British Rail Train Crew Manual - D7000 Class Locomotives With Maybach Engine & Mekydro Transmission - Fault Guide For Drivers
Chief Mechanical And Electrical Engineer  Paddington - Issue Date  November 1963   -   BR 33057/1

More information can be found here Wikipedia - British Rail Class 31
More Information Regarding Preserved Class 35s (Hymeks) Locomotives can be found on the following websites:  Preserved-Diesels