I have the same bus. Many pictures of the systems of the bus can be found here.
Nat_ster's Haul All - Pirate4x4.Com : 4x4 and Off-Road Forum
Your brakes are called "Lucas Girling" hydraulic brakes.
The rear brakes have a park brake that looks a bit like a air brake pot. However, it is a spring that locks the brakes till hydraulic pressure is applied to release the spring.
This can be used as a safety brake system if you loose all hydraulic brakes.
It is one of the most expensive brake systems to over haul. However, a brake job will last a long time if used correctly.
Do you have a auto or a standard transmission?