Suspension - Knocking Noise From Rear While Braking

Date: May 1998

Order No.: P-SI-MBNA-32/04

Supersedes: -

Group: 32

SUBJECT:
MODEL 129.066/.067/.076 (with ADS) UP TO 12/96 PRODUCTION
KNOCKING NOISE FROM THE REAR WHILE BRAKING

A knocking noise from the rear of the vehicle during light braking may occur between four and seven mph. The probable cause is rear axle height reduction valve (Y36/6) generated hydraulic pulses, heard through the metal oil line attached to its HA port. To eliminate this condition, install a high pressure expansion hose to absorb the pulse noise between the Y36/6 valve and the metal line leading to the rear axle circuit.

Repair Procedure

1. Drain the adaptive damping system (ADS) hydraulic oil. (See WIS: AR32.31-P-0630A/Draining and filling pressure oil system at front and rear axle.)

2. After removing the lower engine cover, locate the rear axle height reduction valve (Y36/6) on the right front frame rail.





3. Disconnect the existing rear axle circuit oil line (A, Figure 1) from the HA port of the Y36/6 valve, and carefully push it a few inches toward the center of the vehicle.

4. Connect the short end of the U-shaped oil line (B, Figure 1) to the open HA port. (Position the U-shaped line toward the right front wheel, so it does not contact the front axle level sensor plug connector.)

5. Insert the rubber grommet into the clamp, and run the expansion hose through it.





6. Connect the expansion hose to the open end of the U-shaped line (A, Figure 2).

7. Route the expansion hose forward, along the right of the Y36/6 valve, and use the supplied screw to fasten the clamp (B, Figure 2) to the hole present in the longitudinal member.

8. Connect the open end of the original HA oil line to the S-shaped oil line with the coupling. (Position the S-shaped line so it runs upward.)

9. Cut off a one inch piece of rubber covering (hose), then cut through one side of its length.

10. Place the piece of rubber hose around the center of the S-shaped line, then place the expandable clamp around it.





11. Use the supplied bolt with spacer to fasten the clamp to the outside of the Y36/6 mounting plate (A, Figure 3).

12. Connect the expansion hose to the S-shaped line (B, Figure 3).

13. Refill the ADS with hydraulic oil. (See WIS: AR32.31-P-0630A.)





Parts Information





In Case of Warranty