|Spine Frame Rear Drive Pinion Seal Replacement Procedure
The shop manual gives exploded views, but does not detail the procedure; here's how I did it on a '97 Sporti 1100 - YMMV: Supplies needed: new rear seal, new pinion bearing block o-ring. If you plan on running a synthetic gear lube, ask for a Vitron seal.
Remove the rear tire (see owners or shop manual). You will need a swingarm stand. I use the Lockhart Phillips universal type (white in color) available from Chaparral and others.
Put block or jack stand type supports under the drive box and the rear end of the u-joint. The manual cautions against allowing the weight of the drive to be unsupported, as it may damage the u-joint if it bears against the end-of-travel.
Unlike the Tonti frames, the Sporti (and other spine frames?) rear drive is captured on the swingarm by a funnel shaped bushing that fits into the swingarm. In my case, this was corroded in place, so I had to drive it out using a 5/8" wooden dowel. An appropriate sized brass punch would have worked if I would have had one at the time. Before you do this, remove the bushing & washer from the recess on the outside of the swingarm and note the relationship of the bushing and washer in between the rear drive and swingarm.
Disconnect bolt that secures the torque arm to the drive. You should now be able to pull the drive rearward and remove it, along with the driveshaft.
The drive shaft should pull off the rear end splines. Set the drive unit in a cardboard box or other holder so that the splines are pointing straight up. Remove the u-joint guard and remove the 4 bolts that hold the seal block in place. The block should pull off easily. Remove and discard the o-ring, unless you feel brave about re-using it.
Use 2 blocks of wood or similar to support the seal block while you drive out the seal with a punch or similar. I was able to push the new seal into place with my fingers, after first cleaning the area and lubing it with WD-40.
Clean any and all gunk from the pinion-seal surface with green Scotchbrite.
Assembly is the reverse of disassembly, but I coat all non-threaded bolt surfaces with a light coat of grease to inhibit corrosion. I also used locktite on all threads, except the torque arm bolt, as it has a nylock nut and lockwasher. I also cleaned and lubed all splines and cleaned up accumulated gunk around the u-joints.