Spare Final Drive Project

This is the drive I found with the help of some friends. The drive splines look good. The case is dirty, and ugly, but should clean up nice. The real question is what will the gear set look like. The only way to know is to pull it apart and take a look.

I removed the brake shoes. The friction material looks almost new. I cleaned the friction material up with some brake cleaner and then wiped the shoes (but not the friction material) down with a rag dipped in WD-40. They cleaned up real nice.

There was no gear oil to speak of in the drive. The drain plug isn’t the magnetic type; couldn’t look for metallic splinters. The nuts holding the case were removed and the case opened using the appropriate puller screws from the Cycle Works Many-in-one tool.

I pulled the bearing from the crown gear and cleaned it up. I think it will have to be replaced. There is a rough spot. I’ll try cleaning it some more on the off chance the roughness is a bit of dirt. I’ll also looking at it under the loupe.

The cover cleaned up quite nicely with some simple green, WD-40, and a scotchbright sponge. The breather hole was plugged solid. A pipe cleaner helped get it free of grunge. I dried it with the help of compressed air then wiped it down with WD-40 and put it away.

I used the Cycle Works gear holder to hold the pinion and coupling hub while removing the nut. The holder also helped keep things from moving as I bent down the tabs on the lock plate. Easy.

The parts book calls this the “coupling hub”. It couples the drive shaft to the final drive. This one has quite a bit of wear on the seal surface. The gears also has a noticeable step. I suppose it’s usable, but I’ll be looking for a replacement that doesn’t have quite so much wear.

This is the easy way to remove the threaded ring. The coupling hub nut and lock plate lightly hold the Cycle Works tool in place and an air impact wrench gently breaks the threaded ring free. I looked at the threaded ring afterwards and notices that there was zero wear in the notches in the removal direction, but there was some wear in two if the notches in the installation direction. Looks like the factory installer slipped when tightening down the ring oh so many years ago.

Once the ring was removed I stood the case on end and applied heat until the pinion and bearing fell out. I cleaned up the bearing a little without removing it just to see what it is like. I think it is fine and need not be replaced. I also measured the shim at 0.39 mm. One of the standard sizes was 0.38. I’ll check again when the shim is cool.

I wiped off the excess grunge then brought out the parts cleaner to attack the case. Some Goof Off helped remove parts of the paper gasket that didn’t want to come off easily. After getting the dirt loose in the parts washer I moved to the sink where Simple Green, a scotchbright sponge, and very hot water took care of the rest.

The last step was to coat the exterior of the case with Aluminum Jelly and let it sit for about 15 minutes before again rinsing in hot water and coating in WD-40. The results are pretty good. It looks nearly as good as the bead blasted case that is currently on the bike. I bet another 10-20 minutes of Aluminum Jelly would make it perfect.

I could see the drive splines were OK (certainly not great) and was quite happy to find the gear-set in otherwise excellent shape. Also, I cleaned and oiled the big bearing. What ever it was I felt yesterday is gone. As best as I can tell the needle bearings are also in good shape.

This image shows the new seal in the cover and, in the upper right of the image, another new seal in the pinion retaining nut. That seal faces the drive shaft as it’s job is to keep the oil in the drive shaft out of the final drive.

Bernd, on the /2 mailing list, mentioned removing the axle tube to make seal removal easier. Not needed, I replied. I’ve got this nifty seal puller…. Well, I should have listened for two reasons. 1) its easier to install the seal with the tube removed, and 2) you won’t scratch the tube if you remove it before removing the seal, nifty seal puller or not.

Installing the new seal is a snap with the axle tube removed. After the seal was installed I heated the case again to install the axle tube, then applied a bit more heat and let the ring gear needle bearing slip into place. The assembly was covered to keep dirt and dust out then put away to cool down. I’ll get back to it another day – other duties call right now.

What’s wrong with the second picture? I installed the threaded ring and torqued it down to 80 ft-lbs, then put the coupling hub over the pinion shaft and scratched my head. Something was wrong. The coupling hub lock plate wouldn’t fit.

This picture shows the missing seal ring. I re-installed the threaded ring, torqued it down to 80 ft-lbs, installed the coupling hub, the locking plate, and the nut (also torqued to 80 ft-lbs) then bent a section of the locking plate to stop the nut from loosening.

I used some dry marker on part of the ring gear to check the gear positions. The backlash feels OK. The ring gear was loosely rubbed against the pinion and there was dry marker transfer off the ring gear (pictured) onto the pinion. It’s a bit toward the back of the gear, which is OK (I think) as there was zero pressure applied.

A new gasket was placed on the body in preparation for measuring the needed shim size for the ring gear. Parallels and a depth micrometer were used to measure the bearing hight, specifically the distance between the gasket surface and the upper edge of the outer race. In a perfect world the measurement would be the same all around the case.

The second measurement was the depth of the pocket for the ring gear bearing. The same parallels were used, plus the addition of a 0.185 inch cross piece. The parallel widths will cancel when calculating the shim size. Again, there was a repeatable variance in measurements: 1.605 ~ 1.607 inch. I calculated the shim size twice, using the high and low values for the two measurements to get the full range. The calculation is:

I took an idea from Kees and used a cut off soda can as a seal protector. The shim was dropped into its slot. The gear was placed where it belonged, held up by the bearing. Heat was applied until the bearing/gear assembly dropped into place. A little pressure was used to make sure the bearing was fully seated as the cover cooled.

I was busy yesterday, but will finish up, more or less, today. The ring gear is in the cover and the cover and case are at the same temperature. The hardware has been soaked in parts dip and otherwise cleaned. The vent cap is pretty rusty, and the brake lever really needs to be re-plated.

I turned the ring gear and the pinion just to get a feel of how tight things are before putting the case together. The tightness is due to friction on the new seals. Since the case and cover are both cold they fit together easily; no binding. The cover nuts were tightened in a cross pattern: 1 3 5 2 4 6.

Some naval jelly, a wire brush, and then a file got the rust off of the vent cap. I cleaned and dried the vent cap then hit it with some rattle can paint after heating the paint can in hot water. Experience with this paint tells me it will dry to an aluminum looking color.

I used the Cycle Works tool to hold the pinion coupling gear as I bent the lock tab flat to remove the nut. As soon as the lock tab was flat I noticed that the nut was not tight. I know it was tight when I put the drive together. The nut and locking tab hold the coupling against a bushing/spacer that rides on the inner race of the bearing. If the nut is loose the bearing must have moved. That means that the bearing/shim were not seated in the final drive housing when I installed it the first time.

To check that theory I cleaned the pinion with some acetone, then marked it using a dry-erase marking pen. When it dried I dropped the ring gear back into the case and gave the pinion a spin in the drive direction. When the ring gear was removed the markings on the pinion show that the spacing is wrong. I repeated the test.

I removed the pinion from the case and checked the shim. It is 0.38 mm. Standard size shims are 0.2, 0.28, 0.38, 0.50, 0.63, 0.75, and 1.00 mm thick. I’ll probably try a 0.63 mm shim next, this time making absolutely, positively sure that the bearing/shim are fully seated and that the case if fully cooled before measuring.