What happened to my power brakes?

[Mickey]

I have a power brake booster on my 65 Belvedere. Before I replaced the leaking master cylinder the car would stop effortlessly and quickly. After I replaced the master cylinder with a new one, I have no power brake assist. The pedal is hard to depress and I have to pump the brakes and stand on the pedal to slow it down and stop it. The hoses on the booster are intact and not leaking. What happened?

 

[yella71]

do you have vacuum to the booster ? If so maybe the leaking master killed the booster.

 

[The Rebel]

Things off the top of my head.

No vacuum
Correct master cylinder
Were the breaks bled properly
Check break fluid level
Adjust breaks

 

[davek]

did you bleed the lines? Pass back first ,dr back then pass front side dr side. Rod from booster set right in Mc?

 

[twecomm]

Did you bleed the new MC before installing ??

 

[YY1]

Perhaps silly, but did you remove the temporary locking tab sometimes used to keep the piston in the cylinder before installation?

...or check for part of the hard rubber ring used to keep the actuator shaft in the bore?

 

[Mickey]

Perhaps silly, but did you remove the temporary locking tab sometimes used to keep the piston in the cylinder before installation?

...or check for part of the hard rubber ring used to keep the actuator shaft in the bore?

No, I never thought of that. I got it out of the box and put it in. I was planning on taking it off again to inspect it. I’m also gonna hook up a vacuum gauge and check the motor.

 

[1 Wild R/T]

Was the new master cylinder bore the same size as the old master cylinder?

 

[Geoff 2]

Make sure the check valve [ plugs into booster & hose goes onto valve ] is working.

 

[twecomm]

And.... bleed the MC before you install it on the booster.

 

[Ron H]

Yep as posted above, a bench-bleed of the MC before install or can be done in the car, but lots to be careful about if doing it that way. If there's air trapped in the MC, bleeding the brakes all day won't remove it from the master. Also as posted, if the old master leaked brake fluid into the booster time for a new one.