critique my numbers

stroked88 · Mar 15, 2012

so i took my first shot at playing with a 3link calculator, and took all the measurements off of the crossmember ive partially built, and got everything as close as possible. What do you guys think? im trying to avoid going through the floor with the upper link.

Goatman · Mar 16, 2012

I don't want to oversimplify this, but those numbers really don't mean much. The calculator was designed for a rear application. You don't have anti-squat in the front, you have anti-dive. The force that works most on the links is braking. I won't say those numbers mean nothing, but there are very few people who could really tell you exactly what they do mean. I couldn't, and I've had as much or more discussion with knowledgeable people about front 3 links as anybody. I built my first front 3 link on an XJ about 15 years ago, way before 3 links became popular on Jeeps and rock buggies.

I've said this many times, you can search here and on Pirate if you want, and folks have followed this advise and posted later that it worked. Mount the LCA even with the axle tube. Make the UCA as flat as possible. That's it, all you need to know to make a good working front 3 link.

stroked88 · Mar 16, 2012

even as in perpendicular? and thank you

Goatman · Mar 16, 2012

Yes, perpendicular. For a couple of reasons. One is to get the lower arms as flat as possible, and to make it so the lower arms take all the load of locating the axle so the upper arm only handles the torque load. And, it gives you better ground clearance under the axle.

imtiredzzzz · Mar 16, 2012

Goatman said:
Yes, perpendicular. For a couple of reasons. One is to get the lower arms as flat as possible, and to make it so the lower arms take all the load of locating the axle so the upper arm only handles the torque load. And, it gives you better ground clearance under the axle.

Perpendicular... as in not triangulated right?? I was under the impression that mounting the lowers outboard on the axle was OK, and angling the upper inward was too. :dunno:

And by "locating the axle" you mean up/down throughout the suspension cycle? Not left/right because that's the panhard's job.

GreenMachine1 · Mar 16, 2012

While we're on the topic...

Goatman, how much separation do you recommend at the axle side? How about unitbody side?

beakie · Mar 16, 2012

imtiredzzzz said:
Perpendicular... as in not triangulated right?? I was under the impression that mounting the lowers outboard on the axle was OK, and angling the upper inward was too. :dunno:

And by "locating the axle" you mean up/down throughout the suspension cycle? Not left/right because that's the panhard's job.

he means (I believe) perpindicular as in have the bolt which will be attaching the controls arms at the axle on the same center line as the axle tube itself.

imagine looking at the tube from the side (as if no knuckle) the center of the tube should be even with the center of the bolt... if you look at a stock XJ the lowers attach below the centerline of the axle tube... they drag on rocks, they need to be re-enforced and they transfer some of the axle locating forces onto the upper arms because they are so low.

mount the arms as far out on the tubes as you can, at the knuckles. on the frame side, put them under the frame (makes for good angles but can drag/hang on stuff), or inboard them a bit and tuck them up for a smooth belly... but you DON'T need to tri-angulate them like a 4-link.

as for the panhard bar, mount it high on the axle side, low on the frame side, and as long as possible. course if you have a draglink you'll want to match it's angles for the best setup (less/zero bumpsteer)

there are plenty of pics if need be, but don't over think it, it really is as simple as it seems... once you realize how easy it can be you get to understand it (atleast that's how it worked for me)

Goatman · Mar 17, 2012

beakie said:
he means (I believe) perpindicular as in have the bolt which will be attaching the controls arms at the axle on the same center line as the axle tube itself.

imagine looking at the tube from the side (as if no knuckle) the center of the tube should be even with the center of the bolt... if you look at a stock XJ the lowers attach below the centerline of the axle tube... they drag on rocks, they need to be re-enforced and they transfer some of the axle locating forces onto the upper arms because they are so low.

mount the arms as far out on the tubes as you can, at the knuckles. on the frame side, put them under the frame (makes for good angles but can drag/hang on stuff), or inboard them a bit and tuck them up for a smooth belly... but you DON'T need to tri-angulate them like a 4-link.

as for the panhard bar, mount it high on the axle side, low on the frame side, and as long as possible. course if you have a draglink you'll want to match it's angles for the best setup (less/zero bumpsteer)

there are plenty of pics if need be, but don't over think it, it really is as simple as it seems... once you realize how easy it can be you get to understand it (atleast that's how it worked for me)

Yes, that's it.

I like the Synergy/Poly Performance XJ front link mounts. The lowers are inboard which provide better ground clearance, visualize pivoting around a rock on the trail where the rock is slanted and the frame is hitting against the rock, or going through a v-notch type of rock, the inboard LCA mounts provide better clearance. The UCA mount is inside the frame but under the floor, so the UCA angle will be good and the whole thing is simple to do.

Goatman · Mar 17, 2012

GreenMachine1 said:
While we're on the topic...

Goatman, how much separation do you recommend at the axle side? How about unitbody side?

Around 8" at the axle, but the upper arm being level is more important than the amount of separation. At the frame however it fits, 4" is fine.

critique my numbers

stroked88

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Goatman

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stroked88

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Goatman

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imtiredzzzz

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GreenMachine1

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beakie

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Goatman

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