Brake Help

[the74bronco]

I am having a heck on a time getting my brakes to work and would appreciate any assistance. I have a 1974 with discs on the front and drums on the rear. The brake have never worked that well, so I rebuilt rear brakes and installed t-bird calipers and all new brake lines on the front and replaced my master cylinder. I also installed a Wilwood adjustable proportioning valve. I bench bled the master cylinder and I had a ton of leaks from all the fittings initially. I have tighten and reseated all the line and now I have no more visible leaks. I have bleed and bleed till I am blue in the face (over three big bottles of fluid) still cannot get any pedal pressure. Thinking there might be air getting into the system, but I would imagine I would see fluid leaking? Any ideas?

 

[Broncomt]

Make sure calipers are installed correctly. It is very easy to get wrong. Some are marked left and right. The bleeder must point up to bleed all the air out.

 

[the74bronco]

Just verified that the bleeders on the front calipers are up. Thanks for the tip.

 

[Apogee]

I would recommend doing a plugged-port bench bleed first. Once you've bleed the MC and confirmed it hydraulically locks as it should, then add the rear brake circuit and bleed out the rear brakes fully until you have a good pedal. Next add the front brake circuit and bleed. This should minimize the number of variables you're playing with at any given time.

Also, make sure the adjustable proportioning valve is set for max pressure, as that should make bleeding slightly easier/quicker.

 

[the74bronco]

I would recommend doing a plugged-port bench bleed first. Once you've bleed the MC and confirmed it hydraulically locks as it should, then add the rear brake circuit and bleed out the rear brakes fully until you have a good pedal. Next add the front brake circuit and bleed. This should minimize the number of variables you're playing with at any given time.

Also, make sure the adjustable proportioning valve is set for max pressure, as that should make bleeding slightly easier/quicker.

Thanks I will try and re-bench bleed and see how that goes.

 

[the74bronco]

https://www.flickr.com/photos/148552658@N02/shares/Q50EY8

Here are some pictures of the system.

 

[Rustytruck]

All of those loops in your brake lines make it tough to bleed without a pressure bleeder. Air gets trapped in the loop and doesn't get pushed out in a normal peddle stroke before you release the peddle and the bubble goes back up to the loop. I had better luck with vacuum bleeding. I then built my own pressure pot and bleeding was a breeze.

http://www.speedwaymotors.com/the-toolbox/pressure-brake-bleeding/28686

http://www.speedwaymotors.com/Motiv...ke-Bleeder-Square-Master-Cylinders,33861.html

 

[the74bronco]

All of those loops in your brake lines make it tough to bleed without a pressure bleeder. Air gets trapped in the loop and doesn't get pushed out in a normal peddle stroke before you release the peddle and the bubble goes back up to the loop. I had better luck with vacuum bleeding. I then built my own pressure pot and bleeding was a breeze.

http://www.speedwaymotors.com/the-toolbox/pressure-brake-bleeding/28686

http://www.speedwaymotors.com/Motiv...ke-Bleeder-Square-Master-Cylinders,33861.html

That is good to know. I do have a small harbor freight vacuum bleeder I have been using along with the old school two person method. I put the loops in the lines between the proportioning valve and the frame lines to allow a little flex if needed. I plan on re-bleeding the master tonight and see what that does and then I will look at the loops.

 

[the74bronco]

Ok, So I bench bled the master (Plugged port method) and it held pressure great. I also adjusted my rear brakes till my shoes were just barely dragging and then bled the brakes again (with my vacuum). There still is a lot of pedal travel and I can push the pedal to the floor. I will try and bleed them again tomorrow with the two person method to see if that helps. Any chance I need a larger bore master cylinder for the T-bird calipers?

 

[Apogee]

Ok, So I bench bled the master (Plugged port method) and it held pressure great. I also adjusted my rear brakes till my shoes were just barely dragging and then bled the brakes again (with my vacuum). There still is a lot of pedal travel and I can push the pedal to the floor. I will try and bleed them again tomorrow with the two person method to see if that helps. Any chance I need a larger bore master cylinder for the T-bird calipers?

When you convert from the standard EB/BB/F150 calipers to the T-bird calipers, you're increasing the piston area by approximately 20%. If you want to keep your pedal travel and effort the same as before, then you would need to increase the bore size by ~20%, which is roughly the difference between a 1" and 1.125" bore MC.

If you currently have 5 inches of pedal travel (arbitrarily), then that would become 4 inches with the larger bore MC. That's not going to do a lot with respect to getting your pedal off the floor, so I suspect you may still have air in the front or rear brakes, either of which would result in a low(er) pedal.

 

[DirtDonk]

All of those loops in your brake lines make it tough to bleed without a pressure bleeder...

This. Even though you did a clean job of making up the tubing, I would seriously consider going back to just the minimum number of curves and bends needed, with no high-spots.

I put the loops in the lines between the proportioning valve and the frame lines to allow a little flex if needed.

Good thinking, but also over-thinking it. The flex does not happen there between one part of the frame and the other just a few inches apart. That's why the factory does not use looped hard lines, or flex lines in this area. Where you see the flex lines (factory EB) or looped/coiled hard lines (GM and many full-size Fords) is between the body and frame. In other words, between the master cylinder and the proportioning valve.

And speaking of the lines, is your rear line going to the prop valve and rear brakes? Or am I just seeing it wrong?
The "primary" reservoir/piston of the master cylinder (rearmost, closest to the pedal) always goes to the front brakes. At least on our Fords. The secondary (frontmost, or closest to the grille) always feeds to the back brakes.

I also adjusted my rear brakes till my shoes were just barely dragging and then bled the brakes again (with my vacuum). There still is a lot of pedal travel and I can push the pedal to the floor.

On almost every set of drums I've ever adjusted, I got the best results from a surprisingly high amount of drag. To determine if there is a problem or not I always adjust them up tight enough to hear scraping the entire 360 degrees of rotation. If there's a big difference in the high spots to the low, I might consider turning the shoes to match the drums.
If the difference is minimal the brakes can drag quite a bit and not overheat when driving. You should still be able to turn things by hand, but you're going to feel a fair amount of drag.
If the tire and wheel are mounted, you should be able to turn it with minimal effort, but it should not keep spinning for more than a quarter turn after you let it go. Mine usually stop almost instantly, or in less than 1/8 turn.

Any chance I need a larger bore master cylinder for the T-bird calipers?

Yes. Definitely. But like Apogee said already, I don't think it's causing your pedal to go to the floor either. You can feel the difference in pedal travel, but it sounds like you have more going on.
And you're going to find that with a 1 1/8" bore master, your pedal effort to get the truck to stop is going to be pretty high. That size is considered by most to be about the maximum bore diameter for manual brakes.
A 1" or even a 7/8" bore is better for good effort with manual brakes. But then you run up against the bigger caliper dilemma.
When you replaced your master recently, did you by chance verify the piston size before you installed it? Either by measuring or looking for some markings somewhere? I'd hate to see you fighting this just to find out the wrong one was in the box. But the fact that it was doing this before you changed is a good sign for once!

Good luck.

Paul

 

[the74bronco]

When you convert from the standard EB/BB/F150 calipers to the T-bird calipers, you're increasing the piston area by approximately 20%. If you want to keep your pedal travel and effort the same as before, then you would need to increase the bore size by ~20%, which is roughly the difference between a 1" and 1.125" bore MC.

If you currently have 5 inches of pedal travel (arbitrarily), then that would become 4 inches with the larger bore MC. That's not going to do a lot with respect to getting your pedal off the floor, so I suspect you may still have air in the front or rear brakes, either of which would result in a low(er) pedal.

Good to know. I will work on getting the air out and firming up the pedal and then I will later address the master cylinder size.

 

[the74bronco]

This. Even though you did a clean job of making up the tubing, I would seriously consider going back to just the minimum number of curves and bends needed, with no high-spots.

I will pull out the loops and keep it down hill the whole way.


Good thinking, but also over-thinking it. The flex does not happen there between one part of the frame and the other just a few inches apart. That's why the factory does not use looped hard lines, or flex lines in this area. Where you see the flex lines (factory EB) or looped/coiled hard lines (GM and many full-size Fords) is between the body and frame. In other words, between the master cylinder and the proportioning valve.

Thanks for the info!

And speaking of the lines, is your rear line going to the prop valve and rear brakes? Or am I just seeing it wrong?
The "primary" reservoir/piston of the master cylinder (rearmost, closest to the pedal) always goes to the front brakes. At least on our Fords. The secondary (frontmost, or closest to the grille) always feeds to the back brakes.

I have the large reservoir of the master going to the front brake and the smaller reservoir going to the rear brakes. I have everything bypassing the factory h block. I also have the proportioning valve wide open (no restriction) for now.

On almost every set of drums I've ever adjusted, I got the best results from a surprisingly high amount of drag. To determine if there is a problem or not I always adjust them up tight enough to hear scraping the entire 360 degrees of rotation. If there's a big difference in the high spots to the low, I might consider turning the shoes to match the drums.
If the difference is minimal the brakes can drag quite a bit and not overheat when driving. You should still be able to turn things by hand, but you're going to feel a fair amount of drag.
If the tire and wheel are mounted, you should be able to turn it with minimal effort, but it should not keep spinning for more than a quarter turn after you let it go. Mine usually stop almost instantly, or in less than 1/8.

I can hear a real light drag throughout a 360, but I know it doesn't stop in 1/4-1/8 of a turn. I will crank them up a bit more.

Yes. Definitely. But like Apogee said already, I don't think it's causing your pedal to go to the floor either. You can feel the difference in pedal travel, but it sounds like you have more going on.
And you're going to find that with a 1 1/8" bore master, your pedal effort to get the truck to stop is going to be pretty high. That size is considered by most to be about the maximum bore diameter for manual brakes.
A 1" or even a 7/8" bore is better for good effort with manual brakes. But then you run up against the bigger caliper dilemma.
When you replaced your master recently, did you by chance verify the piston size before you installed it? Either by measuring or looking for some markings somewhere? I'd hate to see you fighting this just to find out the wrong one was in the box. But the fact that it was doing this before you changed is a good sign for once!

Good luck.

Paul

I did not verify the bore size. I will look for a part number. If all else fails I will pull it off and measure the bore. Thanks for all your Help!

 

[the74bronco]

I pulled all the loops out of the lines, adjusted the rear brakes up so the wheel only spins 1/8 of a turn, and bled everything several times. The pedal still goes to the floor on the first pump (with some resistance). The second pump has ok pressure and doesn't hit the floor. Third pump feels pretty good. This tells me I still have air to chase out? Anything else I could be forgetting? I didn't pull the master to verify the bore. I think when it comes to that point I will replace it with a 1 1/8" bore.

 

[Rustytruck]

Are you still running the stock drum brake safety switch ( H Block) or the more modern pressure differential switch ( proportion valve)

There are different brake bleeding procedures for each of those valves. The H-Block should be centered and locked in place while you bleed the brakes and the proportion valve should have a valve pulled out and locked in place or a valve pushed in and locked in place.

Before you bleed again make sure to tap on the calipers to release any trapped bubbles so they float up to the top of the calipers.

https://www.google.com/search?q=for...yHZnBHvWo99O_1wmoSoSCY2MBghvMtt-EZ_1RzzZajzeQ

 

[the74bronco]

Are you still running the stock drum brake safety switch ( H Block) or the more modern pressure differential switch ( proportion valve)

There are different brake bleeding procedures for each of those valves. The H-Block should be centered and locked in place while you bleed the brakes and the proportion valve should have a valve pulled out and locked in place or a valve pushed in and locked in place.

Before you bleed again make sure to tap on the calipers to release any trapped bubbles so they float up to the top of the calipers.

https://www.google.com/search?q=for...yHZnBHvWo99O_1wmoSoSCY2MBghvMtt-EZ_1RzzZajzeQ

I have bypassed the factory H-block and am using an aftermarket Wilwood adjustable proportioning valve. I have in wide open right now, so there should be no restriction. I haven't tried the tapping yet. I will give that a try.

 

[the74bronco]

Ok, not sure were to go from here. I have bled and bled and still can't get any decent pressure on the first pump of the brakes. I have two thoughts:

1. Air is somehow constantly getting into the system. (I would assume I would have fluid leak, but I don't have any)

2. My master cylinder bore size is just too small to move enough fluid to get decent pedal feel. (Maybe why the second and third pump feel ok?)

Thinking about buying a new larger bore master cylinder, but I don't want to just add more variables... Ideas?

 

[72Sport]

Wheel cyl are made to seal with pressure on the inside. Use a minimum amount of vacuum. The more vacuum you use the greater chance you will suck air past the cups or seals. The seals are made to self energize. The higher the pressure on the inside of the cylinder the tighter the seals are held against the bore of the cylinder. Vacuum on the inside of the cylinder weakens the seal.

I am not familiar with the Harbor Freight vacuum bleeder. If the fluid is slowly moving toward the caliper you have enough vacuum. In this case more vacuum IS NOT BETTER. Good luck.

 

[the74bronco]

Wheel cyl are made to seal with pressure on the inside. Use a minimum amount of vacuum. The more vacuum you use the greater chance you will suck air past the cups or seals. The seals are made to self energize. The higher the pressure on the inside of the cylinder the tighter the seals are held against the bore of the cylinder. Vacuum on the inside of the cylinder weakens the seal.

I am not familiar with the Harbor Freight vacuum bleeder. If the fluid is slowly moving toward the caliper you have enough vacuum. In this case more vacuum IS NOT BETTER. Good luck.

Thanks for the tip. I have used it several times, but also have been using the two person method as well. I put teflon tape around the bleeder threads and have been using low pressure. I think I have used over a gallon of brake fluid by now.....

 

[72Sport]

Teflon tape is a bad idea. Small pieces can end up in bad places. It may work fine for a while but if a piece breaks off you could be in trouble. The same thing is true for fuel systems. My Son used some teflon tape on the carburetor fitting. My engine quit about a month later when a piece of teflon ended up between the needle and seat and the engine flooded.

Bleeder screws have a taper lock seal nothing is needed to seal them. If they leak replace them. If you lose your brakes because of the teflon you will be very unhappy.