Front End Success ... sorta, need stabilizer advice

[WanderingBob]

Originally Posted by boywonder

Wanderingbob: Here is a pic of the through-shaft fox damper....it doesn't have any gas charge, and therefore doesn't bias the steering to one side.








Not sure that has anything to do with your issue, but I wanted to ask so others here have more info.


The one you have is essentially a shock, and if you compress the shaft it will extend back on it's own due to nitrogen pressure in the shock body. The through shaft design elminates the need for a gas charged body....and the shaft stays wherever you put it; it's not biased to full extended position.

I will ask about that when I hear back from Agile. Makes sense to me.

Bob

[renegadeoverland]

Question for the group .... if the gas-strut style stabilizer is less than ideal, at least without two to create a neutral zone, why is it so commonly used? My van that was converted to 4x4 by agile has just a single fox gas strut stabilizer. Everything feels fine and I dont feel like the stabilizer is creating a bias so I am curious about the "mechanics of it" type thing.....

[WanderingBob]

[QUOTE=E350;254122]

E350

<<"Bump Steer" is merely "baby death wobble" i.e., a death wobble that does not propagate.>>

Then I do not know what Bump Steer is! When driving back from MT to AK, when I hit a bump the front end would jog over to the side. Going down a steep grade and going around a right turn, I hit a bump and was forced nearly into oncoming traffic.

I have read that the geometry was WAY off on the Salem Kroger front ends. Adding a high knuckle and replacing shocks eliminated what I thought was called "bump Steer". Regardless of what it's called the van is so much safer and more comfortable to drive! Yay!

<<So you already dealt with what carringb describes in post # 8 here?

http://www.sportsmobileforum.com/for...le-3996-3.html>>

I don't see the post you are referring to. I looked at #8 and #28 which is on that page.

Thanks so much

[TomsBeast]

'Nitrogen filled' is just a method by which air bubbles are kept out of the oil, for a better damper. The pressure is so low, it doesn't effect steering centering, that gas pressure wont cause a 'too stiff' feeling, it's damper valving that will make a damper too stiff. I would imagine a steering damper would come with a pretty standard valving and oil weight, for a full size truck or van.



Most high-end damper like Fox 2.0, HAL, Strange, Koni, have a threaded bulkhead that comes apart with a special spanner, for 're-valving'.



Off-road vendors will often work with a shock manufacturer or distributor and develop their own proprietary valving for a say a generic Fox 2.0, but custom valved for say, an e-series van with camper interior. You pay a premium for the damper, compared tot he generic Fox 2.0 because it comes with proprietary valving (Which is fair, since the shop who worked with the manufacturer spent time and money doing the R&D trial an error on their own dime). Again, I wouldn't imagine anything too far 'off the reservation' was used for a steering damper, unless your damper got mixed up with a stiff set of shocks, some parts guy grabbed the wrong one, Fox used shock valving instead of steering damper valving on the one you wound up with?



A little off topic: I've purchased several sets of race shocks that were re-valved for my specific needs, there's a huge difference. I've also sent in shocks to have them re-valved, and I'll say it's pretty 'hit-or-miss' depending on who you are working with, how well you can communicate what attribute you want more, or less of. Believe it or not, 'shock consulting' is a thing, where an expert will spend a day at the track or offroad testing grounds, working with teams to get into the 'Goldie Locks zone' of suspension tuning. My only experience with shock tuning and selection has been with drag race cars, there's a lot to know, and I've only scratched the surface.

[boywonder]

Originally Posted by TomsBeast

'Nitrogen filled' is just a method by which air bubbles are kept out of the oil, for a better damper.

If the damper is not a thru-shaft, it has to have gas in the body. Gas is required since oil is a incompressible fluid; if the body is completely filled with oil there is nothing to compress to allow the volume of the shock shaft to enter the shock body.


With a thru shaft damper the shaft volume exits one end as the same volume enters the opposite end..no need for gas since the shaft volume inside the body is always the same.


If a shock did not have a gas inside the shaft wouldn't move at all..since liquids are incompressible.


In modern shocks....the gas (nitrogen or air) is kept out of the oil either by a piston (disc with an o-ring around it) or a rubber bladder (think really thick walled condom).


Some dampers (thinking old dirt bike Bilsteins here) are designed to have the gas mixed with the oil (emulsion) for proper damping. The valving would be tuned for this emulsion. The problem with these is that they need to be stroked a number of times to get the emulsion going...not sure this tech is used anymore.

[E350]

Good catch WanderingBob! Thank you.

See carringb's post # 8 here:

"OEM linkage is designed for IFS, where the drag link mounting point roughly corresponds with the pivots for each I-beam. That setup doesn't work well for a solid axle. Crossover steering re-establishes your steering linkages with the suspension pivots (which is actually just your tire contact patch and the frame end of your track-bar.

It can induce some bump steer if the drag-link is no parallel to the track-bar. Track bars can induce some lateral motion on the axle (which can feel like bump steer but really is just the body moving relative to the axle) which is why both should be about parallel with the ground."

From this really good thread:

http://www.sportsmobileforum.com/for...ley-16046.html

IMHO, you described "bump steer" perfectly.

Now, if in return for being pushed sideways, the rubber sidewall of that air-filled rubber basketball which we call a "tire" bounced laterally back (for every action there is an equal and opposite reaction) punching back through the tie rod to the opposite tire, and add to that the fact that every punch of the tie rod is steering the rotating tires such that the tires become like a spinning (horizontal) top causing instability (i.e., "wobble") and "Death Wobble" can "propagate" (i.e., increase in amplitude until the vehicle nearly stops rolling).

I think of a top spinning on its axis. I think of a tire spinning on its axle. I think of the tie rod as an off-axis push on the tire, since the tie rod is off-center from the wheel's axle. When you push the top off its axis, the top immediately wants to return to spinning on its axis. In my opinion, that is a reaction to the action of bump steer, which is reproduced in death wobble.

So, yes IMHO "bump steer" is the initiating force of death wobble so I referred to it coyly as "baby death wobble."

I also think boywonder's post #15 above is spot on.
As usual.

And these are just my thoughts based on my experience. Others may have more knowledge and different experience. I respect that.

[TomsBeast]

Originally Posted by boywonder

If the damper is not a thru-shaft, it has to have gas in the body. Gas is required since oil is a incompressible fluid; if the body is completely filled with oil there is nothing to compress to allow the volume of the shock shaft to enter the shock body.

Without getting to far off topic, a damper, or shock absorber, has a piston with a stack of washers and springs, and orifices that the oil passes through. As the suspension moves, that incompressible oil forces the spring washers, opens holes, and oil squirts through. That gives it the damping effect. The nitrogen gas isn't getting 'compressed' per se, it's under slight pressure and only in a nitrogen filled shock (which are kind of a modern thing), there to displace air bubbles from the oil. Void of nitrogen, the damper, shock, what have you, behaves just as a nitrogen one does, oil through orifices, but cavitation can induce air bubbles that get past the seals, under hard use. When that happens, those tiny bubbles act as a spring, within the oil fluid, and make you damper not perform all that well.



About three minutes in starts a pretty good explanation

https://www.youtube.com/watch?v=W4ZZYqRVzLc

[E350]

Tom you likely know more than me about this kind of stuff. So, my guess is that you and boywonder and me are not talking about the same thing.

Because your video does not discuss the gas pressure aspect, only the damping aspect.

Why are these Bilstein gas pressure shocks depicted in their elongated state?

Or better yet, why are they shipped in their elongated state? Poor packaging engineering or some other reason?

I had to use a bottle jack placed sideways to compress the Bilstein gas pressure shocks just to get them to line up with the holes in my dual stabilizer bracket.

I had to use cam straps to compress them to install them at each wheel when I installed Bilstein gas pressure shocks on four vehicles.

Using only one gas pressure shock as a steering stabilizer will cause the vehicle to turn easily one direction and make it equally harder to turn the vehicle the opposite direction.

And it will make "return to center" after the turn nearly impossible.

If a gas pressure shock is to be used as a steering stabilizer you must used two in an opposing orientation.

If you want to use only one shock as a steering stabilizer, then use a shock with only damping (that is what is depicted in your video) and no pressure. But that just adds more resistance on your steering box.

Dual opposing gas pressure shocks add no additional resistance to your steering box. And that is better.

[TomsBeast]

Originally Posted by E350

Why are these Bilstein gas pressure shocks depicted in their elongated state? Or better yet, why are they shipped in their elongated state?

I'm not sure you caught it in the video, but they pressurized the clear demo shock, and made it 'air over hydraulic'.



Just as you suspect, because the nitrogen pressure, albeit low, that captured pressure does push the shock into extension. Most are shipped compressed with a shipping band, so they can travel in a shorter shipping box. You are correct, the gas pressure acts upon the shock as though it has an internal spring. Yep, using a ratchet strap, jack, or just 'strong-arming it' is necessary to compress them a little, to mount them. 100% in agreement so far.



But here's the thing, the 'spring' that most of us have experienced from gas charged shocks is pretty low, n the context of overcoming suspension or steering gear, trying to 'back drive' and steering box.



Caveat: They do sell very high pressure gas charged shocks, high enough pressure where the gas IS the spring, along with a damper in one neat package, that support the weight of one corner of the vehicle. But those are a different animal, and not what we are talking about, here.



Having said that, I've never used a Fox steering damper. I have used a Bilstien steering daper, on a VW bug. Before I bought the gas charged Bilstein one, I wondered the same thing, 'is thing going to make it harder to steer right, than left? Make my bug wander to the left?" It didn't make sense to me, at the time, either.



What I found was no, I couldn't feel the difference in the steering, because the steering box and wheel has so much more mechanical advantage over the system, when compared to the whimpy gas 'spring' in the steering damper. What it did do, when I jacked up the front end, is sloooooowly overcome my 'loosey-goosey' steering box, and turn the steering wheel ever so slowly to the left, it was fun to watch. But again, I never felt it driving down the road, and I commuted 100 miles a day in that car.



Dual vs Single: Fox is an experienced company, I don't think they'd sell a steering damper (intended to be a single) that had so much air bubble suppressing nitrogen pressure, that it would negate the natural self centering you get from built-in caster. I've been wrong before, but it doesn't seem likely.

[TheLetterJ]

If I remember correctly from the way back time machine when I used to regularly rebuild Fox's...

I believe the Fox 2.0 stabilizer was originally developed for the Ford Superduty, shortly after they were released in '99, so their valving should be right on par with what is needed for an E-series. I'm almost certain that it was also valved ever so slightly softer on compression than rebound so that the perceived resistance was the same in both directions. They're generally charged to 150-200psi, so yes, they do push a little, but I've only ever personally been able to notice it on <4,000lb vehicles (Jeeps, buggie's and the like.) Depending how/where you have it mounted, a slight left hand push/pull can be acheived, which is generally beneficial since most roads are slightly crowned and even with perfect alignment will have you drifting slightly right.