Ardent Fabrication Autocross Truck

BOOT said:

I don't like how it's set up to pull back when the diff twist instead of up like a torque arm

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Can you explain what you're seeing? Because I'm not seeing that. The third link controls the pinion angle, and if you look at the second picture, the mounting point of the front end of the tri-link is adjustable so that he can tune the pinion angle change. I would probably replace the frame crossmember to gain another inch or so in mounting height, but I think ArdentFab is trying to keep it bolt-in.

Erik the Awful said:

Can you explain what you're seeing? Because I'm not seeing that. The third link controls the pinion angle, and if you look at the second picture, the mounting point of the front end of the tri-link is adjustable so that he can tune the pinion angle change. I would probably replace the frame crossmember to gain another inch or so in mounting height, but I think ArdentFab is trying to keep it bolt-in.

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Under acceleration, his upper link will be under tension, trying to resist the rotation of the rearend housing, kind of like a 4 link would work. If it were a torque arm, there would be another link from the bottom of the differential to the same mounting area to balance that tension force with a compression force and the net force at the mounting point would be vertical instead of longitudinal.

arrg said:

If it were a torque arm, there would be another link from the bottom of the differential to the same mounting area to balance that tension force with a compression force and the net force at the mounting point would be vertical instead of longitudinal.

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The net force at the mounting point is neither vertical nor longitudinal, it is rotational, hence the name "torque arm". What does that have to do with it? I'm legitimately asking, because I do have a fair understanding on anti-squat, and I think that's what you're saying, but if his geometry is correct (hard to tell from just pictures), a tri-link is just as effective at providing it.

Erik the Awful said:

The net force at the mounting point is neither vertical nor longitudinal, it is rotational, hence the name "torque arm". What does that have to do with it? I'm legitimately asking, because I do have a fair understanding on anti-squat, and I think that's what you're saying, but if his geometry is correct (hard to tell from just pictures), a tri-link is just as effective at providing it.

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I agree with you it should be effective. That was just my interpretation of what Boot posted. Looks like he has enough adjustabilty to move the IC wherever he needs it.

Erik the Awful said:

Can you explain what you're seeing? Because I'm not seeing that. The third link controls the pinion angle, and if you look at the second picture, the mounting point of the front end of the tri-link is adjustable so that he can tune the pinion angle change. I would probably replace the frame crossmember to gain another inch or so in mounting height, but I think ArdentFab is trying to keep it bolt-in.

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A rearnend will try to twist(front-lift), the pinion gear is trying to climb the ring gear if traction/resistance is sufficient. The way that the truck's setup is, when the front housing lifts, where the curved bar is mounted, it will pull back on the straight mounting bar because they are connected with a rod-end/heim-joint. Not lift but pull on the straight bar mounting point. You can even see how that straight bar's mounting point is braced to resist PULL or PUSH

A fixed or triangulated bar torque arm will try to lift(think ladder bars). If the curved bar connected to the straight bar then it would lift not pull because of the three points.

That trucks setup will locate the pinion but I think a torque arm would work better for a truck. I don't claim to be a suspension expert and I can see how it works kinda like a 4 link. Just my opinion.

The sole purpose of that curved bar is to strengthen the connection to the diff. So long as the third link is strong, its tension or compression is moot. The downside of a torque arm is a tendency to brake hop, which is very bad in autocross. A tri-link can still get brake hop, and in RX-7s it was solved by using a section of pool noodle as the bushing in the front mount of the third link. So much clanking and banging that it wasn't streetable, but they stuck like glue. My RX-7 had the factory 4-link/watts, and a competitor had a tri-link/panhard suspension. My car handled good to a point, but then would breakaway and slide. No matter where he turned his steering wheel the car just went that direction. It was an amazing difference.

The curved bar is to keep the pinion angle from changing as it tries to torque twist I thought.

Brake hop is that the same as wheel hop? Wheel hop is caused by too weak of a spring, the springs job is too keep the wheel on the ground. I would suggest stronger/higher spring rate for a torque arm, the mechanical advantage it adds will load the springs more and lesson their effectiveness.

Brake hop is wheel hop under braking. I get it in my Camaro if the rear trans mount comes loose or I have the rear bias up too high. It's a real m0therfucker.

I've always been a drag racer so never herd of brake hop, but a quick google shows there are fixes for it. Well the only hop on hard braking I've experienced is on a wash board dirt road LOL

I plan to make the most of my leaf spring truck and maybe someday I'll convert it to something else but I'd prob use a better truck before this one for any serious mods.

Been a while, lots of changes but will post more pictures later.

Some from LS Fest Texas 2022 at Texas Motor Speedway.