Brake pedal softness. Pushrod length, Speed Bleeders

Im doing the 77 tbird disc brake swap on my 64 Galaxie.

Im using a 72 mustang disc/drum master and the prop valve from the bird. The master has a 1 inch bore which is the same as the dual master i had in there before the swap.

I bench bled the M.C and then put it in the car, i double checked the air using the pedal a few times. I then bled a 4 corners using speed bleeders. The pedal was spongy after bleeding, i bled em again. Pedal still the same . . . . . . . . . . . . . . . . . . i then gravity bled the lines [ i made up new lines for the front so i thought that gravity bleeding would fix it.

I checked out the pushrod with the boot removed, as soon as the pedal goes down the pushrod moves the piston, so i dont think thats the problem.

The thing that is confusing me is this :

As the pedal goes in, i feel a "step", the first half of the pedal feels soft and then the last half of the movement the pedal gets firm, im thinking there is air in the front reservoir and i need to bleed the master again, but i know i bench bled the ****er right. . . . . . . . .. . or the pushrod thing might be ****in me up.

Any other ideas or reasons this could be happening ?

Oh yeah - i have done a search, many of em

Shorten your pushrod a few thousandths in order for there to be a tiny bit of play so the piston is allowed to run all the way back home.

Crack BOTH front lines at the M/C, and have a helper just press the brake pedal to the floor, not fast not slow, and hold it until you close them. DO this twice and you should have the air out of the M/C.

If you still have the initial soft spot, re-bleed the rear brakes, and since I am unfamiliar with your speed bleeder, do it the old fashioned way... OR the way I do it.
It leaves full pedal travel and you do not need to pump it.

1: Crack all 4 brake lines.

2: Press brake pedal to the floor and leave it there.

3: Close all 4 lines before moving pedal.

4: repeat until confident that air is gone.

5: Shouldn't take that long, and if done properly you will have full pedal immediately, as long as the brakes are adjusted properly, and sitting real close to the drum.

My breaks act exactly the same way since I up-graded to a duel master with vacuum assist.

I have an adjustable push rod. The breaks do not have air in them, verified with many different ways to make sure they are bleed.

The first half of the pedel does nothing, then the second half, it grabs very hard at any speed, and pumping makes no differance. The firmness is always at the same place. The breaks work fine at any speed, just that first 1/2 pedel travle that scares me a bit.

I would set the adjustable rod a lot deeper into the master cyclinder, and the problem goes away... but then the break light stays on all the time. My guess a wrong component ..maybe the MC??

Im wondering if it has anything to do with the Proportioning valve.

Another guy told me it could mean a bad master cylinder. Im gonna swap it out to make sure andd also look into the adjustable pushrod.

There is no reason why i shouldn't be able to have a firm pedal, especially with disc brakes

My bet is on the piston inside the M.C being bad

L

I have gotton bad "rebuilt" master cylinders before. That may be a good thing to check. Where did you folks buy the adjustable push rod? I needed one a while back, couldn;t find anyone selling them.

Mustangs Unlimited has adjustable pushrods....

I've had several bad MC's out of the box. That could be the culprit.

I have super firm brakes and they are 4 wheel drum.

A few thoughts that should point you in the right direction.
Put a clamp or vice-grip on both front hoses and the rear hose to block the flow of fluid. The pedal should be hard as a rock with VERY little travel. If the problem persists with the lines blocked something is wrong at the master cylinder or power booster. (Make sure there is no movement of the power booster or master cylinder.) If the pedal is rock hard, your problem is at the wheels. First remove the clamp at the rear axle and try the pedal again. Should have a little more movement than before but still not a lot. Then proceed to the front wheels and remove your clamps one at a time. When your problem shows back up you will know where to look. After doing a conversion I suggest looking at the following:
Caliper mounting. Minimal twisting of the hoses, and most important calipers on the correct sides. The bleeder screw must be at the top of the caliper and not the bottom or you will never get the air out. Next look at the travel of the piston in the caliper whille a helper applies the brakes. You should barely be able to see the piston move at all. If it is moving more than a 1/32 of an inch, that is too much and again you will not get a good pedal. If the piston travel is excessive, try to determine why and correct the problem. One more thing is i would try to put the pushrod adjustment back to it's original postion. The factory settings are usually where they need to be and adjusting the pushrod to compensate for a problem elsewhere is not a good idea. Good luck!!!

Damn dude thats some good info right there

Thanks !!!

I MUST OBJECT!

If you have Brand new lines then that's ok, but if you have front brake flex lines and the rear flex lines that are more than a couple years old DO NOT DO IT!

The rubber and the fibergalss reinforcement fibers in those flex lines are very succeptable to cracking and splitting from the weather and age, and if you squeeze them you will compromise their ability to handle the pressures associated with the brake system.

If you wanna replace them after figuring this out then feel free (I even would recommend it )
But please don't compromise your safety that way.


Gary (*FE*)