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Discussion Starter · #1 · (Edited)
Ok. I finally mustered the nerve to open up my rear shocks. I really, REALLY want to tailor the ride to what I want, more rear rebound damping and slightly less low speed compression damping. So, today I started.


Here is a pic of the guts.
_MG_9685.JPG

I would have liked to have another shim stack to drop in right now, but couldn't find a vendor that would answer me or knew what was in it already. I did get Kartek Racing to respond and he said to let him know what shims are in it and he would recommend a new stack for me.

Here are my kindergarten style handwritten notes. Compression stack has 14 shims. Rebound has 8.
YXZ Shock Phone Cam (2)_LI.jpg

If you are able to read the writing, you'll see that there isn't much to it. My biggest concern was getting the assembly out of the bottom. There is a dust cap on the bottom that has to be pried out to access the bottom cap/seal. A retaining ring held both the reservoir cap and piston shaft assembly cap in. It was a non- issue getting everything apart. It is worth mentioning that a 1/2" allen wrench is needed. I didn't have one, so off to HF I went.

Also of note, you might notice that both compression stacks start out big at the bottom, have a smaller shim above, then go bigger again before the shims get smaller again. My understanding is the small shim in the middle is a transition shim. It separates the low speed part of the stack from the high speed part of the stack.

I know I'm not explaining that well, but here's a low budget graphic. Below the transition shim is low speed, above is high speed (which is in addition to the low speed damping).



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--- <--Transition Shim
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_MG_9688.JPG

Anyway, tomorrow I'm going to drill and tap the reservoir cap to install a schrader valve. Hopefully, Kartek calls me back with a shim stack suggestion. If I'm happy with what they say, I'll tear the 2nd shock down to get ready. I will try to get some decent video. I tried today, but frankly it was shit.
 

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Discussion Starter · #2 ·
This is one of the graphics that I've been looking at.

4-woods-suspension-configuration.png
 

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Thank you, Big kudos for taking the time to post this. I’m taking notes. Any one mention high flow pistons, all the big boys replace the pistons, i don’t know where they source them though, Fox makes them but where to buy is the question.
 

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Discussion Starter · #4 ·
Thank you, Big kudos for taking the time to post this. I’m taking notes. Any one mention high flow pistons, all the big boy use those, i don’t know where they source them though, Fox makes them but where to buy is the question.
I have looked for info regarding the pistons. I found nothing.

Honestly, I don't see the need for them. Changing the shims should allow for quite a change in shock characteristics.
 

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I have looked for info regarding the pistons. I found nothing.

Honestly, I don't see the need for them. Changing the shims should allow for quite a change in shock characteristics.
Yeah, I have never heard Weller say they replace them, but not sure,
 

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If you take measurements of the shims, you can call ADS, King, SAW, etc.. and give them the size of shims you want and order. Ebay has them as well. I've called FOX about ordering new shock guts for the YXZ and they wouldn't help out.
 

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Discussion Starter · #8 ·
Just another quick pic. I believe this happened during assembly at the factory. You'll probably have to zoom in to see it.
YXZ_Shocks_04012019 (13)_LI.jpg
 

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Discussion Starter · #9 · (Edited)
Another pic with a comment. Kartek got back to me. Apparently these shim stacks are unusual. Especially the rebound stack. Chris told me that with the smaller shim in the middle, these are flutter stacks. He's never seen a flutter stack for rebound. He's also not seen a 2nd slotted shim further up the compression stack.

YXZ_Shocks_04012019 (14).JPG

Explanation of the order of things:
Top right is the piston.
The first row of shims is the rebound stack.
The 2nd and 3rd row of shims is the compression stack.
 
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I believe you can buy a kit from z bros racing that has springs and valving. But idk how the stage 3 is. I have stage 2 and had the rebound slowed down last rebuild.
 

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Discussion Starter · #11 ·
I want to see how good I can get them without changing springs. I resigned myself to the fact that I'll be tearing them apart a few times until I get them where I want them (if ever). For me, half the fun is figuring out how things work. I've already learned a ton of stuf about shocks and shim packages.

I'm uploading a video on disassembly right now. Tomorrow I re-assemble.

I'll probably make a separate thread for the videos.
 
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Discussion Starter · #12 · (Edited)
Video also added to 1st post. How come I can't change the thread title?

 

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Here are some tips to point you in (what I feel) is the correct direction.

Front needs to be a bit firmer
Rear softer

Stock compression Valving is over hard early. That makes it harsh on the little chop.
If you valve it soft overall to try and make the little stuff smoother, you end up with a degree of much less bottom out resistance. You must think outside the box and understand how those shims work from a small short flows to heavier faster flows. just following the Fox charts will only get you a narrow band width of ride quality. A wider band width is what you want. Smooth softer beginning and firmer later in the stroke to still have good bottom out resistance.

You can arrange those shims any way you want! Drive your car and realize your changes to how the shocks perform. Once you do this a few times, will give you a better understanding of what is going on inside the shocks with valving and modifications. I would try not to do to many things all at once!! You won’t know what mod made the biggest change? And if it’s for the better or worse?

You will have to modify and or change the valving in the rear BOC, bottom out cup also. It is way over firm at the bottom of the stroke! Some tuners just Eliminate the gold cup on this device so it dosnt work at all. But if you figure it out? It is a good benefit to bottom out resistance while doing the main valving softer. I have modified this to work great for my cars.

If you don’t modify the BOC, you continue to think the main valving is still to harsh, even as you valve it softer. Because on bigger rear hits, the shock will race into that harsh hydraulic stop BOC and you get your rear compression hop!

Front rebound needs to be faster and also run higher spring rates than stock
Rear needs to be much much slower, and with softer compression valving, then you can run higher rate springs that work better for the car. Especially if your going to carry lots of goodies!

Have fun
Good luck

Have fun
 

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Discussion Starter · #14 · (Edited)
Hey! I was hoping you would reply to this thread. Thank you.

I have started off by deleting one of the 6 bottom .008" shims on the compression stack. I also put 2 next thicker rebound shims in at the bottom of that stack. I know. I should have only made one change at a time. Sometimes I'm a goof. Anyway, I'm riding tomorrow to see how it feels.

Regarding the BOC, I looked at it a bit, but didn't take it apart to see what makes it tick. I will look into that next time. I did look at the upper part of the compression stack (above the flutter shim) for quite a while to figure things out. That slotted shim that is just above the flutter shim really confounds me. What is the purpose of the slots? I assume it will lower the overall bending force needed to deflect that shim and allow the lower shims to move more. Why not just go with a thinner shim instead of the slots?

I have not measured the front springs, but I agree that they seem pretty light. I did a half-assed attempt to measure the rear spring rate on my press with a bathroom scale and a ruler. I got 165 pounds per inch. I did it twice, so I figure I'm within a few pounds of what it really is. That's fairly stout for a 1500lb vehicle. I'm betting the fronts are in the 100 lb/in range.
*****edit to add*****
I saw an Ebay add that stated the factory springs are progressive. The fronts are 137-225lbs/inch. The rears are 162-300lbs/inch.
******************

For everyone that hasn't seen the inside of these shocks, here is a pic of the top of the shaft. It shows a 3 port orifice that looks to have a shim that totally covers the three ports. I assume that when the top piston travels into the Bottom Out Cup, oil is forced through those ports, past that shim (probably more than one) and travels through the hollow shaft all of the way to below the main piston where there are two ports cut into the shaft.

BottomOutOrifice.JPG
 

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Discussion Starter · #15 ·
Ride Report

Today was test day. I did a decent mix of terrain, from large rocks at 5mph to tight trails and some old mining road that is fairly poor in condition in some spots while being smoothish in others. My speed probably ranged from 5mph to near 60mph. I was so distracted thinking about my shocks that I forgot to bring my video camera, GPS, compass and food. Thank God I already had water in my buggy.

I am happy. The rear shocks are much improved. They are not perfect, nor will one more change make them perfect. I need to mull over what I observed. In fact, I will be riding more before I change anything again. I am inclined to change the BOC setting next to see how that does. Time will tell though. I really ought to put a camera in position to record one of the shocks/wheels to see what is going on.

First Impressions:
  • Ride is more compliant at both high and low vehicle speeds. Though it is not plush by any stretch of the imagination. My back is thanking me. I was literally grinning after driving the 1st 100 yards.
  • I am inclined to say that there is more body roll, but I am not solid on that. It may be my imagination. If there is more, it is not a lot more.
  • Ride is still harsh at full or near full shock travel. I will be looking into modifying the bottom out cup setting per Pound Sand's recommendation. I don't even know if I'll be able to buy what is necessary for this though.
  • Rear wheel hop during hard braking, especially down hill braking, is nearly gone. The rear tires are staying on the ground much better during deceleration. No more clankity clank. Almost.
  • Forward traction is improved under high wheel spin situations in 2WD when the suspension has to work over small to medium rocks/roots etc... Once again, the tires are staying on the ground better.
  • I can feel the rear suspension working. I don't know how else to say it. Before, it just seemed like the shocks weren't soaking up anything. I know that isn't true, but that's the way it felt to me.

Overall I am very pleased with this first attempt. I didn't break anything and the shocks work better. Without question they work better. I am confidant that I will be able to tailor them to my kind of riding. I also feel like I have to say that setting shocks up for different conditions like sand vs woods riding will likely result in very different setups. I doubt that a one size fits all solution will work well for all types of riding.
 
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Discussion Starter · #16 ·
Close up of Shim Stacks and Piston

For those that are interested.

ShimStacksText.jpg

I've also thought about the enlarged piston port question. I've concluded that opening up the ports is one way to soften the suspension by allowing more oil to flow. It would increase the area that the oil has to act upon the bottom shim in the stack. So, for the same psi of oil pressure, the bottom shim would have more force acting on it and move more. Thus allowing more oil flow. In addition to that, it would marginally increase the bending moment on the shim since the outer port edges are further from the center of the shaft. More oil flow. I don't think that I'm in favor of porting the piston though. Seems like a very small change in port sizes could result in very large changes in damping. It may be that someone could make a piston that has the properly sized ports that would work better with the factory shim stacks. I would go larger on the compression ports and smaller on the rebound ports. I am talking very small changes in size though. Probably <0.005" per port at most.

More on the piston itself. I noticed that none of the edges of the ports were chamfered. That alone could make a large change in flow / damping. I also did not check for straightness. I've read that straightness is important. Some tuners mess with that though, sometimes making one or both faces of the piston concave (increasing damping).

If you look at the picture above, you'll see what I labeled the "Rate Plate". From what I've read, that is like a hard stop to flow. It basically limits how far the shim stack can bend no matter how much force is exerted on the piston. Supposedly, a rate plate makes it more difficult to tune the stack. Great. One more thing to ponder.

This subject is vastly complex. I am in awe of those that are good at it.
 
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Great thread! I appreciate your video and detailed posts. I have often thought about tuning on my own shocks too. My interest would be more towards tuning for different surfaces and track configurations I run into racing a variety of Midwest short courses. I have one set of professionally built shocks and springs. The various tracks differ enough that I feel I could benefit from a different second set up. I happen to have a full set of stock shocks on hand, just might have to get into them and see if I can learn something.
 

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Discussion Starter · #18 ·
Great thread! I appreciate your video and detailed posts. I have often thought about tuning on my own shocks too. My interest would be more towards tuning for different surfaces and track configurations I run into racing a variety of Midwest short courses. I have one set of professionally built shocks and springs. The various tracks differ enough that I feel I could benefit from a different second set up. I happen to have a full set of stock shocks on hand, just might have to get into them and see if I can learn something.
I think you are exactly right. I am sure that you could benefit from having two sets of shocks set up differently for different style tracks. Good luck and let me know if I can be of any help when you do it.
 

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Discussion Starter · #20 ·
any update ?

this is pretty cool stuff
I guess one is overdue :)

I decided that they are close enough right not that I am going to run with them the way they are for a while. I have a couple of hundred miles on them and am still fairly happy with the change I've made. I do want a bit less high speed damping. But, I'm going to wait a while and see how it goes.

I do want to deal with the high speed part of the stack or the bottom out cup at some point, but don't know which way to go with that yet. Poundsand makes a good case for modifying the bottom out cup. My problem is that I didn't take that apart the first time. So, I have no idea how the BOC works or what I would need to do to it.

Another thing that I have been thinking about is the rate plate (thick plate on left). It limits total oil flow at high shaft velocity. I don't know how much that comes into play or if that needs to be modified at all. Since I removed one shim, it should be more of a factor and should have increased high speed compression damping to some degree. My first thought is to put a small shim on top of the stack to get the rate plate back at it's original height before I start messing with the BOC.

112840d1554694276-re-valving-rear-shocks-myself-pics-inside-shimstackstext.jpg

For such a simple mechanism, there is a lot going on.
-Any change in the stack affects high, low and med damping. I took out one low speed shim. In theory that also lowered high speed damping to a smaller degree. However, the Rate Plate is now at a smaller distance from the piston, which may have increased high speed damping. Which has more effect? No way to know until I make another change.
 
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