Mark IX brakes locked up

I fitted a replacement brake booster on the Mark IX during the ground-up restoration and it seems the brakes are “on”. So moving the car is difficult. I can apply the brakes and get a bit more to “stop” (very little pedal travel), but this it’s obviously a problem. How can I address this? The booster is from usual suspect in San Luis Obispo. Can anyone suggest an approach to fixing this please?

Make sure the actuator rod on the servo has play in it. Otherwise the valve will not release brake line pressure.

Pat H

The mk IV has a remote brake booster , right?
In that case problem lies with the master brake cylinder.
In most cases the actuator rod of the master brake cylinder in to tight.

Peter Jan

Thank you for this suggestion. I’ll get under ther and check it out.

How did this work out for you as a follow up to help others who might be having this same problem?


Thank you for your email. The problem persists with a new booster installed. Next step is to see if the hill hold device that is in the brake line after the booster
is somehow the problem. It is not powered, but I think I have to determine if it is the cause. First, I will remove the vacuum feed to the booster to be sure that the problem isn’t the booster. I do not get as much time as needed as I am still employed, but
on the weekend, I’ll be back at it.