Technical Brake system help, please

Hey y’all. Here I am with more brake troubles…but on a different car.

Here is the setup: 1950 Ford, discs in front drums in rear. Hanging pedal with a Corvette-style master cylinder and power brake booster. The system has no proportioning valve, nor residual pressure valve. It’s just the wheel cylinders in rear, calipers up front, and the master cylinder. That’s it.

This has been working fine for 18 years but now that I have had the transmission rebuilt and am ready to put some miles on it, here’s what’s going on.

When the car sits in the shop overnight, the brakes are loose and it rolls just fine; however, drive it down the road for 10 miles or so, stopping at red lights and such (normal in-town driving) and you begin to notice that when you let off the gas pedal, the car is already applying the brakes. OR they are not letting off. When I got it back home today, I pulled it in the shop and jacked up a front tire and it would not roll by hand. I jacked up a back tire and it was dragging more than the adjustment says it should.

The car has never done this, until now.

Since there are not many components to this system, it appears the problem is in the master cylinder, but I am not sure how.

Anyone had this experience on their car, and what did you do to fix it?

 

I just had this happen last year on a OT ‘71 car. My front rubber brake lines were clogged with crap 99.9%. Brakes would apply when I hit the pedal, but pressure would hold in the line, so brakes would stay applied. It would eventually lose pressure as the car sat again. Replace the rubber lines.
It could be pistons in the calipers sticking, but usually I would have a real hard pedal when that happens.

 

Check pedal pushrod adjustment

 

Sounds like your 18 year old brake hoses swelled up and are not letting the fluid back to the master cylinder reservoir. Time to change them.

 

I would say hoses, usually one side goes. I have never seen both front hoses bad at the same time. BUT.. it should do it cold or warmed up if a hose is bad. I would back the adjustment at the back of the master, keep track of how many turns you give it.

 

My vote is front brake hoses as well.

 

Fellas, this is exactly why I come in here- experience. In my 50-odd years of messing with cars, I have never had a brake hose go bad, so it wasn’t even on my radar screen.

A hose change is now on the ‘things to do’ list. Thank you all.

Also, for those who suggested the pedal pushrod adjustment, let me ask…is it possible for that adjustment to change? I mean it is a threaded arrangement that would have to unscrew itself, right? Somehow, I cannot see that being able to occur…but thank you.

 

Could be a plugged return pinhole in the master cylinder too. Have seen that several times.

Dave

 

When I first put my roadster together, the brake pedal free travel felt great, until I drove it for a few miles. Then there was NO free travel and brakes were dragging. I backed the pushrod adjustment off a bit, bingo! Great again. Put a couple hundred miles on it, then it seemed to be to tight again. I thought I simply hadn't tightened the jamb nut down, but everything was tight, I adjusted it again and it's been fine for almost 5,000 miles. I don't know if it was because everything was new, but the pushrod adjustment is very sensitive. Did it move? Did I simply not tighten it? Did the brake shoes wear in and everything get settled? I don't know, but it's easy to try that too.

 

When the problem occurs after a bit of driving, get out and place your hand on the hub area of all four wheels. They should all feel warm from the brakes working properly, but not too hot to touch. If you have one wheel or more that's hot enough that you don't want to keep your hand on them, that may be an indication of the brakes dragging on that wheel. It may help you narrow down where to look for the problem.

You could do the same thing with a hand held IR temperature gun pointed at the drums and rotors.

When you rebuilt the transmission did you have to disturb the parking brake cables or their adjustment? Do the parking brakes set and release properly?

 

Before you do anything else reach down with your hand and feel the pedal movement with your fingers. You should feel that little bit of slack in the pedal before it starts to push on the piston in the master cylinder.

If the car has been together that long it probably is good maintenance to change the hoses and flush the brake system with new fluid anyhow.

 

Not disagreeing with any of the suggestions to replace the hoses, probably a good idea no matter what. The question in my mind is about all the hoses having the same problem at the same time..........front and rear. Usually you expect them to fail at different times. Could the master cylinder be sticking slightly due to some sludge buildup? How long did the car sit while the trans was being repaired? Might just try adding some fluid and bleeding all the brakes to flush the system a little.

 

I’ve had my pedal return spring shift or lose some tension and need replaced/ adjusted and do the same thing.

 

Before you start taking stuff apart, I would drive the car until the brakes are dragging like you said.
Then while hot, loosen up the master cylinder and see if the drag goes away.
If it does go away, then the push rod is too long when the booster expands from heat and is partially applying.

Bill

 

I like it, easy and quick to do, rules out the push rod length. Loosen it, put a shim of sorts behind the ears, take it for a ride and see what happens. Start with a 1/16", then go an 1/8" if something binds them up again.

 

After checking push rod clearance, ask yourself: Does our master cylinder have a residual pressure valve built in? Lots of them do. Maybe it does and it is causing the brake drag. Don't know how or why it would become a new problem though.

 

Makes sense, but how could I tell if it does?

 

OK, so this morning I decided to do a bit of investigation. I did not take the car out driving. It seemed to me that just pushing the brake pedal creates the issue, so I jacked up the front end to get the tires off the ground and spun the wheels. Both front tires rolled smoothly and for about 1.5 rotations.
I got in the car and pretended I was driving and making stops along the route by mashing the brake pedal.
Then I got out and rolled the front tires again. They were noticeably harder to rotate and as hard as I could spin them, they only free-rolled a quarter of a turn. Quite stiffer than before.
I also went and loosened the master cylinder mounting nuts (per a suggestion from member “jutpassinthru”), but this did not loosen the wheels back up. So I guess the pushrod adjustment is okay.
So, it’s tightening up on the front wheels- not so much on the rear…but it is not just on one wheel…seems to be both of them. What are the odds that both front hoses would go bad at the same time?
I am close to thinking the problem is inside the master cylinder.
The brake pedal itself is not in a bind. It is returning to rest position as it always has.
What are the thoughts now?

 

check valve in master?

 

I'm agreeing with ''dwollam'' I'd check the bypass port/s in the master cylinder for a blockage. Not allowing the fluid to return causing the brakes to stick on.

 

When my front rubber brake lines clogged up, both sides did. The drivers side slightly more than the passenger, but both would prevent me from turning the wheel.

 

I'm not a fan of the "corvette style" masters that everyone gets a woody from. BUT... if it got you this far, it is compatible with your system. So put another one on, from a reliable source, not an eBay $19.99 special from who knows where.

I have an OT Belair with a corvette style master on it, which is working fine.

 

It would be located behind the outlet fitting, just a simple spring/disk arrangement usually. To be sure you'd need to remove that, then bleed the brakes again. Or, if we had the actual part number of the master maybe the info is available from the part's source?

 

The more I consider what everyone has said, I am right at removing the master cylinder to check it out and see if I can get a rebuild kit for it, OR simply replacing it entirely, AND replacing both front hoses.
Surely, this would get the system flowing again.
Anyone see any flaws in my logic?.

 

Making this to hard. First thing to do is drive it and then get it to happen. Jack the front and then the rear. See if it's just one wheel or both rear or all or even just the rear. Once you know what is hanging you can address parts that are just for that part of the system. Otherwise your just guessing.

 

Time goes by.
18 years is a long time.

It may be time for a brake hose change and a disassemble and clean.
Sometimes it’s not one culprit, it’s several. Many small issues can manifest and one eventually breaks the camel’s back.
To get it back right means correcting them all.

Brake fluid does not move much and it’s hydroscopic or it draws water.
Wheel cylinder pistons rust in place, Caliper pistons do the same. A sign that there is corrosion in the system is sticky pistons or cylinders.

I advise the you break the system down, clean and inspect everything.

Unrelated..........
I wonder about proper brake bias without a proportioning valve for the rear?

 

18 year old stuff... pitch it. If I pick up an old car with unknowns, I replace a lot of parts just so I sleep better at night.

 

I would go the next step by opening a bleed port on a caliper and see if it releases the caliper(s) while you have your car up in the air and they are dragging. If they don't release, you have sticky pistons in the calipers, which I have experienced. If they release, it's the master cylinder....
My thoughts...
Good luck

 

Not hydroscopic, Hygroscopic.
If you can watch the master with the lid off, when you push the pedal do you get a quick little spurt of fluid up? If so that tells you the vent port is clear. If not clean it out.

 

Or bad flex lines to the calipers.