1940 ford brakes

[68HILLBILLY]

thought I would see if someone could help me with my brake problem. have a good original 40 fordor with factory brakes. car has newer wheel cylinders, lines, master cyl, etc. the last two times I drove the car the brakes were wanting to lock up . when I got back home today the pass rear drum was smoking and no wheels wouldn't turn by hand when I jacked up the car. after sitting for about 2 hrs car moved fine. pushed it by hand back and forth in the garage. brake pedal was very hard when wheels were stuck and loosened up to normal after sitting. this problem just came up after driving fairly regularly all summer. small vent hole in master cyl cap was blocked , I fixed that tonight. didn't have time to drive it after that. any ideas? or comments? thanks

[Andy]

There is a bleed hole in the master cylinder that lets fluid expand when it gets hot. If if is pluged, the brakes will get tighter by themselves. You might put a wire down and clean it out but I would put a kit in the M/C and get it clean. The other possibility is the pushrod is miss adjusted and is holding the piston so for in that the port is blocked.

[CWPASADENA]

Sounds like the brakes (hydraulic Pressure) is not releasing.

Check the free play in the master cylinder push rod. The push rod should have a little end play when the brake pedal is all the way up (Foot of of the pedal). If no free play, adjust the pushrod so you have about 1/16 in. or so end play in the rod.

If the brakes still will not release and you have end play in the push rod, crack a bleader screw open. A little fluid may come out. Close it up and now see if the brakes are released. If so, there may be a problem in the Master Cylinder where the internal bleed hole is not being uncovered when the piston is all the way back in the returned position or it is plugged up.

Try these two things first, these are the most likely.

let us know what you find out,

Chris

[CWPASADENA]

Originally Posted by Andy

There is a bleed hole in the master cylinder that lets fluid expand when it gets hot. If if is pluged, the brakes will get tighter by themselves. You might put a wire down and clean it out but I would put a kit in the M/C and get it clean. The other possibility is the pushrod is miss adjusted and is holding the piston so for in that the port is blocked.

Sorry, I did not meen to step on your post, you can type faster then I can.

Chris

[Hamtown Al]

Duh, fellas, how about the rubber hoses failing and holding pressure? It HAS happened before. I'd replace rubber hose to the rearend first and see if that cured it. JMHO. Al

[68HILLBILLY]

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THANKS FOR the replies , won't get to work on it again till later this week.

[lenmissy]

I had the same problem .I changed the master cylinder .

[Flathead Fever]

Since you said all the wheels were locked up when you jacked the car up, the problem is probably not a hose, the hoses would only effect individual front wheels or both rear wheels but not all the wheels at once. The problem is going to be in the master cylinder. Like others have said, the master cylinder needs to return all the way back until the piston hits the snap ring. When you first step on the brakes the piston in the master cylinder moves forward covering a small hole in the bottom of the reservoir. Once it is past this hole the piston can start increasing the hydraulic pressure in the system. When the pedal is released the piston returns and uncovers the little hole so the fluid can return to the reservoir. If it does not uncover the hole the brakes will stay locked up. You need to have a little free play in the brake pedal linkage for this to happen. Remove the rubber boot from the master cylinder and see if the piston is returning all the way back and is seated against the snap ring. There should be no fluid leaking out the rear of the master cylinder. Check that you have a slight amount of play between the rod and the piston. If you do not have any play check that the rod is adjusted properly, the linkage is not binding up, grease the pedal bushings and check the pedal return spring. If this is all Ok you have something plugging the return port. This is probably rust laying in the bottom of the reservoir.

I went to a Bendix brake seminar and the instructor said that if people would change their brake fluid every two-years master cylinders and wheel cylinders would virtually last forever. Brake fluid is hydroscopic, meaning it attracts and adsorbs water, up to 2% or 3% per year. Once this water is in the system it causes the cast iron wheel cylinders and master cylinder to rust which pits the cylinders causing fluid leaks, the rust particles are abrasive so they wear away at the rubber cups, also the rust plugs up the little fluid ports in the master cylinder.

Take the cap off your master cylinder Check, the master cylinder cap gasket, if it's bad it will allow moisture and oxygen into the system causing rust. What color if the fluid brown or red indicates moistre has gotton into the system. If the brake fluid is black this is an indication that the rubber cups are failing and the master cylinder should be rebuilt or replaced. Your problem could be caused by a small piece of a rubber cup that is plugging the return port. Remove all the fluid, wipe the crud out of the bottom of the reservoir. Make sure the little return port is open. Fill the reservoir up with fluid and apply the brakes several times, Remove the fluid again from the resevoir if its still rusty. Repeat this until the fluid is fairly clear. Fill it back up again and flush all the fluid out of the entire system starting with the right rear wheel, then the left rear, right front and finally left front.

Another problem with collectors cars is they sit for long periods of time, the worst thing you can do to a car. The master cylinder has a residual pressure check valve which always keeps a slight amount of pressure in the system. This keeps the rubber cups in the wheel cylinders pushed against the walls of the cylinders preventing brake fluid from leaking but it also prevents moisture from entering into the system. Moisture cannot enter the system if the pressure in the system is higher than the atmospheric pressure. If a vehicle sits for awhile that residual pressure will bleed off and allow moisture to enter into the system. Even if you do not drive your car you should stomp on the brake pedal once in awhile just to keep that residual pressure in the brake system.

[ajohn]

Everyone's advice is good.Here is another thought.I hope you have changed to silicone brake fluid.If not,count on brake trouble.A seldom driven car will give trouble with dot 3 fluid in a matter of time.I change ALL my cars that have hydraulic brakes to silicone fluid.It makes good sence and you will avoid future problems.

[68HILLBILLY]

thanks again for all the advice and pointers. I do have silicone fluid in the system already . yesterday I adjusted the master cyl. rod so it hads some play, this seemed to fix my problem . drove the car and had no problems with the brakes.

[Dee Jay]

Another thing I've encountered is if there is a rip or tear in the rubber boot on the master cyl,dirt and crud will accumulate and eventually build up to the point that it will not allow the piston to return all the way.If none of the components have been changed and the brakes were working, the length of the actuating rod should not need adjustment. If anything,due to wear,the freeplay should increase unless there is a build up of corrosion in thr piston socket.

[Hamtown Al]

GREAT! Glad to hear you're rolling again without problems. Good job.