Thread: Brake problems on my 48 Plymouth

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I just finished rebuilding the brake system on my 48 Plymouth coupe. First I removed all cylinders and flushed the lines. I then installed all new wheel cylinders, hoses and shoes, the master cyclinder looked like it had been replaced by the previous owner, so I just took it apart lightly honed it and installed a rebuilt kit. Once every thing was back together, I bled the brakes and everything seemed fine for a couple of weeks. Now when I take it out and drive it for a while, the brakes (mainly the rear) seem to get tight and I loose all travel on the peddle. They don't lock up, but the system seems to stay pressurized and the brake light stays on, until the car sits for a while and the pressure bleeds down.

I just came back from a drive and when I returned home I check the rear drums they are farely hot, the fronts are only warm, so I jacked up the car and the rears were real tight the fronts were also tight but not near as bad.

I'm sure that after an hour of sitting the brakes will bleed down. Most people I have talked to say it is the master cylinder or could be a clog in one of my lines or the manifold where the brake light pressure switch is mounted.

Does anyone have any sugestions where I should start, I hate to remove the master cylinder first, if it could be something easier.

Tim:

well I don't know if you have power brakes or not but if you do you might want to look at the power booster ... they can go bad and actually hold the brake padel down abit keeping the brakes slightly applied

No I don't have power brakes. I just rebuilt the stock system for now, seemed to stop the car fine until this problem started.

Thanks for the reply though,

Tim

What kind of proportioning valve do you have? Is it adjustable? Also if the rear brakes are locked up or sticking, start with cracking the bleeder screw at the master for the rear brakes...If it is still locked up..move down the line till you get to the wheel. More than likey the master is no good.

Thanks, I don't have a proportioning valve, system is all still stock, but I will try your process of elimination idea. That does seem to be the best way to confirm the bad master cylinder, before removing it.

Thanks again,
Tim

Look inside your master cylinder. There should be 2 small holes in the bottom of the reservoir. 1 is the supply to the piston and the other allows the brake fluid to bleed back into the reservoir when you take your foot off the brakes. If they get restricted they can keep your brakes locked up.

Sounds like the pushrod is too long, not letting the piston return fully. If that happens, the return passage won't be opened, causing pressure to be retained in the lines. Some kits have deeper rubbers than original, causing that problem. Is there an adjusting system on the rod? I haven't worked on old Mopar brakes in decades, but most cylinders have some sort of adjustment.

Thanks to both of you for the tips, this is my first time back on the site since new years eve. I will check the master tomorrow to make sure the return hole is free or the cups are returning far enough.

Thanks again,
Tim

Let us know how it comes out.