Brakes help.

[71LS5Formula]

Hello to all. Need some with my brakes. The setup. 71 Firebird. 79-81 9inch brake booster for 4wheel disc. 02 Fbody master cylinder (1'' Bore) I had Wilwood master on before and did not like it, but still had the same problem. Wilwood proportioning valve. Front brakes are Baer 4 piston calipers 13 inch rotors. 02 fbody rear brakes. The problem I am running into is with the car off I can build pressure and it feels solid like it should. As soon as I start the car I loose all that pressure. Any help will be appreciated.

Ben

[71LS5Formula]

Need to add that once the pressure is built with the engine off and I go to start the car with my foot on the pedal with pressure built; the pedal will pretty much push to the floor.

[79 Camaro]

When using a vacuum booster typically the pedal will go down a bit when you start it but should not go down to the floor. Air in the system? What happens when you take your foot off the and drive down the road? Brake pedal and stops normally?

[71LS5Formula]

When using a vacuum booster typically the pedal will go down a bit when you start it but should not go down to the floor. Air in the system? What happens when you take your foot off the and drive down the road? Brake pedal and stops normally?

Pedal goes to the floor. I can't get anymore air out of the brake calipers. When i bled the master cylinder i got the air out of there. I let off the gas in neutral and it coast down the road as it should. When driving down the road and hit the brakes; it can be unnerving because it seems like i have no brakes, but it does slow gradually. I can get the rears to lock but after just about all peed l brake pedal travel.

[MonzaRacer]

Most brake systems with power brakes use 1 1/16. I put 1" corvette master on my 66 Caprice w manual brakes.
Also you have to make sure the push rod isn't bottomed out but it can't have much play in the piston of the mater cylinder either.

[71LS5Formula]

I need to clarify something about losing pressure on my brakes. It is the hydraulic pressure that I lose while the engine is running. I am running a 1'' bore master cylinder as recommended by baer's website. Any thoughts or suggestions?

[stab6902]

Sounds like air in the system to me. The vacuum booster amplifies your leg force by a factor 3+, so it makes sense that your pedal travel is longer at a given pedal force with the vehicle running. I wouldn't deviate from Baer's recommended master cylinder size. Did you bench bleed the master cylinder, and then use the "two man" bleed method once it was back on the car, starting with the caliper furthest from the master cylinder?

Also, your rear brakes should never lock before your fronts. Once your brake system is functional, you should adjust your proportioning valve so the fronts lock just before the rears on a dry, high grip surface.

[71LS5Formula]

I did bleed the master. I'll run through bleeding at the calipers again and see what happens. I'll also contact Baer and see what they say tomorrow(jan19).

[$Mike70Z-28]

i had the same problem with the 1" bore peddle will go close to the floor . i changed to the 1 1/16 master peddle went back to normal