Why spline lubrication?

[faffi]

Especially BMWs seems to require spline lubing of the clutch shaft splines as well as final drive splines. But we never hear this about cars. Well, at least I do not. Anybody know what this is required (more) on bikes than cars?

[Littlefield]

One thing is that automotive driveshaft splines are in an oily environment

[wirespokes]

 The lube is more to inhibit corrosion than to provide lubrication.

[Pescatore]

On a single joint cardan shaft I add a tiny bit of grease at the final drive.
That side slides back and forth when the swingarm... swings.

[Wayne Orwig]

Many car splines (except for the clutch) are 'wet'.
Maybe fewer cylinders mean the power pulses are stronger, as in for two revs:
2 cylinders BOOM------BOOM------
4 cylinders boom-boom-boom-boom
More cylinders have more 'flywheel' weight (crankpins, pistons, rods) to smooth the booms out.
And the clutch splines may be deeper than on a bike.
Or BMW uses that VERY expensive lube as a profit center.

[Perazzimx14]

Many car splines (except for the clutch) are 'wet'.
Maybe fewer cylinders mean the power pulses are stronger, as in for two revs:
2 cylinders BOOM------BOOM------
4 cylinders boom-boom-boom-boom
More cylinders have more 'flywheel' weight (crankpins, pistons, rods) to smooth the booms out.
And the clutch splines may be deeper than on a bike.
Or BMW uses that VERY expensive lube as a profit center.

Or just use Wurth SIG 3000. A $20 cartridge has enough to lube every BMW driveshaft in your state, twice. You can also use Prestone DOT4 and Mopar 70W-80 at $19 a liter verses BMW's 70W-80 at $56 for a 500ml bottle. No different than buying Honda branded oils/fluids. You can spend more but do you get more. There cost effective alternatives.

[JHBettsSr]

Especially BMWs seems to require spline lubing of the clutch shaft splines as well as final drive splines. But we never hear this about cars. Well, at least I do not. Anybody know what this is required (more) on bikes than cars?

I was a Master ASE automotive tech for about 20 years. And yes, the manual transmission input shaft splines are supposed to be cleaned and lubed when the clutch is replaced. Most clutch kits come with a small amount of specialized grease.