No. 109-21

Symptom-based workshop manual
Service
109/21 ENU
4407
4
Noise Symptom – Clicking Noises from Around the Front Axle: Observe Specified
Procedure (SY 109/21)
Revision:
This bulletin replaces bulletin ATI Group 4 2106.1, dated October 7, 2021.
Model Line:
911 (991)
Model Year:
As of 2014
Equipment:
Central wheel lock (M-no. 478)
Concerns:
Front wheel mounting
Symptom:
The customer complains about clicking noises from the front axle area when turning or turning at slow
speeds.
Cause:
Micro-movements between the contact surfaces of the wheel and brake disc may occur while driving.
These micro-movements can be caused by the following main causes:
•
•
•
Reduced preload on the central wheel lock
Reduced coefficient of friction between the surfaces
Geometric discrepancies
As a result, the rim material is removed from the brake disc.
The transferred material can weld itself to the brake disc and thus cause a stick-slip effect. This
generates the clicking noises during wheel rotation.
Information
The stick-slip effect is the jerking motion that can occur while two solid bodies are sliding over each other.
This phenomenon occurs when a body is moved whose static friction is significantly higher than the
sliding friction.
Remedial
Action:
Check the components of the front wheel mounting as described below and carry out the appropriate
remedial action depending on the respective test result.
When checking the components, ensure that the sequence described below is followed:
•
•
•
Check central wheel lock; for instructions, see:  Technical Information 'Checking central wheel
lock'
Check contact surfaces of rim, brake disc and wheel hub for friction loss, see procedure: 
Technical Information 'Reduced coefficient of friction between the surfaces'
Check rim, brake disc and wheel hub for geometric discrepancies, see procedure:  Technical
Information 'Geometric discrepancies'
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Information
The wheel design with central lock was originally developed for race track driving. It allows the wheels to
be changed quickly during a race. Today, the wheel and hub designs with central lock for road vehicles
are significantly different to those of pure racing cars. Given this, the following guidelines and precautionary measures must always be observed when removing or installing the wheels on a road vehicle with
central wheel lock.
•
The vehicle must be on a lifting platform and the wheels must be hanging freely (no contact with the
floor) while tightening the central lock nut. This ensures that the wheel is centered correctly on the
hub.
•
The parking brake must not be used to counter the rear wheels while tightening. The parking brake
mechanism does not tolerate the high forces while tightening the central wheel lock and can be
damaged. The damage may not be immediately apparent. This applies in particular to the motorized
electronic parking brake actuators.
•
Impact tools must never be used for loosening, removing or tightening the central wheel lock. The
nut and hub can be damaged and the damage may not be immediately apparent.
•
Only a calibrated, high-quality standard torque wrench with sufficient load capacity and levering
effect may be used for tightening the central wheel lock. The use of torque multipliers is not
approved for use on Porsche vehicles.
•
The specified final tightening torque must be reached while turning the torque wrench with a smooth,
continuous motion.
•
The required lubricant must be applied to the contact surfaces of the central wheel lock and rim
in accordance with regulations. For more information, see:  Workshop Manual '440737 Disassembling and assembling central wheel lock'
•
If the central wheel lock, wheel hub or rim is new, the central wheel lock must be tightened to the
specified final tightening torque, loosened and then loosened and tightened again three more times.
This will eliminate any geometrical discrepancies.
Required parts and materials
Parts Info:
Required parts:
Part No.
Designation
– Location
Number
WHT008186
 Cheese head bolt, M12 x 1.5 x 62
– Fixed calliper on front axle
– PCCB brake system M-no. 450
4 ea.
or
99906704001
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 Cheese head bolt, M12 x 1.5 x 95
– Fixed calliper on front axle
– Grey cast iron brake system
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Materials:
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4407
4
Required materials (usually already available at the Porsche dealer):
Part No.
Designation
Quantity
00004330508
 Mounting paste (100 gram/ 3.52 oz tube)
2 grams/ 0.07 oz
Required tools
Tool:
•
•
•
•
•
•
•
•
Straight-edge, e.g. 12” Starret 380
Feeler gauge, 0.05 mm
Brass brush
Microfiber cloth
Brake cleaner
9451 - Socket wrench
9794 - Assembly aid
9796 - Socket wrench
Preparatory work
Work Procedure: 1
Remove front wheels.  Workshop Manual '440519 Removing and installing wheel with central bolt'
Checking central wheel lock
Information
Reduced preload on the central wheel lock may be due to:
•
Reduced amount of grease on the cone of the central wheel lock or on the thread and external
diameter of the wheel hub
•
A damaged central wheel lock bolt
•
A damaged cone on the rim
Information
If one or more of the central bolts is damaged, it must be replaced. Make sure that the central bolt is sufficiently greased. For instructions, see:  Workshop Manual '440737 Disassembling and assembling
central wheel lock'
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Symptom-based workshop manual
ENU 109/21
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Work Procedure: 1
2
Disassemble central wheel lock.
For instructions, see:
 Workshop Manual '440737 Disassembling and assembling central wheel lock'
Check central wheel lock for sufficient lubricating film  Lubricating film on central wheel lock ,
cracks, deformation  Example of damage and other damage. Damage can occur at the following
points:
•
Wheel hub thread
•
•
•
Central wheel lock thread
Cone on rim
Cone on central wheel lock
Lubricating film on central wheel lock
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Example of damage
Information
If using new parts, the procedure for tightening the wheel as described in the Workshop Manual 
Workshop Manual '440519 Removing and installing wheel with central bolt' must be carried out three
times.
Parts Info:
Parts required if necessary for one side of the vehicle:
Part No.
Designation
– Location
Number
99136108190
 Wheel bolt
– Central wheel lock
1 ea.
or
99970766340
 O-ring
– Central wheel lock
1 ea.
or
99136118900
 Washer
– Central wheel lock
1 ea.
or
99736118700
 Circlip
– Central wheel lock
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1 ea.
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Symptom-based workshop manual
ENU 109/21
4407
Check contact surfaces of the rim, brake disc and wheel hub for loss of friction
Information
A reduced friction coefficient between the surfaces can be due to:
•
Material transfer from rim to brake disc or from rim to driver pin
•
Anti-corrosion oil on the contact surfaces
•
Contact surfaces dirty, e.g. brake dust
•
Hub grease on the contact surface
Work Procedure: 1
Check the mounting surface of the wheel hub and inside of the rim for material transfer or corrosion.
 Material transfer for brake disc/wheel hub
Material transfer for brake disc/wheel hub
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Information
If there has been material transfer from the rim to the brake disc, the brake disc must be replaced.
For instructions, see:
 Workshop Manual '465019 Removing and installing front brake disc'
2
Document material transfer or corrosion, if available, with pictures.
3
Remove front brake discs.  Workshop Manual '465019 Remove and install front brake disc'
4
Check contact surface of brake disc, wheel hub and
rim for dirt and clean them if necessary.
4.1
Clean wheel assembly:
Contact surfaces of brake
disc, wheel hub, rim
Brush off wheel hub ( Cleaning wheel hub
-1-) using a brass brush until all particles
of dirt have been removed. Then spray
microfiber cloth with brake cleaner and rub
off the wheel hub ( Cleaning wheel hub -1-)
with it.
Cleaning wheel hub
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4.2
Symptom-based workshop manual
Clean brake dust off the inner brake disc
hub ( Cleaning brake disc hub -1-) and
brush off the contact surface between the
brake disc and wheel hub ( Cleaning brake
disc hub -2-) using a brass brush until all
particles of dirt have been removed. Then,
spray microfiber cloth with brake cleaner and
rub off the cleaned areas with it.
Cleaning brake disc hub
4.3
Clean the contact surfaces between the
rim and brake disc ( Contact surfaces
between rim and brake disc -1 und 2-) using
a microfiber cloth and brake cleaner (do not
use a brass brush).
Information
Always make sure that the cleaned surfaces are kept
clean until assembly is complete.
5
Check driving pins.
Contact surfaces between
rim and brake disc
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5.1
Check material transfer at the driving pins.
If a material transfer has taken place, the
driving pins must be replaced. Material
transfer on driving pin
5.2
Subsequent torque 22 Nm of threaded
joint for wheel driver pin and then remove
brake disc. If the pins can still be turned,
replace pins and screws and clean the thread
and contact surfaces to remove any
remaining screw-locking material.
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Workshop Manual '465319 Removing and
installing rear brake disc'
Workshop Manual '465419 Removing and
installing rear PCCB brake disc'
5.3
Material transfer on driving pin
Check wheel driver pins for damage. If there are visible signs of damage, replace pins and
screws and clean the thread and contact surfaces to remove any remaining screw-locking
material.
Information
If using new parts, the procedure for tightening the wheel as described in the Workshop Manual 
Workshop Manual '440519 Removing and installing wheel with central bolt' must be carried out three
times.
Checking rim, brake disc and wheel hub for geometric discrepancies
Information
Geometrical discrepancies may be due to the following factors:
•
Damaged parts
•
Wear
•
Use of new and old parts
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Work Procedure: 1
Symptom-based workshop manual
Check brake discs, wheel hub and rim for damage,
e.g. notches or "dents" due to incorrect assembly.
 Example of damage
Example of damage
2
Check contact surface of the rim.
To ensure that the surface is flat, check the rim using
a ruler and feeler gauge.
Uneven surfaces can affect the rim and cause noise.
2.1
Check the inside of the rim for flatness at at
least six different positions (approx. every
60°) using a straight edge (e.g. 12" Starret
380) and a feeler gauge 0.05 mm at the
measuring points Measuring points on
inside of rim -Arrow-.
Document all measurements with photos.
Checking rim
If there are uneven surfaces, replace the
affected rim.
Information
If using new parts, the procedure for tightening the wheel
as described in the Workshop Manual  Workshop Manual
'440519 Removing and installing wheel with central bolt'
must be carried out three times.
Measuring points on inside of rim
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Concluding work
Work
Procedure:
Information
When installing a wheel, the three tightening steps must always be observed as described in the
Workshop Manual  Workshop Manual '440519 Removing and installing wheel with central bolt' and the
following special tools must be used:
•
9451 - Socket wrench
•
9794 - Assembly aid
•
9796 - Socket wrench
The central bolt must be tightened in one continuous movement. This is the only way to ensure that the
specified tightening torque is reached.
1
Install front brake discs.  Workshop Manual '465019 Remove and install front brake disc'
2
Install front wheels.  Workshop Manual '440519 Removing and installing wheel with central bolt'
Invoicing
Invoicing:
For documentation and warranty invoicing, enter the labor operations, PCSS coding and part numbers
specified below in the warranty claim:
APOS
Labor operation
44074941
Reworking wheel mounting (left)
44074942
Reworking wheel mounting (right)
I No.
PCSS coding:
Location (FES5)
4407A
Central bolt for wheel mounting
Damage type (SA4)
9735
Repair in accordance with PAG instructions
References:
 Workshop Manual '440519 Removing and installing wheel with central bolt'
 Workshop Manual '440737 Disassembling and assembling central wheel lock'
 Workshop Manual '465019 Removing and installing front brake disc'
Important Notice: Technical Bulletins issued by Porsche Cars North America, Inc. are intended only for use by professional automotive technicians who have attended Porsche service training
courses. They are written to inform those technicians of conditions that may occur on some Porsche vehicles, or to provide information that could assist in the proper servicing of a vehicle. Porsche special
tools may be necessary in order to perform certain operations identified in these bulletins. Use of tools and procedures other than those Porsche recommends in these bulletins may be detrimental to the
safe operation of your vehicle, and may endanger the people working on it. Properly trained Porsche technicians have the equipment, tools, safety instructions, and know-how to do the job properly and
safely. Part numbers listed in these bulletins are for reference only. The work procedures updated electronically in the Porsche PIWIS diagnostic and testing device take precedence and, in the event of a
discrepancy, the work procedures in the PIWIS Tester are the ones that must be followed.
© 2021 Porsche Cars North America, Inc.
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