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Marty, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 54999
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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We have removed the master cylinder on our 2004 240clk to

Customer Question

We have removed the master cylinder on our 2004 240clk to repair wiring underneath and having replaced the master cylinder the brake servo does not work. The brake pedal performs normally and goes down a little when you start the engine and the servo appears to be making the usual noise when the brake pedal is depressed. We have taken off the master cylinder to make sure the operating rod is correctly aligned and it is. We have pressure bled the system several times and we have a good pedal and can find nothing wrong.Help !
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.

Hi, my name is***** for the long wait on this question. If you have no power assist when driving the car and braking you will need to check the vacuum to the brake booster. If you have good vacuum to the booster you will probably need to replace the booster. The only other thing I can think of is you lost the o-ring on the end of the master cylinder when you removed it. If the o-ring is missing you will not have power assist.

Let me know what you find.