So I have a bike rack in the back of my truck that requires that I remove the front wheel each time I transport. The problem I'm having is that more often than not, I have to adjust something related to the front disc brake to keep it from rubbing when I put the wheel back on. Sometimes I have to move the stationary pad, sometimes I just cant the wheel ever so slightly and today I had to move the caliper over a smidge.

The bike is a Trek Marlin 5. The brakes are mechanical discs, Tektro Zoom I believe.

What should I be looking at? My wife has the same bike except smaller, and it always goes back together perfectly.

TIA, Eric

This generally comes down to the part of the axle that slides into the dropouts being ever so slightly eccentric/off-center. When you have the wheel mounted in the fork and the brake rotor centered, make a mark on the hub and fork-- just a little line, or two dots of paint pen, whatever. Then whenever you mount the tire, line up the marks/dots.

I've had wheels do it. Thankfully my two current disc sets have the exact same spacing-- I don't even have to mess with the caliper when changing between wheelsets.

I'm sorry. I'm a bit confused. The axle moves independently from the hub. If the axel is eccentric/off-center, what will marking the hub accomplish?

Place the mark on the axle/lock nut. It's the axle that's at play. Threaded, QR, axles are not easy to get exactly in the same location always. The tiny gaps between a rotor and the pads that a disk brake have makes this locating of the clamped axle more vital then with rim brakes. hence the through axle. Andy

Look into the Topline UG-2500 series of truck bed bike racks. I have one. It works great and no disassembly required.
Jon