Front drum brakes slowly seize

[Kbrack]

Just bought a 1968 F100, drum brakes all around. Seller said it sat for a while but it test drove fine. Ended up having to get a tow home after driving about 20 minutes on a warm day because the front brakes seized. I've since replaced the master cylinder because fluid shot out when we took the line off which loosened all the wheels while a lift. Assumed there was excess pressure in the line and a new MC would fix it. After install, drove around town fine. Quick trips, nothing extended. Later, had a 30 mile trip which included some highway and after about 20 minutes the same thing happened, the front brakes seized again. Seems it's happening when it gets hot and I'm driving more than a few miles. There's a little play in the brake peddle when it's cool, but after it heats up it gets really stiff and the front brakes seize. Any suggestions on what to check next?

Thanks!

[Kbrack]

Forget to mention...once they cool down, the brakes free up and I'm back in business.

[ultraranger]

Does your truck have manual or power brakes?

[Kbrack]

Should have mentioned that...manual brakes.

[Mach428]

Could the self-adjusters be on the wrong side??? Seen it before.

[1972hiboy]

air in lines, deterioration of a rubber hose on the inside. improperly adjusted brakes.

[ultraranger]

You mentioned fluid shooting out, when you loosened the brake line to change out the MC.

Grab the foot pad on the brake pedal and pull it back towards the seat. If there's some slack (free-play) in the pedal, then this is normal.

If there's no free-play in the brake pedal, the input rod between the pedal and the MC is too long.

If the MC input rod is too long, it will be partially applying the brakes at all times --even when you aren't pressing down on the brake pedal.

[Kbrack]

Thanks Steve. We did replace the input rod when we replaced the MC. Do you usually have to adjust the rod that comes with the new MC? I assumed it would be a standard size. But I'll give it a shot and see if it helps.

Thanks.

[Busboy]

Years ago I ran into a car that had one of the rubber front brake hoses collapse on the inside which effectively caused a "check valve " type of action. The master cylinder would easily apply pressure but the return springs in the brake assemblies weren't strong enough to overcome the restriction thereby keeping the brakes applied. Over time the fluid would leak back into the master cylinder normally. Just a suggestion.

[motzingg]

You mentioned fluid shooting out, when you loosened the brake line to change out the MC.

Grab the foot pad on the brake pedal and pull it back towards the seat. If there's some slack (free-play) in the pedal, then this is normal.

If there's no free-play in the brake pedal, the input rod between the pedal and the MC is too long.

If the MC input rod is too long, it will be partially applying the brakes at all times --even when you aren't pressing down on the brake pedal.

this is exactly what happened to mine. Re-jiggered some of the pushrods under the dash when i swapped to hydraulic clutch, and screwed up the shaft- too long. Took a while to figure out what i did, but loosening the locknut and shortening the shaft fixed the problem.


also, if your brake light switch is sticking out too far that will hang it up. i went and bought a 1/2-14 (i think) nut, they had it at home depot, and used that instead of the crappy sheetmetal crimp nut so instead of the whole pedal pushing on the switch, it compress

[Red Mercury]

You mentioned fluid shooting out, when you loosened the brake line to change out the MC.

Grab the foot pad on the brake pedal and pull it back towards the seat. If there's some slack (free-play) in the pedal, then this is normal.

If there's no free-play in the brake pedal, the input rod between the pedal and the MC is too long.

If the MC input rod is too long, it will be partially applying the brakes at all times --even when you aren't pressing down on the brake pedal.

this is exactly what happened to mine. Re-jiggered some of the pushrods under the dash when i swapped to hydraulic clutch, and screwed up the shaft- too long. Took a while to figure out what i did, but loosening the locknut and shortening the shaft fixed the problem.


also, if your brake light switch is sticking out too far that will hang it up. i went and bought a 1/2-14 (i think) nut, they had it at home depot, and used that instead of the crappy sheetmetal crimp nut so instead of the whole pedal pushing on the switch, it compress

I have had similar problems on my 67.....a problem caused by my own redneck repair actually. I rebuilt the master cylinder and noticed that the original "keeper" washer that holds the pushrod in place in the master cylinder was broken (this is the part that goes between the piston and the internal snap ring inside the master cylinder). So, me being me, I decided to replace that "keeper" washer with a regular flat washer and pinched it slightly to make it grab the shoulder on the pushrod. After driving a few miles and applying the brakes during normal driving, the front brakes would begin to tighten up and not release. The problem turned out to be the flat washer that I thought I was so clever to install. That washer was thicker than the original "keeper" washer in the master cylinder and it would not allow the piston to return quite enough to release the fluid that had been pumped to the front brakes when I was using them. Like the others have said, take a look at your pushrod.

[laharve]

After about 50 miles after I purchased my 72, the rears start to lock up, 4 wheel drum, the pedal was really firm. After cooling it for a couple of hours it would be fine. I found online somewhere, maybe here, that there was a diminsion from the fire wall to the brake pedal from Ford, mine was to much so when the brakes would heat under nomal driving the fluid would not have anywhere to expand to. The solution was to adjust the brake pedal at the master cylinder shaft to allow a little free play when everything is warm. Only about 3 or 4 turns on the fine thread adjustment was all it took. I'm glad it happened because that how I found the brake pedal pivot bolt was just hanging there with no nut. That really was a lucky day for me.

p

[Kbrack]

Sorry it's taken so long to close this out. Turns out it was the brake light switch. The old one had broken and was engaging the brake peddle, thereby pushing in the rod to the master cylinder, even though the brake light wasn't on. I replaced the brake light switch and left much more play in the peddle and she's been driving great ever since. Thanks to everyone for the input.