DMF failure diagnosis

Visual inspection/damage patterns

1. Clutch driven plate 2. Between primary and secondary flywheel 3. Friction surface 4. Friction surface 5. Friction surface 6. Ball bearing 7. Plain bearing 8. Plain bearing 9. Low thermal load 10. Moderate thermal load

11. High thermal load 12. Very high thermal load 13. Friction control disc 14. Primary flywheel 15. Starter ring gear 16. Sensor ring 17. Minor grease egress 18. Heavy grease leakage 19. Balance weights

1. Clutch driven plate
Description
• Clutch disc burnt
Cause
• Thermal overload of the clutch driven plate
occurring, e.g. when the wear limits were exceeded
Effect 
• Thermal load applied on the DMF
Remedy
• Perform a visual inspection for signs of thermal
discolouration on the DMF
For damage assessment refer to:
  • Low/mean/high thermal load
  • Very high thermal load

2. Between primary and secondary flywheel
Description
• Burnt residues of abraded clutch facing at the DMF’s outer edge or in the ventilation holes
Cause
• Thermal overload of the clutch driven plate
Effect 
• Residues of the abraded friction material can penetrate
into the arc spring channel and cause malfunction
Remedy
• Replace DMF

3. Friction surface
Description
• Scoring
Cause
• Worn-out clutch
Clutch lining rivets score on friction surface
Effect 
• Limited power transmission capability
• The clutch is unable to generate the required torque
• Damage to the DMF friction surface
Remedy
• Replace DMF

4. Friction surface
Description
• Localised, dark hot spots
Sometimes many spots
Effect 
• DMF subjected to high thermal load
Remedy
• No remedial measures required

5. Friction surface
Description
• Cracks
Cause
• Thermal overload
Effect
• Loss of the DMF’s operational reliability
Remedy
• Replace DMF

6. Ball bearing
Description
• Grease egress
• Bearing seized
• Sealing cap missing or discoloured brown due to
overload
Cause
• Thermal overload or mechanical damage/overload
Effect
• Degradation of bearing lubrication
 DMF fails
Remedy
• Replace DMF

7. Plain bearing
Description
• Damaged or destroyed
Cause
• Wear and/or mechanical impact
Effect
• DMF is defective
Remedy
• Replace DMF

8. Plain bearing
Description
• Worn out
 In relation to the diameter, the maximum radial bearing clearance for a new part is 0.04 mm, with an admissible increase throughout its service life of up to 0.17 mm
Cause
• Wear and tear
Effect
• Less than 0.17 mm: none
• Greater than 0.17 mm: increased tilting of the secondary flywheel
Remedy
• Replace DMF if bearing clearance is greater than 0.17 mm

9. Low thermal load
Description
• Friction surface slightly discoloured (gold/yellow)
 No tarnish at the outer edges of the DMF or in the
rivet area
Cause
• Thermal load
Effect
• None
Remedy
• No remedial measures required

10. Moderate thermal load
Description
• Friction surface discoloured blue due to temporary
thermal load (220 °C)
• No discolouration in the rivet area
Cause
• Discolouration of the friction surface is a normal
occurrence during operation
Effect
• None
Remedy
• No remedial measures required

11. High thermal load
Description
• Tarnish in rivet area and/or at the outer diameter;
no tarnish on the friction surface
 The DMF was in continued operation after high thermal
load had occurred
Cause
• High thermal load (280 °C)
Effect
• Depending on the duration of the thermal load applied,
the DMF may become defective
Remedy
• Replace DMF

12. Very high thermal load
Description
• DMF discoloured blue/purple at the side or on the back
and/or is visibly damaged, e.g. cracks
Cause
• Very high thermal load
Effect
• DMF is defective
Remedy
• Replace DMF

13. Friction control disc
Description
• Friction control disc melted
Cause
• High thermal load inside the DMF
Effect
• Limited operational reliability of the DMF
Remedy
• Replace DMF

14. Primary flywheel
Description
• Secondary flywheel scores the primary flywheel
Cause
• Friction ring of the plain bearing worn out
Effect
• Noise emission or starter motor operation impaired
Remedy
• Replace DMF

15. Starter ring gear
Description
• Starter ring gear heavily worn
Cause
• Defective starter
Effect
• Noise occurring during engine start
Remedy
• Replace DMF
• Perform starter function test

16. Sensor ring
Description
• Sensor ring teeth distorted
Cause
• Mechanical damage
Effect
• Engine runs unevenly
Remedy
• Replace DMF

17. Minor grease egress
Description
 Slight trails of grease leaking from the openings or
seal caps
Cause
• Owing to design, small amounts of grease egress
are permissible
Effect
• None
Remedy
• No remedial measures required

18. Heavy grease leakage
Description
• Grease egress greater than 20 g
 Housing covered with grease
Effect
• Lack of lubrication of the arc springs
Remedy
• Replace DMF

19. Balance weights
Description
• Loose or missing
 Indicated by clearly visible welding spots
Cause
• Incorrect handling
Effect
• DMF out of balance
 Loud humming
Remedy
• Replace DMF