power brakes. Pedal stiffer after driving ?

[Canadian1968]

I have 68 with factory bendix front disc. When I start the car the pedal is a bit soft, after driving for  few minutes the pedal get harder and much more responsive ? Any thoughts ?

[garner7555]

Sounds like you may have a small amount of air in the lines.   Or could be that you aren't making enough vacuum?   Any more details you could share?

[Canadian1968]

hmm why would air change as I drive the car more ? I don't even have to drive. If I sit in park and keep the rpm for about 30 secs it does same thing . Its orginal bendix booster. I bleed the master cylinder and then did the lines when I re installed everything after doing my engine bay.  I have had a small leak trying to track down but I think some of it is aactually just the lid of master leaking a bit.

[garner7555]

So if the car is idling the brakes are not as responsive as when the RPMs are slightly higher?   Like 1400 RPMs?   Still need more details about how the pedal feels and when it feels that way in relation to the other things in the car.   Hopefully we can help you get it sorted out so that you can get safely back on the road.   

[Canadian1968]

The car stops fine in all conditions. The pedal stiffness and sensitivity changes .
I can start the car brief warm up ( 1 -2 mins) then back out of the garage. pedal at this point is soft , I also have a hissing noise that sounds like it is coming right from the pedal when it is depressed. Drive down to first Street corner ( maybe 200 meters) . pedal is still soft but car has no problem stopping next stop pedal is noticeably firmer. After some more drive time at a cruise (2000 2500) rpm pedal is firm and much more sensitive . Hissing noise is still there but not near as noticeable . Foot hard on the break pedal at stop (warmed up) does not seem to sink at all.

[garner7555]

It sounds like your brake booster may be leaking.     The hissing you hear is most likely a vacuum leak inside the booster.  I would start there first and see if that fixes all your issues.