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Discussion Starter #1
My '72 Bronco has been abused by me for over 19 years with its stock based suspension in all aspects of four wheel terrain but as a wise man once said "one can only wheel his junk for so long":flipoff2:

My desire for stronger axles and better suspension lead me to my current build. Recent upgrades include 35 spline, shaved full width D60 F&R rear axles, new steering box and linkage w/ram assist, extended front radius arms and King 2.5's and now 12" of wheelbase in form of a four link rear. Ive been collecting parts for the last few months to soften the $ blow and frequently studying here to get the nads to cut out my leaf spring mounts and get to it! Opinions or advice from the rockcrawling world is greatly welcome.

Started with a GLO bridge/truss for the upper axle links:

I added the rear gussets.

47" Lower links are 2"x.250 DOM with 1.25 FK rod ends and 45" uppers are 1.5"x.250DOM with 3/4 FK rod ends.

All bracket tabs are from BTF and the lower link frame brackets are from the 4XDoctor in Burbank.


More to come in the next post...
 

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Discussion Starter #3 (Edited)
The non traditional upper link frame mounts were a small concern of mine but Ive seen a few done with no reported problems and it lets me get them right up against the framerail with no crossmember, a second bracket for some adjustability has been designed into the bracket. Upper axle link tabs are 3/8" thick and will be reinforced with gussests before calling it done.


Side and bottom view of links mocked up




Overall intended wheelbase is 104". I know those lowers will take a beating at that long of a length but Im hoping that compromise will be neglible with some sleeving and a 40" tire. I ran the numbers on the calculator heres the design summary:

Anti-Squat 80.00 %
Roll Axis Slope -0.01 in/in ("-" = roll understeer; "+" = roll oversteer)
Roll Center Height 29.16 in
Roll Axis Angle -0.47 degrees ("-" = roll understeer; "+" = roll oversteer)

Instant Center X-Axis 86.03 in
Instant Center Z-Axis 27.13 in

I do not want to be afraid to drive this on the street so I aimed for - understeer, is this correct? Nothing is fully welded at this point so please post up with comments or suggestions if you have any, Ive got thick skin. Oh and thanks to anyone who gave input on the 4 link subject to this board. I have most likely read and taken your experience to heart when designing mine, it has proven itself invaluable to me. When this is complete I'll hopefully have more info to pass along.
 

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Discussion Starter #4
Oh yeah forgot to mention the upper axle link mounts are just tacked and will be moved around to make room for some small heim spacers.
 

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damn, that's the same damn thing I am doing right now. my lowers are 48" eye to eye. And I am trying to keep 40* on the uppers , so I went 36". There isn't much room between an EB frame for much more. I went with evo 1.25 rod ends on all 4 axle sides and bushings on the frame sides.

sweet build. nice truss. Ill be watching this post :smokin:

I like those #s, Do you have a picture of the 4 link calculator. If you dont mind I would like to use some measurements.
 

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I'm here to learn, too. With my limited experience on 4 links, I'm curious if the horizontal separation of the lower links on the frame side will be too much.....?? Most dual-tri four links that you see here have the lowers much closer on the frame side. What do you guys think? Again, just asking to learn...not criticizing.
 

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Both sets of links do not need to be triangulated in order for the suspension to work well. The more triangulation that both sets have, though, helps keep the roll axis flat. His is dead on at a slightly negative slope for better high speed manners. The Uppers are not at a very wide angle to each other. but since the lowers are also triangulated (even just a little) it should not be a problem. In my opinion anyways. I think that this 4 link looks really nice, I have been playing around with my setup and the calculator and I have been shooting for numbers similar to yours. Nice work, let us know how it performs for you.
 

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that looks real nice im trying to get up the nerve to cut off all my stock rear susp also, keep us posted please.
 

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I Also Can't Say Much About Whats Right Or Wrong When It Comes To 4 Link But I Like To Say The Way He Ran The Link Bars Is What The Monster Trucks Run I Also Ran A Wide Spread On A Off Road Truck That I Have It Will (should) Work Fine . I Belive That Rock Krawlers Run Them Tight Together To Get The Most Artickulation On The Axel For Slow Moveing Rock Krawling I Think The Wide Spread Is Better For High Speed Jumping And Staybillity So It Kinda Depends On What You Are Planing To Do With The Truck Again I'm Not Possitive More Resurch Is Best Anyway It Looks Like It Is Comming Along Well Good Luck !
 

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So how do you like the shaved 60?
:D
If'n it were me I would have triangulated the lowers a lot more. Attaching them to the frame rails makes it such that when you are flexed up and climbing the torque forces through the link will want to flip you over on the side. Triangulating them toward the center of the rig tends to lift the center rather than lifting a side. Also I've seen many times where the ball of the heim pops out of the cage so I'd run the that upper chassi heim in the verticle versus the horizontal position. Also why don't you make that upper chassi bracket with multiple points of attachment so you can choose what you like for squat/antisquat. I like to make the verticle separation at the chassi half to the same amount as at the axle amount in 1 inch increments.
 

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I think it looks great. I really like the geometry.

My biggest concern would be the driveline angles with the uppers that much shorter than the lowers, the pinion will point down a little at full droop. I would cycle it and see what you get. Hopefully it isn't a problem, if it is, it's easy to fix.
 

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Discussion Starter #14
Thanks for the encouraging comments everyone. I have the link spreadsheet at home and will post it later tonight.

Teeny: Shaved 60 looks good thanks man, but I'll tell you how I really like it when I fill it with oil :D I really appreciate your comments and knew going into this that the points you expressed were downfalls from the rockcrawling point of view. (Tim and I have argued this in the past) If I were to make changes as ones you suggest do you think desert prerunning capability would be sacraficed? Im thinking so but I could be wrong. Would the frame jacking you're describing be worse than with leaf springs? If not I'll deal with it, my Bronco was pretty predictable with leafs.

Gordon: Thanks for the input, link lengths were my main area of concern. Wow 2" difference in the upper and lower links is a lot? Maybe you cant tell but the upper axle mount is well forward of the axle centerline. I thought the uppers might be too long but for sure I will take your comments into consideration, punch some numbers, cycle the rear and post my findings. You're right it is an easy fix but I hope it doesn't change much of the other "ideal" calculations. More later thanks again!
 

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ownerbuilt said:
Thanks for the encouraging comments everyone. I have the link spreadsheet at home and will post it later tonight.

Teeny: Shaved 60 looks good thanks man, but I'll tell you how I really like it when I fill it with oil :D I really appreciate your comments and knew going into this that the points you expressed were downfalls from the rockcrawling point of view. (Tim and I have argued this in the past) If I were to make changes as ones you suggest do you think desert prerunning capability would be sacraficed? Im thinking so but I could be wrong. Would the frame jacking you're describing be worse than with leaf springs? If not I'll deal with it, my Bronco was pretty predictable with leafs.
Your prerunning wouldn't change, but I think you will notice a big difference in rockcrawling. It will act different than your leaves as the suspension cycles differently. I'd just hate to see those upper chassi heims fail on you when they don't need to. I'd also be a bit suprised if they didn't bind at full axle droop, but that depends on how much droop you have. How long of Kings are you using and how much up and down travel? If you only have 2 inches of difference between the uppers and lowers then I doubt you'll get enough pinion change to warrant concern at full droop, but as suggested, drop it all the way and make sure drivelines and joints aren't binding. That whole note about having the uppers 70% the length of the lowers is total B.S. unless you just like having your diff. pointing at the dirt when the rear end drops out. Keeping them the same or close to the same length will help ensure equal archs of travel and keep the pinion from pointing down. Course they need to be pretty parallel to eachother when viewed from the side as well. Anyway nothing is welded solid so now is the best time to get it as good as it can be. With the adjustable points for the upper chassi link ends you have pretty much taken the brain work out of what you think you want the AS to be at when on flat ground. Rest of it looks good, can't wait to see it in action. Oh and what's the final wheelbase?
 

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Hey Mike are you moving the front axle at all? I would think that stretching the front a bit might be a big help in the high speed stuff. The EB is notoriously front-heavy, and any amount you can stretch the front to get a little more of the front end weight shifted toward the rear would probably be a good thing. I know the D60 is a fat pig under there when looking at crossmembers and oil pans and steering linkage, so its no piece of cake but perhaps worth the effort. Actually now on second thought I believe you and I have talked about this before, I just don't recall what conclusion you came to. I want to get to around 102-104" wheelbase myself but I probably won't put it all in the rear, I'd like to get the front stretched out some too if I can.

Dusty
 

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I am no expert on 4 links, but it looks like the upper frame end of the links would bind on full droop with the heims laying horizontal. I could be wrong, just bringing it to your attention.
 

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ownerbuilt said:
Wow 2" difference in the upper and lower links is a lot?
No it's not. I'm sorry I thought I read that your uppers were 36" and your lowers were 48" Looking at the pictures I can see that clearly is not the case. Disregard my previous comments, except for the one where I said it looks great.
 

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if it was my rig i would be worried about the link seperation of the uppers. i would redo it if it were me....either with a dual triangulated setup, or shorten the links ect
 
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