Drum locking issue.

[James Romano]

Hi. I've been working with a problem that I can't seem to pin down. Last week I had an issue with my front brakes slowly locking up. It started as a slight groan and as I headed home, brakes were nearly locked to the point of being un-drivable.

I tore into the problem by backing off the pads, allowing time to cool and removing the drums. I replaced both wheel cylinders as both sides were locked. I also put in all new springs, greased up the pad/plate contact points and checked all the lines. I figured with replacing the front wheel cylinders, I'd be ok. The old ones were all rusty on the inside as I took them apart to investigate.

Since then I also sorted a leaking front left brake line and bled the fronts again.

Took the car out today with all the confidence in the world... nearly didn't make it home as the same issue reared it's head as soon as I put hard pressure on the brakes in traffic. Pulled over and let the car sit for a good half-hour. Drove it home... parked it in the garage as it was too late to do anything with it.

All new SS lines, new dual Master Cylinder, booster was rebuilt.. everything is new in the system accept the two rear wheel cylinders and the pads all around. They looked good. Wagner DOT3/4 fluid in the system.

Adjusted front brakes to spin with a little friction. Both front wheel bearings were torqued to tight to set the bearing, then backed off to zero and set to very minimal torque.

What the heck could be causing my fronts to lock-up like that? I didn't check the rears yet, but I will this week. The problem happens after I drive a little while, then go into any kind of stop-and-go situation... or hard braking. The brakes are not releasing pressure once it gets hot. Let it cool a while, and brakes are good.

Thanks in advance!

 

[Davea Lux]

Sounds like the travel rod for the master cylinder is set too long. Do your brakes start to engage as soon as you touch the brake pedal? You should have 5/8"-3/4" free play on the brake pedal. If you do not, the travel rod has an adjustment nut on the end of it. Remove the master cylinder and back off the adjustment in 1/2 turn increments until you get at least 5/8" free play.

Dave

 

[CBODY67]

I'm presuming your car has a power drum system? Generally, "pads" are for disc brakes, "brake shoes" are for drum brakes. BTAIM

The apparent self-application after driving for a while is interesting. Usually, when that happens, it's due to contaminated brake fluid causing the rubber in the master cylinder top to expand and put more pressure on the brake fluid, as if the brakes were being applied, and stopping the car. But with your DOT fluid, that shouldn't be the issue.

There should be no reason for the brake lines to be anywhere near hot engine exhaust manifolds, or similar, so heat-induced pressure shouldn't be it, either.

The booster's push rod for the master cylinder might be it. But once it was adjusted when it was new, with them usually not ever being adjusted afterward, or a rebuilder possibly not having any reason to alter their adjustment, it MIGHT be an issue, though.

From what I read, there is ONE thing that might be an issue, especially as you mention that after things cool down, it "drives" again. You mentioned the front brake adjustment having a slight drag. Of course, that's when the drums/linings are "cold", not warm, I suspect.

Possibly the most bullet-proof way to adjust drum brakes is with an Inside-Outside Brake Caliper. Set the caliper to the inside diameter of the drum, then adjust the shoes to match on their side of things. Install the brake drum, adjust the wheel bearings, and it should be done "to specs", with no drag. To me, it sure beats the old use of a thin screwdriver and brake spoon, as the wheel spins.

On the earlier disc brakes, the pads actually lightly rubbed the disc brake rotor. But on drum brakes, no lining contact until the brakes are applied. There used to be a general rule-of-thumb of adjusting the shoes/linings "up" enough to prevent the wheel from being able to spin it, then backing off the adjustment a certain amount of "teeth" on the adjuster wheel. End result was "no drag" by the brake shoes/linings on the drum. Which is why using the caliper can make things more consistent and quicker to do.

Once that initial adjustment is done, then do several stops in Reverse to let the automatic adjusters do their thing.

When you are driving and the brakes start to stop the car, can you manually pull upward on the brake pedal (with your foot) to make any difference in the brakes locking-down? Just curious.

Just some thoughts,
CBODY67

 

[Davea Lux]

If the travel rod is set too long to where the brakes are not fully releasing, as the fluid heats up it will apply more pressure.

Dave

 

[CBODY67]

Effectively as if the driver was "riding the brakes"?

 

[Davea Lux]

Effectively as if the driver was "riding the brakes"?

Either will eventually heat up the fluid, but when the driver stops riding the brakes, they should still release with a properly adjusted travel rod.

Dave

 

[413]

What year and model car? What type of system? Did you convert the system from or to anything different than original? When did this problem start.

 

[ceebuddy]

Brake hose swelling internally and now acting like a valve, not letting fluid back after applying brakes?

 

[James Romano]

Sorry... 65 Sport Fury

Still original drums. Converted to dual mc. All new lines front to back.

The travel rod is between the booster and MC? I was thinking there is too much fluid in my system as well. There is no "fill" line so how much room for expansion should be given. I remember back in the day that we filled these things till top?

 

[James Romano]

If the travel rod is set too long to where the brakes are not fully releasing, as the fluid heats up it will apply more pressure.

Dave

This is what it feels like. Feels as if the brakes are slowly being applied with no release until cooled off.

 

[CBODY67]

Correct, there is no "FULL" line, BUT probably about 1/4" below the top of the master cyl fluid reservoir sections would probably be fine. Considering the bad things that normal brake fluid does to paint, no desire to if to run over the top of the reservoir. With no "ADD" line, probably it can be a good deal "low", as long as the intake ports at the bottom of the cyl have a bit more fluid than each of the wheel cylinders and lines will need when the brakes are applied. Which should work for all drum-brake vehicles. Should be some pictures in an FSM, somewhere, too.

On vehicles where the master cyl is mounted at an angle, then it might be better to get more toward the top of the reservoir, but not run over, for general principles. Those applications will end up with less fluid in the reservoir(s) due to the tilt factor.

Enjoy!
CBODY67

 

[James Romano]

Ok. I'll remove some fluid, and take a look at that rod. I'll make some small adjustments to it and see where this goes. I'm also looking into an inside/outside caliper to have in my tool box.

I'll report back what the results are. Thanks!

 

[68 4spd Fury]

I'll throw this out there, as it happened with me, but never heard of it before. I re-did my system too, pedal on down, (didn't add power though). Replaced the master with a rebuild from NAPA. After a bit, had the same issue you described on the rear wheels, tuned out the piston in the master had broken between the two sections. I would say this points to the quality of the rebuild, the FSM shows the OEM piston as a two piece unit with the rear sliding into a bore on the front. This one, at least at first, was a one piece piston.

 

[James Romano]

I'm thinking it's the rod. I had a single bucket and now it's a dual. Not sure what the length is supposed to be for a dual, but I can tell by what's already mentioned, I didn't have any "buffer" in the pedal. I adjusted the rod and now I have some play before I feel the brake engage. I just have to take it out for a test drive

 

[Big_John]

The length of the rod is the same across the board. It's in the FSM.

What I think happens is people leave out the gasket that goes behind the MC and it effectively lengthens the rod. I had to play around with my Barracuda's rod to get it right... Obviously someone had been screwing with it.

But, just to make sure.. Get the brakes to lock up again and back the nuts off that hold the MC to the booster. If they release... There's the problem.

If they don't there's two other possibilities. I've seen where the hoses will collapse inside and act like a one way valve. That's usually after someone let the brake calipers hang on disc brake cars, and I assume you have new hoses, so I kind of doubt it is the problem. I have also seen the brakes

 

[James Romano]

I thinking it could very well be that I had too much fluid in the reservoir. Because the brakes released after I let it cool down tells me I failed to account for fluid expansion.

Just not used to these old cars..lol. I'm too used to everything being labelled and more obvious. You need knowledge to work on these old gals...which I gain one day at a time.

 

[swisherred]

Im curious about which master was installed...the dual drum master or dual disc master...as the disc master has different sized chambers for different pressures....wonder if this could be adding to things.

 

[James Romano]

Definitely a dual drum. I put the time in to research which type. I put in the type/style from 67 and up. I wanted the look of OEM and not a plastic or chrome aftermarket looking piece that obviously doesn't belong there. Going from single to dual is the safe option.

 

[78Brougham]

That sure is purdy!

 

[Davea Lux]

Im curious about which master was installed...the dual drum master or dual disc master...as the disc master has different sized chambers for different pressures....wonder if this could be adding to things.

This installation is the correct midland booster with a drum master cylinder, that is not an issue. Nice clean job, by the way.

Dave