Shock Shim Setup

I'd like to tune out the sharp front rap I get hitting 1" type bumps like from sunken manhole covers and, ideally, washboard. Right now, I've deleted the sway bar which helped quite a bit but it's not quite there. I've done some reading, looked at shim charts, and looked at the Shim Stacker software but, of course, am looking for a simple answer. Has anyone used that software? My concern is gathering all the necessary shock input parameters beyond shims.

Anyway, my understanding is that for high speed movements like I want to soften, I should focus on the smaller discs at the bottom of the compression stack. Small changes can be significant. Any thoughts on whether to swap, for example the one 1.350/0.012 for a 1.350/0.010 OR the 1.1/0.010 and 0.95/0.010 for 0.008 thicknesses?

Or should I look elsewhere in the stack?

Truck is a 96 X-Cab 4X V6 with stock bumper, no winch. Tires are 315 70 16 Es. I've got Fox 2.5 coilovers with 14" 600 lb springs at about 2.5" lift and the following compression shim stack:

Dia/Thickness
1.8/0.008
1.6/0.006
0.8/0.010
1.6/0.008
0.8/0.010
1.6/0.010
1.425/0.010
1.350/0.012
1.1/0.010
0.95/0.010
0.80/0.020

 

You should post this in the long travel thread, you are far more likely to find folks with this level of shock tuning experience in that thread. I believe what you want to soften that high speed compression harshness is a flutter stack that lets the shock quickly absorb those hits.

 

Thanks for chiming in and the suggestion. Certain areas of Tacoma World sure get more traffic than others. If this festers too long, I'll advertise more. I think what I've got is a sort of double flutter stack. Reading that article is what gave me the direction of thinning the smaller discs for softer high speed response. I had thought the idea is that a lot of oil has to move quickly so the whole stack opens up which brings the smaller, inherently stiffer discs into play. But, reading the bit about flutter stack and washboard, maybe that's not it. The upper 1.8/0.008 and 1.6/0.006 discs correspond to the way softer side of Fox's pyramid shim chart and they're backed up the smaller .8 flutter shim so that "should" loosen them further. But, I still get a good whack on my standard test bump - a bridge transition. Actually, all my discs are on the thinner side based on the chart but there are more of them with basically two extra 1.6's. My nitrogen regulator arrived today and lots of shims and a wrench are on the way. On way or another, a shim is getting changed.

So, the question is still out there... which are more the high speed related shims?

 

Never used that software. Done alot of tinkering on shocks myself. Alway could never get rid of that harsh feel from driving those same things you describe. I consider the two to three smallest shims high speed. Also your top two biggest shims are thin so not much to go there. One other thing to look into is the free bleed in the piston, they usually come with one , if needed you can add another. But its funny I always see Foxs too soft they flow so much oil through piston vs anybody else. But most of newer foxs dont and theres different pistons.

 

I was going to say you should try a flutter stack, but it looks like you have one. Beyond that it looks like you have too many shims after that. I'm no pro, but I've valved a few shocks now and I would start there. My truck kinda had a similar set in the rear and was terrible. I added a flutter and took out 1 shim, now I can't even feel a cattle guard when the rear wheels go over it.

 

For reference, I have a 96 Ext cab V6 long travel with bumper and cable winch. When I was using just the coil over I had it valved to #65 comp and #90 rebound, also had only 1 flutter shim (bad idea). It was #45 comp and blowing through the travel when I added winch (even before too).

You are stock bumper and no winch, and shorter arms so less leverage. I think you need to lighten it up a bit.

 

Excellent!! Thank you, Jon! I've got the thinner discs, nitrogen regulator, and shock wrench here. Lacking clean workbench space. I'm going to try modelling a #30 after the flutters which means light discs but with some "extras" to help slow things down. I'm guessing Fox put in that extra flutter for a reason. Then we'll see how that goes. Hopefully will have something to report by next week.

 

The biggest shims are for lower speed or initial impact like pot holes.
The smaller shims are for high speed or full travel for off road hits.
So for the street adjust the big shims.
I'm running all .012s and .015s a #80 with a flutter valve and going to a custom #95 rebound for the dunes so .008 and .010 are on the soft side and could be too soft. Too soft can feel harsh because of not enough damping... My shocks rode like a Cadillac

A #40 compression would be the softest I would run and #50 rebound..
But to reduce harshness back down your pressure from 200 to 170-180 or less, I think 150 is the min, running 200 psi just makes the shock more harsh.
So before you re valve back your pressure down because your stack is soft already......

Also ck your tires, too much tire pressure could be the problem... Those tires are probably too stiff for your truck.

you could try this compression stack for a really soft shock with a #55 rebound.
.006 1.8
.008 1.6
.010 1.425
.010 1.350
.010 1.1
.010 .8

or add a flutter valve to soften small bumps
.008 1.8
.008 1.1 or .8
.008 1.6
.010 1.425
.010 1.350
.010 1.1
.010 .8

These are based on a #40 stack will most likely be too soft for off roading but ok for trails ect.

 

Thanks, Steve. That's a lot of information and a different perspective re the larger shims. I do wonder about having the three 1.6's in there. Not many people seem to run that way and others have suggested there're too many discs in there. Lowering the nitrogen pressure is easy enough to try. I tried "airing down" the stiff E tires to 28 and rode around the neighborhood. It helped a bit and I'm sure going lower would help more. I've liked the Fierce Attitude tires the truck came with. They seem very durable. But, they are worn and I will be getting new ones soon. Maybe a smaller diameter. That would allow me to lower the springs and improve the control arm angle (whole new shim recipe?). Most of my driving is on gravel logging or mining roads so usually no big whoops. OK, more to think about. Now you've got me thinking more toward a more typical pyramid with single flutter. Staying closer to published charts could be an advantage.

 

Yeah I thought that was a type o, all those 1.6 could be why it's stiff. Your stack needs to be progressive.
I would stick to the std charts to start. And work your way up...

 

I would advise against having only the biggest shim and then a small shim (flutter) right off the piston. I would do atleast two shims then a flutter. I tried only one and ended up hole punching the shim into the piston.

 

maybe that only works with the thicker shims??? Nice to know....
Maybe with the thinner shims don't run a flutter valve.
With a .008 or .010 shim it's going to be soft anyway.
I think you only need a flutter valve if you're running a .012 or .015 shim to soften the small bumps...
I run the .012 with the flutter valve and no problems running the dunes....

I would say for OP to get a good base line start with a 55 or 60 compression stack and 65 to 70 rebound stack and see how it rides...
And go from there, if you're in the middle of the chart you should be able to run a std stack...

 

OK, guys, thanks for the help and sorry for not getting back to this sooner. I didn't get any notice you were posting and got busy in the yard. My shim plan is to stick with the original one flutter stack, take out the others, and then go with a standard base stack under that. Anyway, the shock is out of the truck as of today. Spring is off. Now, how to bleed the nitrogen? I was hoping for a Schrader valve type fitting. What I've got instead appears to be an allen screw filled with a hardish plastic plug. What's the next step?

 

Not sure I have remote reservoirs...

 

I found this, don't know if this is what you need.
and another tool...

https://www.kartek.com/parts/fox-pe...gen-in-shocks-that-dont-have-a-reservoir.html

https://www.kartek.com/parts/fox-sh...en-filling-tool-for-18-allen-seal-screws.html

 

You need a needle fill tool. Very common on Icon shocks. They tend to hold a true charge for much longer peroid of time

$18 Motion Pro 08-0075 Nitrogen Needle Kit

https://www.amazon.com/Motion-Pro-08-0075-Nitrogen-Needle/dp/B000GTYOGG

 

Hmmm. I wish it was as simple as a needle valve. I think I'm f'd with the allen plug style. Gotta admit this has become a very frustrating hobby. I'm stubborn, but a $350 specialty tool to fill shocks because the stock shims are wildly inappropriate pisses me off. I mean, I told the vendor what & where I drove. These'll be much better than you had before they said. Well, the ride is so rough you can't even talk on a moderately rough gravel road. The tiniest bump slams the whole truck like it's riding on steel rods. What was Fox thinking???

So, tuning them sounds like fun. Let's gather supplies. Get the nitrogen regulator and no loss valve - for Schrader. Get the spring compressors. Get the special shock wrench. Get the shims and try to figure a stack by trial and error. Pull the shocks and take them apart to then uncover this. When do I cut my losses? This just became not fun anymore.

Thanks for helping, but I'm pretty bummed right now. If I can "safely" bleed the N2 to get at the shims, maybe some local shop can recharge them for me. For those interested in learning from my mistakes, the shocks are Fox 2.5 Factory's on a 96 Tacoma. I don't recommend them unless you want to devote your life to them.

 

You need to pick out the plastic ball and use a nitrogen needle (listed by Anthony - $15) to deflate and re-inflate.

Tuning is very time consuming which is why not a lot of people do it an even fewer master it.

 

Thanks, Ryan! I appreciate your chiming in to help. I'll say it again, you were right about waiting for adjustables and that stock shocks need tuning.

 

OK, progress achieved thanks to help here. The plastic ball is out revealing what looks like a portal for a needle. Needle ordering commencing. I'm feeling much better now. Sorry about the tantrum.