Brake Master Cylinder - Update/Bleeding/Testing
83mercedes02TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: October, 1983 REF. NO. 42/82
SUBJECT: A. NEW BRAKE MASTER CYLINDER MODELS 107 AND 126
B. SPONGY BRAKE PEDAL - ALL MODELS
C. UNNECESSARY REPLACEMENT OF BRAKE MASTER CYLINDERS - ALL MODELS
A. New Brake Master Cylinder - AH Models
Since July 1983 a new master cylinder has been installed in vehicles with doublediaphragm brake booster. The new master cylinder has a 1" diameter primary piston for the front brake circuit (formerly 15/16"). The rear brake circuit secondary piston diameter of 3/4" remains unchanged.
Production Phase-In
Model Chassis Chassis End Number
380 SL 107.045 028726
380 SE/SEL 126.032/033 048642
500 SE/SEL 126.036/037 036886
380 SEC 126.043 007912
500 SEC 126.044 007818
300 SD 126.120 050790
Parts Information
Part Name Part Number
Brake Master Cylinder 004 430 26 01
B. Spongy Brake Pedal - All Models
Insufficient bleeding of the brake system may be the cause of customer complaints of spongy brake pedals. In this case, thorough bleeding, according to Operation No. 42- 010, is necessary (see Service Microfiche).
When using a bleeding unit, it is essential to step down fully on the brake pedal several times while bleeding the brakes.
If the spongy brake pedal condition persists, complete bleeding might be necessary a second time. Contact your Field Service Manager for further information on this subject.
C. Unnecessary Replacement of Brake Master Cylinders - All Models
Recent tests of brake master cylinders, returned under warranty, have proven that most of the units are functioning properly.
If complaints related to the brake master cylinder occur, the following test should be performed before any part is replaced:
1. With the engine turned off, actuate brake pedal several times to exhaust vacuum in the brake booster completely.
2. Depress brake pedal by applying a moderate pedal pressure. Maintain force for approximately one (1) minute. The brake pedal travel must not change during this time.
NOTE: With the engine running, the brake pedal will go down further as vacuum builds up. This may create the false impression that the brake pedal travel is excessive.