Solved!! Sticky brakes where to look servo or master cilinder?


Active Member
As the title suggests i have sticky brakes. As soon as I hit the brakes 2 or 3 times the pedal gets really firm and the brakes tend to stick. In my opinion it is al four brakes. The brakes are all new calipers.
I have a 3500 of 1976. It has a dual system and the airvalave is not mounted on the servo but on the master cilinder. If i release the air valve things are right again but after hitting the brakes and revving the engine they stick again. There is quite a vacuum on the aire valve! really have to apply some effort to lift the valve.


airvalve on master cilinder:

remove the cap to release the pressure:

I hope that someone could point me in the right direction!

thanks in advance
Last edited:


Well-Known Member
I'm going to say it is the air valve that is at fault.
Hopefully somebody who actually knows how it works will be along soon to explain why I'm right. Or shoot my diagnosis down as foolish.


Active Member
thanks for the reply I think the same thing but the plastic is not stuck at all. I think something in the master cilinder is not going back and holding the pressure on the brakes.


Active Member
I was already looking what rebuilds would cost ( although mine were rebuild just one year ago) but then I thought what else ould have happened that it suddenly appears?
And yes there was a hose disconneccted

the one in the picture at the tip of the pen. The under vvacuumhose of the servo was disconnected.

Connected that hose and presto braking pedal not so firm anymore......... but brakes were free!!!

have to bleed the brakes soon for firmer pedal!!

I am a happy camper though!