DIY tuning the Sachs shock

Hey guys, just wanted to check in and make sure I am going about this right before I screw something up...

I am trying to unscrew the top of the cartridge in my WR's KYB OC forks, so I can get to the midvalve. See picture below:



Since KYB put the bottom-out dealie (left side) on with a crimp, there's no getting that off (thanks, KYB!). Am I correct in stating that the "cap" (the shiny billet machined part on the top/left of the cartridge tube) will unscrew from the rest of the tube?

If so, I am going to make a clamp to hold the tube, and another special tool to engage with the four "slots" on the spring seat with a hex or some wrench flats on it.

I made a quick attempt at it in the garage by just sticking a 1/4 inch rod through the holes at the bottom of the cartridge, and grabbing the "cap" with pliers; apparently that thing is on there TIGHT, I bent the rod and nothing moved on the cap.

No evidence of peening on these parts, so that's good. I suspect there is loctite? I applied a little bit of heat but I don't want to damage anything in the tube...

You have it right. Make a good clamp like race tech sells. Heat the top of the cartridge to about 300F. It is tight.

I know this is old, but I thought it was interesting so I wanted to dig it up and try to get some commentary.

When you say "damping factor" are you talking about the coefficient (force per velocity) or the ratio (relative to critical damping)? Based on your comments about using SMD calcs and the spring rate and mass, I suspect it is the latter?

I'd be curious to see your math behind this. All my previous experience is with racing car suspension (pavement and offroad), and there the damping ratio is often on the order of 0.5 to 0.75. 1.0 seems high to me, but it may not be.

I was finally able to get into the midvalve today, and I found some interesting things. First, I had to make a tool to unscrew the cartridge cap:



After I got that apart, I was able to disassemble both shim stacks. On the rebound side (6mm ID) I had this:

23 0.11 (7X)
14 0.11
22 0.11
20 0.11
18 0.11
16 0.11
14 0.11
12 0.11
9 0.2
9 0.2
16 1.5

I didn't have the balls to try a bleed shim like Sparked, I just moved the crossover up to behind the 3rd 23x0.11 and left it that way. I may go back in and mess around with a bleed or something later.

On the compression side of the midvalve (8mm ID), I had this:
24 0.11
24 0.11
24 0.11
20 0.11
18 0.11
16 0.11
14 0.11
12 0.11
10 0.3
10 0.3
22 0.4
17 2

Interestingly enough, the float measured quite a bit less on my bike than some of you guys have reported. Using feeler gauges between the backer shim and the cup, I measured about 0.7mm of float. Using the "subtraction method" I came up with about 0.9mm (depending on the actual thickness of the shims, not sure if it's 0.11 or 0.12 or something else). I got this number as follows:

Sleeve length: 5.80mm
(minus)
Piston Recess: 0.90mm
Cup Recess: 2.00mm
Shim Stack: 1.99mm
Float = 0.9 mm (ish).

Obviously I'm wrong with one (or both) of these numbers, I just split the difference and called the float "0.8 mm." Any thoughts on how yours differ, guys? I think we have the same shim stack but that's only from memory...

Even though I had less float than expected, I still wanted to try to tighten it up, given the symptoms the bike has. So, I added a 10 x 0.20 shim to the midvalve stack, which should bring the float down to around 0.6mm. This may prove to be too little, bit it's worth trying I think. From my reading around, 0.6mm seems to be fairly common on enduro/offroad bikes anyway.

I filled everything back up with oil (stock oil level was 120mm, I'm at about 110mm right now) and buttoned the bike back up, but I won't have a change to ride it for a couple weeks (out riding in CO starting on Wednesday!). Should be interesting to see how it works. I have the ideal test coming up, there is a rocky enduro in 2 weeks and I'll probably take it to the MX track right around the same time.

Yes, I am talking about the damping ratio. On this page, SMD is used as an example, I'm referring to Lambda. https://en.wikipedia.org/wiki/Damping

So 1 is critically damped, 0 is completely undamped, etc. I should have mentioned that I was referring only to rebound. For compression damping I end up with much less, a bit less than 0.5

The other big thing is that I'm not including my weight in that calculation. If I did the damping ratio for rebound would be more like 0.7 rather than 1.0. And that seems to make sense given that my suspension feels pretty bouncy when I sit down but about right when I stand up.

My math is using the equations from the wiki page, they're on my other computer but I'll post an example in a bit. It would be great if you could check that I'm doing this right.

I'm right there with you. I've got a RaceTech 6.4 on my 2012 TE310 and it seems to be just right. I've got 0.48's in the front.

Very interesting. I'd love it if you would share the calcs. I would have "expected" 1 to be too high (in that you slow wheel return), but again, all my experience is 4-wheeled race vehicles, so they have a different dynamic than a bike with a standing rider. Seems like it's working for you...

I'd love to, I'd like to see what mine calcs out to be too. I assume you are just using c/2 sqrt KM ? The biggest thing is making sure you get the K factor right (you can't just use spring rate, due to the motion ratio of the linkage; you probably know this, though).

Ok, So here's an example for the shock:

Column: Description: ............ Units: . Formula: ......... Value:
B ..... Linkage ratio ........... .........Entered .......... 3
C ..... Weight .................. lbs .... Entered .......... 120
D ..... Mass .................... kg ..... C/2.2 ............ 54.54
E ..... Spring Rate ............. kg/mm .. Entered .......... 6
F ..... Effective Spring Rate ... N/M .... E*9.8*1000/(B^2) . 6533.3
G ..... Damping Coeff ........... N s/cm . Entered .......... 110
H ..... Effective Damping Coeff . N s/m .. G*100/B^2 ........ 1222.2
I ..... Damping ratio ........... ........ H/2/sqrt(D*F) .... 1.024



Offhand, I'd guess that getting a better estimate for the linkage ratio and the weight would be important if the numbers are to mean anything.

You've got the motion ratio (linkage ratio) squared, so that's good; a lot of times that gets missed. The issue here is that, obviously, it's sensitive to the exact ratio due to the square factor. You ought to be able to get a good feel for the approximate average ratio by just measuring the distance to the bump stop when your rear suspension is topped out, and dividing by wheel travel spec. Looks like your numbers should be right, although I didn't check the math. When I get a moment, I will run the numbers for my bike...

Unrelated question, back on the topic of forks and float: do either of you guys have measurements for the sleeve, cup washer, piston recess, and total shim stack height for your bikes? I'm curious why I had less float in stock form... My (stock) shim stack looks to be the same as yours, so I wonder if they changed the sleeve, or something else?

Changing gears a little bit here, I did some work on the Marzocchi 45 shivers on my TE610 today. These forks are a little bit goofy, so I thought people might be interested in what I found, even though I haven't been able to thoroughly test them yet.

Stock BV:
23x0.15
23x0.15
23x0.15
14x0.1
23x0.15
21x0.15
20x0.15
19x0.15
17x0.2
15x0.2
13x0.2
17x2 (base valve body)

Stock MV compression:
22x0.3 check plate (approx. 1.4mm float)

Stock MV rebound:
23x0.1
23x0.1
23x0.1
23x0.1
23x0.1
23x0.1

The bike is honestly not that bad, but maybe a bit harsh on really rocky stuff, and maybe not quite enough bottoming resistance. With the way I use it (fast trail riding, dual sporting), it works pretty well. Still, I like to tinker, and I wanted to try a real midvalve on it, so here we go.

The midvalve tap is 8mm ID, so you can put shims right on it. The only problem is that the exposed "sleeve" length is only about 1.6mm, so that's all the space you have for the shim stack and the float. To start, I tried:

22x0.1
22x0.1
22x0.1
20x0.1
18x0.1
16x0.1
14x0.1
12x0.1
10x0.15
18x0.25

This ends up with about 0.6-0.7mm float.

I don't "love" this stack because I'm not sure there's enough taper/space in the stack before the backer, so the face shims can't really deflect back very far, so it's sort of progressive. But, given the MV setup, without adding some shims to space the piston out (which I didn't have handy), there's not much I can do.

For the BV, I ended up with this:

23x0.15
14x0.1
23x0.15
21x0.15
20x0.15
19x0.15
17x0.2
15x0.2
12x0.1
17x2 (base valve body)
(Just removed 2 face shims and changed the pivot from a 13 to a 12mm to soften up a bit).

The other thing I did was drill the base valve piston. The stock ports were pretty small (3mm dia), and there was room to go up to 4mm. Restackor predicted a flow restriction with the softer stack at higher speeds, which may or may not be a problem, but I wanted to make sure it wasn't. Here's a photo of the valve, with 1 of the 4 drilled (I did drill all 4, this is for illustration only):



On the rebound, I didn't really have a good sense for what was good or bad about how the forks felt, but a straight stack just didn't feel right to me. I didn't want to get too crazy and build something terrible, due to my limited experience, but I did add a crossover to try to speed up the low speed a little bit:

Rebound:
23x0.1
23x0.1
16x0.1
23x0.1
23x0.1
23x0.1
23x0.1

I'd like to use a smaller crossover, but 16 is what I had so I stuck it in there. I need to go back and see what Sparked used in his forks on rebound and try some more changes on mine.

For the Restackor junkies out there, here is the stock TE610 at 15 clicks out (out of about 25) compared to the revalve at the same setting:



I was all set to ride this today, but my peg bracket bolts broke very early into the ride, so I didn't really get to try it out. Oh well! I will update soon enough!

UPDATE: I ended up putting 2x 6x8x0.2 shims under the mid valve piston, which gave me room to add 2x 8x10x2 shims to the base of the stack. Not sure if this is necessary or not, but I feel much better about the stack like this.

Rode the bike very quickly yesterday, and it feels PLUSH. Time will tell if it's too soft or not, but I think this is a good starting point!

Ok guys, looking for a little bit of advice here.

2012 WR 300, 170 pound C rider.

Current stacks:
MV (0.6mm float):
24 0.11
24 0.11
24 0.11
20 0.11
18 0.11
16 0.11
14 0.11
12 0.11
10 0.3
10 0.3
10 0.15 (I added this to reduce float)
22 0.4
17 2

BV:
24 0.11
24 0.11
24 0.11
24 0.11
12 0.11
22 0.15
20 0.15
18 0.15
16 0.15
13 0.15
11 0.25
18 0.5
18 1

I raced a hare scramble on this today, and I wasn't completely satisfied with it.

In fast stuff (grass track, dual track), it feels fine, although on fast chop it's a bit harsh. There were a few sections on the course with embedded rocks, about 6-8 inches in size, all sharps edges pointing in random directions. If I could stand up and blast through the section in 2nd gear, the bike skipped right over and felt great. However, some of the section were slick, off-camber, or in corners (and I'm slow), so I had to go through them in 1st gear, much slower. At that speed, there is a LOT of feedback into the bars, and it really wore me out.

Based on the mud on my forks, I had about 3 inches of travel left today. There were zero jumps, just rocks and log crossings and mud holes, so I don't know if that is acceptable or not.

So, what do you guys think? Should I mess with the base valve or the mid? I could open the float back up, or I could soften the base stack up some more... Thoughts? Recommendations?

Wanted to dig this one back up and post some info.

On my WR300, I have made some changes. I am now running 0.44 fork springs (I weigh about 170-175 w/o gear) and oil around 110mm. I've gone back to stock on the midvalve. I have some conflicting measurements, but I think the float is around 0.6-0.7mm with the stock stack:

24 0.11 (3X)
20 0.11
18 0.11
16 0.11
14 0.11
12 0.11
10 0.3
10 0.3
22 0.4
17 2

On the base valve, I have gone even softer:
24 0.11
24 0.11
24 0.11
12 0.11
22 0.10
20 0.10
18 0.15
16 0.15
13 0.15
10 0.10
11 0.25
18 0.5
18 1

(Similar to stock, with 3 face shims removed, first two shims in HSS switched from 0.15 to 0.10, 10mm clamp)

I have a trail ride and a 2-hour hare scramble on this setup. Bottoming resistance is pretty good, the race had a mini-moto section with some 3-5 foot jumps, some g-outs, and a ton of whoops, and I never bottomed. I think it might have a bit too much bottoming resistance, honestly, so I may go a bit softer on the HSC on the BV. It's obviously softer/plusher than stock.

Looking for some help:

Has anyone ever replaced the seal on the OD of the nitrogen piston in a Sachs shock? If so, where did you get it? Is it just a regular o-ring? What material?

I'm not worried about the seal in my WR's shock (it's only 1 year old), but my brother has a 10 year old TE410 that I am going to be servicing the shock on, and I think it would be sensible to replace the seal on the nitrogen piston while I am in there.

Also:

Does anyone have a 28 OD x 0.20 or 0.25mm thick shim for Sachs rebound (16mm ID)? A 30x0.20 or 30x0.25 would work also!

I need one to revalve my rear rebound, and I'd rather not pay the $15 shipping for one shim.

Opened up my WR's rear shock today. Stock stacks (all shims 12mm ID)

Rebound:
38.25
38.25
38.25 ring shim (34.20 center)
38.30
36.30
34.30
32.30
30.25
26.25
22.25
18.30
17.9 x 2.0 washer

Compression:
44.20 (5X)
32.15
42.20 (2X)
40.20
38.20
36.2
34.2
30.25
28.25
24.25
22.3
33.5x2.50 washer

My main intent was to make some changes to the rebound, but I also tweaked the compression while I was in there. For rebound, I ride/race a lot in an area with lots of small, steep sand whoops in singletrack, and the bike was kicking, even with the comp dialed most of the way in. On the compression side, the bike feels decent, but I think it's stiffer than it needs to be, given that I rarely ride on the track.

I had a limited selection of shims, so this is what I ended up with for rebound:

38.25 (2X)
38.3
30.2
36.3
34.3
34.2
34.2
32.3
32.2
30.25
28.2
26.25
26.2
24.2
22.25
22.2
20.2
20.3
18.3

So, I dropped the ring shim (I don't think I want a preloaded stack), added a crossover, and then added some stiffness to the high speed stack. My original plan was to go to a larger clamp shim, but the nut and the washer are only 18mm so you're sort of stuck with that unless you buy/make a different washer.

For compression, I just lightened it up a bit. I removed one face shim and one of the 42.2 high speed shims. In hindsight I think I should have gone to 20 or 21mm for the clamp, but oh well. I'll get some rides on it, see how it feels, and go from there.

EDIT: REVISED STACKS

I am going to pull my shock back out and put in the following revised stacks. On the rebound side, the performance is the same as the stack above, it's just a lot cleaner. I also moved the crossover up above the 38.3 to soften up the small stuff (or try to). On compression, I'm just going a bit softer (smaller clamp) and more linear (2nd early crossover) than the stack above.

Compression:

44.20
28.10
44.20 (3X)
32.15
42.20
40.20
38.20
36.2
34.2
30.25
28.25
24.25
22.25
20.25
33.5x2.50 washer

Rebound:

38.25 (2X)
38.3
28.15
36.3
34.3
32.3
30.25
28.3
26.3
24.3
22.3
20.3
18.3

I did ride the bike on Sunday with the rev1 stacks. It felt pretty good. At 15 clicks out on rebound it was still a little too "bouncy", although the kick off whoops was a bit better. I am going to try 10 clicks out, I think it will be close. The comp was a bit more plush but not soft enough.

Kyle,
I've been working on a friend's 07 WR 250, both 45mm zoke forks and sachs shock. Still fiddling with the fork, with some custom base valve pistons I had turned on a lathe with larger holes. Not ready to recommend any stacks yet, though. That is still a work in progress.

On those earlier Sachs (without the check ball and spring), the rebound adjuster is a pretty large bleed, and it flows in both directions. Consequently, it's more of an overall softer/firmer adjustment for both circuits. Undesirable, but it is what it is! The compression adjuster is more normal, affecting mostly compression. We've found the stock rebound too light, needing to run the rebound clicker IN to the point where it starts to make the compression harsh (seems to get really harsh with rebound around 10-12 clicks out), forcing us to run compression all the way out as a compensatory move. So we made the rebound firmer and firmer in a few trials, and compression softer. Ultimately, we took the rebound crossover completely out, and got rid of the 18 clamp. Here's what we have on our latest try:
Nov. 2013
Reb 3
38.2
38.25
38.25
38.3
36.3
34.3
32.3
30.3
28.25 (these could be changed to .3,
26.25 but we didn't have them)
23.3
24 washer
nut

Comp
44.2
44.2
44.2
32.15
44.2
42.2
40.2
38.2
36.2
34.2
32.2
30.2
28.2
26.2
23.15
20.15
18.3
34 x 2.5 washer
32.2 (merely a wear plate - not involved in valving)

Piston at 90mm
nitrogen at 150psi
Maxima Light Shock Oil

We had a pretty intense tuning day just last week, and three riders, 170, 220, and 240 before gear, really liked the shock with rebound at 15 clicks out (before was 10). It was the first time we could keep the rebound clicker out far enough to NOT make the compression harsh. At 15 out the low speed rebound was fast enough for good traction on hills and bumpy acceleration, and we were getting very controlled return after jumps and G-outs. We did vary a bit on what we like for compression, but were around 2-2.5 turns out on both LSC and HSC.

That's awesome man! Really good and interesting data. Your overall ideas exactly match mine, I completely agree about the reb. adjuster too.

That rebound stack you are running is WAY stiffer than even my modified stack; 23m clamp, WOW! I am not going to go that big, but maybe I will try a 20mm clamp instead of the 18 I have in there now, try to dial the adjuster out some more (currently at 10 clicks).

I've done a couple of the Marz 45s, and I really like the way they turned out on my 610. If you want to bounce some ideas around, I'd be glad to. One thing I have done is convert the stock checked mid to a regular active mid with about 0.7mm of float. The bike is amazing, it eats rocks and yet I can pound sand whoops all day and never bottom. I just made a slight change to mine to firm up the base a little bit because I was running the comp adjuster pretty far in, but I think (hope) it will still work really well. On some level, I wish I could get the KYBs on my WR to feel that good...

Do you know what that "wear plate" shim on the compression stack is for? I couldn't figure out what that thing was doing.

Yes, very cool that we're on the same page. Our rebound stack looks stiff, but it sure doesn't feel that way in use. First several trials we kept having to go back to 10 clicks out to get control, so we kept running into that compression harshness. It took 'this much' rebound shimming to get us to 15 out. I was hoping to be closer to 20 out so the clicks would be in little smaller increments, but it's pretty good where it is. I'm now thinking that the rebound adjuster circuit is SO large above 15 clicks that we're not gonna be able to run any farther out with ANY kind of stack. Keeping the goal in mind, we just need to be far enough out that we're not affecting compression, so we can leave that to the shim stack and adjuster. Hey - if you feel like throwing that rebound stack into your Restacker let me know what the graph looks like. It's gonna look very firm at low speed, unless there's a way to add the bleed in!

I don't really know about that wear plate, but I just left it in there. Many shocks don't have such a plate between similar surfaces. But hey, it's a replaceable surface, not a bad idea.

These 45 zokes are a very nice fork in terms of their build quality. But those stock stacks... WOW! They must have been Friday stacks!

Here's the output from ReStackor:



Paint munched the quality up pretty bad but you can still read it.

The green line was my first revalve, basically I was trying to get it to feel like the stock stack did at 5 clicks out, except at 15 clicks out. I got some good ride time on that stack and the rear felt "busy." It didn't kick horribly, but it didn't keep it quite as controlled as I wanted. The blue line is what I am going to try next. The green line is what you're running.

What was the stock shim stack in the Shivers on that WR250? Checkplate mid, I assume? I've opened up several sets of those, and I swear every one is different. My TE had 3X 23.15 face shims, some 0.2 thick stuff in the HSS, and a 13mm clamp (so pretty stiff overall). My brother's 410 had a comically light stack; 2 23.1 face shims, a very short taper (all 0.1s), and an 11 clamp. I've also done a couple from 125s, and have seen some fairly light single-stage stacks in the mix. There are also several different piston designs; all can be drilled out, but the limit varies. I took my 610 all the way to 4mm, some of the other pistons you can't go much beyond 3.3-3.5.

Very interesting. Your blue stack looks very good! Heck even my dark green stack looks good, just firmer. Coefficient in the 60-70 range isn't bad!

Same here on the forks, every fork has something different. And some have a little side bleed hole on the MV piston, and some have none! That's gonna change setup considerably. We first drilled the holes as large as we could, then I had the custom pistons made. Here's what we found in the 07 but no way of knowing if it's been altered:

Comp
23.1
23.1
23.1
23.1
14.1
22.1
20.1
19.1
17.1
15.1
14.1
12.1

Reb
22.1
22.1
22.1
22.1
22.1

Float
1.4mm / .055”

MV
23.2
21.3
20.3
19.3

Do you think a midvalve that stiff is really just a check plate?