Since it released almost instantly after shutting of the engine, I think we can rule out heat as heat would've required more time to dissipate heat.  I think this almost certainly has to do with vacuum. 

What is strange is that modern vacuum booster check valves trap vacuum in the booster (so that you still have some power assist even if your engine stalls).  So with a modern booster, even after you shut the car off, the check valve should prevent the booster vacuum from dropping.  However, I do not know how it was set up on these older cars.

Nate - Madison, Wisconsin

 

56 Ford Customline Sedan

 

Happend to me on my 85 Mercedes 300d. Was a rear disk brake caliper that didn't release completely. Built up heat and slowley locked up the brakes. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

I wish you guys would figure this out, my Dad's 93 Aerostar does the same thing, it hangs the front brakes, changed everything except the booster and the owner. still does it, but not as often.

Gary Ryan San Antonio.TX.

Have someone check out the booster.There are a couple of valves inside that direct vacuum and normal air to each side of the diaphragm.One of them is defective.

  

You should never overlook the basic, simple stuff and assume its a failed component. I learned this today with a similar brake problem. My 58 brakes did the same thing after I drove it awhile. The brakes would start to drag, and come in hot. I have a dual master, GM style with a 7" booster, torino discs in front, stock drum in rear, all new stuff, new lines, CPP adjustable proportioning valve. So after some research, and advice ,I tried adjusting the rod that pushes the master. That's when I spotted the problem, the rocker linkage on the end of the rod had a rather large cotter pin in the pin holding the linkage. It rotated and was resting on the mount, keeping the brake slightly engaged. The more I drove it and built up heat and vaccume, the tighter the brakes got. Glad I spotted that. Good luck





thanks, Mark

Ron,

I think you have your answer. I'd reconnect the booster and try a series of short runs from home and see if you get the problem again. If you can correct it with removing the vacuum line, then more than likely it's your booster. If not then possibly something sticking but check and drive will usually find the problem.

Try the booster first then go from there.

Cheers

Warren

  

Grizzly (Aussie Mainline)

Hey guys, quick update. Came out from dinner and all was back to normal. I disconnected the power brake vacuum line and plugged it just in case. Car ran great all the way home, brakes worked fine (except w/o power assist, obviously), so not sure if that was the root cause or not. May be able to dig into it this weekend, although im not too sure how to start diagnostics on something like this...



I sincerely want to thanks everyone who took the time to read this and chime in on it. You were all very helpful, and i truly appreciate the time you all took to read and respond.



THANKS!

Ron Grove

Wauconda, IL

Yes, that is what happened. Car was idling for 10 mins or so with bbrakes effectively locked up, and pushing on the pedal, rocking the car back and forth didnt free them. Pedal was very very very stiff, at the top of the travel (rest position), and the brake lights were stuck on.



I shut off the car and walked around to the trunk to get out the tools, and the brake lights were off, and when i put the car in neutral it rolled freely.

Ron Grove

Wauconda, IL

Ron

If I understand you correctly the brake problem (locked brakes) will disappear when the engine is turned off and engine vacuum to the booster drops off. As was suggested by Ted you can disconnect the hose from the manifold to the booster and cap it. Then you can drive the car with non power brakes until a fix can be found. Another thing to try with locked brakes is to open the wheel cylinder bleeders ( last resort). When you do find out what it was, let us know. Pete

Hey guys, thanks for the thoughts.... Some additional info:



No recent work done on the car. Last time i worked on the brakes was when i flushed the fluid 2 summers ago. Evryething else on the car is working fine.



If the piston was cocked in the mc, wouldnt the pedal be loose/sloppy? In my mind, it would have to be cocked in the depressed position to hold fluid pressure, right? But the pedal had no play in it whatsover; it was firm and at the top of the travel, there was no looseness or play that would indicate that the piston was cocked at the bottom. Of the bore. Am i thinking about this right?



The hoses were bought from tee bird prods, and usually they have good parts, but no idea of the origin or age for sure.



Like i said, weird thing is that once i turned the car off the pressure released very quickly. Thats what makes me think its the check valve, but i have a tendancy to fixate on what i think the problem is without looking at all the facts...


Ron Grove

Wauconda, IL