1972 F250 Catching/dragging front brakes at random times while driving

[UH60L]

My truck has been off the road for about 6 months (water pump/blown head gasket, no money...). Last year, I started noticing that every once in a while while driving, I'd just start hearing and then feeling a horrendous screeching/grinding in the front end. I'd stop and pump the brake pedal a few times, get a clunk and then keep driving and it would be fine. So I took it to the local Les Schwab (for those not familiar, it's a locally grown tire shop franchise on the west coast...). The first thing the guy asked was "when was the disc brake conversion done?". I said "never, it came from the factory with them". He looked at me like I was stupid for second... then confirmed that yes, my left caliper was sticking.

Long story short, the rotors still appeared to be good. So, I went through the process of finding the correct parts and ordering them or buying locally. My truck is a 1972 F250 Custom, 2WD, 360, C6 auto. I made sure I got the correct calipers, per my VIN (since they used 3 different ones that year) and even new mount bracket bushings (round metal shells with rubber inside). I won't lie to you, the mounting bolts came out extremely difficult, and even with new bushings and grease, I had to gently tap the heads with a hammer to get them back in (all the while holding metal brackets and wrenches between the caliper and bracket to keep the bushings from pushing out...).

Everything was good, brakes working great, no noise, then I started having, I guess you'd say "brake fade". I'd be stopping, good brake pedal pressure, then there would be sort of a clunk and the pedal would drop an inch or so and then catch again. A little reading/researching led me to believe my master cylinder was failing. SO I bought a new one. Meanwhile I pulled the engine for the blown head gasket. about a month ago, I replaced the master cylinder while the engine was out. (bench bled, then bled on the truck) Got seemingly good pressure and new fluid out of all 4 bleeders. Finally got the truck running again and started driving it, and on the second day, I got the brake fade thing once. Then the third day I was driving through my neighborhood and it started grinding and screeching again (feels like right front). Stopped, pumped brakes, kept driving. It's happened twice now in 4 days.

So, is it wheel bearing pre-load? Is it a bad rebuilt caliper? Is it just getting stuck on the mount bolts instead of sliding like it's suppose to? I lost my job in May. Unemployment is about to run out. If I can ever get another job, this truck has to be me daily driver. Any thoughts would be appreciated.

Sorry for the long post...

[cep62]

I've had the rubber flex lines cause issues before.
Did you use a silicone grease on the slides with the rubber ?
I've heard petroleum grease can cause the rubber to swell up , making it tight.

[UH60L]

One flex line is new and the other is only a couple years old.

If by "slides" you mean the mount bolts, yes, I lubed one side with "brake caliper grease" and one side with whatever I had at the time (prior to finding and buying the caliper grease). I'll have to look at the tube of caliper grease to see if it's silicone... I'm certain the other grease wasn't though...

Here's the thing though, when this first started happening over a year ago, the previous brake job I did roughly 6 years ago, I didn't replace the bushings or lube those bolts. Drove fine for 4 or 5 years...

When I went to back out of the driveway today, the right front brake made a loud squeal/grind noise, then a pop and the truck rolled normally. No more brake issues the rest of the trip today. But I noticed although there is good pedal pressure, I don't think it's stopping as quickly as it should.

[bluef250]

Suggest that you check the "Brake Pressure Differential Valve Switch" for debris. The switch is often ignored