Bronco 4 Link Help

rcmbronc

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I have a early bronco I am building basically like a pre runner. I have extended front radius arms with 14" King Coil Overs. In the rear I have a Camburg 9 inch rear end with a four link. The lowers are Ballistic fab arms with the shock mounts on the lower control arm.

I need some help with some advice to get rid of the rear roll oversteer. Here is my 4 link calc. I cant seem to figure out what I need to change to get rid of the over steer. I am assuming flatter lower links but dont want to drop the front mount and just moving the rear mount up and in front of the axle does not really help the numbers. The rear lower mount is where it is because that is as far back as I can move the rear axle with the 40" long lower arms. I may need to shorten or build new lowers. Front lower mounts are already a bit below the frame. It does help to lower the entire truck but not alot. Any ideas?

I am a bit high on ride height so maybe I just need to really lower the truck. I will check those numbers next.
 

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rcmbronc

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Here is what it looks like of I lower the truck 4 inches which I will try. Looks better.
 

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Bert is my name

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Do you have clearance is my first thought. For lowering the truck and or moving the mounts up. Link suspensions have a sweet spot. But 4 inches sounds like the math is wrong on your set-up. Like shortening one set of links or lengthening the others.
 

rcmbronc

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I was able to drop the truck about 2.5 inches and the handling is night and day better. I still need to fine tune the bump stops and the secondary spring stops on the coil overs but for now seems much better handling wise.
 

Bert is my name

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The wheel base on the e.b. is fairly short. Do you actually have the room to package the suspension as designed? Does a 40 inch lower link put the roll center of the vehicle where it belongs or is that just a guess. Placement of weight, lower to upper length bias. Placement of links. There are a ton of variables that a two dimensional 4 link calculator cannot account for. If dropping the truck improves handling I would assume that the theoretical roll center is too high and lowering the truck is only a band aid to the true problem with the geometry of the suspension. Remember that front suspension geometry will also cause jacking and other scenarios that will affect rear roll center. Is it truly a problem with rear geometry?
 

Bert is my name

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I lengthened a set of front arms on an early bronco and pushed them inboard. It was fairly unstable. That was with rear leafs. Lesson learned. I moved a leverage point to close to the rear. That truck was all over the road. The front driveshaft of a truck is about the maximum distance rearward that you can place the front radius arm mounts. On a bronco you start to get beyond the center point of the chassis and the front end starts causing all kinds of roll center issues. Big wheel travel in a short wheel base gets real difficult without going to an a arm suspension.
p
 

rcmbronc

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The front has Cage extended arms. They are mounted to the frame centerline. Room is certainly an issue. The front end I had before with rear leafs and it handled pretty good. All I changed up front was to coil overs and then the 4 link rear. The truck really just acted like it was rolling with the roll center to far away from the CG. Lowering it did help but like said kind of a band aid. I did not want it as high as it was any ways,. I actually want it a bit lower yet. I may still have to lengthen the wheelbase of the truck to help with the handling. This will require a tank relocation and cross member removal. I think i could flatten the lower rear arms a bit then and help with the roll over steer.
 
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