4Matic System - Changes and Information

TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS

Date: October 1991

Ref. No. 28/6

Subject:
MODELS 124.230/290 (4MATIC)

A. ELECTRICAL SELECTION SWITCH INSTEAD OF SERVICE VALVE
B. BLEED VALVE FOR CENTRAL DIFFERENTIAL LOCK (ZS) CLUTCH
C. MULTIPLE-DISC CLUTCH FOR FRONT WHEEL DRIVE (AV) WITHOUT CONTACT PRESSURE
D. MODIFIED 4MATIC HYDRAULIC UNIT (A7/2)
E. HYDRAULIC DIAGRAM
F. ELECTRICAL WIRING DIAGRAM

A. ELECTRICAL SELECTION SWITCH INSTEAD OF SERVICE VALVE




As of May 1991 production, the service valve previously used to turn off the 4MATlC system is replaced with a normal operation/service selection switch (S7/3). The switch is located on the right inner side of the component compartment wall (Figure 1).

To turn off the system, unplug the connector and reinsert it in position "Test". The 4MATlC warning lamp comes on and indicates that the system has been turned off.

To turn the system back on, switch off the ignition, unplug the connector and reinsert it in position "FUNKTION". The ignition must be switched off, otherwise the 4MATIC warning lamp will remain lit.




Before performing any diagnosis or repair of the hydraulic system, release system (accumulator) pressure at the pressure release screw (15, Figure 2).

To do so, open the pressure release screw (16) approx. 1/2 turn. The hydraulic oil will flow to the hydraulic oil reservoir via the return line. When closing the pressure release screw (16), torque screw to 20 Nm.

B. BLEED VALVE FOR CENTRAL DIFFERENTIAL LOCK (ZS) CLUTCH




As of May 1991 production, the transfer case is equipped with an additional bleed valve (EZS) to bleed the hydraulic lines and the piston area of the central differential lock (ZS) clutch (Figure 3).


C. MULTIPLE-DISC CLUTCH FOR FRONT WHEEL DRIVE (AV) WITHOUT CONTACT PRESSURE

To increase comfort, contact pressure is no longer applied to the front wheel drive (AV) clutch. As a result, the oil flow limiting valves in the hydraulic unit have been eliminated. When performing the Hydraulic System Test, the following tests, as described in the Model Year 1990 Introduction Manual for 4MATlC, are no longer required:

"Application Pressure of Front Wheel Drive (AV) Multi-Disc Clutch",

"Checking Residual Pressure in Return Line N".




Modified 4Matic Hydraulic Unit (A7/2)




Hydraulic Diagram

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Electrical Wiring Diagram

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Electrical Wiring Diagram