A discussion about shocks

[kmas0n]

I get the general concept of shock valving and that at different velocities, small discs or shims deflect under the pressure of shock oil (hydraulic oil?) being forced through tiny holes in the piston. The greater the pressure (large event) exerted on the discs the more these "shims" will deflect. Other shims behind them help reduce the deflection, so this is called a shim stack.

Does the relative position in the shock body of the piston affect the properties of these shim stacks? Basically, if the piston is fully extended 12" away from completely collapsed, such as an airborne event with a 12" travel shock, Is the first inch of that travel and different than the last inch or anything in between. Or is it totally linear? Does it work differently for a high-end shock with a reservoir? For the sake of clarity let's leave bypass shocks out of this

Do cheaper off the shelf shocks even have shim stacks or something completely different?

 

[toximus]

Does the relative position in the shock body of the piston affect the properties of these shim stacks?

Only on a bypass shock.

 

[Brianj5600]

Reading some on race-dezert a while ago there was talk about softening the damping by lowering the nitrogen pressure as kind of a band-aid for over damped shocks. The suggestion was not to worry about revalving unless you are going to have the shocks off. Revalve at that point and go back to 200 psi. If this is true, which was not disputed, then it seems like dampening would increase as the shock compresses due to increased pressure in the reservoir.

It would be cool to have some sharing of DIYers valving projects. No sharing of shock tuning from venders, only DIY shim stacks and changes in shock performance. I am going to start getting a nitrogen set up/shims and start on getting mine more like I want.

 

[kmas0n]

Reading some on race-dezert a while ago there was talk about softening the damping by lowering the nitrogen pressure as kind of a band-aid for over damped shocks. The suggestion was not to worry about revalving unless you are going to have the shocks off. Revalve at that point and go back to 200 psi. If this is true, which was not disputed, then it seems like dampening would increase as the shock compresses due to increased pressure in the reservoir.

It would be cool to have some sharing of DIYers valving projects. No sharing of shock tuning from venders, only DIY shim stacks and changes in shock performance. I am going to start getting a nitrogen set up/shims and start on getting mine more like I want.

I would like this as well. Recently I purchased all of the equipment needed and I've been playing with the valving a bit. I've gotten it to a place in pretty happy with but Would be cool to hear what others are doing.

 

[pcoplin]

The main piston is only velocity. It doesn't know where it's at in its travel.

That's the purpose of a bypass shock (internal or external), it's positionally sensitive.

 

[Brianj5600]

The main piston is only velocity. It doesn't know where it's at in its travel.

That's the purpose of a bypass shock (internal or external), it's positionally sensitive.

Thanks Paul, does changing nitrogen pressure have an effect on damping?

 

[mrblaine]

Thanks Paul, does changing nitrogen pressure have an effect on damping?

Generally no, in context, very specific context, yes. If a smaller shock is suffering from piston plunge, one method of diagnosing that is to increase the nitrogen pressure to see if it still blows through the valving. That really isn't an effect on damping since it is blowing through the shock's ability to control compression shaft speed, but it can tell you what is going on.

If they are using high nitrogen pressures on a normal straight tube shock with a remote reservoir to "control" damping, they need bigger shocks or slower ground speed, or smaller events, or some combination thereof.

 

[pcoplin]

Like Blaine says, generally no. But I've found in large changes in pressure, yes it does. But my guess is just resisting the IFP movement (shaft compressing the nitrogen). Nothing to do with the valving.

On our race car in the rear we had been tuning it at 275 psi (single shock trailing arm car so high pressure to resist the cavitation). We had ADS do something with them and they only charged them to 150. Not only did we lose a couple inches up air spring, it was mushy as hell. We thought they had messed up the valving, until we checked the pressure. After we drooped out and added the proper pressure, it was back to SMASHING the desert.

 

[Brianj5600]

I would like this as well. Recently I purchased all of the equipment needed and I've been playing with the valving a bit. I've gotten it to a place in pretty happy with but Would be cool to hear what others are doing.

Its a couple of hundred bucks to get started.

To fill the shocks You will need...

Regulator

Hose

access valve

As well as a nitrogen bottle from your local supplier. I spent $130 for a small bottle.

You can get shims from polyperformance. They sell them in stacks labeled #30, #60 #90 etc. There is a chart on their site to convert those numbers to shim thicknesses. It's about $15 a stack. Get the goat built thing that helps you hold the spacers on when installing shocks.

Did you also buy something like this?

https://www.amazon.com/dp/B087Z8BWK9/?tag=wranglerorg-20

 

[mrblaine]

Like Blaine says, generally no. But I've found in large changes in pressure, yes it does. But my guess is just resisting the IFP movement (shaft compressing the nitrogen). Nothing to do with the valving.

On our race car in the rear we had been tuning it at 275 psi (single shock trailing arm car so high pressure to resist the cavitation). We had ADS do something with them and they only charged them to 150. Not only did we lose a couple inches up air spring, it was mushy as hell. We thought they had messed up the valving, until we checked the pressure. After we drooped out and added the proper pressure, it was back to SMASHING the desert.

That's awesome, now you have everyone tuning with pressure.

 

[kmas0n]

Did you also buy something like this?

https://www.amazon.com/dp/B087Z8BWK9/?tag=wranglerorg-20

Yup

 

[pcoplin]

That's awesome, now you have everyone tuning with pressure.

Information doesn't mean recommendation. Anyway, not answering his question would be rude.

 

[Brianj5600]

That's awesome, now you have everyone tuning with pressure.

Don't worry, I am sure I'll try a lot of things that don't work.

 

[pcoplin]

Don't worry, I am sure I'll try a lot of things that don't work.

Are they Foxes? Just keep it at 200 and do all of your valving changes around that. If you get to the point of excessive valving, you have to jack the pressure up. But that's a bandaid for too small of piston.

 

[Brianj5600]

They are 980-02-039 and 980-02-034. I don't plan on any high speed stuff.

 

[Brianj5600]

This is a weird way to set pressures. Set the pressure way over target, release pressure in long hose then check the pressure while allow re-pressuring. the hose. YouTube can be great, but can also be this.

 

[kmas0n]

I've had pretty good luck over pressurizing by about 10 psi. Even my loss-less chuck seems to let about 10 psi escape. But I also don't sweat it being 10psi off

 

[kmas0n]

@pcoplin
What's the difference in a piston for a fox 2.0 smoothie with remove reservoir vs. the piston for 2.0 performance series with the ifp? Larger holes? They both use the same shims correct?

 

[pcoplin]

@pcoplin
What's the difference in a piston for a fox 2.0 smoothie with remove reservoir vs. the piston for 2.0 performance series with the ifp? Larger holes? They both use the same shims correct?

The Performance piston is thinner, lower flow, and not designed for bleed holes. The Performance series uses a serrated bleed shim. But they take the same 1/2 inch post shims. Some have an additional 1.25 size diameter shim in them, but I'm finding that size in the OEM-valved Factory shocks too.


You can get the Factory piston without bleed holes opened, but the four partially drilled holes are there.

For some reason the Factory 2.0 piston is now coming with the preload oring, which in the past has been mated with the PTFE bronze wear band, not the standard turcite one. It seems to have increased the friction in the shock, been meaning to call Fox and see why the change.

 

[Brianj5600]

I've had pretty good luck over pressurizing by about 10 psi. Even my loss-less chuck seems to let about 10 psi escape. But I also don't sweat it being 10psi off

How do you know you lose 10 psi? I found checking the pressure loses pressure. It has been over 20 years since I have charged a shock and don't remember exact loss in the checking process, but I was losing pressure every time I checked it. The guy in the video had about a 7' of hose to pressurize .

What size Nitrogen cylinder should I buy?