1939 Ford Brake adjustment?

mjdunn

mjdunn

Senior Member
The brakes are dragging on my 1939 Ford. When I decelerate to stop I can feel that the brakes are partially engaged and instead of rolling it just stops. The pedal has no play in it and the brake lights are stuck on. After it cools down it works properly. Does it need a brake adjustment and how do I do it?
 
Just like the other guy, your master cylinder push rod needs to be shortened slightly (the rod is adjustable?) or else something is stopping the peddle from returning properly (spring missing?)
The master cylinder piston is being stopped from fully returning, and so still holding pressure in the line. The rod should have about 1/16th of an inch clearance.
This is the most likely cause.
 
With the brake lights stuck on that is a first sign that you have something wrong with the master cylinder. If you have had this car for a long time or just got it the first inspection is the brake system. Since most old cars are only occasionally driven the master cylinder is the first sign of brake trouble as the moisture in the air is drawn to brake fluid. This causes the parts of the braking system to oxidize and perform poorly or not at all if there is just the slightest of leakage.. This doesnt happen as easily on your daily driver as the brakes are constantly used and the moisture is some what evaporated by the heat in the system or the airflow. Setting idle is a problem.

Next and this goes to everyone, If you own an old car you need a service manual, not the owners manual, a service manual like Motors or Chilton that covers the repair and maintenace of your car or a copy of the service bulletins if available. These books are availble online or you can purchase them at the swap meet for 20-30$ or less. "Motors Manual" will give step by step instructions in some cases of how to perform maintenace tasks and is a define requisite no matter how mechanically inclined you are.

Now back to the problem, the brakes drag. First check to see that the pedal is fully returning and has a return spring attached and the floor mat or carpet isn't bunched up top prevent its return. Second, check the master cylinder condition by pulling back on the dust boot to see that the mastercylinder bore has not begun to oxidize and prevent the piston from fully returning to rest. Replace the boot after checking. Third, check the free play in the pedal push rod, if it's tight to the pedal and the master cylinder piston there is a problem. Check that for now and report back.
 
Since the car has fully cooled down there is 1 -1/4" play in the pedal and it springs back just like it is supposed to. I am presently at a car show so my ability to work on it is limited.
I will see how it works driving home (20 miles) and I can check it out more at home. Thanks guys for your help.
 
Just as a precaution, during the drive, it wouldn't hurt to gently lift the pedal with the tip of your toe to make sure it is on the up stop.

If you have all brakes dragging, it would be the master cylinder. If just the rears, it could be a failed/failing hose. If just one of the fronts was sticking, it would be the hose on that side.

Mart.
 
Did not make it home. I had to stop 6 miles from home. I will let it cool down and then see if I can drive it the 6 miles home. My wife was following me so I am home with a cool drink.
 
Just crack a bleeder to release pressure. Try and drive using gears and emergency brake and only use the brakes when necessary. Stop after and release pressure as soon as you feel them dragging.

Here's a idea (only for a short distance). If you can't adjust the pushrod, back out the three bolts that hold the master cylinder in place about two turns each. The cylinder will be loose, but ok for a short drive home. Make sure the brakes will actually work before trying this.

It might get you home, but ideally you need to shorten the push rod to achieve the same goal properly. I'm just trying to think of what you could do at the side of the road.

Another idea: use your car to tow your wifes car home. Let her do the braking for you. you can still put your brakes on in an emergency, you might just have to release the pressure afterwards.

And pick a quiet time to drive it, not in heavy traffic.

Good luck,

Mart.
 
Like the other guys, I think it has to do with either the master cylinder or the flex line - because of the brake lights. However, if all that fails, then try backing off on the parking brake cable adjustment yoke. That was my fix.

One time I had my shoes relined and I could hardly even get the rear drums back on. Then they would drag like heck. The calipers told me the lining thickness was right. Helpful guys here offered various advice: grind the new lining, turn the drums, shorten the horizontal link between each shoe, replace wheel cylinders, drive it 60mph for an hour to wear in the shoes - when it stops smoking it will be fine, get drunk and go inside the house and forget about it for a while..... Well, I tried it all.

When I got out of AA rehab, an old buddy of mine came over and said, "Loosen up on the parking brake cable." Says I, "I don't think that's the problem; since it wasn't a problem before the shoes were relined." (The shoes were relined not because of wear, but because of leaking wheel cylinders.) He said, "OK. I'm going to crawl under and back off on the cable myself then. Then try to install the drums. EUREKA! He was absolutely correct. Thank heavens I did not do some of the other well meaning recomendations. Take your time. Don't do anything drastic. Two heads are better than one. Explore each recomendation carefully and logically......

Mike
 
Well,I got the car back home. When I got to the car,where I left it, the brakes were operating normally. I pushed the pedal one time to check it and then drove the car the 6 miles home without useing the brake pedal. In the garage, I put it in neutral to see if I could push it by hand. I push it a few inches and it would stop, like the brakes were engaged. I checked the pedal and it had very little play. So that means that on the drive home the brakes tighten up without me using the brakes at all. Since the brakes work properly when they are cold and sieze up when they are hot from driving, I would think that would mean that the problem is in the brake drum area and not the master cylinder. Would yo'all agree? My therory is that the brake shoes are too close to the drums and they are creating heat, expanding and pressing against the brake drum. Then they cool down and work OK.
 
As you use the brakes, the cylinders get warm. This causes a slight expansion in the fluid in the system. If the system were sealed this expansion would build up the pressure in the system and make the brakes drag. This drag would increase the heat and pressure and put the brakes on harder until the cycle repeats untl the brakes are locked.

There is a port in the master cylinder called the recuperation port. The port allows the excess fluid in the brake lines to flow (more seep than flow) back to the master cylinder reservoir.

If the push rod is too long, it does not allow the piston to travel back past the recuperation port, meaning it cannot allow fluid expansion in the system. The port may be blocked, that would cause the same problem.

The very first part of the travel of the piston crosses the recuperation port, effectively sealing the system and allowing bthe pressure build up to apply the brakes. too much travel before the port is closed caused excessive lost motion in the system and a low pedal. This is the opposite of the problem you have.

I have used washers to shim a cylinder before now to make sure the port is open but travel to close it is minimised.

Mart.
 
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MJDunn, When you ask a question in a situation like this, most of us mechanic types will give you the most likely fault. There can often be many possibilities.
Dick, Mart, and myself have tried to explain what we think the problem might be.
We are all on the same page, by the way.
The MOST likely cause is at the master cylinder. You are johnny on the spot, and like Dick said, I think it's about time you did some research, and learned a bit about how the master cylinder works.
As it happens, what you did by driving home was quite dangerous. You could have boiled your brakes, leaving you with no brakes at all. That apart from cooking everything up.
You never said anything about recent brake repairs and so I think we three are still on the right track. Go and check that the piston in the master cylinder is fully returning to the rest position. Make sure the return spring is returning the pedal to its rest position, and that there is about a 1/16" movement of the rod where it goes into the piston, before it starts to push the piston. If you have a lot more, the piston is probably sticking down.
If it is, then have someone recon it.
 
I had this problem at one time with my F1 and fixed it by adjusting the master cylinder rod to a shorter length. I had been overly enthusiastic in trying to get the best top pedal response. With much experimenting it turned out, if I remember correctly, that only about a half turn adjustment made the difference. I suggest you back off the rod adjustment, even if it means you obviously then have too much play in the brake pedal, then go for a drive and see if the problem remains.
 
All of you have been very helpful. I do need to learn more about the brakes and I will get a Service Manual as soon as I can. As you can tell, I have had very little experience working on brakes. I have only had the car for three months, so I don't know about any possible recent brake work. I will check out all of the things you mentioned, starting with master cylinder. I will report back as I make progress.
 
MJDUNN, Good theory not using the brakes but you killed that trail by pushing on the brakes when you got back in the car. Even thought you did not use them, the initial trial hit on the brakes pressurized the system. Had you just got into the vehicle and driven it without touching the brakes your trial may have worked better. Second question how did you stop the car when you pulled in the driveway, thats another pump on the pedal.

Put your car up on jack stands so you can crawl under it and remove the dust boot off the master cylinder, if the pedal has free play then the master cyclinder push rod has to have free play, If there is an excessive amount of free play in the pedal push rod then check for crud around the master cylinder piston, looks like white oxide or is orange in color from rust. If that is present its a pretty good sign that there are problems with the master cylinder.

It's doubt full that the parking brake is on as the problem only exists after the vehicle is driven and if left to rest disappears.

You cant over heat fluid to cause it to expand as the system is not a closed system, all you will do is boil the liquid. The vent port in the cap prevents any internal pressure to build up in the system as well as the reserve area cavity in the master cylinder would allow for the silght expansion of fluid not direct it to a wheel cylinder.
 
To all you guys that helped me with advice. Well, I shortened the rod and it did not help. I have ordered a new master cylinder and will report back after I install it. Don't worry I have help installing it from someone that knows a lot more than I do. However, I am learning.
 
Can we assume that the piston is sticking in the bore? Otherwise what was the reasoning behind ordering a new one?
 
mjdunn said:
To all you guys that helped me with advice. Well, I shortened the rod and it did not help. I have ordered a new master cylinder and will report back after I install it. Don't worry I have help installing it from someone that knows a lot more than I do. However, I am learning.
Click to expand...

Learning is what we are all here for.
 
Bluebell said:
Can we assume that the piston is sticking in the bore? Otherwise what was the reasoning behind ordering a new one?
Click to expand...

When I did the test drive after shortening the rod I found that all four wheels were affected. From that I assumed that the source of the problem would be in the master cylinder. Besides that, you said "The MOST likely cause is at the master cylinder." and many others agreed.
 
Also the fact that the brake lights are coming on - point towards the MC - and hey it is not a bad thing to have a few $ invested in one of the most important parts of your car.

When you get your friend to help you fit it - ask him questions - pay attention - do the spannering - that way not only will you learn stuff that you yourself can pass on to others one day - but you will get that feeling of having' done' the brakes rather than having got them done.

Keep us posted - I have just rebuilt my hyd brakes and it does make quite a difference having that middle peddle doing what it is designed to do !
 
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