Evaluation criteria for evaluating flexible discs (M5 2018-2022)

Function of the flexible disc: 

The flexible disc is also designated the elastic permanent coupling. It connects two shafts like a prop shaft and can influence among other things the characteristic frequency of the propeller shafts due to its spring stiffness.

It dampens torque peaks, shock pulses (clanking from the transmission toothing) and decouples noises.

The two shafts to be connected must be aligned perfectly. A centering of the shaft ends with sufficient radial stiffness is essential to ensure the start-up behavior.

Due to a centering with radial stiffness, the occurrence of greater centrifugal forces is avoided, which can also occur with precisely aligned shafts as a result of the elastic behavior of the flexible discs.

Structure of flexible disc: 

• Inner structure of flexible disc (function: torque monitoring)

1. Thread packages
2. Steel bushes
   • Exterior view of flexible disc (function: Decoupling, damping & angle compensation)
3. Outer material made of rubber

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The following figures show the evaluation criteria of flexible discs, according to which these should

not  be replaced  !

Evaluation OK 

• Visible cracks in the rubber part, but no threads visible (→ only optical change)
• Crack size and number of cracks are irrelevant for the evaluation
• Flexible disc is fully functional and ready for use
• Remaining service life expected > 50% of the total service life

Evaluation OK 

1. → No exchange required

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Evaluation OK 

1. → No exchange required

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Evaluation OK 

1. → No exchange required

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Evaluation OK 

1. → No exchange required

Courtesy of BMW OF NORTH AMERICA, INC.

The following figures show the evaluation criteria of flexible discs, according to which these should be replaced! 

Evaluation not OK 

• Visible cracks in the rubber part and  threads visible
• Component with limited operability
• Remaining service life expected < 50% of the total service life

Evaluation not OK 

1. → Exchange of the flexible disc is recommended

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Evaluation not OK 

1. → Exchange of the flexible disc is recommended

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Evaluation not OK 

1. → Exchange of the flexible disc is recommended

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Evaluation not OK 

1. → Exchange of the flexible disc is recommended

Courtesy of BMW OF NORTH AMERICA, INC.