Suspension shims.

[Nathan S]

OK, I understand the basics of altering valving - more/thicker shims means more/stiffer dampening, etc.

My question is about the higher level stuff - if (for example) I wanted to decrease my high-speed dampening without altering the low speed dampening, what should I do with the shims/oil weight to acheive this?

[brent j]

My 2 cents worth.

Keep the same weight of oil, changing this will change everything.

Remove or reduce in size, shims from the top of the stack. Generally the smaller size ones. The larger, lower shims control low speed comp. The upper shims, to a certain degree, limit how much the lower shims open and this gives your high speed.
If you remove shims put in some sort of spacer as changing the overall stack height (making it lower) can increase your high speed by reducing the amount the low speed (lower shims) can open.

What sort of shocks Nathan? I have a set of OHLINS that use tapered plates above the shim stack to limit high speed comp. (I think anyway)

Confused? I am 

Brent

[Nathan S]

Yamaha monoshocks in general, but the immediate project is rebuilding a YZ125E shock for my YZ125D.

[brent j]

Haven't touched one of those yet but my mate wants me to have a play with his spare YZ250D shock. He found his G is so much smoother and now wants the D the same.............................

[Lozza]

Big thing is are you prepared to pull that shock apart 50 times and blow 10 seals in the process.After that you'll be an expert
I think there is a lot in the actual piston design and how it directs oil at the shim stack.Added to this is yesterday's thinking was 20wt oil, small ports and a few shims, now it's 2.5wt oil with huge ports and big shim stacks.I'm a DIY type person but I am quite happy to defer to the experts on suspension.You have seen the difference a well set up shock can make.
 

[Nathan S]

Yes I am willing to pull it apart 50 times if I need to - but if I can get some pointers (thanks Brent, hi Walter) before I start then it might be able to get it down to 20 or 30 times.

[brent j]

Walter, was that a good, bad or indifferent  :-\mmmmh?     

Brent

[eno]

"Because it's in our DNA to DIY" I had an old pair of RedWing shocks that were originally made for something like a CB750. They had heaps of compression & rebound damping, I suspected that they were not responding rapidly enough for MX duty. So I stripped them down, I liked the build on them, rebuildable, big tough rods, steel piston rings.
Anyway I removed a couple of shims, tried them...Hmmm still too slow in damping, particularly the compression, stripped them again & bored out the compression galleries, then the rebound galleries( slightly smaller).
Tried them...Hmmm better, lets see now, I'll drill those suckers out as big as possible, try it out...Uh oh! not enough damping. Re-strip, add more shims again, try it out...Yeah getting there. But still very harsh on the topout, probably had something to do with me cutting the topout springs shorter to gain a little more travel.
So I thinks to my self "you know ya should really buy a set that are professionally sorted", so I did, a set of Falcons.
The Falcons have been good, no temperature build up like the old shocks, nice soft transition at topout, they probably are due for a checkover after a couple of seasons racing. What always amazes me is the amount of fine crud that always gets into both the forks & rear shocks over time.
The experience I gained from the RedWing experiments, made me much more aware of the inner goings on of hydraulic damping & what makes for a good shock.
The next time I go shock shopping I'll definately try a set of YSS as when the marketing for these started I read into the description all the primary things that make for a good shock are there. I will be interested to see how they compare to the Falcons.
I'm kinda with Lozza on this one, leave it to the professionals.

[brent j]

I’ve still got an awful lot to learn Walter



Eno, Being a fellow kiwi I too have the so called kiwi ingenuity or as my dad puts it “the desire to stuff about with something I probably should never have touched in the first place”
I suppose I’m never quite satisfied with how things are. I’m always looking for some kind of improvement. Sort of “if I got it this good perhaps I can get it better” type thing.

I’ll always defer to someone who knows more than me (plenty of them) and learn as much as I can from them. You made progress with your shocks but think how far you could have gone if you kept trying? Mind you time becomes a limitation after a while. I’d guess most of the top people in suspension started out with an old pair of shocks, a hammer, a hacksaw and just kept trying what worked and what didn’t.

I’ll never be an expert but I enjoy learning. Gaining that little bit more knowledge and finding an improvement (hopefully) or even finding out where I went wrong. 
And lets face it, when you ride as slow as I do you need all the help there is!!!!!!!!!!!!!

Like the signature on Walter’s posts says “suspension is fun” and my back really agrees!

Brent

[TonyB]

Mr YSS, my brand new second hand KTM 495 (1983 model) has a WP rear shock. The spring part number ties in with the parts manual for a 495MX, but the rear of the bike seems to be too low, I only measure about 290mm from tire to under guard (claimed travel is 320mm aprox) fully extended. I'm thinking this may be the 420GS shock which looked like it dropped the rear end for enduros. So this got me wondering would you have a replacement shock that acts like a modern shock and that would fit my bike? A very rough measurement eye to eye on shock was about 450mm., not sure of travel though on actual shock.

[TonyB]

Thanks Walter, one other thing (sorry to hijack post) but as a layman would the way the piston works be very different from the old monoshock made in the 80's., say on a yz465 and thje ktm495? I am struggling to understand what changes have been made in modern shocks. Am I wrong in saying that modern shocks use shims as per the older shocks or is there an additional item on the piston to let bulk oil through if it hits a sudden square bump.? I noticed on the fox offroad catologue their coil over shocks use shims on the piston, thats why i thought i would ask the question..

[YSS]

Thats correct , but only one of many changes from the old school.