Bleeding Hydraulic System

Bleeding Hydraulic System

The multi-disk clutches in the transfer case and in the rear axle only engage reliably when there is no air in the hydraulic system.

Special Tools:

1 Hydraulic system
(vehicles with service valve)



Check hydraulic oil level in oil reservoir.
Service valve in test position (A).
To bleed, start engine and allow to run for approximately 30 seconds at 1000 to 2000 rpm.
After bleeding, move service valve again into operating position (B).

2 Rear axle differential lock (HS)



Remove 4MATIC control unit (N30/3) from the mount and disconnect the 25-pin coupling.
Connect the 25-pin cable harness with the test cable (02) to the socket box (04). The 4MATIC control unit (N30/3) remains disconnected (unplugged).

3 Actuate the rear axle differential lock valve (A7/2y3) by bridging from socket 8 to socket 2 (ground) on the socket box.



Start engine and allow to idle. Service valve in operating position.

4 Open breather (67) on rear axle center piece assembly until the hydraulic oil escapes without any bubbles.




5 Bleeding multi-disk clutches of front axle drive train (AV) and center differential lock (ZS)



Unscrew the hydraulic lines of the front axle drive train (AV) and center differential lock (ZS) on transfer case and hold in container. Start engine and allow to idle until the hydraulic oil escapes without any bubbles (approx. 20 seconds).




As of transfer case no.26 617
Open vent valves (EAV, EZS).
Start engine and allow to idle until hydraulic oil escapes without any bubbles (approx. 20 seconds).

6 Then correct hydraulic oil level in oil reservoir.