Sprinter brake test procedure

Carl Elliott

Roger et al,
Below is the Dr. A published procedure to "test" if your brake pedal is indeed too soft or normal.

Here's how to tell if your Sprinter brake pedal action is "normal" OR in need of immediate service attention:
     Engine running, push lightly on the brake pedal. Mushy and sinking seemingly endlessly toward floor? This may be NORMAL.
     Engage Park and handbrake. Shut off the engine and then step on brake pedal 4 or 5 times. This releases the vacuum from the booster servo and reservoir-you should hear a loud hiss when pressing pedal each time until the vacuum is expended.
     Engine still OFF, ALL vacuum expended, now step on brake pedal and exert a steady force. Pedal should move a relatively short distance (compared to before) and stop hard without further sinking- REGARDLESS of how long you exert foot pressure.  

This is the TRUE test of the brake master cylinder. If pedal slowly sinks to floor during this test- you have a problem.
     Now step on pedal again and exert steady pressure while starting engine. With engine now running- the pedal should begin sinking steadily toward floor. This is NORMAL and indicates the engine's vacuum pump and the brake servo are working properly.
     Take foot off the brake pedal and run the engine for a few seconds at 1500 rpm to build vacuum. Go back to idle speed, step on the brake pedal slowly-see the difference and the much greater sink distance compared to engine "off" and vacuum released?
     Still convinced it's excessive pedal travel? Try this test-Engine running, move Sprinter to a downward sloping driveway, place in neutral and SLOWLY creep downhill. Gently apply brake pedal pressure and note how little pedal travel is needed to stop and hold the vehicle-now push harder-see how much pedal travel remains?
     This long, soft, pedal travel is a normal characteristic of the Sprinters vacuum booster design when engine is running."
From Dr. A via  Byron 07NH CA    Thursday, March 29, 2012 8:41 AM


-Carl E.  2007H  NW WA