Suspension - Front Air Suspension Knocking/Thumping
Date: March 6, 2008Order No.: P-B-32.22/18d
Supercedes: P-B-32.22/18c dated February 27, 2006
Group: 32
Revision History
Revision Date Purpose
d 3/6/08 Note Added Pertaining to Warranty Information
c 2/27/06 Additional Information on Symptoms and Repair Options
b 8/8/05 Addition Information on Repair Options for the Front Axle Air Suspension Strut
a 9/8/04 Additional Information on New Airmatic Valve Tool
- 01/14/04 Initial issue
SUBJECT:
Model 220.170/175/183/184, up to VIN 360985 without Active Body Control (ABC)
Leakage or Knocking/Thumping Noise from Front Air Suspension Strut(s)
If you receive customer reports in the above model vehicles of the Instrument Cluster's Multifunction display indicating "Stop Car Too Low" and/or diagnostic fault code 1517-001 [Critical Vehicle Level At Front Axle], and/or a knocking / thumping noise emanating at the front Airmatic suspension struts, perform the diagnostics and repair procedure listed for each scenario.
Scenario 1: "Stop Car Too Low" and/or Diagnostic Fault Code 1517-001 [Critical Vehicle Level At Front Axle]
The above message displayed within the instrument cluster and the diagnostic fault code may be the result of the suspension strut's encapsulated head bearing leaking through the sealing compound. In order to diagnose this condition; spray a solution of soapy water around the Airmatic line connection and the sealing compound (Figure 1). Rock the front-end of the vehicle. If air bubbles develop around the connection line and sealing compound, then the air strut's encapsulated head bearing requires resealing. In such cases, reference WIS document AR32.22-P-1600I for repair procedures.
Scenario 2: Knocking / Thumping Noise
The knocking and or thumping noise at the front Airmatic struts are attributable to settling effects of the head bearing, and possibly also in conjunction with leaks from the head bearing. For this reason in the event of knocking and or thumping noises from the front axle suspension strut, the head bearing requires resealing. In such cases, reference WIS document AR32.22-P-1600I for repair procedures.
Note:
When the repair kit is used, the settling effect which is responsible for the corresponding noise is compensated by the head bearing being pre-compressed again. This then eliminates the noises from the head bearing area. It is not necessary to replace the suspension strut. Only in absolute exceptional cases when a proper repair of the head bearing with the repair kit did not lead to a satisfactory conclusion, should the replacement of the suspension strut be taken into consideration.
Note:
DO NOT replace the strut assemblies for instances of leaks on vehicles below VIN 360985.
If during the leak test as performed in scenario 1, there is a lack of pressure in the suspension strut, it may be that in the full rebound travel condition the air spring plunger separated from the support bearing (Figure 2). In this case to test whether there is a leakage at the encapsulated head bearing; proceed as follows.
1. Fill the air suspension strut using STAR Diagnosis.
2. During the filling process, pull the air spring plunger of the air spring downwards firmly by hand and press onto the support bearing so that air does not escape between the air spring plunger and the support bearing (Figures 3 and 4).
3. Once the Airmatic suspension strut is filled with air, perform a leak test on the head bearing using a solution of soapy water.
After resealing the Airmatic strut's encapsulated head bearing, proceed as described above when filling the air suspension strut (Figure 3 and 4).
Note:
DO NOT replace the Airmatic strut assemblies on vehicles below VIN 360985. Warranty claims will be denied in cases where the strut assemblies were replaced as a result of leaks at the encapsulated head bearing (Figure 1), and or the air spring plunger separating from the support bearing (Figure 2). Leaking head bearings and separated air spring plungers can be effectively repaired and filled with air.
Note:
Use the repair kit specified in the parts ordering notes. It is recommended that both front suspension struts be resealed (one parts kit per strut is required). Use the o-ring specified in the parts ordering notes, only if the existing o-ring was damaged during installation.
Note:
In order to aid in the removal/installation of the Airmatic strut's residual pressure brass valve (step 8 & 20 of WIS document AR32.22-P-1600I), a special socket has been developed. The Airmatic pin socket is double-ended in order to accommodate the two different size Airmatic valves used in production. The MBUSA Special Tool (W900 589 00 07 00) was automatically released to each Mercedes-Benz dealer at the end of August 2004, and is also available through the parts system for individual purchase.
Note:
WIS document AR32.22-P-1600I, instructs to use the commercially available tool hot air gun 3000 W model K-25-R, manufactured by Firma Zinser Schweisstechnik GmbH. This tool is not available in the USA. Instead workshops should use either of the heat guns shown above.
Special Tool Information
Parts Information
Note:
The following allowable labor operations should be used when submitting a warranty claim for this repair. This information has been generated on February 27, 2006. Please refer to Netstar --> Star TekInfo --> Star Time for the most current labor time allowance.
In Case of Warranty, use the table above.