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FD/driveshaft math & the why of maintenance

 
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SugarHillCTD
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Joined: 10 Oct 2007
Posts: 4240
Location: Now in Eastern Pennsylvania

PostPosted: Thu May 18, 2017 7:11 am    Post subject: FD/driveshaft math & the why of maintenance Reply with quote

After my driveshaft & final drive mishap a few weeks ago (while TRYING to get to HMX) I started wondering just how much work those parts do.

Also wondered why many K100/K1100 driveshafts seem to have a lifespan of about 100,000 miles or 160,000 km.

Doing some simple math and using my RS wheel/tire assembly measurements I came up with a couple startling figures.

80" tire circumference will turn 792 times/mile.

The FD ratio of 31:11 will have the driveshaft turn 2233 revolutions/mile.

So by the time the bike hits 100,000 miles, the driveshaft will have completed 223,344,000 revolutions- yeah almost a quarter of a billion.

Now remember the universal joints constantly change angle, so during each one of those 223,344,000 revolutions the bearings in the "U" joint end caps are constantly moving.

Boggles the mind, huh?

Just one of the multitude of things that runs through my mind at 3am.

Moral of this post? Getting near 100k miles or 160k km? Check your driveshaft!! It has been through lots of hard work.
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John & Cathy

'92 K100RS4V Pearl White SOLD
'04 K1200GT
IBA Several-SS1k, BBG, 50CC NYC to S.F.
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N41EF
Flying Brick Rider


Joined: 23 Mar 2014
Posts: 406
Location: Aiken, SC

PostPosted: Thu May 18, 2017 7:52 pm    Post subject: Reply with quote

Thats just the rotational load, what about the bike going over bumps, changing the ujoint angle which would flex and cause the joints to flex as well and turn.I didn't realize how small the joints are. Throw in there is no way to lube the original ones I think it's kind of a time bomb, waiting for the worst possible time to go out.
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2014 R1200RT Water Cooled
2001 R1100S Light
1993 K1100LT. Nissan Ice Blue.(Gone)
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SugarHillCTD
Site Admin


Joined: 10 Oct 2007
Posts: 4240
Location: Now in Eastern Pennsylvania

PostPosted: Sat May 20, 2017 6:20 pm    Post subject: Reply with quote

Yeah Chuck- It is amazing that the U joints last that long......
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John & Cathy

'92 K100RS4V Pearl White SOLD
'04 K1200GT
IBA Several-SS1k, BBG, 50CC NYC to S.F.
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beemrdon52
Brick Rider


Joined: 02 Mar 2015
Posts: 44
Location: Las Vegas area

PostPosted: Fri Oct 20, 2017 1:49 am    Post subject: Reply with quote

Hello Ya'll,
My K 1100 LT now has 102,xxx miles.
My FD wiggles from 3-9 o'clock.
I am looking for a nice, low mile replacement. (anyone?)
While I have the FD off, I will be looking at the drive shaft.
What should I look for?
Thanx
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1996 K1100 LT SE, Aspen Silver 148,xxx mi.
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SugarHillCTD
Site Admin


Joined: 10 Oct 2007
Posts: 4240
Location: Now in Eastern Pennsylvania

PostPosted: Fri Oct 20, 2017 5:50 am    Post subject: Reply with quote

Here is MY opinion.

Obviously when I have the shaft in my hand, both joints should feel smooth but slightly stiff. The stiff part has two reasons.

-First being smooth and stiff indicates that you are installing a part that will be reliable.
-The second reason will become evident when you do install it. If the forward joint isn't stiff and won't stay pointed straight it will be a real pain to slide up into the swingarm and get it onto the output shaft. DAMHIK

Also all the splines should look sharp and undamaged.

Others should add some opinions also.
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John & Cathy

'92 K100RS4V Pearl White SOLD
'04 K1200GT
IBA Several-SS1k, BBG, 50CC NYC to S.F.
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