Rolling resistance/Final drive failure? - BMW Luxury Touring Community
 
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post #1 of 3 Old May 12th, 2010, 10:25 pm Thread Starter
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Rolling resistance/Final drive failure?

I finally got around to replacing my cowbell rear disk rotor for one that is non-floating, thereby eliminating the irritating ringing noise I've lived with the past two years. Much nicer ride now.

While I had the wheel off, I turned the hub to gauge any roughness in the bearing. I could feel no roughness, but there sure was a lot of rolling resistance. Way more than I would have expected. I wonder if this is a symptom of improper shimming.

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post #2 of 3 Old May 13th, 2010, 6:41 am
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Re: Rolling resistance/Final drive failure?

Quote:
Originally Posted by BayLT
I finally got around to replacing my cowbell rear disk rotor for one that is non-floating, thereby eliminating the irritating ringing noise I've lived with the past two years. Much nicer ride now.

While I had the wheel off, I turned the hub to gauge any roughness in the bearing. I could feel no roughness, but there sure was a lot of rolling resistance. Way more than I would have expected. I wonder if this is a symptom of improper shimming.

Comments?
There is significant resistance to turning the hub, even with the final drive off the bike.
There are no outward signs of improper shimming.

It has been suggested by a mechanical engineer on this site (Niel, IIRC) that it might be possible to establish a method of checking preload by measuring the breakout torque of hub rotation. However, this would be a complicated and very precise measurement, and lots of data would have to be generated before any measurement was meaningful. As he noted, given a fully assembled drive, as soon as the crownwheel gear starts to turn the input pinion shaft, which occurs as soon as the gear lash is taken up, measurement of the torque value necessary to rotate the hub is meaningless since multiple components are providing resistance to rotation.

Short answer: the subjective sense that you have that it is hard to turn the FD hub is meaningless WRT crownwheel bearing preload.

If you want to know if your preload is within specs, open the drive and measure it.
If you want signs of impending bearing failure, change lube frequently and check for metal on the drain plug magnet; by most accounts an unreliable indicator at best.

IMO, roughness felt during wheel rotation is not an indicating of "impending" failure, rather it is an indication that the bearing has already failed, what is impending when roughness is felt is a destroyed oil seal and lube on the rear wheel; and that will occur pretty soon.

Last edited by CharlieVT; May 13th, 2010 at 7:39 am.
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post #3 of 3 Old May 13th, 2010, 8:23 pm Thread Starter
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Re: Rolling resistance/Final drive failure?

Thanks, Charlie. Despite the (apparent) high resistance, my gas mileage continues to be 40-ish mpg. So I guess it's normal.
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