Brakes for an '48 F4

Hivolt5.0

Hivolt5.0

Senior Member
I have question on brake lines. I've been restoring a '48 F4 over the past few years and I'm finally at the stage of installing new brake lines. It is still running the factory drum brakes fore and aft. It has brand new wheel cylinders and flex lines. I'm converting it to power brakes with a dual chamber master cyliner. The new master cylinder is from a '70s Chevy big truck and it has a 1 1/4 bore just like the original single chamber master cylinder. The factory brake line size is 1/4". I have some 10 lb residual valves and I have a willwood proportining valve as well.

Here are my issues. The input/output of both the residual valves and the proportioning valve are 3/16. The master has one outlet that is 9/16 (goes to the small bowl) and one outlet that is 1/2 (goes to the larger bowl).

Here is my question, would it be ok to have a mixture of 3/16 and 1/4 brake lines?

My thought is to come out of the master cylinder and convert to 3/16 line - go through the residual valves - and then into the proportioning valve. From the proportioning valve I would convert to 1/4 line and run that to the wheel cylinders.

Or should I just run 3/16 line all the way to the wheel cylinders and then convert to 1/4?

I would imagine a 1 ton truck would need lots of fluid volumn and of course I want it to be safe.

Your thoughts?
 
This is a very interesting post as I am also restoring an F4 but a '49. I have all my brakes done but haven't made any of the brake lines yet.
Do you need the residual valves with a drum brake system? I don't know but, I seem to remember reading somewhere that you only needed them with disc brakes. I would try to find some adapters and stay with 1/4" lines throughout. Those big wheel cylinders may not get enough fluid thru the 3/16" lines. Also, just a thought, since you are not changing the brakes just the master cylinder, do you need a proportioning valve?
I have considered changing to a dual master cylinder on my truck but, I wasn't sure what to use. I have my master cylinder sleeved with stainless and rebuilt and a rebuilt Hydrovac Booster ready to install. Are you installing the new master cylinder in the original position?
 
Hivolt5.0 said:
I have question on brake lines. I've been restoring a '48 F4 over the past few years and I'm finally at the stage of installing new brake lines. It is still running the factory drum brakes fore and aft. It has brand new wheel cylinders and flex lines. I'm converting it to power brakes with a dual chamber master cyliner. The new master cylinder is from a '70s Chevy big truck and it has a 1 1/4 bore just like the original single chamber master cylinder. The factory brake line size is 1/4". I have some 10 lb residual valves and I have a willwood proportining valve as well.

Check the Chevy master for internal residuals located behind the tube seats. Most/all drum brake masters had them until the mid '70s, because the drum brakes required them.

Here are my issues. The input/output of both the residual valves and the proportioning valve are 3/16. The master has one outlet that is 9/16 (goes to the small bowl) and one outlet that is 1/2 (goes to the larger bowl).

All of the stand alone aftermarket residuals and adjustable proportioning valves I've seen have 1/8" pipe inlets/outlets, that allow adapters for different line sizes (3/16"/ 1/4" etc) and styles (SAE/AN).

Here is my question, would it be ok to have a mixture of 3/16 and 1/4 brake lines? Your thoughts?
Click to expand...

I would use 1/4" lines, out of the master cylinder and into closely located residuals (if none are in the master), and through a rear adjustable proportioning valve, all the way to all wheel cylinders.

Big trucks, like your F-4, usually have more powerful and larger brakes on the rear, just the opposite of cars and light trucks. (I think your rear wheel cylinders are 1/8" larger than the fronts, as well as wider shoes). The reason is a large truck GVRW will be twice or more the curb weight when fully loaded, and most of it will be on the rear axle. Now, if you intend to drive the truck loaded, or as designed, there would be no need for a prop valve. BUT, if you use it like a "bare bones" street rod, the rear brakes will probably be too aggressive, and an adjustable prop valve will tame them.

 One other oddity, if the rear brakes ARE larger, your Chevy master's larger chamber (and related outlet, regardless of thread size) should go to the rears, and not the fronts, because your rear brakes are dominant, just the opposite of cars/light trucks. :)


 
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49fordv8f4 said:
.....Do you need the residual valves with a drum brake system? I don't know but, I seem to remember reading somewhere that you only needed them with disc brakes....
Click to expand...

Modern disc brakes never needed or used residuals, as master cylinders were firewall-mounted by the time discs arrived. The exceptions are rare '50s Chrysler and Kinmont discs that used powerful return springs.
Installing disc brakes with floor mounted masters may require 2 lb aftermarket residuals to prevent fluid syphoning.
 
I agree with V8 Bob. With a floor/chassis mounted master cylinder, you do not have the "head" of pressure from the fluid up in the chamber like a firewall mounted unit. Therefore, a residual valve is usually required. 2# on the front discs and 10# for the rear drums is a good starting point. For drum/drum, may need 10# for both ends.
 
Thank you for all of the responses. Let me post some pictures of my setup and this may help clarify things. Sorry I didn't post pictures earlier.
 
Sorry for the picture delay. So here's what I have:
- A Master Cylinder from a big Chevy truck (I can't find the part number but will continue to look. It has a 1 1/4 bore just like the originial MC)
- A Willwood adjustable proportioning valve
- 10 lb residual valves for both front and rear
- A your typical dual diaphram vacuum booster

A fellow Ford Barn'er cut the bracket out that allowed me to adapt the three bolt MC to the four bolt vacuum booster and I bought a length of rod from Speedway to connect the factory brake pedal to the booster.

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It all fits nicely though I did have to angle the mounting bracket when I welded it together to allow the booster to clear the frame.

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I made the bracket to mount the proportioning valve beside the MC out of 1/4 inch round rod.

Reading through all of your posts, I agree that running the 1/4 inch brake lines is preferable as I have read/heard that the brakes on these big trucks need lots of volumn. Since the rear wheel cylinders are larger than the front ones, I assume the larger bowl on the MC should feed the rear brakes?

So back to my original question, If I came out of the MC with 1/4 lines and adapted them down 3/16 to feed into the proportioning valve and immediately from the prop valve into the residual valves and then adapt back up to 1/4 lines. Do you think this would be ok and not cause any major issues?

I know there will be a pressure difference going from the 3/16 to 1/4, but if I keep that 3/16 to a small area (the proportioning valve right in to the residual valves) seems like it be ok. The residual valves would help hold the brake line pressure right?
 
Ok, I think I've figured out what I'm gonna do with these pesky brake lines. See the above pictures of the MC and proportioning valve as reference.

I'm going to use 3/16 line from the MC into the residual valves and from the residual valves into the proportioning valve. While the MC is a couple of inches higher than the wheel cylinders I don't want to take the chance of the brake fluid draining from the wheel cylinders back into the MC. In the picture above, the inputs for the Prop Valve are at the bottom and there is one output on top and two on the ends.

For the front brakes I'm going to continue with 3/16 line and then convert it to 1/4 line at the flex line.

For the rear brakes I'm going to convert it to 1/4 line exiting the proportioning valve and it will stay 1/4 line all the way to the rear wheel cylinders. Since the prop valve's purpose is to adjust the front/rear brake bias, I should be able to use it to adjust the brakes (front to rear) so that they work properly.

This way I only have three line conversion points. I rear a lot of different posts on brake line size here on the HAMB and on the FordBarn and read one post where Cheverolet (I believe) used two different size brake lines on some of their cars, 3/16 going to the front and 1/4 going to rear. If I have any issues once it is all together, the way I'm running the line should make it "easy" to adjust as needed.

I appreciate all of your input; never thought running brake line would be so challenging!
 
During this saga of trying to determine what to do with the brake lines I emailed Wilwood brake's help line and I wanted to share their response with you all. I asked them the same questions that asked of you all.

"Thank you for your interest in Wilwood Disc Brakes. We do recommend using the proportioning valve to help adjust the rear brake balance on a street application.

The 10 pound residual valve is also necessary on drum brakes, as the mechanical springs of the drum system can push and make the fluid travel back towards the master cylinder.

It will not be a problem to mix 3/16 and ¼ inch brake line, although for drum brakes, most of your line should be ¼ inch.

Regards,
Wilwood Disc Brakes"
 
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