The brake circuit distribution is arranged diagonally. The rear brake circuit is controlled by brake proportioning valves, which are located at the underbody over the rear axle (arrow). The identifying number is embossed on the regulator housing (e.g. 3/40).
Important!
Check both brake circuits. Replace brake proportioning valves in pairs.
Collect running out brake fluid in the collection tray.
Inspect
Remove the front wheels. Check the brake power control regulator with MKM-558-A or equivalent checking device. Remove the air vent valve and fit MKM-558-1 or MKM-558-2. Observe the manufacturer's instructions.
Important!
Measure brake line pressure on front and rear axle simultaneously and diagonally.
Pressure Check:
Measure
Build up pressure by operating the brake pedal.
Steady the manometer reading for the front axle at the given test level. Read off the measured value for the rear axle and compare with the values in the Table - see Technical data - Pressure information for brake proportioning valve. Check pressure up to a max. of 100 bar.
Remove checking lines from brake calliper and wheel brake cylinder and repeat check on second brake circuit.
Remove test equipment, correct brake fluid level and, if necessary, bleed brake system and check for leaks - see operation "Brake System, Check for Leaks".
Important! 
Inspect 
Measure 