Earlier, while pulling a trailer (with my 85 4x4 truck) and braking hard, I questioned if my brakes were stopping adequatly, as it did not lock-up any wheel, front or back, while I was exerting strong pressure on the brake pedal.

(The question of "if" one would ever want to lock-up a wheel while pulling a trailer is not the topic here)

During the same week, a car attempting to pass me on a curve, was forced to brake-hard in abandoning their passing-attempt and locked-up their front wheel(s*).

*I could see their left front wheel momentarily lock-up, thru my left rear-view mirror, with their tires screeching. This experience reminded me that brakes lock-up during hard braking.

I have performed the tests on my brake booster (or some call it vacuum assist), as recommended in my Toy owners manual, and it has worked as indicated.

My truck has new rear brake shoes with less than 1000 miles, and front pads and turned rotors have about 14K "easy-brake-use" miles on them.

I think the brakes work fine except for hard braking I think they could brake more.

My question is this: Should the "front wheels" lock up during hard braking or are they not designed to do so?

I think I can get the rear bakes to lock up with some adjustment to the "load sensing proportioning and by-pass valve."