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JeepSpeed, Prerunner and Competition Tech Forum For Discussion of Modications related to Prerunning, JeepSpeed, KOH, Rock Racing, and any other speed based competitions

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  #46  
Old May 10th, 2004, 13:50
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BrettM BrettM is offline
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Re: Pre-runner type suspension stuff

hmmm, maybe i can get one of those ultra stealth cell-phone cameras

I'm leaving MI friday, should be back before tuesday, anytime you want after that, the sooner the better for me of course, except for Thurs the 20th, that's my birthday.
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  #47  
Old May 10th, 2004, 14:00
XJJPR XJJPR is offline
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Re: Pre-runner type suspension stuff

Quote:
Originally Posted by Paul S
I can soak up the worst on road dips around while drinking my double tall non-fat latte.

Paul
CRASHitt,

See everything with Paul has to do with wieght, even his NON_FAT LATTE!



hinkley
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  #48  
Old May 10th, 2004, 14:02
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David Taylor David Taylor is offline
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Re: Pre-runner type suspension stuff

Crash "They'll be no hanging on these arms, or their mounts, everything is above the framerail. I can cover the whole driveline with a flat belly plate"

Works for me.




http://www.ofoto.com/PhotoView.jsp?&...1232488 62103
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  #49  
Old May 10th, 2004, 14:40
Blazair Blazair is offline
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Question Re: Pre-runner type suspension stuff

Quote:
Originally Posted by racerdave
Remember back a few post ago when it was suggested that you change the motor mounts? YOU MUST DO THIS IF YOU ARE GOING TO GO FAST! In one of my Cherokee's we went jumping and we busted the mount out of the block on the passenger side. I eventually fixed it, but this should be your highest priority. Get the good mounts in the motor/trans. And change the bolts in the block to the motor mount to grade 8. You don't want to go to all the trouble of creating a trick rig only to be sidelined with a busted block....learn from our mistakes
"first things first, the rest will come easy"
highmobilityinc.com
Where can I get some of these?
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  #50  
Old May 10th, 2004, 21:16
RobertF RobertF is offline
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Re: Pre-runner type suspension stuff

This is in reference to quality, rebiuldable, revalvable, mono-tube, reservoir shocks.
What makes a gas charged shock extend after compressing it, is the gas pressure working on the cross section of the shock shaft.
The gas is pushing on the divider piston, which is pushing on the oil which is non-compressable, which is pushing on the only thing that can move out of the shock body, the shock shaft, and it's cross section is the area being pushed upon.
The shock piston has some form of bleed that allows the pressure to equalize on both sides, it is not a divider piston.
The bleed in some shocks is a notched valve shim, most a drilled bleed, some a replaceble jet, and some, like the MX-6, an adjustable tapered needle.
This bleed circuit aids in adjusting the low speed damping, when the shock is moved slowly, the oil bypasses the valving through it.
When the shock is moved faster, the bleed reaches its limit of flow and the oil must move through the valving.
The valve stack can be designed to give different low and high speed damping. This is not the speed the vehicle is traveling, but the speed the shock is moving.
Valving can be progressive, digressive, single stage, dual stage (low speed, high speed), and triple stage (low, mid, and high speed). You do not have to limit yourself to the five or so generic stacks Bilstein sells once you understand how to configure them.
Do not judge a shock by what some journalists say after bolting generic valved shocks (some which aren't even valvable) on vehicles that aren't even close to yours.
Some companies will not sell you valving because most people don't know what the hell they are doing.
Beyond valving, you can have bypass circuits with valve stacks controling the bypass.
I do not see why, with proper R&D work a good compromise of rockcrawling and prerunning valving can't be had. (and I don't mean by screwing the knob of a Rancho in and out, don't get me going on those, they don't even have valve stacks)
I gave an example of a large pressure change on a 14mm shock because thats what 5150's and 7100's are.
9100's are 22mm shaft shocks and the pressure is working on a larger area, but still not a huge change.
Most of the perceived stiffness from raising the gas pressure is stiction from the seal (the gas pressure gets behind the seal) grabbing the shaft so hard, the shock resists moving on small bumps, but still will move through the travel the same on a larger one, so no real benefit, just a harsh ride and high seal wear.
Paul S's fading problem with his rockcrawling valved shocks sounds like too low gas pressure allowing them to cavitate and foam up inside when driven hard. I'm sure they wanted to keep seal stiction to a minimum with a low pressure to keep the shocks as supple as possible.
Remember, suspension is a subjective thing, you only know the best you've been in, untill you're in better!
Keep up the R&D work, thats where the advancements will come from!
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  #51  
Old May 10th, 2004, 21:50
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BrettM BrettM is offline
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Re: Pre-runner type suspension stuff

Quote:
Originally Posted by RobertF
Remember, suspension is a subjective thing, you only know the best you've been in, untill you're in better!
ain't that the truth!
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  #52  
Old May 10th, 2004, 21:59
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Re: Pre-runner type suspension stuff

Richard,

Are you thinking of building the Red XJ(with the custom 3link long arms ), MJ, or your main rig? You have some great options there. If your going to be around this coming Sunday I'll stop by and chat, I need to stop by Eric's house as well and ask him some questions on disconnecting my ABS so I can install the Dana 44 in the rear.

Joe
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  #53  
Old May 10th, 2004, 22:27
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Ed A. Stevens Ed A. Stevens is offline
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Re: Pre-runner type suspension stuff

Quote:
Originally Posted by RobertF
This is in reference to quality, rebiuldable, revalvable, mono-tube, reservoir shocks.
What makes a gas charged shock extend after compressing it, is the gas pressure working on the cross section of the shock shaft.
This may help?

Blow up a balloon about half full, and poke your finger into it. The pressure will lightly push out your finger with a resistance force related to the cross section area of the finger. Fully inflate the balloon, and it will push back with more force (as hard as you are willing to press before popping the balloon).

The resistance force you feel expelling your finger is isolated on the cross section area of the penetration (same as the cross section of the piston shaft), it does not force the finger sideways, even as you feel the pressure on the sides of your finger because the force is equalized on all sides of the finger (same as the shock shaft). The side force is equalized, but the extra pressure still restricts the blood flow to your fingertip, the same way the extra pressure adds friction at the shock seals (stiction).

Finding the pressure to achieve a balance between stiction (maximum pressure without excessive seal friction) and cavitation (minimum pressure needed to prevent fade) is trial and error unless you have considerable experience tuning shocks (IMO).


Quote:
Originally Posted by RobertF
The valve stack can be designed to give different low and high speed damping. This is not the speed the vehicle is traveling, but the speed the shock is moving.
Valving can be progressive, digressive, single stage, dual stage (low speed, high speed), and triple stage (low, mid, and high speed). You do not have to limit yourself to the five or so generic stacks Bilstein sells once you understand how to configure them.

I have not rebuild a shock in many years, and never to the detail you describe, but what you describe is much of what we discussed when we were getting our 1600 car race shocks supplied and tuned by Curnutt. The review discussion after each race was focused on how the chassis performed and when it failed to perform, the shock speed when they did not work to an advantage.

The conditions were a challenge to describe and relate to shock speed: rear pogo kicking only in medium speed whoops or front lockup on high speed corregation ripples when easy on the brakes entering a whooped turn, as much as when the problems occured (early after a stop, or long into the lap). The valving changes (and a few spring rate and shock mount changes after monitoring temperatures) after each race debrief provided progressive improvements that resulted in a significant improvement in the ride and the sustained speed we could race without pain and breakage. Curnutt built bypass ports into the shock bodies to progressively alter the position sensitive dampening (long before Lightning Rod external bypass shocks) but the improvement isolated to changing the valve stack, by someone as experienced as Curnutt, was enlightening (to the point that I ignored learning how to improve on what he gave to us before each race).

Have you found a good reference guide on how to tune the valving?

My XJ modifications have been fairly static in the past few years, and a multipurpose crawler that runs well at speed, with more sophisticated shocks, may motivate me into playing with the XJ more (at least until I start building motorized toys for the kids). The direction you guys are taking (to higher speed performance as well as crawling) is where my interests have been for a while (my interests have been isolated with minimal feedback other than reviewing Jeepspeed forums).
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  #54  
Old May 10th, 2004, 23:23
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Goatman Goatman is offline
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Re: Pre-runner type suspension stuff

Quote:
Originally Posted by Joe
Richard,

Are you thinking of building the Red XJ(with the custom 3link long arms ), MJ, or your main rig? You have some great options there. If your going to be around this coming Sunday I'll stop by and chat, I need to stop by Eric's house as well and ask him some questions on disconnecting my ABS so I can install the Dana 44 in the rear.

Joe
I work this Sunday, but you can stop by there and say hi. I'm only working on my yellow XJ. The red one (with the URF prototype long arms) is just a motor donor, and doors and other misc stuff, then it's going to the scrap yard. The MJ is tempting, and it's 2wd, but it's sort of a reserve rig for if I totally destroy the yellow one one day. Old yeller is the baby, and the goal has always been to make it do as many things well as possible, so prerunning is the next step. We like Johnson Valley so much, and it's a great place for running fast as well as the really good rockcrawling trials.......so might as well have a rig that can do well at both.
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Last edited by Goatman; May 10th, 2004 at 23:26.
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  #55  
Old May 11th, 2004, 00:18
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Re: Pre-runner type suspension stuff

I'm not sure if the boss will let me out of the house for the whole day, but I'm working on it. But I'll give you a call once I get to Bakersfield to see where your at. I'll do all the running around first that way you can work. But I'll give you a call.

Joe
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  #56  
Old May 11th, 2004, 02:07
marcusguy marcusguy is offline
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Re: Pre-runner type suspension stuff

Concerning the pressure thing:

The best I can describe the difference between 100psi and 250psi, is that it just feels a little tighter. Someone who only rode with me occasionally wouldn't notice the difference. The difference is about the same as when I first start driving on a cold winter day vs. after prerunning and driving on hot-slightly-faded shocks. Again, my father wouldn't even notice the difference, but I notice that the suspension moves a little less.

I talked with motorsports rep at bilstein when my shocks were making some noise once, and he asked me how much pressure I was running. I told him 100psi (wanted to see how smooth it was) and he said that was the problem. He said that the shocks are designed with a certain pressure in mind and that pressure is needed for the seals to work right and to keep the dividing piston from ramming the end of the shock or resevoir.
Quote:
can tell you that when my non-remote Res. SAW's were valved for desert running I was never able to overheat them, now that they are valved for rocks they fade after about 20-25 minutes of very rough, fast driving.
I'm confused about this because the stiffer your shocks are valved the more heat they will produce and the more they will fade.

I don't know if I have ever 'over heated' my shocks because I've never had any lasting damage. They get very hot (especially at lower pressure) in 2-3 hard prerunning miles, but I've never blown a seal or boiled the oil. I have felt them fade, but only due to the thinner hot oil.

FYI Valvoline's pyroil power steering fluid works well as shock fluid. it's 5w hydraulic fluid and has something in it to keep it from foaming.

Marcus
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  #57  
Old May 11th, 2004, 08:46
Jeff 98XJ WI Jeff 98XJ WI is offline
 
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Re:Crashes new suspension?

So enlighten me as to why many of the new mods and things you west coasters do are "top secret" No pictures allowed? You're not planning to market the custom stuff, so what's wrong with keeping others up to date on progress and the thought process behind your design? Perhaps you just don't want to deal with a million questions? I don't know. I like to see progress on a design and know why someone would do something the way they are. Maybe it's just me? Jeff
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  #58  
Old May 11th, 2004, 08:49
Paul S Paul S is offline
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Re: Pre-runner type suspension stuff

Quote:
Originally Posted by marcusguy

I'm confused about this because the stiffer your shocks are valved the more heat they will produce and the more they will fade.

I don't know if I have ever 'over heated' my shocks because I've never had any lasting damage. They get very hot (especially at lower pressure) in 2-3 hard prerunning miles, but I've never blown a seal or boiled the oil. I have felt them fade, but only due to the thinner hot oil.

FYI Valvoline's pyroil power steering fluid works well as shock fluid. it's 5w hydraulic fluid and has something in it to keep it from foaming.

Marcus
I thought it was do to the fact that at the softer 'crawling' valving they were working much harder at higher speeds than the proper 'high speed' valving did.
I was only running 100psi, so Robert's comment on pressure could play into it too.
Paul
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  #59  
Old May 11th, 2004, 08:57
Paul S Paul S is offline
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Re: Crashes new suspension?

Quote:
Originally Posted by Jeff 98XJ WI
So enlighten me as to why many of the new mods and things you west coasters do are "top secret" No pictures allowed? You're not planning to market the custom stuff, so what's wrong with keeping others up to date on progress and the thought process behind your design? Perhaps you just don't want to deal with a million questions? I don't know. I like to see progress on a design and know why someone would do something the way they are. Maybe it's just me? Jeff
No one wants to be tail gunnner (excluding Mil), so we keep secrets from one another in order to get an edge, j/k. I'll tell you my top secret weapon that doesn't require any pictures, light weight!!!
Paul
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  #60  
Old May 11th, 2004, 09:42
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Re: Crashes new suspension?

Quote:
Originally Posted by Jeff 98XJ WI
So enlighten me as to why many of the new mods and things you west coasters do are "top secret" No pictures allowed? You're not planning to market the custom stuff, so what's wrong with keeping others up to date on progress and the thought process behind your design? Perhaps you just don't want to deal with a million questions? I don't know. I like to see progress on a design and know why someone would do something the way they are. Maybe it's just me? Jeff
It's pretty simple, my camera is unable to download pics at the moment!

CRASH
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