17 April 2016

Moto Guzzi V700 / Ambassador /Eldorado Rear / Final Drive Rebuild

Really this is only half a rebuild as the pinion didn't need any re-shimming and was in great shape. That being said, I haven't found any rebuilds with pictures that cover the early stuff, and I do some things a little differently than others, so hopefully this will prove helpful. I cut my teeth on vintage BMWs so it's only natural that this procedure involves extensive use of the freezer and a heat gun.

Follow these steps at your own discretion and use your head and the proper PPE. I'm not responsible for anyone hurting themselves or ruining their drive.

The rear drive in pieces. Note, I removed the large outer bearing from the flange prior to reassembly. Also note that I installed studs into drive where it formerly would bolt onto the swingarm.

First, we have the replacement drive splines. You'll need to put the inner needle bearing race onto the splines. I perform this by freezing the splines for about 5-10 minutes, then heating the bearing race with a heat gun to the point that you'll need welding (or other thick) gloves to pick it up, you don't have to go crazy. Once it's hot, remove the splines from the freezer and drop the race right on, you shouldn't even need to drive it on, it should just fall right into place.

Next, insert the new splines into the crown gear. Again, this is accomplished with heat and freezing. Put the splines with the bearing race attached back into the freezer and heat the crown gear, again don't go crazy, this isn't a BMW and the tolerances aren't as insanely tight. Drop the heated crown gear right onto the spline piece, it should drop in easily and you'll have plenty of time to rotate the crown gear with ease to line up the bolt threads.

Now it's time to bolt it on. Some people replace the tab washers with 8mm Schnorr locking washers as it's two steel pieces bolting together, but there's nothing wrong with the tab washers, just a matter of ease of assembly. Use Blue Loctite on the M8x1.25 bolts and torque them to 31 ft/lbs. I used an impact gun to remove these bolts during disassembly, but I'm a stickler for torque settings so I used a torque wrench on reassembly. In order to hold everything in place while I torqued everything down properly, I wrapped rubber hose (in this case radiator hose that I cut in half) around the outer diameter of the splined flange (to protect the metal) and put it into a vice (not too tight, just enough that it won't move excessively while being torqued down).

Time for the large bearing to be installed on the crown gear/splined flange. Again, heat and cold are your friends, freeze the crown gear assembly and heat the bearing. I heated the bearing until the residual gear oil that degreasing didn't remove completely just began to smoke a little. When it's that hot it will, like everything else so far, drop right into place on the crown gear assembly. These pieces will have to go back into the freezer, but let everything cool down to room temperature before you go and do that. Go have a beer or take a cigarette break and once it's cooled down enough, put it into the freezer.

After about 10 minutes of letting the assembled crown gear shrink in the freezer, begin heating up the aluminum flange. Get it nice and hot then go grab the crown gear out of the freezer and set it down on the work bench, spline side facing up. Pick up the flange (using gloves of course) and set it squarely on top of the crown gear and position it over the bearing. If everything is heated and cooled correctly, this will require minimal to no force. Once it's on, double check that the bearing is seated squarely in the flange.

Let everything cool down to room temperature again. Once the temperature on both pieces has normalized, you can put in a new inner seal. You're now about 50% done with reassembly.

Next we go to the bare housing for the rear drive. We must insert the outer final drive seal. Unlike other seals, the flat side of this seal must be facing down when you press it in (so the back side of the seal where the spring retainer is kept should be facing you). It doesn't hurt to gently heat the rear drive housing, then oil the seal and use a socket to press the seal into place.

Once that seal is in, I press in the steel axle spacer into the rear drive housing. Again, light heat, cold housing, and it should tap in nice and easy.

Now that the smaller outer seal and axle spacer are in, drop the copper shim that goes between the seal and the needle bearing/race into place.

Once the copper shim is in place, again it's time to apply the hot and cold process. Freeze the outer bearing race and heat the rear drive housing. It should still be warm from the last heat application, but it isn't enough, get it hot enough so that you can't leave a finger on it for more than 10 seconds. When it's hot again and the bearing race is nice and cold, drop that in (it may need a few very light taps from a soft mallet, like plastic or brass at the most). Once in place, you can drop in the needle bearing cage.

After the needle bearing is in place, it's time to reinsert the locking plate. Simply lay the locking plate back into placel; the slotted side is secured by the rib in the housing, and the screw secures the plate against the bearing race. I use blue loctite here and once installed, I put additional punches in the plate to keep it in place.

At this point, it's time to put the gaskets and spacers on the crown gear aluminum flange. I grease both sides of the paper gasket, put it on, put the spacer in place, then grease both sides of the other paper gasket and apply it to the spacer. The grease should keep it in place and prevent the holes for the bolts sliding around when you insert the assembly into the housing.

Once the crown gear assembly is inserted, I insert the bolts and locking tabs (you don't want to use Schnorr washers here as the flange is aluminum) and tighten them down, but don't apply the specified torque yet.

Next I insert the pinion gear assembly (with new gasket and o-ring) into the housing and rotate the pinion gear to make sure nothing is binding up anywhere (note: I installed studs on my rear drive instead of bolting it on, this helps a little during this test as it prevents the pinion gear housing from rotating when you rotate the pinion).

Once this is confirmed, I torque down the crown gear assembly (in a star pattern) to 18 ft/lbs and then bend the locking tabs back into a locking position. Re-test the rear drive motion and test for free play.

Once that all checks out, it's time to fill the drive with 300ccs (approximately, you're filling until it begins to leak out of the level plug) of gear oil. Unlike the transmission, GL-5 is ok to use here instead of GL-4 as there aren't any brass or bronze bushings to get eaten up by the sulfur of GL-5. It should go without saying, but replace all crush washers on the drain plug, filler plug, and level plug on the rear drive before doing this.

And that's that. Make sure there aren't any obvious leaks and you're ready to go.

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