Front Brakes Don't Work - Need Help!

[Dens240]

I am struggling to get sufficient brake pressure at the front calipers on a 72 240Z. 

I have a rebuilt booster, new master cylinder, new (rebuilt) calipers at both wheels. The rear drum brakes work. After much work and brake bleeding, I have fluid at both front calipers. However, when the brake pedal is pressed, the cylinder pistons don't move at all. I would suspect that I have a leak somewhere that doesn't allow sufficient pressure to engage the brakes but I don't see any fluid leaking anywhere in the system.

Any ideas/thoughts welcome.

[SteveJ]

Post photos of the front calipers showing the bleed screws.

[Dens240]

Photos of each caliper below:

[zKars]

Did you check the clearance between the end of the brake rod sticking out of the booster and the inside of the master where it will touch? I’m guessing there is way too big of a gap. Should be 1/32 or 1/16 max.

Also check and make sure the reaction disk is in place. 

[Dens240]

I did check the length of the booster rod vs the depth to the piston. I adjusted the booster rod length so that they are within a few 1/10s of an inch of each other. I haven't checked the reaction disk in the booster. I assume that I need to open the booster to check that? When the MC is removed and I depress the brake pedal, the booster rod extends, although I haven't attempted to measure the force. The booster was rebuilt by Prior Brake Products in Mesquite, TX.

[zKars]

Assuming you mean a few hundredths….  0.0625 is a 1/16. 

The reaction disks just keep biting people in the a z z as when you pull the rod forward or out to adjust the tip length, the disk often follows and drops down into the body of the booster, then you put the rod back in and don’t notice the extra 1/4”.

Other than that, make sure you bleed the master as well

 

[Zed Head]

50 minutes ago, Dens240 said:

However, when the brake pedal is pressed, the cylinder pistons don't move at all.

Does the pedal go to the floor or does it stay high and firm?  If it goes to the floor can it be pumped up?

The pistons don't move far at all under normal operation  Are you saying the the wheels still turn with the pedal down?  Not really clear...

[Dens240]

Yes - the wheels still turn with the pedal down. I can get the pedal to go pretty much to the floor. I sometimes seems like it will pump up but doesn't always stay "pumped"

[Dens240]

Another data point - When I push the brake pedal to the floor, the brake pressure differential warning light comes on. Also, sometimes there is an audible "poof" that allows the pedal to go lower. Not sure if that's a pressure relief of some sort in the booster?

[zKars]

If you hear air sounds from the booster, but the booster is just rebuilt, right? then not likely the diaphragm is leaking, then maybe the check valve in the line to the booster is leaking.

 

[Dens240]

I'll look at the check valve

[Dens240]

FYI - The check valve is also new