1997 F150 single cab, stepside, 4.6L automatic
front discs, rear drums.

I’m at a loss to fix this issue. My front left brake locks up under medium to hard pressure, at just about any speed. It’s ridiculously unsafe, and I spun out in the wet at one point because of it.
the truck dives hard to the left under medium to hard braking and locks up even in dry conditions.
when I let off the brake it does not stay locked, wheel spins freely. Pedal feels fine.

so far I have replaced:
Drivers side caliper
Both front discs
Both front pads
Flushed/bled all 4 brakes

and the issue is still the same, or worse. I feel the only thing left to even change is the flexible hose, that’s my next step, but visually it appears fine and I typically hear of people having different symptoms. I believe my truck only has rear ABS, as I don't see the large HCU module near the drivers side, just the proportioning valve under the master cylinder.

has anyone had this issue or any idea where to go next?

 

Replace the hose and caliper on the RIGHT side of the truck.

The problem is that the left side is working well but the right side is either late, delayed, or weak. This creates a severe imbalance in braking forces causing the left side to activate sooner and stronger.

Had this on my F250 a while back. It was the hose itself that was restricted causing weak flow to the rt front caliper.

 

I would replace BOTH hoses on general principle.

 

I agree. Brakes are to be serviced on both sides per axle. In this case, I would replace both hoses and pressure bleed the system.

 

Well, I think some or both of these ended up fixing it.
I replaced both hoses, and passenger side caliper, then bled both thoroughly.
(I returned the drivers side caliper since it was doing the same thing, and I'm not made of money!)
At first i was cursing up and down because this seemingly did not fix the issue, kept skidding, but i figured I’ll go brake like hell just to see if I can maybe get it “unstuck” and I was right. My theory is that after clamping down hard in one spot, it made a sort of groove where it began to “bite” and I wore it out after doing a couple 60-0 passes, getting a little better each time. Thank y’all for recommendation and insight!

 

Well, I thought it was fixed. She still locks up (front left only) under hard braking, but it’s only slightly better. My truck at least brakes in a straight line now, so it’s reasonably safe. The only real thing I can think of that may cause this, is maybe a bad tire on that side? The inner edge (closest to engine) is just slightly bald from a bad alignment that I’ve already fixed, but 80% of the contact patch is fine, so I don't think that would be the issue either.
any ideas are welcome, not sure where to go from here and I'm too broke to take it into a shop currently.

 

No offense, but working brakes aren't optional. If you have an accident, you're really going to be broke. You've done all the work you can. It's time to get a fresh pair of eyes on the situation. Someone else might see what you've been staring at all along.

The only other thought is check all the hard lines to see if there is a crimp/dent to be found.

 

Bingo. I wouldn't dare drive a vehicle around on a regular basis knowing I had questionable brakes. Especially since now you posted it on the Internet.

We had a very bad limo crash a few years ago due to something as simple as a poorly maintained brake hose that cost the lives of 16 passengers and 1 limo driver. 17 people dead because of in-op brakes and a $20 brake hose! More so they knew they were having brake problems to start!

Since then, anytime I do work on not only my brakes, but others vehicles, I make absolutely sure that I can stand up in front of a judge to take an oath that I did "everything I was able to do to prevent it" in case it ever went that far.

Brakes are no joke.

 

x2 for sure