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."

I just replaced my front rotors and front pads. I can say that i can lock them up easily. Of course my tires are not the best. I used brembo rotors with stock pads. I have not even touched the rear brakes yet, i am planning on doing a rear disc setup.

unless you have abs, they should lock up. of course, you want all 4 to lock up simultaneously, but sometimes with disc/drum combo configs, you get the front two to lock up first, or the back two (what you don't want, obviously, is either right or left side locking up without the other).

possibly air in the brake lines maybe? could maybe be a froze up or corroded caliper? 14k miles is not enough (well, shouldn't under normal conditions) to wear out pads or rotors.....and if they were worn out you would know it by the awful sounds or the vibration or shaking. did you try (sans trailer, that is) to lock them up, or will they not lock up at all? you'll know you have something amiss if one side locks up before the other.

What size tires are you running?

That old style brake setup is designed for the stock 235/75R15 (~29") tires. My '86 Runner's brakes never worked well either, especially when running 33's and 35's (never could lock up tires on dry pavement). The later style brake setup (aka "V6" brakes) is much more powerful. My T100 (v6 style brakes) can lock up 35's.

Thanks for the input. I will have to check futher. The following should add additional clarity (I hope).

This 85 does not have abs.

If there was air in the line(s) I would expect some spongy-ness, which I can not detect.

If I had a froze-up or corroded caliper I would expect each wheel to lock / not-lock differently with some pulling to one side or the other, and have at least one or more of the wheels to lock up. I have a slight drift to the right with the operative word being "slight." This may be a clue I'll need to look at.

I use both a summer tire and a winter tire and have the same experience (i.e. no lock-up) with both on dry pavement (asphalt).

My summer tires are Winston "Winner" LT235/75R15 with a non-discript highway tread design and have a 7.5" width on the ground. I see nothing unusual here.

My winter tires 30x9.50R15LT (Grand Auto) with mud tread and a 7.5" width on the ground. These are larger than the standard "235" but seems to me ought to lock-up.

All my subsequent stopping trials were sans any trailer and in 2WD.

Usually when pulling a trailer in the winter, and especially when the roads are wet, I'll lock-in the front hubs and then if I need to stop "hard" I can shift into 4WD on the fly and have all the wheels pull the same (or lock-up the same as the case may be, which has not happened yet).

I am getting a sense that the 85's just may not lock up.

Anyone see a flaw in my logic so far?

Try adjusting your rear drum brakes and even flushing your brake fluid.

Could also be worn out rubber brake hoses that are expanding under high pressure therefore not giving you full brakes under heavy braking.

A few things come to mind especially when you said you were pulling a trailor 1)your pads glazed over 2)brake fluid needs changing, brake fluid absorbs water over time and boiling point decreases 3)you heated up brakes so much the fluid started boiling. Flush your system and replace with DOT 3 and better yet DOT 4 fluid. Don't know how heavy your trailor was/is but it probably over exerted your brake system. Thats why bigger heavier trailors have their own brakes because the brake system alone on the tow vehicle is not designed to take the extra force.