Ok all new parts other than the booster on my 61 Sunliner' power drum brake system. Had an issue with the brake light staying on...then on a hot day of driving it the brakes started hanging up. Let it sit for awhile...lights go off and you get some pedal back...did a quick adjustment on the rod and it seemed ok...until today. Nice 88 degree day and the Family and I were in the car all day long..notice the pedal would get increasingly firmer after driving awhile, we would stop and shop,eat, etc, and I would come out and the brake lights were off and I had a little pedal back. Drove it back to the shop, let it cool off, pulled my shop manual and trouble shot it. Key off pumped the pedal 6 times and fired it up, pedal got softer like it should, brake lights went on and off like they should. Think maybe I need some more adjustment on the rod or a bad booster?
Sounds like the fluid is getting hot, do you have a brake line close to a exhaust header ? Another thing is air inthe system. If the fluid gets hot it will try to boil and the fluid doesnt travel very far especially if its drum brakes. With drums you might have them getting hot, my 68 firebird would get funky feeling when the brakes started getting hot on it, i replaced all 4 drums and went to high quality brake shoes and that cured mine.
Check the pedal pushrod, and make sure that there is free-play. I shoot for about 3/8" at the pedal. If there is insufficient return travel, pressure is not completely released when the pedal is released. The system can "pump-up" during use, bleeding back down over time.
Checked all the lines and nothing out of the ordinary as far as how and where they are ran, system bled fine, adjusted properly, etc.. I'm hoping it's just a matter of adjusting the pushrod a few more times. That's a great way to put it...the pedal doesn't come back, also very little pedal at all times, but way less when warmed up
Just back off the pushrod by small increments until they stay free. I'd go by 1/8" at a time or just count the turns in case it needs to go back the other way. Bob
Made a simple version of the gauge shown in my 61 manual to measure the amount of brake rod going into the master..I was about 3/8 inch out to far. Turned it in until just under an inch per the book, bolted it all back up, got good pedal, and good pedal return. No more brake lights staying on due to fluid pressure build up..whew getting on a plane early and if this didn't work I'd be at Sins in the minivan!
It was fortunate that you found a hard dimension to go by, but a little trial 'n error would have got you there too. Bob
check to make sure there is some clearance between the depth of the master cylinder piston and the plunger on the outboard side of the booster. when you tighten up the master cyl it may be getting pushed by the booster.
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