Stincky downshifting...Can someone explain the mechanics?

[FOGDART]

Question about the '87 K75S that I inherited last month.  It's only got 17K on it but while riding it home from ND to OR I noticed the downshift from 4-3 and occasionally 3-2 was pretty sticky unless I carried some RPM as I downshifted.  I looked it up here when I got home and read that it could be a symptom of the transmission input splines needing lube.  So, this weekend I pulled it all apart, cleaned things up, lubed the splines with Guard Dog, put it back together and, SHAZZAM!, it downshifts just as sweet as can be now.  Love it!

But the mechanic in me is questioning why lack of lube on the input spline affects the downshift.  I don't understand the mechanics of this phenomenon...Anybody got an answer that a halfwit like me might understand?

BTW...I went into this job assuming I wouldn't need a clutch alignment tool as I planned to leave the clutch alone.  When I went to reinstall the transmission, it wouldn't line up...looked from behind and the friction plate was obviously off center.  I have no idea how it moved as I was very careful pulling the transmission straight back and I can't imagine it moving anyway... :dunno2:...even used guide pins I made from long bolts.  Loosened the clutch bolts enough so the friction plate would move then finger tightened them and used the transmission itself as an alignment tool.  Took a couple tries but it slid in eventually.  Once it did, I carefully pulled the transmission back and torqued the clutch bolts and slid the transmission back forward. Other than that unexpected issue, the job was pretty straight forward.  Spent more time cleaning parts that actually wrenching. This was my first experience working on a BMW...I am very impressed with how this machine was designed. 

[The Mighty Gryphon]

I am guessing that the friction disc needs to float a bit to allow things to fully disengage.  Dry splines inhibit the free movement of the various clutch parts to enable complete disengagement and the unloading of the transmission. 

Yes, these bikes shift very nicely when the clutch splines are lubed.  Whenever I hear someone talk about clunky downshifting, I automatically assume they have never done the clutch splines.  It's an ugly job, but one that pays back with really big rewards.

[FOGDART]

Thanks, TMG...  That makes sense.  I love it when little fixes make a big difference but it drives me nuts not understanding how it happened.  My brain is beginning to unspool now!

[Chaos]

This was my first experience working on a BMW...I am very impressed with how this machine was designed.

BMW hit a high water mark with the early bricks.  Fairly simple, easily maintained and utterly dependable, with enough quirks to make them interesting.

[drut]

"BMW hit a high water mark with the early bricks.  Fairly simple, easily maintained and utterly dependable, with enough quirks to make them interesting. "
 + 1

[FOGDART]

Yeah... I was a little intimidated when I first looked at this bike but after pulling the transmission to do the spline lube, I'm actually looking forward to getting into it next time!  Everything seems really well thought out.  But for now, I think it's ready to go a lot of miles before anything serious will need to be done.  17K miles, new tires, fresh fluids, fresh lube on all the splines, running smooth as silk....and it's a damn nice looking bike for being 28 yrs old! Every time I go into the garage I stop and admire it.  :riding:

[Tuco]

Nice, but I wish all you guys would quit posting pics of your K75S'. So far I'm acting like an alleged adult and talking myself out of adding one to the fleet. Don't know how long I can hold out before my MBOD kicks in. (Multiple Bike Owner Disorder).

[The Mighty Gryphon]

Tuco, Man, you know you need something for classy toodling around town!  Save the LT for the open road.

[stokester]

Nice, but I wish all you guys would quit posting pics of your K75S'. So far I'm acting like an alleged adult and talking myself out of adding one to the fleet. Don't know how long I can hold out before my MBOD kicks in. (Multiple Bike Owner Disorder).

Don't fight it...

[gazman]

Tuco ditto I to have to fight the urge

[Scott_]

Tuco ditto I to have to fight the urge

+1 here too.......
I have to keep telling myself I already have 2 1100's, I don't really need a 75. Though sometimes I think it would be better for daily commuting... :dunno

[Motorhobo]

It's still cheaper than crack.

[F14CRAZY]

It's a pain, and I still think it's dumb that the clutch has to be lubed, but I've got pulling the trans down to an hour and 15 minutes.

I've found that when the clutch disc hub isn't aligning with the trans input shaft it'll line up if you press the clutch release lever