Brakes - Noise From Engine Area When First In Motion
Group 34Brakes
Bulletin Number
34 03 91 (3382)
Woodcliff Lake, NJ
May 1993
Product Engineering
This Service Information bulletin supersedes S.I. 34 03 91 (3382) dated January 1993. It limited the models affected to four door models, and corrects a production date.
Please remove and discard S.I. 34 03 91 (3382) dated January 1993 from your S.I. binder.
SUBJECT:
Excessive Noise From Engine Compartment After First Starting Off (ABS Self-Test)
MODELS:
3 Series (E36) - Four Door Models Only
Situation:
A customer complaint may be received of a noise (described variously as a "rattle," "groan," or "growl") that occurs only after the engine is started and the vehicle is put into motion (either forward or reverse).
This noise occurs within the first 30 feet or so of travel and only lasts approximately one second.
Cause:
This noise complaint usually results from the customer hearing the pump activation portion of the ABS self-test.
It is imperative that the customer is made aware that the self-test noise cannot be eliminated; it can only be reduced. The self-test is necessary and the noise heard during it is unavoidable.
Correction:
Reduction of this noise is not always possible; however, in certain cases, a reduction in noise level can be achieved by installation of insulated brake lines (vehicles produced before 03/92 only; vehicles produced 03/92 and later incorporate other measures to reduce pump noise). Refer to the following procedure in the case of customer complaint of excessive noise.
1) Determine if the ABS self-test noise is just audible or whether an excessive amount of noise can be heard (compare to known good vehicle). Excessive noise ("groaning," "growling," "droning," etc.) can be reduced, but there will always be some audible noise as an unavoidable consequence of this necessary self-test.
2) Check visually the brake lines make contact with each other, paying particular attention to the lines between the tandem master cylinder and the ABS hydraulic unit. Also check the lines between the ABS hydraulic unit and the wheels.
3) Check the rubber insulation on the left and right front wheel brake lines, making sure that they are properly aligned in the openings through the inner fender panel.
4) Check the rubber mounts on the ABS hydraulic unit for proper installation. The rounded ends go toward the body, and the squared-off ends go toward the ABS hydraulic unit.
5) If no cause for this noise complaint can be located with the abovementioned checks, install rubber-coated lines between the tandem master cylinder and the ABS hydraulic unit. Part Numbers:
34 30 4 394 727 (1 pc.)
34 30 4 394 728 (1 pc.)
Note:
When installing brake lines, make sure that they are free of tension; i.e., it should be possible to screw on the line connections by hand.
6) Bleed the brake system (refer to Section 34, Operation 34 00 47 in the E36 Repair Manual). Select "50-ABS" with the BMW Service Test or MoDiC, then select "Special Functions" ("ABS Evacuation Routine"). This will activate the ABS pump for approximately 60 seconds to facilitate bleeding all air from the pump circuits.
7) After having bled the brake system, it is now possible to check the amount of noise reduction by means of the "ABS Evacuation Routine" of the BMW Service Test or MoDiC.
Caution:
After 2 activations of this routine (60 seconds per activation), allow the system to cool down for at least two minutes. If the self-test noise is still heard within the passenger compartment, carefully bend the rubber-coated lines against each other until the noise is eliminated.
Note:
After 03/92, E36 vehicles were produced which incorporate other noise reduction measures. On these vehicles, the self-test noise cannot be reduced by the installation of the rubber-coated brake lines.
Parts Information:
Rubber-coated lines are available as follows:
P/N Qty. Required
34 30 4 394 727 1
34 30 4 394 728 1
Warranty Information:
Parts and labor are reimbursable under the terms of the BMW New Car Limited Warranty of 4 Years/50,000 Miles.
Notes:
1) Under no circumstances may both labor operations be claimed for the same vehicle.
2) Installation of rubber-coated lines on a vehicle produced 03/92 or later will not further reduce the noise level of the self-test; therefore, these installations should not be performed.