I have a 1960 Mk X with a brake issue.

Currently, with the engine running, if I push on the brake pedal, the brakes activate and then stay activated for 10-20 minutes.

There is a vacuum line going from the engine to a vacuum canister through what looks like a check valve and then into the brake booster.

If I remove the vacuum line from the engine to the canister, the brakes don’t lock up but I have no assist and the braking seems to mostly come from the front brakes at that point.

if I bypass the canister and check valve and run the vacuum line straight into the booster, the brakes activate as soon as the engine starts.

The booster is newly rebuilt, bought from a reputable source. I know that doesn’t mean it’s automatically good but it wasn’t done by an amateur.

Any thoughts as to what might be the problem or how to troubleshoot more.

the repair manual I have doesn’t show the vacuum canister or check valve on any of the diagrams and the shape of the canister or check valve doesn’t show in any of the parts catalogs I have.

any help is appreciated.
Thanks.

 

It sounds like either the master cylinder isn't returning after the brakes are applied, OR the Air Control Velve on the servo is stuck and won't allow air back into the servo after vacuum is released into it on brake application, and the application ceases. Its the vacuum on one side of the big piston and air at atmospheric pressure that gives the boost to the brake effort. When the brakes are released, air has to be able to pass into the chamber to kill the vacuum. This is done via the air control valve.

Alternatively, pressure is remaining in the brake hydraulic lines even though the brake pedal is released. This could be the master cylinder.

The vacuum canister and valve is the "Reservac tank" and "Brake Check Valve", and are there to maintain a reservoir of vacuum in cases where manifold vacuum is diminished like an engine stall. This allows assisted braking to be maintained better. The check valve is a well-known failure item as it is a Mazak casting and can corrode to the point of just being powder ! The Mark 2 saloon as the same tank and valve.

What is the service history of the brakes ? Recent servicing/replacement ?