Exhaust System - Rattling/Hissing/Humming Noises
Date: February 2004
Order No.: S-B-49.10/08
Supersedes:
Group: 49
SUBJECT:
MODELS 129, 170, 202, 203, 208, 209, 210, 211, 215, 220, 230, 163, WITH ENGINES 104, 111, 112, 113, 119, 137, 271, 275, NOISES IN THE
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 218
EXHAUST SYSTEM
This Service information contains the following guidelines and tips which are intended to help with the cause of noises within the exhaust system.
The suggested work steps and the procedure are intended to provide assistance in the event of noises in the exhaust system which may not be
immediately and conclusively definable.
NOTE:
As a result of the above, please replace only the part requiring replacement as determined by the procedure as indicated within this Service
Information.
There are possible causes for the noises within the exhaust system, these include:
^ Shields loose on vehicle underbody.
^ Heat shields loose on front and rear mufflers.
^ Exhaust system which is under tension.
^ Monolith in the catalytic converter is loose.
Additionally, as a remedy ask your customer:
^ Under what condition does the problem arise (temperature, engine speed, vehicle stationary or while driving?).
^ Is the noise or condition reproducible in the workshop?
First, while performing the diagnostic work, determine the noise and classify into the following groups:
A. Rattling Noises
B. Humming Noises
C. Airflow and or Hissing Noises
D. Foreign Object / Collision Damage to the Exhaust System
A. RATTLING NOISES
Lethal Danger!
Lethal or serious injury due to vehicle toppling from lift. Do Not use a 2-post frame contact lift for any work described in this operation. Use a
drive-on lift for all work to be performed as noted in this Service Information. Ensure that vehicle is properly positioned onto and while resting
on the lift.
NOTE:
A second person must be inside the vehicle in order to operate the accelerator for the subsequent tests.
- Drive vehicles onto lift and attach exhaust gas extractor hose to tailpipe.
- Place selector lever of the automatic transmission into "P", if the vehicle has a manual transmission place the shift lever into neutral. Engage
parking brake fully.
3. With engine off and vehicle raised up, perform "Tapping Test" (Figure 1) on entire exhaust system, including catalytic converters, exhaust
pipes and mufflers with a closed fist - wearing safety gloves, trying to locate source of noise.
Danger!
Observe all work safety procedures while working on the vehicle while beneath the lift. Wear protective glasses and gloves. Be aware that
sections of the exhaust system being tested/inspected may still retain some residual heat from prior operation, wear protective gloves at all times.
Danger from hot exhaust/components and sharp edges such as heat shields, brackets etc. wear protective headgear while working underneath
vehicle at all times.
- If the above "Tapping Test" is inconclusive, go to Step 5 below.
- Remove all underbody noise encapsulation panels.
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 219
"Tapping Test" (Figure 1)
NOTE:
Place selector lever of the automatic transmission into "P" if the vehicle has a manual transmission place the shift lever into neutral. Engage
parking brake fully.
- Have the assistant in the vehicle start the engine.
- With engine running, perform listening test on the entire exhaust system (as necessary for each side of the exhaust system) using self made
auxiliary pipes of approx. 24 inch length and 1 - 2 inch diameter, constructed of either aluminum, rubber or other suitable material (Figure 2).
Auxiliary Pipes for Listening Test (Figure 2)
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 220
NOTE:
Perform listening test at idle first and then at varying engine speeds, moving the auxiliary pipe along the entire exhaust system at various
distances approx. 1 - 4 inches, thus trying to localize the noise (Figure 3).
Performing Listening Test on entire Exhaust System (Figure 3)
8. If the above "Tapping Test" and listening test are inconclusive, perform a "Warm Tapping Test" (Step 9).
Danger!
Observe all work safety procedures while working on the vehicle while beneath the lift. Wear protective glasses and gloves. Be aware that the
exhaust system being tested/inspected in Step 9 below will be hot during this test step operation, so wear protective safety gloves at all times.
Danger from hot exhaust/components and sharp edges such as heat shields, brackets etc. wear protective headgear while working underneath
vehicle at all times.
9. Switch off engine and perform "Warm Tapping Test" on entire exhaust system (while still hot) with closed fist (wear protective gloves)
(Figure 1) trying to locate source of noise.
NOTE:
If exhaust system components are found to be making noise in the Cold, Warm or both Tapping Test(s):
^ Replace only the affected part
^ Do not perform preventative replacement
^ Ensure that replacement components are properly installed without tension.
10. If the above "Warm Tapping Test" is inconclusive, proceed to Step 11
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 221
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 222
11. Check that the heat shields (arrows, Figure 4 shows incorrectly installed) are firmly and correctly (Figure 5 and 6 shown correctly seated) on
the underbody.
Use your finger to incite vibrations in the heat shields and to tap the exhaust system (Figure 7)
12. Check brackets, connection points, chrome trim panels, retaining bolts on the manifold and all exhaust suspension points and cross struts for
firm seating and any fractures. If any damaged parts are found repair or replace as necessary.
If for example, a rattling noise is due to a loose shield or bracket: secure shield or bracket.
B. HUMMING NOISES
Danger!
Observe all work safety procedures while working on the vehicle while beneath the lift. Wear protective glasses and gloves. Be aware that
sections of the exhaust system being tested/inspected may still retain some residual heat from prior operation, wear protective gloves at all times.
Danger from hot exhaust/components and sharp edges such as heat shields, brackets etc. wear protective headgear while working underneath
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 223
vehicle at all times.
1. With vehicle on the ground, have assistant start engine.
NOTE:
Place selector lever of the automatic transmission into "P", if the vehicle has a manual transmission place the shift lever into neutral. Engage
parking brake fully.
2. Gently using your foot press the tailpipe in the direction of travel (forward), this stresses the exhaust system, note if the noise is changing. If
so, the exhaust system is the cause of the noise and further tests on the exhaust system will be necessary.
NOTE:
No Change in noise during Step 2 above indicates that the exhaust system is NOT the cause for the noise.
3. Raise vehicle on the lifting platform.
Danger!
Observe all work safety procedures while working on the vehicle while beneath the lift. Wear protective glasses and gloves. Be aware that
sections of the exhaust system being tested/inspected may still retain some residual heat from prior operation, wear protective gloves at all times.
Danger from hot exhaust/components and sharp edges such as heat shields, brackets etc. wear protective headgear while working underneath
vehicle at all times.
4. Visually check the seating of the rubber exhaust suspension rings in the brackets.
NOTE:
Specification: centrally seated and slightly undertension.
5. Check for correct seating of rubber suspension ring (Figure 8).
B1: Humming Noises and droning noises occurs ONLY at idle speed
NOTE:
Place selector lever of the automatic transmission into "P" if the vehicle has a manual transmission place the shift lever into neutral. Engage
parking brake fully.
1. Raise vehicle on lifting platform and have assistant start engine and allow engine to run at idle speed.
Danger!
Observe all work safety procedures while working on the vehicle while beneath the lift. Wear protective glasses and gloves. Be aware that
sections of the exhaust system being tested/inspected may still retain some residual heat from prior operation, wear protective gloves at all times.
Danger from hot exhaust/components and sharp edges such as heat shields, brackets etc. wear protective headgear while working underneath
vehicle at all times.
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 224
- Check all struts and stops of the exhaust system for firm seating.
- Carefully insert a suitable metal wedge tool (flat bar etc.) between the exhaust system and the vehicle floor.
CAUTION!
Do not damage the vehicle underbody when inserting and using the wedge tool.
4. Insert wedge tool at various points of the exhaust system (Figure 9).
NOTE:
If the applied stress from the wedge tool changes the noise heard, follow Step 12 Section A of this Service Information. If no change to the noise
was detected, proceed to next section (B2).
B2: Humming Noises and droning noises which occur between 1000 and 2000 RPM
1. Raise vehicle on lifting platform and have assistant start engine and run engine between 1000 and 2000 RPM. Listen for noise.
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 225
2. Hang any suitable weight (4lbs to 6lbs. e.g.: brake disc) from bracket of the rear exhaust system as shown in Figure 10. The aim here is to
change the vibration response of the exhaust system.
NOTE:
If the applied stress from the additional weight (Step 2 above) changes the noise heard, follow Step 12 Section A of this Service Information, if
not proceed to the next section (B3).
B3: Decoupling the Exhaust System
1. Unbolt the exhaust system bracket at the transmission end (arrows, Figure 11).
NOTE:
Do not unfasten the exhaust system mounts.
2. Unfasten rear cross strut (arrow, Figure 12) and unhook rubber exhaust mounts.
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 226
3. Replace installed exhaust mounts with rubber rings (arrow, Figure 13)
NOTE:
Provisionally use part number: A107 492 00 82
NOTE:
Model 230 only: If necessary remove existing stops on the exhaust system.
- Warm up engine with front and rear brackets and rubber mounts (A107 492 00 82) unfastened and removed.
- Operate the engine (via the assistant in the vehicle) within the engine rpm band where noise occurs as indicated by the customer.
NOTE:
If the noise changes, the exhaust system is the cause, proceed to section B4. If no noise change - proceed to Step B5
B4: Noise from Exhaust System Changes
NOTE:
REMEDY: relieve stress in exhaust system.
- Loosen all bolted connections from exhaust manifold joint onwards.
- Remove vehicle from lift and perform test drive.
- Drive the vehicle a short distance of approx. 65 feet.
- Put vehicle back up onto the lift.
- Carefully retighten all previously loosened bolted connections and ensure that the entire exhaust system is secured without any tension in any
way.
NOTE:
Fasten the bolted connections starting at the manifold and ending at the muffler.
B5: Modifications to the Exhaust System that do not Show Detectable Change in Noise
NOTE:
As performed, preceeding Test Steps indicate that the exhaust system is not the cause. In cases of doubt, install and evaluate an exhaust system
from an equivalent vehicle.
C: Airflow and or hissing noises
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 227
NOTE:
The occurrence of airflow or hissing noise usually indicates a condition with the bodywork of the vehicle (airstream / aerodynamics). However, it
may also be caused by a slightly crushed/deformed rear muffler tailpipe or by the exhaust being pushed forward (towards the front of the vehicle)
by contacting a foreign object when reversing or otherwise bumping/contacting the exhaust system (arrow, Figure 14).
D: Foreign Object / Collision Damage to the Exhaust System
NOTE:
Noise complaints may arise from damage to the exhaust system occuring during vehicle usage. Examples of the cause of such damage include:
bottoming out of the vehicle while driving over objects, from objects (road hazard) thrown up from the road surface or from bumping the exhaust
system on obstructions.
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