Front brakes hanging when engine is hot and vacuum discoonnected

I have a 63 car FHC with a front brake hanging problem.
Car is fitted with a full series 2 brake system in front. It has the original dual MC system one circuit rear one front supported by the original bellow.
All brake system is new or overhauled. Apart from disconnected brake servo, where only coupe brass filter is replaced.

When car is cold one can push «one million» times. And all works good.
With a little driving, and engine is hot the front brakes start sticking more or less by itself. First I disconnected the vaccuum below from the brake MCs. That helped a little, then 500 yard driving and front brakes got really stuck.

Then I opened the bleeding nipple on one front caliper and car rolled again…

Then another 500- to 1000 yards and brakes were hanging again. Very little braking. Once or twice. Hand brake is very good on the car.

Then brakes were hanging again. Release pressure on bleed nipple front caliper again. And car rolling again.

My idea is here:

Heat cause liquid to expand. And faulty MC front brakes allthough completely new trap liquid in MC somehow.

Any thoughts?

Rear brakes work 100% ok, with and wo brake servo connected.:blush:

Is it both fronts?

The first thing Id check is head space of the actuator rod, into the master.

Hi, yes, both sides front. I only have adjustment on rear brakes. I have adjusted that now, 5 mm, started engine, let it go for a while to be hot, now brake are sticking all four corners. So I will loosen the rearbrake adjustment screw to where it was and no sticking. On rear brakes at least.
I do think you are right with your idea then, since rear brakes started sticking after engine was started and screw adjusted rear MC.

A Jaguar friend here in Norway suggest that vaccum bellow act as a pressure bellow and ge proposed switching the two connections on the MC for the front brakes.

Ole this is a very common issue and there are numerous threads on the topic, often very lengthy.

Found out of it. Adjustment pin on new rear brake master cylinder was too long. One can obviously get two lengths on these pins.

Overhauled the old short pin, took off the long from the new MC fitted the short and trouble solved. Vacuum bellow OK.

Brakes all good.

So message is; check lengths of MC pins/rods when new MCs are purchased. Mine was 10 mm too long.