Need Hybrid Bag/Hydro Advice

I just cut and pasted this out of my thread in the suspension forum after some one told me this is the best place for my question.

My application's probably a little different than most of ya'lls:

This isn't a show truck, it's a serious swamp runner, but I've heard this is the place to go to figure out my suspension.The deal is with this tall of leaf springs. They're really stiff and I needed traction bars to control springs wrap. So terrible ride and very little flex.

Occasionally I hit a deep mud hole that drops off unevenly and I worry about flopping on my side. With this I could level out. I could go lower all together in some situations where all be goin' crazy. And I can drop it alot lower for gettin' in and out, and I could go a little higher than ride height for really deep stuff or just to be cool.So I'm already in the process of doing a 4 link, and after hours of searching. Someone suggested hybrid hydraulic system controlled by bags. It's been done on a few tall trucks but other than a few pics that I couldn't see enough detail in, I haven't got the right info from them.Another guy told me this was the place to go for this kind of stuff. I've seen some setups but they weren't quite enough info and my setup will be a little different.

After talkin' to guys who've experienced some of the 4x4s with this system and a few engineer friends who off-road, we've got an idea, but I really want to do it right.

So the plan is to use hydraulic tie rod cylinders at each corner to a shorter cylinder with a larger bore under the bed. This way I can get a mechanical advantage from the bag.Without serious math an example would be: 2" bore 20" stroke at each corner connected to a 4" bore 10" stroke mounted in a cradle under the bed connected to a heavy duty bag with a 10" stroke. So the bag would compress the horizontal cylinder 1" and the ones at the corners would extend 2".(this is just an example that might not be exact)

So I need to figure out:1) the ideal size cylinders to match.2) are you connected both the ports on the cylinder to the other cylinders port? or just the top ones(a friend suggest putting schrader valves on the lower port and adding nitrogen to tune the shock effect)3)any advice you have

I'd love to see some pics. If you've run this what did you like what would you do different. Tips, ideas, whatever.

If you have a buddy running this setup send him this way.

I think that the idea has merrit. Calculating the proper hydraulic cylinder size is simple enough. What you would need to know is...

How much wheel travel do you have/need?

Are the cylinders going to be mounted directly on top of the axles in a 1:1 configuration, if not how are they going to be mounted and how much leverage will they have?

Do you have a bag that you want to use that has 10" of travel or are you pulling figures out of the air? There are many different sized bags that will have different effects depending on your needs.


I would use a schrader in the cylinders only as a negative spring (this one is a bit tough to explain, any bagged situation that will see "air time" should have a negative spring) it would have nothing to do with dampening.

My friend has some 10" stroke 2800 lb bags that he's givin' me. I'll try to get more info off of him.

The cylinder will be mounted directly over the axle like it was a typical coilover.
By negative spring mean keeping it from maxing out?

My truck's 94 GMC Ext Cab FullSize on 2.5 ton rockwell axles with rear steering and 54" boggers with the little lugs cut off.

Ok, once you get all of the parts figured out, let me know.

A negative spring doesn't necessarily keep the suspension from maxing out, but can be tuned to do so.

My buddy hasn't got back to me with with the bag specs.
But I'm to the point I need to figure out the size or rams to get.

I don't have specific travel numbers I'm going for. This is not a rock crawler by any means.
This truck will be a straight up mud bogger. I'm going 4 link for a better ride and I'll have the suspension articulation in uneven situations. I don't think I'll have much situations to max out the rams in a way that will damage them. My normal ride height won't be near max height and I'm not going to see extreme articulation.

I'm wanting to have a 20" stroke ram at the corners and I'm wanting a 2:1 ratio from the bagged ram. So I need to figure out the best bore stroke combos to get this effect.

I'm assuming that the shorter cylinder would be a 10" stroke and I just need to figure out a combo with very close internal volumes.

Here's a list of with cylinder specs for different bores and strokes.
http://stores.daltonhydraulic.com/-strse-Tie-dsh-Rod-Hydraulic-Cylinders/Categories.bok

I was also wondering how the street truck/import guys who run this type of suspension are setting it up.
Do they connect both ports on each ram to other? Or just the top ports?

I'm lookin' at runnin' Dominator D2600 bags.

I'm not sure what a Dominator D2600 bag is, but that doesn't matter. What I need to know is how much actual travel the bag is capable of and the outside dimention of the bag. As for how minitruck guys run their bag/hydro systems, I don't know. Also since you are running 20" cylinders on each corner does that mean that you want 20" of travel? If you are trying to match hydraulic rams, you need to be sure that you are using a specific amount of each ram in order to properly calculate sizes.

The D2600 have 9.75 usable stroke and a max diameter of 7.5".

I plan to have about 20" of travel. I will set it up, so that my ride height has the ram extended approximately 13-15" so I have the ability to go a good bit lower or "slam" it when parked.

I'm not worried about over extending the ram. That could be controlled with limiting straps.

By calculating internal volumes I find that 2.5" bore 20" stroke has a volume of 98.21in^3 and a 3.5" bore 10" stroke would have a volume of 96.25in^3.

So I figure this would give me close to a 2:1 ratio. I can experiment with different viscosity fluids to manipulate rate of transfer.

Edited: 4/23/2008 3:28:37 PM by oh4sho

If you have ever had the chance to see the " Hero's" truck up close it has one of the coolest hybrid systems I have seen. It might be something worth looking at.

You got link?