The return of gearbox fun!

[Bing]

Hey guys,

I finally had the time I needed to get in the shed and get started on the bike.

I have the final drive off, the swing arm is off and the gearbox out.

Checking those components the final drive feels firm. The drive shaft doesn't have any play. The gearbox on the otherhand has a distinctly notchy feel it should be smooth shouldn't it?

Please feel free to weigh in with any suggestions, hints or tips.
    

[Semper Gumby]

Yep should be smooth.  Mine always is when I pull it off.  I usually check every gear by hand.

How many miles on this box?

Is the box making noise?  Normal gearboxes whine a bit in 4th gear but make no other noises.  Hollow "thunks" while shifting usually mean something needs to be shimed.

Is the magnetic plug covered with shinney chunks or is it just dirty fuzz?  (Dirty fuzz is normal)  

Does the oil coming out of the tranny look like fresh gear oil or does it look like chocolate milk? (Water contamination through speedo cable)

What does the tranny input spline look like?  When you re-install this make sure you only put grease (Honda Moly) on the tranmission part of this equation plus a little dolip on the tip of the end of the clutch actuating rod (in the center if the tranny input spline).  DO NOT put any grease on the inside of the friction plate (the female part of this equation).  If you do the tranny input spline will push this grease to the center of the clutch where through centriugal forces it will be slung onto the forward half of your clutch friction plate.  This contamination will render half your clutch useless.  The other half will end up being burned and scored and will cost you big bucks to replace.  

The picture in the Clymer manual showes white grease on the female portion.  (Resist the urge to do the same!)  You may clean the female part of the friction plate but do not grease! (With a tooth brush and only with outward strokes.  Do not push dirt and cleaner into the clutch.)

Ask me how I know these things....  

[Bob_Roller]

My first guess, would be bearings .

How does the rubber boot that covers the speedometer drive cable at the  transmission look ?

Water gets by the boot at the top, where it seals against the cable sheath, when it loses it's 'grip' on the cable sheath .

The bearings in the transmission on my '81 R65 succumbed to rust damage, after about 5 years of getting water into the transmission, until I figured out how the water was getting into the transmission .

[Bing]

Thanks guys, that's what I thought.

The speedo drive boot is intact but fairly hard. The oil in the box is clean and there are no major parts on the drain plug 'yet'. But I didn't get many k's on the bike myself before the g'box grumble took it off the road. Didn't want to push my luck with the possibility of the back wheel locking up.  

The input spline and the finaldrive/wheel spline both show a little wear but nowhere near as bad as some of the photos I've seen on here. Thanks for the grease/spline advice that sounds like it was an expensive lesson!

If I were to replace the bearings myself is the end float measuring plate an absolute requirement or can I get by just miking the bearings?

Any way I approach this it's going to be an interesting exercise. Thanks again for the advice guys.

[Bing]

Forgot to mention the bike probably has 137,000 kms!

[Bob_Roller]

I've never gone into a BMW airhead transmission, but from what I've heard, it's a necessity to get the shimming correct by measuring the the gap with a plate with a hole drilled/milled into it .

My transmission had 78,000 miles (126,000km) on it, and I was getting an increasing amount of metal on the magnetic drain plug, plus a low frequency 'rumble' for about 15,000 miles .

The rumble or vibration went away with the transmission rebuild .

You could clearly see rust and pitting on the bearing races and balls .

If you do go into the gearbox, make sure you replace the shifter pawl spring as well .

Our chief moderator here, Justin B. has gone into an R65 gearbox, I'm sure he can give some tips on the process .

[Rob Valdez 79 R65]

One of the easiest quick tests is to grab the input shaft and push and pull it.  There should be a slight movement, but not too much.  There are tolerance numbers published somewhere...

[Semper Gumby]

The warranty on my gearbox expired at 80,000 miles.  The bike now has 98,700 miles (164,500 Kms) on it and still going strong.  (Knock on wood).