67 master cylinder

[Jek9016]

My restored 67 has power brakes with an aftermarket (Bendix?) booster, drum rear disc front.  I replaced the leaking master cylinder (several times) with a replacement unit that is for front disc brakes.  However, the brakes work, but drive like there is no power assist. The power brakes worked perfect with the old master cylinder, so I have no reason to suspect the booster is failing.   I also have a proportioning valve.

Anyone have an idea how to fix this???

thx

[z28z11]

Assuming the booster is working correctly, look at the end of the old master and determine the depth of the seat for the actuator rod (the piston end) - there are two different lengths, depending on the application/year of the setup ('69's had a shorter rod). If that matches correctly, start chasing the booster, check valve and vacuum source.

My $0.02 -

Regards,
Steve

[JKZ27]

And, make sure you're not losing vacuum around where the master bolts to the booster.