i put disc brakes with power booster on my 35 truck every thing is new. have rear drum brakes work good yard driving when you drive on the hwy the front brakes will lock up after about 6 stops you can break the line loose at the mc and it has pressure built up then the brakes are good for about 6 or 7 more stops. everything is mounted on the firewall.
If you have pressure at the master cylinder junction this is a sign that either the piston is not fully returning to seat and fully exposing the return port opening or the master cylinder is equipped with an internal check valve that would be used for a drum brake application. First is to check the push rod free play as already suggested to insure the pedal is returning fully, the next step is to identify what application the master cylinder is for, disc brake car or drum brake car. If you have the correct disc/ drum master cylinder do you have the ports plumbed correctly and you have not gotten the hook up reversed and plumbed the disc side to the drum side of the master cylinder.
That was the first thing I thought of. So many think they should go this way. On Master Cyl. the front line goes to back, and back line goes to front . Everytime someone tells me this, I have an idea that is what it is. Always look for simple problem first.
I had a new, not rebuilt, drum/drum master do this on my drum/drum 41 chevy. It turned out to be a bad master.
the master cyl is for disc front and rear came with a new port valve for disc drum brakes i will check pedal rod today thanks
If the rubber lines are used (Old) sometimes they hold the pressure and don't release fully, then next time the brakes are applied, they lock. This happens mostly on a daily driver (Recently, my 85' pick-up), but was an easy fix by replacing the front rubber hoses. If nothing "Previously mentioned" fixes the problem, try it.
He's cracking the line at the master cylinder to release the pressure so that eliminates everything after the master cylinder. Loosen up the nuts holding the master cylinder to the booster when there is pressure built up as a quick check. If it goes away, the booster rod needs to be adjusted.
What they said - Miss adjusted push rod or bad master. You can use a bit of clay or RV seam sealer to check the installed gap if you can't tell by wiggling the brake pedal.
As CrAZy as this sounds, also make sure the master is not filled ALL the way to the top. I have personally had a locking brake problem (twice on different cars!!!) that was due to nothing more than the fluid not having anywhere to expand to, which in turn applied pressure to the brakes. I've also helped a guy on his Harley that had the exact same problem. I literally just removed brake fluid until it was about 1/4" below the top and solved the problem. I know, sounds nuts and you may thing i'm full of shit, but it DOES happen. Maybe not in your situation, but it's just another thing to look at. Tony
thanks engine man did not know there was a adjustment in the front of the power booster turned it in about 3/16 brakes are working good
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