DIY tuning the Sachs shock

I couldn't find a thread about tuning these shocks, and I think we need one, so here it is.


Here's what I've done recently. On an '11 TE250, I put a 6.0 spring on the back. This got the sag numbers right on, but the rebound damping wasn't right. I don't know if it was right with the old spring or not, I didn't bother checking. Anyway, so the problem was that if I turned the rebound adjuster in far enough to keep the back end from kicking I had no traction on bumps, which made it really hard to climb rocky hills. Turn the adjuster out and I could get traction, but the back end kicked. In between, I got the worst of each: kick and no traction.

So, I pulled the shock apart to revalve it. The plan was to add some shims to the high speed part of the stack, and remove some from the low speed. This has worked for me before on other bikes. When I got the shock open I discovered that there was no crossover shim, which would have made figuring out the high and low speed part easy. Since this was now a bit beyond what I've done before, I bought the Shim Restackor program and plugged in the measurements for the shock and used it to make up a new stack.

The stock rebound stack:


38 0.250
38 0.25
36 0.300
34 0.300
32 0.250
30 0.300
28 0.250
26 0.300
24 0.25
22 0.3
20 0.3
24 clamp

And what I came up with. I had to use the same shims, as I didn't have any 16mm ID shims around. I also changed the fluid from the stock Castrol 5wt to Redline Red, which is apparently about a 6 wt. (but they call it a substitute for 10)


38 0.250
38 0.25
24 0.250
36 0.300
34 0.300
32 0.250
30 0.300
28 0.250
26 0.300
24 clamp

And here's what the Restackor program has to say about them. Stock is on top, modified below. The dotted curve is with the rebound clicker set at 18, the smaller dashed lines are with the adjuster full in or full out.




Anyway, the results were exactly what I'd hoped for. I did some brief testing yesterday evening and while I wasn't able to ride in very different conditions it worked well where I did ride. Now the rear only loses traction with the adjuster all the way in, and it only starts to kick when the adjuster is 18 clicks out. 12 out felt about right. I couldn't tell any difference between a change of less than 6 clicks.

Here's a little video I took of the testing. It's two runs up the same trail, one looking at the front wheel, next at the back wheel. It seems I need to do something about the front now. Maybe some tractor weights on the front fender- or lean forward a bit more.

http://vimeo.com/38698037

Anyway, that's my story so far. Has anyone else done any work on the shock they'd like to share?

Good stuff. I guess you're getting good results with the shim program?

Well, so far it's "good result", Singular. But it probably would have taken 4-6 guesses to get to where the program got me to on the first try. So as far as I'm concerned, it was already worth it. I already have some spreadsheet math that helped me along in the past, but it wasn't nearly as sophisticated as the restackor code.


I had a race yesterday -first race for this bike- and it did very well. I'm pretty slow, but I never felt like the bike was holding me back.

Good deal. Two stagging the stack was a good move, IMO.

I may have to give the program a try. I've tried a couple and felt they were so-so, but they do help you get to the problem faster. Unstanding what the problem is in the first place might be the toughest part. Most guys probable would have been messing with the compression stacks for a long time trying to fix your problem. Good catch.

BTW guys, he just gave you a much better stack for anbody running a 5.8+ spring rate. Maybe even less. ???

Well, it's definitely not an "enter your bike, weight, and terrain; here's your shim stacks" sort of program. Maybe someday that'll exist. Rear rebound is the valving I understand best so it was a case of 'have hammer, find nails'. Are there any guides to setup that you'd recommend? I've found a few online, but they're mostly geared towards MX- I mostly ride woods.

Yeah, even with a decent program it's still not that easy.

As far as setup, I just generally lean things toward the soft side. Soft then actually firming up as you go faster seems to impress most of the guys I do work for. Something you can ride for hours without feeling beat up.

And that's just what I need. This bike already feels pretty good in that regard, and I don't want to give that up.

Poking around online, it looks like the fork rebound has a similar digressive curve that the shock rebound had. The front end was a bit flighty before I put the steering damper on, so I think that'll be my next step.

Yes, I agree. I have the same fork and it's not real bad, but it needs work. I have a damper also, so it's not been on my short list to do anything with the forks, but I need too.

Curious what's your weight geared up?
I went to 6.0 on my 2011 310 and now going to a 6.8 spring (couldn't get the sag numbers right). I weigh 236lb geared up.

About 250. Strange, the 6.0 should be between about right and a little stiff for you. I stand up on the pegs when measuring the race sag. If you sit down that'll put your weight back further and change the numbers.

Hijacking my own thread, now it's about the KYB forks instead of the shock

So I dug into the front rebound today. Getting them apart was a pain in the butt. Strictly speaking, it was making the tool to get them apart that was hard. The actual disassembly is pretty easy once you have the right tool. I measured some things, did a bunch of spreadsheet calcs, re-built the stacks, and put them back together. I had no oil, so I can't test them yet, but I'm pretty hopeful. I basically took the rebound damping curve of the shock that I liked, and scaled it for the forks. I already had some spare shims that fit, and they were necessary.

The stock fork rebound stack: (6mm id)
23 .12 x7
14 .1
22 .12
20 .12
18 .12
16 .12
14 .12
12 .12
9 .2 x2
16 clamp

My first try:
18 .1
23 .12 x3
14 .1
23 .12 x2
22 .12
22 .1
18 .12
16 clamp

The 18 face shim has me a little nervous. I don't think the restackor program is calculating it properly, so I fudged it. The point of the shim is to give a little free bleed without drilling holes in the piston. The shock already had a bleed hole, and from what I could see, the forks didn't have one but need it.

Here's the graph. Stock on the left (yuck), modified on the right (fingers crossed).

Did you set it up that way because the program only allowed for 11 shim stacks?

No, I have the full version which lets you use as many as you want. Messing around with the stacks it just turned out that way. BTW I think the pro version is definitely worth the extra $.

Yes, it's not enough extra cost to not get it.

I've just never looked at dyno graphs of stacks, so it's a whole new demension for me. Just trying to get my head around it.

what weight oil would used in a sachs rear shock?
what pressure nitrogen?

I think I used 5w and about 165 psi?

thanks for that info. don,t supose there is a good video of someone doing the shock service, particularly the bleeding upon filling?.

I didn't see one, but the descriptions that others gave on this site were complete enough for me. It's not much different than any other modern shock, so a video for one of those should be good enough. It was the easiest shock that I've done- but I didn't drain the fluid all the way which saved a lot of effort.



Just as an update, the new fork valving is working fairly well. It's taken away the twitchyness of the front end to some degree. It's not quite the improvement that fixing the rear end was, but it was worth the effort. I was noticing a bit of kicking from the back, so turned its adjuster in to 8 clicks out which seemed to fix it.

Good deal.

Shocks are pretty much shocks when it comes to rebuilding them. An Ohlins would probable be the closest to the Sachs as far as a vid would go.

Do you have a spec for where to set the reservoir piston?