Who wants to guess the solution?
Ok, so I've been having this problem on the Austin gasser recently, and I finally figured it out today, but it was very unusual, and thought it might be fun to see if anyone here wants to take a guess at what I found that solved it?
Not long ago the car started acting like it had more compression when slowing down, or maybe the brakes were dragging. It mostly happened after I drove at freeway speeds for a few minutes, but more recently it also started happening after driving for 20 min. or so at around town speeds. I'd let off on the gas and it would start slowing down.
Last night I was coming home from the cruise and on the freeway about 55 mph, when the frontend started to get a vibration. I let off the gas and it slowed down even more than usual. Pulled off the freeway, and when I stopped I could smell brake lining that was hot!
Got under the car and spit on the front calipers to see them sizzle!!!! The rear backing plates were only lukewarm, no issue there. After sitting for a few minutes it cooled down, and I headed home the last couple miles on suface streets. Pedal was very hard and high, with little travel!
Today I got in the garage and started checking things on the entire brake system, and discovered the problem. Here's a few details to get you started:
All new lines and braided SS hoses, new calipers, wheel cylinders, brake shoes, master, etc. Basically new everything front to rear. Master cylinder is a late model Subaru with power booster, and I'll tell you right off it wasn't the problem. Disc fronts (GM Metric, drum rear, also GM)
OK, let's see if anyone wants to give it a shot!

 

You had air trapped in the line.

 

Nope! That's was my first thought too.

 

i have never messed with anything having to do with brakes so this is a 100% guess and it may not even make sense...

you had some lines crossed

 

E-brake dragging like it wasn't adjusted correctly?

 

Nope!

 

Sticky caliper slide pins?

 

well since you say its a gasser I will assume its highly modified. You didnt say if you had anything like a hydroboost or anything crazy like that. a loose power steering belt can cause a pedal to be stiff if such a set up is had.

or it could be something really simple like broken pedal linkage.


IM CURIOUS!!! TELL USSSSSSS

 

Here's my stab in the dark. I ran into a similar issue on a restored 69. the owner installed a SSBC disc brake kit on and couldn't figure out why the front brakes were over heating. Turned out to be the calipers, they had phenolic pistons in them, they seized because the master was from a vette and the brake bias and improper adjustment was overworking the front brakes. I'm thinking it's a caliper issue. Or, maybe a linelock problem, assuming you have one.

 

You had your reservoir stuffed full with no room for heat expansion, which subsequently caused the caliper to expand as the brakes and fluid heated up.
P.S., I was sure about the air in the line. I chased a problem exactly like you described and that's what it ended up being.