Final Drive Design Weakness? - BMW Luxury Touring Community
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post #1 of 4 Old Oct 15th, 2012, 9:51 pm Thread Starter
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Final Drive Design Weakness?

Having recently joined the "4 percent" group I was curious if anyone else had noticed this with the FD. In order of appearance we have a tapered roller bearing, pinion gear, ring gear, and a caged roller bearing. Because the pinion gear is between the ring gear and the tapered roller bearing, wouldn't that cause the torque generated by the ring and pinion set to load up on the caged roller bearing? It just seems to me that if the drive-shaft turned the other direction and the pinion gear was between the ring gear and the caged roller bearing, the torque and subsequent lateral load would be applied to the tapered roller bearing. Hmmm........

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post #2 of 4 Old Oct 15th, 2012, 10:08 pm
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Re: Final Drive Design Weakness?

The lateral load developed by the ring and pinion is a fairly small percentage of the torque load applied, and the fact that the ball bearing is HUGE in comparison to the tapered roller means that it has probably higher lateral load capacity, and in fact sees most of the lateral loads applied by the wheel in different riding conditions. Any lateral loads applying force to the left by the wheel are ALL taken by the ball bearing.

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post #3 of 4 Old Oct 16th, 2012, 1:51 am
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Re: Final Drive Design Weakness?

Yea!....What Dave said...

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post #4 of 4 Old Oct 16th, 2012, 10:06 pm
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Re: Final Drive Design Weakness?

Engineering design almost always ends up being a compromise, be it based on cost, space restrictions, performance constraints or even in some cases aesthetics. That being a given, in an ideal world we might have seen a tapered roller bearing each side of the crown gear, we would (most likely) have also seen a much more expensive bike with possibly a larger and more ugly FD gear casing. My point is that the whole drive system would have been engineered fit for purpose whilst meeting the design criteria. It is highly unlikely that a company as large as BMW "just got it wrong". Where they may have fallen down is in training of their assembly techs in the correct preload setting operation.Others may have a different view, that's mine.

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