4 link for dummies

[earlybronco72]

Here is some more confusion Patrick. My lowers are 48" long from mount to mount, and the upper is 24". Seperation on the axle and seperation on the frame plays into this. I don't know how, I had a friend design mine. I just built it.

[Lars]

When I was playing with the calculator yesterday, I located the forward ends of both lower and upper links at the same station in the x-direction (fore/aft) which is what the Poly Performance mounts do. I found that with that geometry, it was completely possible to get an antisquat value in the 85-95% range. As Galen pointed out in an earlier post, the calculated value is strongly dependent on what you set as the CG (vertical direction). Unfortunately finding the real height to your vehicle's CG off the ground isn't exactly easy. Thus having adjustable brackets makes sense.

Short story: the Poly Performance frame brackets seem like a good idea to this novice.

To second some of what Joe mentioned, I buy steel and fasteners from Jorgenson and Fastenal respectively, for work. Good prices. Of course when I buy steel it's usually more than a couple of sticks of tube since our projects tend to be bigger than that. Good service though.

[crawlin68]

Yeah, it makes lots of sense. The two things that are hard to accomplish with the PP kit (No disrespect to Highlander) are (1) having 40* seperation between the uppers and lowers (I.E. if uppers are 18* from the frame and lowers need to be at least 22* from the frame) and (2) the length of the uppers should be between 50% and 70% of the length of the lowers.

Disclaimer: As with most other 4 link statistics, these are just things I've seen mentioned as important factors. I have no experience to back it up (yet). After I build mine I will probably be able to tell you what doesn't work well.

Well HURRY UP!! LOL! Seriously, thanks for the info. What I need to do is get on the calculator and start plugging in numbers. It's just that every time I open that durn thing up, I just stare at it for a while and start think "you know...leaf springs aren't all that bad"!

[crawlin68]

I wish that you guys lived closer to sit down with me in front of the computer and show me how to use this calculator thingy. I think things will make A LOT more sense once I grasp that.

[720Racer]

.....Seperation on the axle and seperation on the frame plays into this....

I believe this affects the roll center and roll axis. Part of the calculation is to project the links out to where they intersect, then connect those points. The height of this imaginary line off the gound is roll center, and the angle up or down is the axis. It's alot clearer on the calculator's graphics.

I wish I knew how to "take a picture" (read cut and paste) of the screen with the calculator open, then I could attach it for more clarity.

[Lars]

Well HURRY UP!! LOL! Seriously, thanks for the info. What I need to do is get on the calculator and start plugging in numbers. It's just that every time I open that durn thing up, I just stare at it for a while and start think "you know...leaf springs aren't all that bad"!

Yer right. Leaf springs aren't that bad. It depends on what you are trying to make them do. I have a spendy set of Deavers on the back, damped by a spendy set of Bilstein shocks, and I try to keep the monkey motion minimized with a WH-style antiwrap bar. It works for me- but I have puny 35" tires, a wimpy 5.0 V8 for an engine (thank goodness for powerful motorcycles so I'm not tempted to change), and I'm allergic to driveline abuse. I don't have the energy to rip everything including my exhaust and OBA tank out to install a 4 link, but as with so many things, if I knew then what I know now...

[crawlin68]

Here is some more confusion Patrick. My lowers are 48" long from mount to mount, and the upper is 24". Seperation on the axle and seperation on the frame plays into this. I don't know how, I had a friend design mine. I just built it.

You are not allowed to post in this thread any more! You need to go straight to the Principles office young man!

[earlybronco72]

"you know...leaf springs aren't all that bad"!

Not to be the bad one, but how many leafs have you twisted beyond use? I liked how my leafs worked, but love how the rear is now. I will never have to worry about twisting up a leaf spring again.

[Lars]

I believe this affects the roll center and roll axis. Part of the calculation is to project the links out to where they intersect, then connect those points. The height of this imaginary line off the gound is roll center, and the angle up or down is the axis. It's alot clearer on the calculator's graphics.

I wish I knew how to "take a picture" (read cut and paste) of the screen with the calculator open, then I could attach it for more clarity.

(Ctrl) PrtSc (control/printscreen) then paste to MS Paint or similar. Save it as a jpeg on your desktop. Attach to reply. Like this:

[720Racer]

I wish that you guys lived closer to sit down with me in front of the computer and show me how to use this calculator thingy. I think things will make A LOT more sense once I grasp that.

Pat,

Seriously, take some PVC pipe and some duct tape, and put a some lowers and uppers under your rig. Then take some measurements. All 12 measurements are "distance forward from rear axle", "distance off the ground", and "distance out from center of the frame". Put them in the calculator and you'll see what's going on. Then you can reverse it and adjust the #'s on the calculator, and go move the links to match. It's not as scary as it looks when you first open it up. Every time I change something I save it as V1.1, V1.2, etc. I couldn't refine my #'s till I got all my brackets, b/c I didn't really know how the measurements would change.

[720Racer]

(Ctrl) PrtSc (control/printscreen) then paste to MS Paint or similar. Save it as a jpeg on your desktop. Attach to reply. Like this:

Nothing happens when I push them?

[Lars]

Pat,

Seriously, take some PVC pipe and some duct tape, and put a some lowers and uppers under your rig. Then take some measurements. All 12 measurements are "distance forward from rear axle", "distance off the ground", and "distance out from center of the frame". Put them in the calculator and you'll see what's going on. Then you can reverse it and adjust the #'s on the calculator, and go move the links to match. It's not as scary as it looks when you first open it up. Every time I change something I save it as V1.1, V1.2, etc. I couldn't refine my #'s till I got all my brackets, b/c I didn't really know how the measurements would change.

The problem, for me at least, is that while I can for sure come up with something that appears to locate the axle, how well does it actually work in practice? Mark's comment about finding one that works and plagiarizing the hell out of it has a lot of merit. My best ideas were someone elses...

[Lars]

Nothing happens when I push them?

Hold down ctrl. Hit PrtSc (usually on upper right of keyboard). You just saved the screenshot to the clipboard. Now open Microsoft Paint (should be on your computer if you are running XP). Hit ctrl V or Edit/Paste. You should see your screenshot. Then save it as something.

[720Racer]

The problem, for me at least, is that while I can for sure come up with something that appears to locate the axle, how well does it actually work in practice? Mark's comment about finding one that works and plagiarizing the hell out of it has a lot of merit. My best ideas were someone elses...

I agree. FM gave me the inital idea of lowers from the t/c yoke out, and uppers from the inside of the frame in. I passed a HUGE (seriously 50" + tires) YJ on a trailer a few weeks ago, but I was short on time. I wanted to follow him 'till he stopped and ask him how it worked. It was exactally what I am planning on doing with mine. It's so much eaiser to let someone else do the R&D, and then just impliment their findings.

[blwngsket]

Just came across some installed pic's of Jacks set up.

http://classicbroncos.com/forums/sho...=100294&page=3

Tony