1970 brake issue. Bad booster or?

[All Stock93]

Still trying to figure out what's going on with the brakes.
Got the car out of storage last spring. Did new wheel cylinders and shoes in the rear. Also replaced the rear flex line.
Replaced front flex lines
Have good clean fluid supply to all four corners
Bled breaks, all air seemed to be eliminated from system. Great pedal feel with the car off. Start the car, pedal goes to the floor. Brake light comes on
Pulled Master Cylinder, found it to be leaking. Replaced Master cylinder, bench bled and installed. Bled brakes, great pedal with car off. Start the car and pedal goes to the floor. Brake light comes on
Bench bled master again, this time on the car. Pumped for a while, I'm confident the air is out of the master
After reconnecting brake lines to master I have great pedal feel. Start the car and pedal goes way past the spec travel distance but doesn't feel like it hit the floor, I didn't try to force it to the floor. No brake light.
With the car running, the brakes are bad. Pedal is soft, will not pump up and give firm feel when car is running, but will pump up enough to get the brake light to go out. Stop pumping, all pressure is lost and pedal will go to floor
With car off, brakes feel great


The check valve is good.
I set the master cylinder push rod free play to .010 with a feeler gauge, not be eye lol

Anyone got any tips?
Still air in the system or a bad booster?

 

[Noobz347]

I do not know your braking system [at all] but the question comes to mind:

Is the booster connected at the correct port to the correct vacuum source?


That pedal should [not move at all] when you crank the engine.

My alternate thought is that the relief valve on the booster may have failed.


If nothing else, here's a bump for you... and this: @horse sence

 

[All Stock93]

Disc front, drum rear. Bendix Booster.
I have taken all the slack out of the rear shoes
The booster is still connected to the original vacuum source and I did verify the check valve is working
When pumping the brakes, I can hear and feel an air leak between the master cylinder and the booster

Brakes were working last fall, just not well. Replaced rear brakes, front and rear flex lines and master cylinder only. Now I have no brakes LOL

 

[horse sence]

Good chance the diaphragm in the booster has a hole . Is the proportion valve centered ? If not one end or the other may be shut off ,if the valve tripped you will not get good brakes until you recenter it and blead the brakes again.

 

[horse sence]

You need one of these centering tools for the proportioning valve to do a propper brake bleed ,make sure to order the correct size. Unscrew the brake trip switch in the proportioning valve ,it the white two wire switch ,use a light and you will see the notch in the internal piston ,someone will have to push the pedal to center it . If the notch is to the front open a rear bleeder and step on the pedal slowly ,it will move back ,if it is to the back loosen a front bleeder and step on the pedal ,it can be done by one person but way easier with two .
Once the valve is centered and the tool screwed in place then bleed the brakes. When finished unscrew the tool and replace the white trip switch

 

[All Stock93]

Thank you for the help.

 

[Mcmahst]

You should test the booster with a hand held vacuum pump. Good luck.

 

[Nostalgia]

How did this end?

 

[All Stock93]

Car is back together and on the road
The Master Cylinder failed and leaked brake fluid into the booster. Had the brake booster rebuilt by Power Brake Booster Exchange (formally Booster Dewey) They did a great job. Took about two weeks from the time I shipped it out until I got it back. Their communication was great for the entire process. Would recommend
Had the Master rebuilt by Apple Hydraulics. This experience was ok, I guess?
Took them three weeks to get the job done, when I got it back, it leaked during bench bleeding. Had to send it back again, waited another 2+ weeks. Warranty jobs receive no priority and emails go unanswered. Phone calls are 50-50 that someone will answer and if you get voicemail, forget it, they won't be calling back

Once everything was back together, the brakes still sucked. Adjusted the rod out until the brakes started to drag then shortened it by about 1 turn and they worked great.

 

[9T02R]

Thanks for the update. Liked your performance report on the vendors. "adjusted the rod out" would be the master cylinder push rod? Brian

 

[All Stock93]

Yes, master cyl push rod.
It took me quite a few tries to finally get good pedal feel