Technical Brake issues on a 42 ford

Hey everyone.

I am a new member here. I was a Ford dealership technician for 12 years. I have built a few old muscle cars. I am having an issue I can't seem to resolve. I just inherited my father's 1942 ford 1/2 ton pickup. He bought it already done. I have found a lot of silly mistakes on it. It seems to be a lot of quality parts ***embled poorly by someone that didn't care. It has been chopped and lowered. The driveline has been modernized. It has newer stock style disc brakes in the front with ssbc disc brakes in the rear. It has manual disc brakes with an under floor master cylinder. Here is the problem.

The pedal went to the floor the first time I stepped on it. I found that the calipers were mounted upside down on the front. I switched them out and bled them. The pedal did not improve much if at all. I replaced all of the hoses with braided steel. Still no major improvement. I replaced the under floor master cylinder with one designed for 4 wheel manual disc brakes. I also added an adjustable proportioning valve and 2 lb. residual pressure valves on both lines.

The pedal is better. But, it still hits the floor after sitting a short time. It pumps up and holds after 4 or 5 strokes of the pedal and does not sink. The pedal will feel that way for a few minutes of sitting. The brake performance is a little weak when I drive it around the block. The brakes will stop the truck, but will not lock up during a panic stop. I have pulled all four calipers and see no signs of a leak. Every brake line is new and tight. The hoses are new....I bench bled the new master and proportioning valve. I seems like there is still air in the system. I can't seem to get all of the air out. Any advice would be greatly appreciated. This is the first under vehicle master cylinder I have ever worked on.

Thank you

 

1/4" or 3/16 brake line?

 

I'm not a brake expert but, does it require proportioning valves?

 

3/16" brake lines

 

Without the proportioning valve, the back wheels would lock too easily. The truck is very light in the rear.

 

Well that was my only go to lol, i look at the dynamics. Stupid question but i have to ask because everybody would ask me, rpv's aren't backward?

 

And what is the m/c from?

 

I got willwood valves. They are labled pretty well. I did install them correctly as per those labels. They could be labeled incorrectly. I don't see willwood making that mistake. The master cylinder is from Leeds brakes. I called them and told them what I needed. It is a ford 2 chamber manual disc master cylinder. I believe it is a 1 inch bore. I have the proportioning valve wide open so the rear brakes are at 100% for testing.

 

Man I'm at a loss, sounds like you've touched all the bases. The only thing i do different is run 1/4" to the rear end if it's a long run.

 

That might be a future step.

 

Sounds very much like there is still air in the system. Verify the master cylinder piston is retracting fully when the brake pedal is released. There needs to be some free play in the pedal. If there is insufficient free play the master can't get a full cycle to pressurize the system properly and all the air can't be removed.

 

Make sure the pedal can fully stroke the master cylinder before the pedal bottoms on the floor, and that the pedal does not interfere or bind with the floor while full stroking. You'll never get a good bleed if the master cannot fully stroke.
The best way to bleed is using a pressure bladder while slowly full stroking the pedal, but simple pedal bleeding will get the job done, just takes longer.
When you have some pedal and can build pressure, clean all connections and fittings with denatured or isopropyl alcohol and "stand" on the pedal to leak check. Any weeps or leaks have to be repaired before a good bleed can be accomplished.
What type fluid are you using?

 

Thanks Bob, now i feel dirty lol

 

I am using DOT 3 fluid. The master cylinder bottoms out about an inch above the floor. I adjusted the pedal so it is. Fully releasing as well. I had my son lift the pedal off the floor as high as it would go and set the rod about a 1/4 inch shorter then that. It seems to be getting full travel. Next time I try bleeding it, i will double chect that it is fully up before the next stroke.

 

I have about 1/4 inch of free play at the top of the pedal. The brakes feel like they are clear from dragging.

 

Do your brake lines go through a frame bulkhead? Sometimes those p*** through bulkhead brake fittings are difficult to get the air out of.

 

Are you're bleeders at the very top of the caliper, you might have to remove the caliper and block and bleed them with the valve straight up

 

The pedal has to have it's own return spring, and with the pedal fully returned to it's rest, needs only minimum (1/32"-1/16") free play on the push rod to the primary master cylinder piston. Excess free play just results in wasted pedal travel.

 

No, the lines are uninterrupted from the proportioning valve to the rear and from the metering block to the front.

 

The pedal has its own return spring as part of the pedal ***embly.

 

The factory style front calipers are on factory style spindles and are clocked at the top of the calipers. The rear ssbc calipers are close to the top. I did remove them and block them to bleed them just in case. There was no difference. I think the air is trapped in one of the main lines in a spot where it sweeps up to go over the frame.

 

You may need to vacuum bleed to get the trapped air out of that area.

 

You might be right. I was trying to get it done without buying another vacuum pump.

 

Are you bleeding these by yourself, or with a helper? How?

I normally work alone, and have found it helpful to rig up a remote video link using my phone on a modified microphone stand to see what’s happening at the caliper, while inside the car pushing the brake pedal with my foot and watching it on my iPad. I use a check valve at the bleeder.

A friend swears by vacuum bleeding. I have the tools to do it, but have never had any luck with this method.

Pressure bleeding seems like a good idea. I’d like to try that some day.

Gravity bleed may work for you, especially if you’re starting with empty tubes.

Then there’s the reverse bleed, using a large syringe to force fluid from the caliper to the master. I haven’t tried that one.

This all ***umes that you have the pedal to m/c set up right. Good ratio, enough pedal travel, right pushrod clearance.




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I have been bleeding them with my son helping me. I am actually looking into reverse bleeders right now. I hear they work well for tough to bleed systems. Since my master cylinder is level if not slightly lower than my calipers, air pockets are a big issue. Gravity bleeding will not work. I've heard that the self bleeding bleeder screws work well. I've also heard people have gotten stuck with bad self bleeders out of the box.

 

Where are you rpv's located? Close to the mc?

 

Both are within 4 inches from the master cylinder. The rear line rpv is a little closer.

 

That's aggravating the **** out of me. And you're getting good fluid from the bleeders? Solid fluid, no air?

 

Solid fluid. I'm going to double check every connection and try a reverse bleeder on it. If that doesn't do it, I don't know what will.

 

Seriously what's the chance it's the master? I know it's new but that doesn't mean anything. If you can pump 4-5 times and build a pedal, the rpv's should keep it there. With the master at or below the calipers, gravity will pull the fluid back toward the master. The rpv's prevent that, or at least they should. So maybe they are defective? Hell I don't know lol. You're giving me a headache