Desperate brake help.

65 GTO Clone, 400 *** Drum brakes. My front brakes keep grabbing and I get a very hard high pedal even after a short 5-7 mile trip. When I wait a bit, they release just enough for me to get home. The brakes catch and release just fine when in garage and not on the road. I just replaced the front rubber lines that go from the wheel cylinder to the steel line but it didn't help. What else can I do? It's a new master cylinder and I didn't see anything wrong with the wheel cylinders. Going to get a disc conversion eventually but would like to take this thing out since it's a new crate motor. Someone help. Thanks much.  

don't know all that much about brakes but is sound like a heat issue, when drum brakes get too hot they stick/lock up, i would think that they work fine in the garage because there would be no heat build up, i would take another look and look for very small amount friction (pads and contact area) which could be the source of heat,

Hope someone else can get a little more specific  

I found out a bit more just now......as soon as I loosen the bleeder valve from the master cylinder, I get a normal pedal and the brakes release. This is telling me it's a fluid matter,.. correct? I had my wife assist with bleeding from the MC (she pushed pedal) and I did hear air escape. Is it possible the amount of air in lines are giving me the problem? I bench bled the MC before install. What else can I do to correct this? Thanks again.  

do the brakes hiss when applied,

I think possibly it could be heat issue but also something to do with your brake vaccum booster, if the booster is faulty you will loose your power brake this will account for feeling in the pedal but i wouldn't expect this to cause grabbing,

i think you should check you connections for the vaccum booster first, and try testing the front brakes in the garage but with the car on so that the power brakes are ingauged, you will need vaccum for this to work  

OK....I found out for sure the problem but unsure how to fix it. As soon as I made it home the front brakes were locked again of course. I opened the bleeder on the master cylinder and all went back to normal. Normal pedal and brakes released. Where do I go from here on fixing this...it's obviously a pressure/fluid problem. Help!!!!

My master cylinder has 1 bleeder and a 1/2 inch fitting is all. It's a small cylinder, round with no reservoir if any of this matters.  

When you bleed the brakes did you bleed all 4 wheels and start at the farthest wheel from the master cylinder.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

I bled the passenger front first then the drivers side after installing the new hoses. I did not bleed the rear two. They (rear 2) were also not bled after install of master cylinder. Can this be the problem? Wish I knew more about brakes. Thanks for the help.  

It's possible I always bleed all for wheels when the brake system has been crack open always bleed the farthest wheel from the master cylinder frist and so forth.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

OK...I think I narrowed it down to my wheel cylinders. I noticed that with drums off and the brake applied, the pistons on wheel cylinder do not contract back into the piston much at all. When these cylinders go bad, can this happen? It was hard to tell the difference if the one was leaking or was just covered in grease near the piston. The springs are strong and should be pushing pistons back in. I ordered the cylinders and they're on their way here. The thing is this happens on a short trip. At start up and the first mile or so all is ok but after that I run into this problem. (Heat issue with the cylinders?????)


There is no air in the system...all 4 corners were bled. Master cylinder new and working fine. Tell me it's the wheel cylinders cause after that I'll be lost.  

Ya it could very well be the wheel cylinders they could be partially clogged with rust.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

I'm not certain, but I think some of the older 4 wheel drum systems used a "residual pressure" valve that held a certain amount of pressure in the lines to speed up the response of the brakes. Check to see if yours has one. Also I would have upgraded to a split master cylinder for safer braking unless it is a concours restoration.
Steve  
Trying to help... 'cause we don't all have to learn the hard way!

That is correct on most older brake systems .You can convert as Barney said (dual chamber)I would suggest using an afermarket propotioning valve (adjustable)  Contact SSB ,Master Power  they have budget kits and will help you avoid spending money on the wrong items or excessive money in the wrong place.Some usable parts can still be found in salvage yards(brackets,residual press valves,hoses should never be re-used.If the wheel cyl are not pitted rebuild kits are cheap,use a hone and assembly fluid when re-assembling for a long lasting job.Dual chamber is safe because if fronts fail you still have rear and vice versaHave someone pressure bleed brake system if you can get a good price-fill master ,open bleeder,have someone depress pedal and hold down,tighten bleeder then release pedal.  

first get rid of the master cylinder PLEASE.My 66 lemans had the same setup until I went right thru a stoplight.Your on a budget so all you have to remember is its a A-body.any will swap.olds buick even chevy.Mine proportional valve montecarlo,master cylinder trans am and front disc setup 70 culass.If you need a front disc setup I have 2 sets 1 is off 70 gp the other is the 70 cutlass.Im going 4 wheel disc front 89 bonne rear from a GTA rear.As for your problem its one of two air still in your lines or if powerbrake booster has a torn diagham.for the first start pass rear loosen line at wheel cylinder let it run until it uses half the fluid and reconnect.dr.rear ect.then bleed again make sure you dont pump the pedal all the way down while bleeding.as for the second take master loose from booster look at both for fluid leak as it will suck fluid into the engine sometimes even on the inside of the firewall.If fluid can get out air can get in.A little trick for leaks clean all fittings then stray a little paint on each.we all know what brake fluid does to paint.gran dad taught me that one.