750S final drive oil leak

[richbourne]

My 1974 750S leaks a little oil from the final drive (drips from the rear drum onto the right side of the rear tyre). It only really does this when left on its side stand.

Rear drive big seal issue?

[pehayes]

That is an old bike and old rubber parts.  Could be anything.  Big outer seal, smaller inner seal, gaskets, o-rings, could be the passing oil from the transmission, past the output shaft seal, and down the shaft tube.  Start by draining, measureing, and refilling both the transmission AND the rear drive.  With clean containers, you can reuse the lubricant.  Unless you know a recent rebuild history of this drive, I'd just start by replacing all the consumables in the old drive.

Patrick Hayes
Fremont CA

[bigbikerrick]

What are the symptoms when the small inner seal goes bad, same as the big seal? ( oil on rear wheel)How difficult is it to replace the small inner seal? I have an oil leak on my eldo, and I am thinking it may be the small inner seal.
Thanks Rick

[pehayes]

You need to remove the rear wheel to inspect the hub of the rear drive.  If the big seal leaks, then oil oozes outward toward the perimeter and generally the center of the hub stays dry or greasy.  If the inner seal leaks, then the internal hub will have a significant puddle of oil as well as dripping and oozing out toward the perimeter.

Yes, the smaller inner seal is technically more difficult to change than the larger/outer seal.

First, you need a simple punch driver to take out the axle spacer.

Second, you need spousal permission to bake the drive in your oven (think smoke) so that the aluminum expands and the outer race of the inner bearing falls out (or you have an outside oven) (or you fabricate a special puller like I did) (or you have the factory puller tool).

Third, once the bearing race is out of the way the seal prises out easily.
Caution: make sure you observe and inspect the inner seal before removing it.  Remember, you are looking at it from INSIDE the oil chamber.  So, the new seal installs 'backwards' or with the labels/dimensions facing away from you.  The opposite of the direction that most grease seals are installed.

You might need paper gaskets, o-rings, etc based on your particular model.

Patrick Hayes
Fremont CA