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Drive line lash


jfixit

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I've become accustomed to a lot of drive line lash in my RT and was wondering what the culprit is. This isn't a complaint because it seems to be a BMW thing, just wondering why so much slop from power on to power off or maybe better described as clutch in/clutch out during slow speed maneuvers i.e. driveways and parking lots.

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I've become accustomed to a lot of drive line lash in my RT and was wondering what the culprit is. This isn't a complaint because it seems to be a BMW thing, just wondering why so much slop from power on to power off or maybe better described as clutch in/clutch out during slow speed maneuvers i.e. driveways and parking lots.

Roadcrafter, that seems to be a major trait of shaft drive motorcycles.. Trans gear dogs have some slop to allow decent shifting,, torsional dampener in the input shaft allows some windup,, some backlash in the ring & pinion,, all add up to slop you can feel.. Then to make it worse the engine only has 2 large cylinders so the dropped throttle engine braking is pretty severe & there is no chain in the drive line to softly eat up the play.. Large throttle bodies don’t help either as the throttle gain is pretty quick..

 

My GoldWing is also pretty bad,, & I just rode the new MotoGuzzi Norge today & that was also pretty bad..

 

Twisty

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What is "a lot?" I have about a half inch of free turn ("slop") in the rear wheel when the bike is in gear and up on the center stand, but I don't really notice it while riding. I've been told that's normal. (TADT - They all do that). wave.gif

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I believe that they use bevel gears for the ring and pinion instead of hypoid gears like cars do. Bevel gears have far more play. I don't know if there is a reason to do this other than cost, but if they don't have a valid reason, I would like to beat them with it!

 

My R1200RT was supposed to have less than the R1100RT and it has the same or more. My Boxer Cup has very little and the trans shifts much better. Is this variation from unit to unit?

 

For a bike that is so wonderful in so many ways, this is certainly one of its worst features.

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I believe that they use bevel gears for the ring and pinion instead of hypoid gears like cars do. Bevel gears have far more play. I don't know if there is a reason to do this other than cost, but if they don't have a valid reason, I would like to beat them with it!

 

My R1200RT was supposed to have less than the R1100RT and it has the same or more. My Boxer Cup has very little and the trans shifts much better. Is this variation from unit to unit?

 

For a bike that is so wonderful in so many ways, this is certainly one of its worst features.

 

Greg, there is probably no reason for BMW to use hypoid gear placement.. As a general rule hypoid gear placement is only about low 90% efficient & spiral bevel gears are closer to 98-99% efficient.. Hypoid gear usage requires a very high degree of machining precision & set up precision & any gear walk caused by compliant housings or short pinion support bearing centers will cause gear noise.. On the other hand hypoid gear placement can handle a lot more torque than spiral bevel gears.. As long as you don’t need the high torque handling ability of hypoid gear placement then spiral bevel gears are more efficient, much easier to set up to begin with, easier to run quietly, & there is no reason they would have any more backlash as long as the spiral is designed correctly..

 

Twisty

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The difference between hypoid gearsets and bevel gearsets is the alignment of the input and output shaft axis.

 

Bevel gear sets have the shaft axes intersecting. Hypoids have the shafts axes displaced. Hypoids can be thought of as somewhere between a bevel gear and a worm gear. Hypoids are not as efficient because of the sliding effect of a worm gear - which is very inefficient. I understand the rear axle on a car is typically only about 90 percent efficient.

 

Despite their poor efficiency, hypoids were used in rear wheel drive cars so that the driveshaft didn't protrude into the passenger compartment as much.

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