New brakes suck

[bmfm64]

Hi All,
Quick run down on the truck is I rebuilt the entire truck and got it to 95% just before last summer. I spent the summer driving it but I did cautiously. The entire truck was disassembled and every nut/bolt was gone through. I did a 5.3/4l60e swap and added a 12 bolt posi to it. The truck is a 70 SWB on a custom suspension. I also ran new brake hard lines front and rear and added stainless steel flex lines through out.

Now for what I'm here about- The brakes suck. I used the CPP front brake setup as well as their 12 bolt, bolt on rear disc swap. For the booster, I used a 7 inch dual diaphragm chrome guy off ebay. I had a ebay special master cylinder/prop valve but have since swapped it out to a Wilwood universal M/C with a 1" bore. Seen here- https://www.summitracing.com/parts/WIL-261-13269-P I have bench bled the master a couple times, and both regular foot and power bled the entire system a few times as well. No leaks in the system at all but I still have a soft pedal and can get the pedal to go to the floor. Any ideas?!?! I'm wondering if the bore size needs to be increased possibly?

I'll try to add some pictures but am pretty rusty on forum picture posting.

[bmfm64]

Here's a pic of the truck- hopefully it uploads.

[geezer#99]

Did you change the pedal ratio?
Was it a manual brake (no booster) truck originally?

[bmfm64]

Originally Posted by geezer#99

Did you change the pedal ratio?
Was it a manual brake (no booster) truck originally?

It had power brakes before, the new booster/master have different mounting plates though. I had to drill a different hole in the pedal so the rod could attach. Instead of the Z bar setup the old booster had, this one goes straight into the booster.

[geezer#99]

You’ll need to measure it then.
You need 4.5 to 1 pedal ratio for power brakes.

[bmfm64]

Originally Posted by geezer#99

You’ll need to measure it then.
You need 4.5 to 1 pedal ratio for power brakes.

What do I measure? pedal travel? Sorry this part of brakes is new to me. Thanks for taking the time to help.

[Andy4639]

I had factory disc brakes on my 71 with 11" booster. I to found a deal on a 9" booster chrome. I hated it, it never did feel right. I went back to the 11" booster and now have my pedal feel back and the truck stops fine.

[geezer#99]

Originally Posted by bmfm64

What do I measure? pedal travel? Sorry this part of brakes is new to me. Thanks for taking the time to help.

Measure from the top of your pedal where it swivels on the bracket to the bottom of the pedal.
Also measure the top down to where you have the pushrod hole.
Now divide the long measurement by the short measurement.

For example if your pedal is 18 inches long and the measurement to your rod hole is 4 inches, you divide 18 by 4 which equals 4.5.
That’s your ratio of 4.5 to 1.

[bmfm64]

Originally Posted by geezer#99

Measure from the top of your pedal where it swivels on the bracket to the bottom of the pedal.
Also measure the top down to where you have the pushrod hole.
Now divide the long measurement by the short measurement.

For example if your pedal is 18 inches long and the measurement to your rod hole is 4 inches, you divide 18 by 4 which equals 4.5.
That’s your ratio of 4.5 to 1.

Awesome, thank you! I'll check it out when I get home.

[davepl]

If it's going to the floor then you're either compressing air (most likely) or leaking fluid past a piston (unlikely).

Don't get distracted by assist or bore sizes or pedal ratios yet. All of that stuff is secondary to the fact that the pedal is going to the floor, which can't happen in a sealed system no matter how wrong or right those ratios are.

[toolboxchev]

Originally Posted by davepl

If it's going to the floor then you're either compressing air (most likely) or leaking fluid past a piston (unlikely).

Don't get distracted by assist or bore sizes or pedal ratios yet. All of that stuff is secondary to the fact that the pedal is going to the floor, which can't happen in a sealed system no matter how wrong or right those ratios are.

That would be an option as to why its doing what its doing. If a master goes bad and the vac from the booster sucks the fluid past the seals you will never see the fluid sucked into the booster.

[HO455]

Originally Posted by davepl

If it's going to the floor then you're either compressing air (most likely) or leaking fluid past a piston (unlikely).

Don't get distracted by assist or bore sizes or pedal ratios yet. All of that stuff is secondary to the fact that the pedal is going to the floor, which can't happen in a sealed system no matter how wrong or right those ratios are.

Dead on from davepl. Bore size and ratio issues show up as hard pedal with weak brakes or as touchy brakes that are hard to control.

[Zeroman]

I have an entirely new system as well, and could not get the brakes bled to save my life. I probably went through 2 gallons of fluid over a three week period trying to get them bled.

I know what you guys are going to say, but I ended up taking the truck to Brake Check.

I had to wait until "the old guy" came into work because all of the younger mechanics had no clue.

It was pretty reasonable...they only charged me $75, but they had to gravity bleed the system for about 1 hour. They did this by having all of the bleeders open simultaneously, and continuously pouring fluid in the master cylinder.

When they got fluid without bubbles they closed the bleeders and pressure bled the system the old fashioned way without any vacuum, or forced bleeding.

In all it took about 2 hours. At times they had two to three guys working on my truck. I think they came out on the raw end of the deal money wise.

[Kennuck]

Just throwing it out there but are your bleeders at the top of the calipers. You'll never get all the air out if they are installed on the wrong side with the bleeders on the bottom.

[bmfm64]

Originally Posted by Kennuck

Just throwing it out there but are your bleeders at the top of the calipers. You'll never get all the air out if they are installed on the wrong side with the bleeders on the bottom.

I forgot to add this tid bit- Yes I made sure caliper are installed correctly with the bleeders in the up position.

[Mike C]

Don't the power setups usually have an 1 1/8" bore master as well? Something also to consider.

[sprint_9]

How are you bleeding the brakes? You need 1 person to pump the brakes and hold the pedal and 1 to bleed the caliper. Ive found vacuum bleeders to only be a good start the process.

[bmfm64]

Originally Posted by sprint_9

How are you bleeding the brakes? You need 1 person to pump the brakes and hold the pedal and 1 to bleed the caliper. Ive found vacuum bleeders to only be a good start the process.

I’ve done it both ways. No difference.

[Bigdav160]

Originally Posted by Mike C

Don't the power setups usually have an 1 1/8" bore master as well? Something also to consider.

This is true. Manual brakes typically use a 1" bore. This gives more hydraulic advantage with more pedal travel as a trade off. The original booster bracket has a small amount of lever ratio also.

I suspect the OP has a variety of things going on. Small booster, wrong master and pedal ratio problems

[HO455]

Is the master cylinder the highest component in the system? Do all the lines have a downwards slant away from the master cylinder (no loops)? If gravity bleeding doesn't help then I would be suspicious of the master cylinder. It wouldn't be the first brand new master cylinder I have seen not work properly. (It took three on my Javelin to get a good one) I am assuming you have checked every tubing connection for leaks. Use a dry paper towel to check for leaks as a small leak will be very evident on a clean dry paper towel.

[RichardJ]

Did you check the booster Pin length for either MC?

[aerotest]

Regarding brake bleeding: Motive power bleeder. Try it and never go back. Pedal mashing only works to emulsify the air in the system temporarily.

[ZEKE68]

Last time I worked on my brakes after I had bleed them for a while, I ended up pulling the calipers off of the disc and pushed the pucks to the bottom like when you are changing pads. That pushes the fluid back to the master cylinder and it seemed to make a difference. You have to watch and not overflow the master, taking some fluid out as needed. Then refill and push the pedal after reinstalling the calipers to refill. Sucks bleeding brakes by yourself which is how I usually have to do it.

[bmfm64]

To answer a few of the questions-
Yes the master is the highest point, no loops in the lines but yes the lines do have a couple spots where they go back up after having a downward slope- Possible there is getting stuck in the lower part?
Yes I've checked the pin length and am good there as well.
I've changed the master cylinder to twice, every time bench bleeding the cylinder and then installing. Two different manufacturers as well- both have yielded the same results.

[Trackman101]

Does this motor have a cam? How much vacuum does it have?