular mod, but past that I won't vouch for me! I do, however, have reasonably good mechanical aptitude and comprehension.
    Ok, so with the disclaimer out of the way, here are my thoughts. I don't think it would be easy to effectively shim the rebound circuit. I pulled it out to have a look (I have a spare damper with the dud bottom nut); it is, as you'd expect, basically a needle valve which varies the orifice size of a moving damper unit( it moves up and down in the cartridge) . There is a piston, but it has a check plate on one side and the other side is open (ports uncovered). The ports are also recessed on the uncovered side. In order for this piston to not affect compression damping as well, the ports need to allow for unhindered flow of oil on the compression stroke; in this direction the lightly sprung check plate permits oil to flow through the ports as well as the central orifice.
    Upon rebound, the check plate closes and the oil is forced to return through the orifice alone, so it's size totally controls the rate of rebound. In order to shim the rebound circuit, you would have to use shims that only partially covered the ports so as to still allow compression of the fork, you would also have to use a smaller check plate so that some oil passed through the ports on rebound (otherwise the shims won't do anything). All of this is going to seriously mess with the effect of the rebound adjuster (as the orifice will only be partially responsible for rebound behaviour. I'm not saying it can't be done, but I think it would involve a lot of trial and error to get a setup that still allowed unrestricted compression whilst allowing both the shims and the adjuster knob to have a significant effect. After all, you still want to be able to externally adjust rebound (at least to some extent) after the mod.
    So that's my take on it. I will no doubt consider this possibility further as it would be nice to be able to tinker with rebound as well as compression, But in the mean time I reckon just stick with the existing mod; it is simple, effective, and gives lots of tuneability.
    FWIW, I would be keen to hear other peoples thoughts on this matter (MrP? Derby? Jayem? Bueller?)
    Cheers,
    Steve
    Last edited by Stevo the Devo; 01-17-2009 at 07:40 PM.

  14. #64
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    So it's not a shimmed rebound piston.

    If this is the right picture, any shims would need added under nut. But looking at the piston there is no way it would work, this is only a one way piston. It would need to be like the Manitou two way flow rebound piston in the picture. There is three nice tapered ports for the oil to flow through and the check valve on the backside. It would be nice if the Manitou piston could be used.

    Just wondering, what is the O.D. and the I.D. of the marz piston?

    You could probably get another compression piston from Marz, flip it over, shim it and use it for the rebound side.

    Heck that's the only "tuning" Push offers on there Rockshox mods. They replace the stock rebound piston with their "two stage" shimmed piston. That just goes to show you rebound must be an important part of suspension tuning.

    Edit: I looked through the pictures in this thread again and found the compression pistion. It is only a two port not three like Manitou, but it would work on the rebound side if the I.D. bolt hole is the same and the thread depth on the rebound rod is long enough to get the nut plus shims.
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    Last edited by spacoli; 01-17-2009 at 08:27 PM.
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  15. #65
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    Steve, Since you have an extra damper, when you get a chance, can you see if the compresion piston can be installed on the rebound rod? Thanks
    I can fix it............... my dad has an awesome set of tools

  16. #66
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    Quote Originally Posted by spacoli
    Steve, Since you have an extra damper, when you get a chance, can you see if the compresion piston can be installed on the rebound rod? Thanks
    Since the mod has a TPC type damping, it would be worth studying how the Manitou TPC shimmed rebound works. TPC is based on pushing oil - how it is pushed and if it includes the rebound piston would be key questions, I think.

    It does appear that, if sizes match up, the compression piston could work on the rebound side.

    P

  17. #67
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    Quote Originally Posted by Mr.P
    Since the mod has a TPC type damping, it would be worth studying how the Manitou TPC shimmed rebound works. TPC is based on pushing oil - how it is pushed and if it includes the rebound piston would be key questions, I think.

    It does appear that, if sizes match up, the compression piston could work on the rebound side.

    P
    Hey guys,
    Will check the fit in the next day,or so and let you know. In terms of rebound tuning, I'm not quite sure how the shims work; for compression, the amount of force and speed varies due to terrain, but the rebound force would seem to me to be a relative constant ie the spring force. With an air spring it will be stronger at full compression, meaning the end-stroke rebound will tend to be slightly faster, which is the opposite of what you want, but I can't figure out how the shim stack could be made to work harder (slower rebound) with a higher force and less (faster) with a lighter force. Any ideas?
    The other option is to see if the rebound side of the compression piston could be altered, but again I don't see how this could yield the desired effect, and it would be unaffected by the rebound adjuster, thereby reducing its practicality. Hmmm, now I'm intrigued...

  18. #68
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    Quote Originally Posted by Stevo the Devo
    Hey guys,
    Will check the fit in the next day,or so and let you know. In terms of rebound tuning, I'm not quite sure how the shims work; for compression, the amount of force and speed varies due to terrain, but the rebound force would seem to me to be a relative constant ie the spring force. With an air spring it will be stronger at full compression, meaning the end-stroke rebound will tend to be slightly faster, which is the opposite of what you want, but I can't figure out how the shim stack could be made to work harder (slower rebound) with a higher force and less (faster) with a lighter force. Any ideas?
    The other option is to see if the rebound side of the compression piston could be altered, but again I don't see how this could yield the desired effect, and it would be unaffected by the rebound adjuster, thereby reducing its practicality. Hmmm, now I'm intrigued...
    I'm no expert, but I would think it would be more controled and consistant with the shims. I thought that was the idea with a shim stack depending on the stack arangement. It would be just the opposite as is. there is a fixed piston that only lets so much oil pass through. The shims would bend and allow the oil to pass with the increase rebound speed at full compression.

    This maybe why Push does a two stage rebound? I know when I had my DHXC Pushed the rebound felt way slow. They told me not to worry, it's because of the two stage rebound, they explain why but I can't remember. The shock feels great to ride.
    I can fix it............... my dad has an awesome set of tools

  19. #69
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    Quote Originally Posted by spacoli
    I'm no expert, but I would think it would be more controled and consistant with the shims....

    I know when I had my DHXC Pushed the rebound felt way slow. They told me not to worry, it's because of the two stage rebound, they explain why but I can't remember. The shock feels great to ride.
    A rebound shim stack would allow you to run a slower free bleed rebound which would open up on bigger hits (more spring). This creates a more controlled and wider range of damping than an orifice damper.

    P

  20. #70
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    Quote Originally Posted by Mr.P
    A rebound shim stack would allow you to run a slower free bleed rebound which would open up on bigger hits (more spring). This creates a more controlled and wider range of damping than an orifice damper.

    P
    Yeah thats what I thought, but I don't get why it's better. It would mean that on smaller stutter bumps the shock will be more likely to pack up (due to the slower free bleed), but on bigger hits it will be more likely to buck (due to the shims opening). Seems to me that whilst a shimmed piston is preferable for compression damping, the rebound damping requirement is best suited by the orifice damper curve (less damping at low speed/spring pressures and more at high speed/spring pressures). I think this is where position sensitive damping is better that speed sensitive.
    Now opening the topic up for anyone to shoot holes in my logic...
    Cheers, Steve
    Last edited by Stevo the Devo; 01-18-2009 at 09:17 PM.

  21. #71
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    Quote Originally Posted by Stevo the Devo
    Now opening the ropic up for anyone to shoot holes in my logic...
    Cheers, Steve
    YOur logic is correct. Or at least I agree with it.

    But you can get similar results with a shim stack and zero bleed. I'm a fan of zero bleed. Meter all the flow, control it to the last bit. Separate compression from rebound.
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  22. #72
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    Quote Originally Posted by Warp
    YOur logic is correct. Or at least I agree with it.

    But you can get similar results with a shim stack and zero bleed. I'm a fan of zero bleed. Meter all the flow, control it to the last bit. Separate compression from rebound.
    Hey Warp,
    Thanks for chiming in, much appreciated. I agree that, like church and state (couldn't resist the analogy) rebound and compression are best kept separate.
    The good thing is that in this cartridge (TST2) they are already separate; the passive damper in the top of the cartridge does all the comp damping (and maybe a tiny bit of rebound) whilst the piston on the rebound rod does all the rebound damping (it has a one-way piston).
    I guess this topic came up as the comp damper mod is easy, so I (and others) were hoping a similar thing could be done with the rebound circuit. Maybe there is little to be gained. I can't help thinking that position-sensitive rebound damping is better that speed-sensitive (although the reverse may be the case for compression). Cheers, Steve

  23. #73
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    It's a poorly kept secret....

    Quote Originally Posted by cgd
    many thanks for the depth of your response, i was only ever aware that compression damping was controlled by orofice systems. how ignorant!

    thanks again.
    Die hard Manitou fans have known the secret of shim stacking for years... It's an art as well as a science!
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  24. #74
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    Quote Originally Posted by spacoli
    I'm no expert, but I would think it would be more controled and consistant with the shims. I thought that was the idea with a shim stack depending on the stack arangement. It would be just the opposite as is. there is a fixed piston that only lets so much oil pass through. The shims would bend and allow the oil to pass with the increase rebound speed at full compression.

    This maybe why Push does a two stage rebound? I know when I had my DHXC Pushed the rebound felt way slow. They told me not to worry, it's because of the two stage rebound, they explain why but I can't remember. The shock feels great to ride.

    You can not change the rebound piston. It would all need to be redesigned in order to make it work, as in make it all bigger diameter. Also to note that due to the size of the rebound piston you would n ot have enough room to design a two way valve that would 1 flow enough on the compression (blow-off) and then 2 have a shim big enough to be any better than what it is now. Maybe in the future but right now it is what it is.

    I know what you are trying to do, good idea, but not feesable with the size constraints of the current cartridge body.

    Tom MTD USA
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    Bugger!

    Quote Originally Posted by Marzocchi Tech Department
    You can not change the rebound piston. It would all need to be redesigned in order to make it work, as in make it all bigger diameter. Also to note that due to the size of the rebound piston you would n ot have enough room to design a two way valve that would 1 flow enough on the compression (blow-off) and then 2 have a shim big enough to be any better than what it is now. Maybe in the future but right now it is what it is.

    I know what you are trying to do, good idea, but not feesable with the size constraints of the current cartridge body.

    Tom MTD USA
    Oh well, there goes that idea! Thanks for at least stopping us wasting time on it, Tom. BTW, thanks for organising the new damper for my fork; since fitting it I have had zero problems and the fork feels very very nice. Looks like you've won me over to the dark (Marzocchi) side. Cheers, Steve

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