I’m going to powder coat the swing arm so I need to remove the drive shaft. BMW used two different drive shaft designs on the airheads changing the design in the 1981 model year. This 1983 RS has the second design drive shaft.
Drive Shaft Design
The older drive shaft design used a solid shaft. One end of the shaft attaches to a flange mounted on a universal joint that attaches to the transmission output flange and the other end has a bell housing that connects to the rear drive that is attached to the shaft with a shrink fit.
The newer drive Shaft–introduced starting in the 1978 model year, but showing up on different models in different years until 09/1981 when all airheads had this new swing arm–has a spring and two yokes. The larger yoke includes the bell coupling that attaches the shaft to the rear drive but it is free to spin on the drive Shaft. The smaller yoke is attached to the drive Shaft via splines so it spins with the drive Shaft. Behind the smaller yoke is a coil spring. The end of the drive Shaft with the smaller yoke also uses a flange mounted in a universal joint to attach to the transmission output flange.
As the engine abruptly changes RPM (up-shifts and down-shifts, hard acceleration and braking) the rear wheel and rear drive are rotating and have a lot of resistance (aka, inertia) to any sudden changes in rotation speed. Torque is what changes the speed of rotation. When the speed of rotation of the rear wheel, rear drive and drive shaft change quickly, an opposite rotation is created (Newton’s 3rd Law: For every action, there is an equal and opposite reaction). This resistance to a change in rotation deforms the drive shaft (twists it). This stores energy in the shaft that is released later. The result is stress on the driveline components and jerks in the driveline as the drive shaft twists and untwists. And changes in the torque applied to the drive shaft lifts (acceleration) and lowers (deceleration) the chassis of the bike–which is familiar to any airhead rider–and that affects handling.
When I say “twists the drive shaft”, I don’t mean this is the same as rotating the shaft. The shaft does rotate, but the change in how fast it rotates causes the metal in the shaft to twist and untwist during and shortly after a sudden change in rotation of the drive shaft. The shaft acts like a watch spring that is wound up (stores energy) and then unwinds (releases energy). This twisting/untwisting puts stress on the rear drive, drive shaft, clutch and transmission and makes driveline jerky which also affects handling by jacking the frame up or down.
With the yokes and spring, a sudden change in rotation causes the yokes to ride up the ramps and compress the spring, and then return to the bottom of the ramp as the change in rotation of the drive shaft decreases. The spring absorbs the force of the sudden change in rotation smoothing out the change over time a longer time. This reduces the stress in all the drive line components (transmission, clutch, drive shaft, rear drive) and improves handling.
I’ve removed the drive shaft from a 1977 R100RS using a Cycle Works tool, but it doesn’t work with the newer, spring loaded drive shaft. I need a different Cycle Works tool to remove the drive shaft on this 1983 RS. That’s the price of progress. 🙂
Cycle Works Driveshaft Removal Tool 1955-1980
Here is a link to the description of this tool.
I used this tool to remove the drive shaft on a 1977 R100RS and you can see how I did that work here:
Cycle Works Driveshaft Spring Compressor Tool 1981+
This the tool used to compress the drive shaft spring so I can remove the snap ring that secures large yoke with the bell coupling from the drive shaft.
Here is a link to the tool description.
This is the tool I used on this project.
I made a video showing assembly of the Cycle Works drive shaft spring compressor tool and how I used it to remove the drive shaft.
Assemble Cycle Works Tool
The tool consists of two threaded rods, two aluminum plates, a narrow one without a large hole in the center and a wider one with a hole in the center. There are two larger coupling nuts, two regular nuts and four thick washers as shown in the picture below.
In some versions of the tool, the long threaded rod is replaced with two smaller rods and coupling nuts used to construct the longer rod. This was done to reduce the size of the shipping box.
The narrow plate has two tapped holes the threaded rods thread into. Each rod is secured with a thick washer under a nut. I screw the rods far enough into the plate so the end of the rod is even with the bottom of the nut.
The wider aluminum plate with the hole in the middle has a counter bore hole on one side that fits around the bell coupling. The other two holes are not threaded and slide over the threaded rod.
I put the narrow plate underneath the flange of the drive shaft.
Then I attach the wider aluminum plate with the hole through the threaded rods with the the counterbore hole over the bell coupling. I secure it with two thick washers and the coupling nuts. I hand tighten the coupling nuts to snug up the tool on the drive shaft.
Remove Drive Shaft Snap Ring
I use a box end wrench and turn one coupling nut a full revolution and then the next so I compress the spring uniformly. Three turns of each coupling nut is enough to expose the snap ring.
There is a notch on the end of the drive shaft for a small blade screw driver. I use a short shaft, small blade screw driver to start as it’s easier to maneuver. I lever the snap ring out of its groove until the snap ring is about even with the top of the drive shaft. Then I use a longer shaft, small blade screw driver with its additional leverage to pry the ring all the way off the drive shaft.
Remove Drive Shaft Components
There is a retaining ring under the snap ring and I try to remove it with a magnet. It would not come loose. And, I wasn’t able to separate the bell coupling from the drive shaft by pulling on it.
The drive shaft bell coupling should slide off the the shaft. But mine doesn’t do that. So, I push bell coupling and the drive shaft back into the swing arm. The bell coupling is captured inside the the narrow part of the swing arm. I use a large drift with a hammer on the end of the drive shaft and a couple firm raps on the drift separate the bell coupling from the drive shaft. That frees the bell coupling and retaining ring from the shaft.
I remove all the parts of the drive shaft assembly.
Drive Shaft Parts Order and Inspection
The drive shaft has splines, but the upper portion of them have been machined away so the bell coupling can slide onto the drive shaft, but not be directly attached to it. I inspect the splines for damage but don’t see any cracks, chips, rounding or other signs of abuse.
There is a collar that slides over the splines and rests against a shoulder on the drive shaft. The spring rests on the collar. The collar shows no signs of being abused.
The spring slides down the splines and rests up against the collar. I don’t have spring height that indicates if the spring is sagged or still servicable. But, the bike has 83,000+ miles so I’m going to replace the spring anyway.
The small yoke has splines that secure it to the drive shaft splines. I inspect the splines and the ramps for wear and tear. There are horizontal ridges on the inside of the ramps. There is a small chip on one edge of a ramp. The splines are not worn or damaged.
The larger yoke shows some scuffing and wear at the bottom and sides of the ramps. There are no chips on the edges of the ramps.
The splines in the bell coupling that engage the rear drive splines show no signs of wear, chips or rounding of the spline profile.
The bell coupling mates with the small yoke on the drive shaft as shown below. It’s a tight fit on the drive shaft.
The bell coupling is secured to the drive shaft using a retaining ring under a snap ring. The spring force pushes on the retaining ring to keep the snap ring in its groove. The bell coupling does not have splines so it is free to turn when there are large changes in torsional force applied to the drive shaft. The force of the compressed spring transmits the torque from the transmission to the bell coupling and the rear drive it attaches to.
The retaining ring has a groove machined into it on one side which pushes against the snap ring. The other side of the retaining ring that faces the inside the bell coupling is flat.
The snap ring fits into a groove on the end of the drive shaft and the retaining ring keeps it seated in the groove. The snap ring has a ridge machined into one side that fits against the groove of the retaining ring. The side of the snap ring that faces you when looking into the bell coupling is curved.
The snap ring and retaining ring must be assembled in the correct orientation. The snap ring is “USE ONCE” and must be replaced. If you don’t assemble them correctly, or reuse the snap ring, you risk having the drive shaft fail.
2019-06-29 Add link to 1977 drive shaft removal work. Minor edits.
2019-07014 Update when new drive shaft design introduced per Robert Fleischer note.