[Bagd72Chevy]

To answer some questions:

I am the alignment tech, usually. I've done all my own alignments for 20 years and build tube chassis off road racers on the side. I did not expect this level of tech discussion on this forum, but I'm glad we are having it.

However, this last alignment was done by one of our techs and it did not drive well after, hence why I put it on the machine myself. The truck drives fine until you get over 60mph or then it wants to dart around. Not wandering softly, it goes left or right abruptly. Everything in the front end is new (replaced by me) except the steering box, only because I don't really know what it is. I thought 67 year trucks didn't have power boxes or the frame indention to have one but this one does making me wonder what I have from the previous owner.

The truck is a 1967 GMC, but I truly have no idea what was done to it before I got it. Assuming it had factory 1967 front suspension. The control arms are not rubber bushed so its earlier.

I put 3" drop spindles for a late 80's C10 with a 1" wide rotor and have Camaro rotors to get 5x4.75" bolt pattern.

Ball joints were changed to match the spindles and tie-rods were changed to match the spindles. I used a Tapered reamer to open up the holes in the center link to fit the larger tie-rods from the 80's trucks.

Rear leaf springs were disassembled and rebuilt with all new bushings. Rear axle is a Ford 8.8 with 4.10 gears and a Posi mounted on top the springs. 15x10 slot mags with 295/50R15 tires. Front wheels are 15x8.5" and I forgot tire size. I'm actively trying to change to 7" front wheel if I can find 2 more slot mags.

It drives like it has bump steer, confirmed by the alignment machine. I prefer to run more caster than most but I usually stay in the 4-6deg range. Both sides were at 7deg from my tech that did it last, I did not change anything this go round just gathered data. Now that I'm thinking about it I wonder if the issue has to do with differences in the 80's center link vs the 67. I did not put them side by side to verify they were the same but I don't recall people changing them when they put the later crossmember assembly in.

The truck has a supercharged LSA engine but I'm scared to take it to the track until I sort this steering issue out. That and it will be much more enjoyable if I can just relax and cruise down the highway. I've been looking into Rack conversions but I'm hesitant because I have never ran into this issue before on any of my other C10's so trying to figure out why this one is doing this.

My thoughts are that the upper control arm is at too much of an angle and the camber change is causing the track width to narrow resulting in the bump steer.

So, I will follow up tonight or tomorrow with pictures if I can snake my phone in there and I will take angle readings on both arms and the tie-rod.