When the truck was restored, only the depression chamber had been opened. It was very clean. Additionally, very clean Lockheed fluid came out of the pilot valve, so we decided not to take it apart. We converted it from Lockheed to silicon fluid, with a product totally compatible. The truck braking system behaved properly during 5 years but eventually developped a leak towards the big depression chamber.
This Hydrovac being of the third generation, we could never find a repair kit for it. We decided to give it to a Professional who restored it entirely.
The renovated Hydrovac was mounted on the truck, filled and vented with all the braking system March 11, 2017. A road test was successful.