Question about transmissions

[69ZEFF65]

Well I couldn't find my original thread about engine spacers and a possible solution to a misalignment of my transmission output coupling and the the drive shaft coupling so I'm back with additional information on this odd to me problem.

The bike: 1979 R 100S VIN 6165010, one owner bike complete with extensive service and repair records. No documentation or visual indication of a bent frame or accident. The frame has undamaged factory paint and all components line up and assemble with no need to pry or persuade to install.

The problem: The output flange of the transmission does not line up with the drive shaft flange unless I adjust the swing arm pivots nearly all the way to the left, this leaves the wheel out of whack at the fender and the right side pivot pin almost to its stops. if the swing arm is centered the drive shaft binds in the tube.

Findings so far: All motor spacers are correct and in place as installed at the factory. The output flange of the motorcycles transmission (finned later model case) is located approximately 10mm further to the left in relation to the trans body than output flange on my spare transmission that has a smooth early style case. This is just the way the castings have measured out and is not due to damage or modifications.

Additional information: I had a chance to visually compare the output shaft locations and general clearances of drive shaft couplings and transmission dimensions when mounted on a number of '75-84 airheads and the one in my R 100S is clearly not the same as the others I inspected just last weekend.
I have installed a new larger tube swing arm from a later model RS bike but the stock swing arm and drive shaft assembly had damage consistent with a misaligned swing arm that caused the drive shaft to bind inside the tube.

My questions: Do I have the wrong transmission in my bike? Is there a difference between a mono shock transmission and a dual shock one in regards to the location of the output flange? Does an early GS have a transmission that has the output flange located differently? What about an R 65 transmission, are they different?

My quandary: I'm a /2 guy and somewhat new to airheads, this is an extremely nice and well documented bike and its a keeper and rider but I want it to be correct. I have been told all the airhead transmissions are the same and interchangeable so just what am I missing here?

There may be a reward for the solution to my problem!!!

[20774]

In case you wanted to see what was posted in the old thread:

http://www.bmwmoa.org/forum/showthread.php?t=60494&

[69ZEFF65]

I am just stumped on this and hope somebody can give me a clue as I have not got one! People who know me will confirm this.

[doktortim]

I am just stumped on this and hope somebody can give me a clue as I have not got one! People who know me will confirm this.

Trannies from 81 on had no fly wheel. They have a clutch carrier, a different clutch and different input shaft than the earlier Airheads. It is possible to do the conversion. There is a number on the bottom of the tranny that can prove what the case was when new, early or later type.

But you cannot just bolt an 81+ tranny into your 78 clutch and flywheel.

You need to confirm which clutch/tranny you have. Original type, or complete update to later type.

Sounds like you've been fankenbeemered by someone who was not concerned with details.

[69ZEFF65]

I'm aware of the different flywheel and the conversion steps involved but my issue is with the "output" side of the transmission not the flywheel or any conversion or deception by the original owner.

Just to clarify this a little: The flange on the out put shaft of the transmission does not line up properly with the coupling on the forward section of the drive shaft. The frame is not bent. I have discovered that the output shaft and flange are approximately 10 mm left of the same components on a spare transmission of the the same era.

I would like to know if any other transmissions were available for any other air head BMW motorcycle from that time period that would explain how this could be so.

[GeorgeRyals]

Since the frame is not bent, add 10 mm of spacers on the left side, line your swingarm up with the output shaft and go riding.

[GeorgeRyals]

Measure the trans from the centerline of the clutch push rod to the centerline of the output shaft to eliminate different case design diferences from smooth to ribbed. I'm pretty sure there are not two transmission designs with 10 mm difference between the input shaft/clutch pushrod and the output shaft.

[44006]

Change spacers and or stacks of washers however you need to get the shaft centered in the tube and the wheel near centered in fender and go ride it.

You can twist the engine somewhat if needed by manipulating spacers if necessary rather than keeping changes equal per side.

[wecm31]

Trannies from 81 on had no fly wheel. They have a clutch carrier, a different clutch and different input shaft than the earlier Airheads. But you cannot just bolt an 81+ tranny into your 78 clutch and flywheel.

I am currently hunting around for a spare transmission for my bike. Mine is in the queue awaiting rebuild, I want to get a used one to bridge the gap and get riding.

Is any 5 speed box from 1981 onward a straight bolt up for my bike??

thanks for the info....