In our experience the most common cause of the brakes "locking on" is a blocked rubber flexible hose. The rubber hoses tend to swell internally causing them to partially block. When the brake pedal is pressed the high pressure system forces the fluid through the hose and the brakes operate as expected. However, as the pressure on the pedal is released the fluid cannot return under lower pressure through the partially blocked hose causing the calipers to stick on. It is also very common to see that the eight caliper hoses have been replaced but that the two “rat trap” hoses below the pedal have not.
The hoses should be replaced every 12 years / 96000 miles as part of the major hydraulic service.
For all RHD cars the ten hoses you require for the braking system are:
4 x CD6242, 3 x CD6248, 1 x CD6243, 1 x CD6244, 1 x CD6247.
For all LHD cars the ten hoses you require are:
4 x CD6242,1 each of the following: CD6243,CD6244, CD6247, CD6248, CD6245, UR19939
All of the hoses listed below have been tested and approved to the following standards (equivalent to European TUV rating): SAE J1401, FMVSS 106, CMVSS 106, TSD 106, ADR 7/00, GB 16897, ISO 3996 and JIS D2601.