Tried to take the '79 on a dump run yesterday and He just wasn't havin' it. I was pulling a 3,000 lbs horse trailer with about 2,000 lbs of debris in it and i was spinning both rear tires going up a gravel hill. got to the top of the hill and smelled brakes. got out and the front left brake was smoking. Turned it around, drove the 1-mile back home. Hit the brakes to turn into my driveway and the pedal was very hard, truck didnt really want to stop and the brake light came on. dropped the trailer and finished the dump run with a different truck.

upon inspection later that day, the front left spun freely until i hit the brake pedal. after that the front left was dragging again. jacked up the front right, and it was also dragging.

i'm thinking this is a failed master since it affects both sides. my first thought was a collapsed hose, but it was braking straight, with a very hard pedal, and a hose wouldnt affect both sides, unless both hoses failed at the same time ... which is possible, but not real likely.

any thoughts?

 

Disc brakes always drag a little .

Going up a hill would have nothing to do with it. they had to be dragging before you started up.

There are several things it could be but bad calipers would be the most likely. if they don't back off that tiny fraction of an inch each time you let off they're going to get hot fast.

 

All true, I agree they were dragging from the start, I was just trying to highlight how much they were dragging.

I’ve never had a stuck caliper free up over time. Usually when they stick they just stay stuck. I also can’t think of a time where I’ve had both go bad at the same time.

that said, this truck hasn’t left the yard for at least a year. I think last year I drove it around the section just to get things moving. But it didn’t act up on that 4 mile drive last year. It’s been a yard truck used once and a while every couple years since about 2014.

 

Either ... a caliper has a piston sticking ... or ... you have a brake hose leading to that caliper that is damaged from age and a inner piece in the hose is loose acting as a check valve.

Loosen the bleeder valve on that caliper like real quick and shut it real quick (we want to just test for pressure, not loose a lot of fluid here).
IF nothing changes, no spurts and brake stays tight, likely caliper.
IF fluid spurts out and the brake releases, it's the hose bad.

I see that you say it affected both front brakes. I'm not sure on a 2wd, ... but a 4ed has three brake hoses on the front brakes, one is the drop down from the frame, and then one to each caliper. It could be the drop down hose is bad.

 

When you say dragging does that mean you have front wheels raised off ground and can't spin it by hand? Or you can spin it but it has some resistance?
I have to think calipers also, but it could be MC as well. Did you remove MC cap and look inside to check condition of fluid? If piston is hanging up in MC the rear brakes could/should be affected as well even though the drum brakes have springs to pull shoes away from the drum.....but they won't move much if the fluid pressure remains due to piston hanging up.

 

A third possibility is the combination valve mounted on the frame.
That would also affect both sides equally.

The fluid pressure test can be used to test each component. If it’s a pressure retention issue rather than a stuck caliper, you will be able to find it or narrow it down by cracking bleeders and breaking tubes loose momentarily.
Just work your way up the line until you don’t have pressure.

 

All good information provided. Had similar experience four years ago though with my 1995 Ford F-150 SWB Eddie Bauer when I descended the Sonora pass coming from the West side to the East. There were grades at 27% and 15 MPH, even though I kept the E4OD transmission in first gear I had to use my brakes allot, was carrying a pretty heavy load in the bed. Only use the Eddie Bauer during trout season and stow it after the last outing. Well my front driver's caliper piston was hanging up, not reacting far enough back into the caliper. Brake pedal felt the same as yours, very stiff with very little movement. Got to the bottom of the grade, pulled way of the road (US 395) open the hood and parked the driver's side front with the wheels turned into the prevailing wind and ate lunch in the truck. About forty minutes ensued and I poured a bottle of water onto the caliper, it was still very warm, but decided to re-commence driving since it was flat road ahead of us. The brake resumed normal feel, but could smell burnt disk brake pad, and became less noticeable as time and miles went by. Kept the speed down to below 35 MPH for ten miles and gradually back up to the posted speed limit.
After getting home, investigated and noticed the caliper piston had rusted on the top outer portion, caused from being stored (sitting) which prevented it from retracting enough to clear the rotor, creating friction (heat). Changed both front calipers, had rotors turned down and re-packed both front wheel bearings. So the similar problem was caused by no-use, the truck sitting for eights, even though it was covered and under the truck port (live about two miles from the ocean) and we get the prevailing wind coming off the ocean which is corrosive.

 

I've had caliper pistons stick closed and cause dragging and I've had them stick open causing soft feeling pedal. Replacing calipers solved the problems. And each scenario was on daily drivers.

I clean and grease slide pins and bleed brakes regularly. Replace hoses around 15 years of age. For me in multiple cases it was pistons.

 

And anything is possible on a vehicle that sits for extended periods. Literally anything.
You might have dead snakes wrapped around each caliper!😁

 

so after sitting for 5 hours while I was at work, i jacked the front left and it spun freely. Would coast on its own for a turn or two after giving it a spin. After pushing on the brake pedal and letting off, it would barely spin. At first I couldn’t spin it at all but then with both hands I got it to turn, but it took both hands to get it to turn. About 30 minutes later I checked the passenger side and it was very stiff too. Ir would turn but took both hands.

I’ve had stuck calipers several times on various vehicles, but I’ve never had two at the same time. And they never acted like this. When they were stuck they were just stuck and wouldn’t ever let free after a period of time.

I’ve had blocked brake hoses several times too. They would make the brakes drag but would eventually free up over time and let loose. Which is exactly what these did, but I’ve never had two do the same exact same thing at the same time which is why this seems odd.

That’s why I was thinking the brake master. Combo valve crossed my mind too.

the fluid is nasty so anything is possible.

i guess it is time to start cracking lines and see what happens. Might be a while though. I’ve got 4 buildings that need a roof and a dozen trees to clean up still from the derecho earlier this year. Plus I got two other vehicles to do Brakes on before this one.

Lots of fires to put out, this was just a real downer because I could have used it twice that day.

 

Yes, bummer indeed.
Sorry to hear but it does sound like you’re narrowing it down to holding pressure. Maybe there is enough moisture in the fluid to be causing some rust issues downstream. Or even upstream in the master I suppose.
I guess you’ll find out.

 

I had a similar menacing problem many years ago on my first ‘78. It just about drove me around the bend, trying to figure it ou. Turned out being the vacuum booster the master cylinder attaches to. The piston on the booster was so corroded, when you hit the brake pedal it wouldn’t release after you let off. Always a hard pedal, until you let it sit for awhile. I had several people tell me the boosters are never the issue, but believe it or not, I had a ‘75 Cadillac at the time, and one night I was just reading its owner’s manual, and that was mentioned as a possible cause for the symptoms.