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fox 40 rc2 revalved.

englertracing

you owe me a sandwich
Mar 5, 2012
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La Verne
I'm posting because I have been unable to find any info on 40 modifications.
Id like to share what I have done and hear what others have done.
stock
16.6 x 0.10
14.5 x 0.10
13.5 x 0.10
9.6 x 0.25

mod
16.6 x .10
15.5 x .10
14.5 x .10
13.5 x .10
9.6 x .25

I weigh 170 middle pack expert. blue spring clickers at lsc 11 hsc 10 reb 11 preload just touching spring

I loved my 40 when i bought it. I raved about it I rode them at my spot glendora mountain road. Its really steep few corners with football sized rocks all over the place and a mix of decomposed granite. its pretty high speed fork worked great.

So at my first race at fontana downhill a relatively smooth course with more corners than im use to i noticed my fork were riding mid stroke through all the corners making my bike feel wack and stink bugyy tightened the preload down. still nose down all the turns g outs and whatever the bike road low in the front. tightened the lsc and hsc to 0 still rode low. Photos taken during the race all showed the bike running low in turns.

I was convinced that the bladder had blown. so i took it home and tore it apart (I have done alot of mx forks and shocks, and a few fox shocks for buggies) so i wasn't at all scared of the 40. i had to make some tools for it. the bladder was perfect no air in the damper either. so i thought about changing the valving the mid valve was too small to mess with so i figured id add a face shim to the bv.

I went to a local guy named Dewayne Jones he is an old man who services mx suspension and use to race national pro mx. i told him what i wanted to do he said its the right direction but that i should ditch the hsc adjuster and soley rely on the stack. I did not want to make a change that drastic and loose the adjustability i had.

The shim is an oddball ID so i dug up a 15.5 and i put it to geather with all new parts and bled it very very thouroghly. and reassembeled the fork with new SKF seals which are great!!!

The result. I went from 0lsc 0hsc 100% preload to 11lsc 10hsc preload touching spring

its stiff but plush. it rides up in the stroke it feels awsome i couldn't ask for a better feeling fork.

Thanks Nazi of grammar.

Today, 09:35 AM
 
Last edited:

jonKranked

Detective Dookie
Nov 10, 2005
86,486
25,014
media blackout
stock
16.6 x 0.10
14.5 x 0.10
13.5 x 0.10
9.6 x 0.25

mod
16.6 x .10
15.5 x .10
14.5 x .10
13.5 x .10
9.6 x .25

I weigh 170
middle pack expert.
blue spring
clickers at
lsc 11
hsc 10
reb 11
preload just touching spring

I loved my 40 when i bought it. I raved about it I rode them at my spot glendora mountain road. Its really steep few corners with football sized rocks all over the place and a mix of decomposed granite. its pretty high speed fork worked great.

So at my first race at fontana downhill a relatively smooth course with more corners than im use to i noticed my fork were riding mid stroke through all the corners making my bike feel wack and stink bugyy
tightened the preload down.
still nose down all the turns g outs and whatever the bike road low in the front. tightened the lsc and hsc to 0 still rode low. I was convinced that the bladder had blown.
so i took it home and tore it apart (I have done alot of mx forks and shocks, and a few fox shocks for buggies) so i wasn't at all scared of the 40. i had to make some tools for it.
the bladder was perfect no air in the damper either.
so i thought about changing the valving
the mid valve was too small to mess with so i figured id add a face shim to the bv.

I went to a local guy named Dewayne Jones he is an old man who services mx suspension and use to race national pro mx. i told him what i wanted to do he said its the right direction but that i should ditch the hsc adjuster and soley rely on the stack. I did not want to make a change that drastic and loose the adjustability i had.

The shim is an oddball ID so i dug up a 15.5 and i put it to geather with all new parts and bled it very very thouroghly.
and reassembeled the fork with new SKF seals which are great!!!

The result.
I went from
0lsc
0hsc
100% preload
to
11lsc
10hsc
preload touching spring

its stiff but plush. it rides up in the stroke it feels awsome i couldn't ask for a better feeling fork.
grammar nazi, at your service.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
Do you have the old damper with the adjusters on the bottom?

You're on the right track with your config, personally when I had that damper I doubled up the two compression face shims. Something you might also consider trying is running more on the HS adjuster and less on the LS, I found that offered stronger mid-speed support without the harshness / small bump sacrifice you get with too much LS. The old damper doesn't have a lot of support so even with the slight revalve, I ran (and would run) the HS adjuster fairly close to closed. Also don't ditch the HS adjuster, it really does provide most of the stiffness on the stack.

The new inverted damper is a huge improvement in all directions though, with noticeably more compression range on tap, and a much more reliable bladder system. If you're into this stuff, it could be a good upgrade for you later on.

Another thing is it's worth using the right oils (you may already be, but I'll mention it anyway). The damper uses shock fluid because it has a low volume, the factory spec'd Fox RED is relabeled Silkolene Pro RSF 10wt (47cSt, 300 VI). Personally I'd stick with that oil for the damper, the high VI reduces damping fade with heat. They also have a bushing lube oil (Fox GREEN 10wt) which is used for the lowers and works very well at reducing stiction combined with those SKF seals, worth trying if you aren't already using it.
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,592
1,086
La Verne
Do you have the old damper with the adjusters on the bottom?

You're on the right track with your config, personally when I had that damper I doubled up the two compression face shims. Something you might also consider trying is running more on the HS adjuster and less on the LS, I found that offered stronger mid-speed support without the harshness / small bump sacrifice you get with too much LS. The old damper doesn't have a of support so even with the slight revalve, I ran (and would run) the HS adjuster fairly close to closed. Also don't ditch the HS adjuster, it really does provide most of the stiffness on the stack.

The new inverted damper is a huge improvement in all directions though, with noticeably more compression range on tap, and a much more reliable bladder system. If you're into this stuff, it could be a good upgrade for you later on.

Another thing is it's worth using the right oils (you may already be, but I'll mention it anyway). The damper uses shock fluid because it has a low volume, the factory spec'd Fox RED is relabeled Silkolene Pro RSF 10wt (47cSt, 300 VI). Personally I'd stick with that oil for the damper, the high VI reduces damping fade with heat. They also have a bushing lube oil (Fox GREEN 10wt) which is used for the lowers and works very well at reducing stiction combined with those SKF seals, worth trying if you aren't already using it.
Inverted dampner and factory spec fluid.
Although I was considering using smart performance inc 215 oil like I run in my mx bike. It's around 3x the price of the fox oil. But I wanted to change as few variables as possible so I would know if its the oil or the shims making the difference so for now all factory fill.

Yea Im leaving the hs adjuster in. But dewayne swears it will cause what he calls "cavitation" but by his description sounds more like shim flutter. So he wants me to try a stack with a larger clamp (bigger than 9.6) and no hs adjuster. but it works so.well now that I find myself giggiling every time I ride it.

If anyone else reading has any experience please post. This info is just not out there, or I just can't find it.

Also I must add that the result of going from 0 out on lsc to 11 out did reduce pedaling efficiency. But the feel it gives is awsme.

Also I didn't originally post it but the hsc spring has a 0.090 preload spacer and I actually run around 20 out but with the spacer its equivelent to roughly 10 out +/- a few on everyone elses.
 
Last edited:

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
A few points:

- Having the high speed adjuster further in will not cause cavitation like your friend suggests, in fact if anything it will reduce the possibility of cavitation by increasing pressure in the main [piston's] chamber. Increased pressure in chamber = less chance of excessive pressure drop behind piston = less chance of cavitation.

- I don't think there will be any benefit to using different damping oil as the factory product is very good for the purpose. I wouldn't change it unless you have a specific reason for doing so (I can't think of one), and if you are, I'd make sure the VI (viscosity-index) value for it is equal or better than stock.

- From what you've said and done so far, I think you have a better idea of how to work on a damper than your guru does. You've stuck with the factory oil, made one change at a time, and a fairly subtle one at that. If you are happy then there's no reason to change it.

Finally, I'm not sure what exactly you're looking for / asking here. You've changed your valving, you seem to know what you're doing, and you're happy with it. :thumb:
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,592
1,086
La Verne
A few points:

- Having the high speed adjuster further in will not cause cavitation like your friend suggests, in fact if anything it will reduce the possibility of cavitation by increasing pressure in the main [piston's] chamber. Increased pressure in chamber = less chance of excessive pressure drop behind piston = less chance of cavitation.

- I don't think there will be any benefit to using different damping oil as the factory product is very good for the purpose. I wouldn't change it unless you have a specific reason for doing so (I can't think of one), and if you are, I'd make sure the VI (viscosity-index) value for it is equal or better than stock.

- From what you've said and done so far, I think you have a better idea of how to work on a damper than your guru does. You've stuck with the factory oil, made one change at a time, and a fairly subtle one at that. If you are happy then there's no reason to change it.

Finally, I'm not sure what exactly you're looking for / asking here. You've changed your valving, you seemw to know what you're doing, and you're happy with it. :thumb:
well first off I'm here because after searching around before I ever opened my 40 there were really no threads like this. Nothing... So I put this up so someone unhappy with their 40 could give it a go.

Second I'd like other people to put up their shim stack mods or whatever they have done to a 40 and how it worked.

My lbs is scared of taking stuff apart and If they can't do it surely none of their customers are competent enough to rebuild or modify a 40 lol :)

Spi oil may be the best oil. Everyone on thumped talk loves it http://www.smartperformanceinc.com/215VM2KMMOREINFOQA.htm

I have not tried it in my 40 but I will because I have a bunch.

And the old man... He says cavitation.... Which is pulling gas out of fluid in my book usually happens below the mv in a fork. Stiffer bv decreaces cavitation. But he says cavitation what he's really talking about is flutter or shim bounce he's 60 years old his word for shim bounce and flutter is cavitation. He is saying that the hsc spring causes bounce or flutter. And that I should build a stronger stack and not need the hsc spring. Just like an mx fork.

This is actually cavitation

Dewayne calls flutter, bounce cavitation. which is incorrect. I showed him this video but he still likes likes to use the word incorrectly.

Hmm I must be hard to understand.
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,592
1,086
La Verne
Udi can you post up what you have tried and a description of how it worked?
I just feel like a lot of mtb riders are scared to service their forks.
And the ones who do are scared to change anything.
So hopefully we can help someone wanting to improve their ride for cheap.

For mx bikes thers forums dedicated to fork and shock valving it seems a lot more mxers are working on their own stuff.
I think its funny how squeemish my lbs and their dh expert is (he had his suspension expert tune his clickers for him.... Hahahha)
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
You're on the right track by the sounds of it, however I am inclined to disagree with your friend's recommendations to ditch the HS spring, as this spring is what allows you to have acceptably low levels of HS compression but hold the stack closed long enough to allow an acceptably high level of LS compression, and is also what reduces the effect of the LSC adjuster on HSC. It's there for a good reason.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
Udi can you post up what you have tried and a description of how it worked?
I just feel like a lot of mtb riders are scared to service their forks.
And the ones who do are scared to change anything.
So hopefully we can help someone wanting to improve their ride for cheap.
Plenty of people on here re-valve and tune their own suspension. I think the Fox guide is useful, but in fairness the damper is a little finicky to work on for someone who may not have the experience and tools / clamps required.

Personally I thought the damper had a fairly adequate range of compression in stock guise - perhaps an extra face shim for steeper tracks or heavier riders and it's good to go.

Spi oil may be the best oil. Everyone on thumped talk loves it http://www.smartperformanceinc.com/215VM2KMMOREINFOQA.htm
By all means try it out and let us know your opinion. Sounds a little marketing-heavy to me, one thing in particular that I believe is unprofessional is the choice to not publish actual numbers for oil viscosity and viscosity index. Not giving any indication of viscosity is actually a little ridiculous.

While the viscosity itself doesn't make a HUGE difference in shimmed dampers, the stock Fox oil (47cSt) is relatively thick compared to most suspension fluids. Without an actual cSt value on the oil, you have no idea whether you have gone to a thicker or thinner oil - thus you have no idea whether the changes you feel in the damping are due to viscosity change or the fluid itself. This virtually voids any perceived improvement because you don't know what caused it.

Also keep in mind that a lot of what that article mentions doesn't apply to DH, it talks about the fluid requiring a warm-up period, that's not something you get on a 2-5 minute DH run. It also talks about "irreversible failure" of other fluids in 20 minutes... aside from that probably not being true, there are very few proper DH runs that are 20 minutes long. :)
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
How 215.VM2.K5 works as a “vibration cancellation fluid” (you knew we were coming to this) is that it cancels out the vibrations or frequencies that the suspension system generates when converting big movements into smaller ones. It other words, the 215.VM2.K5 transmits and/or captures the oscillation of a high frequency vibration back into the suspension before it has a chance to reach the bike and rider. This is sort of like placing your hand or finger on a vibrating guitar string – the vibration is stopped and withheld even when the string is struck over and over.

No explanation of how this is achieved or through what principles. To the best of my knowledge, this is not actually possible, and I also believe their explanation of the causes of arm pump is largely incorrect. Coupled with a complete lack of technical data and I'd suggest that it may not do quite what it claims.
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,592
1,086
La Verne
Well I have used the oil and I'm not sure it lives up to his hype but.... It stays clean and it stinks like hell which imo qualiy oils should do.
Steeper stack?
Like u used something larger than a 9.6 clamp?
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
No I said an extra face shim (the 16.6 x 0.10) for steeper *tracks* haha.
Steeper track = more weight on front = need more damping.

I used to have the old damper (non inverted) and ran this:

16.6 x 0.10
16.6 x 0.10
14.5 x 0.10
14.5 x 0.10
13.5 x 0.10
9.6 x 0.25

But that thing struggled compared to the inverted one, I actually ran my inverted one completely stock for a long time and had no issues with it. I think sometimes if they have a little air inside it can reduce compression damping a little, so maybe bleeding yours properly helped it too.

I have one of my inverted carts apart at the moment and I'm probably just going to add one 16.6 x 0.10 on the stock stack and call it a day, just so I don't have to run my HS fully closed (currently am) and to back off the LS adjuster a bit too.
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,592
1,086
La Verne
You're on the right track by the sounds of it, however I am inclined to disagree with your friend's recommendations to ditch the HS spring, as this spring is what allows you to have acceptably low levels of HS compression but hold the stack closed long enough to allow an acceptably high level of LS compression, and is also what reduces the effect of the LSC adjuster on HSC. It's there for a good reason.[/QUOTE

Well I did think it was kind of neat when I opened it up. I wondered why my moto forks don't come this way. I should be able to build a stack that would not need the hsc spring but because of the small diameter of the shims any changes made are relatively large. There's plenty of shocks and forks with no hsc spring. I do see what you are saying though. Maby I can't build a stack with high enough lsc and low enough hsc..... I didn't think about it that way.
I thought about experimenting with different spring rates on the hsc adjuster.
I don't think ill be removing the spring because I'd spend far more time trying to get it to work than riding my favorite trails.

Has anyone tried anything with the mid valve or rebound?
I was reluctant to mess with the mid. Float could be reduced easily tho.

Also I had an idea to make up a few parts on the lathe that would allow the bladder to be pressurized with a few psi which coupd result in better performance if cavitation (public definition not Dewayne Jones definition) is occuring.

It would basically create a chamber for the bladder to be pressurized in I'm just not sure how the bladder sealing system will react to this.
Ktm's wp forks use a bladder and about 15lbs nitrogen pressure this bladder looks more like an old style 40 bladder.

Mxtech suspension sells kits for kyb and showa (honda kawi yamaha Suzuki). To put a bladder instead of a spring 700$
Maby Thats why I think its a cool idea to pressurize the bladder.

I believe the downside of cartridge pressure is higher press on the rod seal means more friction from the rod seal.
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,592
1,086
La Verne
No I said an extra face shim (the 16.6 x 0.10) for steeper *tracks* haha.
Steeper track = more weight on front = need more damping.

I used to have the old damper (non inverted) and ran this:

16.6 x 0.10
16.6 x 0.10
14.5 x 0.10
14.5 x 0.10
13.5 x 0.10
9.6 x 0.25

But that thing struggled compared to the inverted one, I actually ran my inverted one completely stock for a long time and had no issues with it. I think sometimes if they have a little air inside it can reduce compression damping a little, so maybe bleeding yours properly helped it too.

I have one of my inverted carts apart at the moment and I'm probably just going to add one 16.6 x 0.10 on the stock stack and call it a day, just so I don't have to run my HS fully closed (currently am) and to back off the LS adjuster a bit too.
did you add one of the 14.5?
I wanted to try the 16.5, but a 15.5 is the closest I had. I would still like to try and see if I notice a difference.
 

drastic.

Monkey
May 16, 2011
145
0
pleasanton, ca
Subscribed for interest.

Where do you guys pick up shims to play with valving? And is there a site or a quick explanation of what size shims affect what part of the stroke?
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,592
1,086
La Verne
Subscribed for interest.

Where do you guys pick up shims to play with valving? And is there a site or a quick explanation of what size shims affect what part of the stroke?
You can buy individual shims from mx tech but the 7mm I.d. is an odd size they don't carry.
I'm not sure where Udi got his but I taped a 6mm I.d. shim to a piece of wood and used a carbide burr to open it to 7mm.

As far as the shims jobs.
It's about velocity not stroke displacement.
The large shims close to the piston the 16.6 14.6 are low speed like braking, pedaling, berms, g outs
The smallest one furthest from the piston 9.6 is the clamp it affects high speed like rocks, curbs, hard landings

Adding more 16.6 will affect ls and hs. But more on the ls side
Making the 9.6 bigger will stiffen the hs and ls but more the hs.

Making the 14.6 a 15.6 would mostly stiffen the low speed and do almost nothing to the hs.

Google shim restackor
Theres a million Combonations and more than one way to skin a cat.

Thumpertalk suspension forum is a great resource our stacks are simple compared to an mx bike.
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
You can buy individual shims from mx tech but the 7mm I.d. is an odd size they don't carry.
I'm not sure where Udi got his but I taped a 6mm I.d. shim to a piece of wood and used a carbide burr to open it to 7mm.

As far as the shims jobs.
It's about velocity not stroke displacement.
The large shims close to the piston the 16.6 14.6 are low speed like braking, pedaling, berms, g outs
The smallest one furthest from the piston 9.6 is the clamp it affects high speed like rocks, curbs, hard landings

Adding more 16.6 will affect ls and hs. But more on the ls side
Making the 9.6 bigger will stiffen the hs and ls but more the hs.

Making the 14.6 a 15.6 would mostly stiffen the low speed and do almost nothing to the hs.

Google shim restackor
Theres a million Combonations and more than one way to skin a cat.

Thumpertalk suspension forum is a great resource our stacks are simple compared to an mx bike.
Within reason, most adjustments to the shim config of a single-stage stack only make fairly much linear changes in the damping curve, ie comparable effect at both low and high speeds. A (single stage) shim stack is basically a slightly nonlinear spring - changing any part of it within the confines of the original maximum and minimum shim sizes will basically just increase or decrease the overall stiffness for the majority of speeds you'll ever see (unless your valve geometry is really whack or your ports are super close to the damper tube for example). However, shims closer to the sealing shim have a larger overall effect than shims further back (assuming you have a somewhat pyramid shaped stack) simply because they're of larger diameter.