1971 rear axle drive

[nohandels]

After looking at my R75 a little closer I decided to tare it down to the frame and do it over the right way. What other seals should I replace while I'm at it?
I found the rear axle drive to be leaking into the break chamber, so the seals need replacement. My question is: can I do this myself or will I need to take it in to be done?
My second question: Doe's anyone make a hydraulic add on system for the brakes? Of do those of you who ride this vintage bike feel you really need this?
Thanks,
Doug

[pmdave]

I firmly believe that if you're going to own an airhead, you need to do all your own maintenance and repair. Some components, such as the heads, transmission, and final drive, can be sent out to specialists. The first step should be to procure a shop manual that describes all the procedures with illustrations.

Concerning the final drive, it's not difficult to replace the "big" seal, but it does require heating the cover and keeping track of the shims. My first question with an airhead final drive concerns the splines. If the splines are worn more than about 30%, it's time for a spline rebuild. That's expensive, but you can save by doing the disassembly/reassembly yourself.

If your splines are still decent, replacing the big seal is a matter of unbolting the cover and extracting the crown gear/cover together. Note the position of the shims. With the cover supported on blocks, heating the cover (I use a propane torch kept moving around) allows the gear to drop out the bottom. Note the thin shims behind the bearing. It's also smart to feel the bearing. Don't spin it, but slowly rotate it feeling for irregularities. If there is any question about the big bearing, replace it. While you're at it, check the wear pattern on the gear tooth faces. If the pattern isn't centered on the crown gear faces, the shims need to be adjusted. It's not difficult, just detailed. See the shop manual.

While you're inspecting the crown gear, feel for any scratches in the surface just to the inside of the splne area. If there is any roughness, smooth it out with emery paper, so it doesn't chew up the new seal.

The new seal is pressed in, then the large shim(s) and the crown gear with bearing. Support the cover on blocks, heat the cover, and the gear/bearing will drop in. Grease the small thrust washer and place on the end of the crown gear. The grease holds it in place while you're assembling.

Whenever taking anything apart, it's very important to clean the housing first. I use a metal oil drain pan, a bristle brush, and spray "clutch and brake" cleaner. Likewise, before assembling a part, I clean out any gunk first--say the cavities inside and outside the case. Be sure that little oil drain hole is clean from the spline area to the outside.

As a minimum, you'll need a new seal, and a new cover gasket. The rest depends on what you discover as you take it apart. If you find either of the gears chipped or seriously worn, it's cheaper to find another used final drive (with 90% splines) in the same ratio.

There is also a seal at the input gear, to keep the final drive oil and the shaft oils separate. However, removing the input gear requires some special tools, and you may find it cheaper to send the parts out to a rebuilder. Doing all the cleanup work is half the labor, so go as far as you can, and don't worry about not being able to complete the job yourself.

pmdave

[pmdave]

Oh yeh, the brakes.

IMHO, hydraulic brakes on the rear wheel of an airhead are more of a problem than they are useful. Stick with the drum brakes, which require little maintenance and supply as much rear wheel braking as you need.

It's an airhead. Keep it simple.

pmdave

[flash412]

When the ring gear seal leaks, it should go out the weep hole under the axle nut.

When you have oil on your brakes, it is probably because the o-rings on the brake shaft need replacing. Remove the rear wheel. Mark the "S" on the brake shaft with a punch so you know which side is UP. Mark the upper brake shoe with a punch. Remove the brake shoes. Soak them in LACQUER THINNER to get any oil off them. Mark the location of the brake are on the end of the brake shaft. Remove the nut. Remove the arm. Remove the shaft. Replace the o-rings. Reassemble in reverse order. Problem solved.

Oh yeah... lube the o-rings with 90wt after you install them. Buy them from your local Ace Hardware store (or equivalent) unless you like paying ten times too much for parts that BMW does not manufacture.

[nohandels]

When the ring gear seal leaks, it should go out the weep hole under the axle nut.

When you have oil on your brakes, it is probably because the o-rings on the brake shaft need replacing. Remove the rear wheel. Mark the "S" on the brake shaft with a punch so you know which side is UP. Mark the upper brake shoe with a punch. Remove the brake shoes. Soak them in LACQUER THINNER to get any oil off them. Mark the location of the brake are on the end of the brake shaft. Remove the nut. Remove the arm. Remove the shaft. Replace the o-rings. Reassemble in reverse order. Problem solved.

Oh yeah... lube the o-rings with 90wt after you install them. Buy them from your local Ace Hardware store (or equivalent) unless you like paying ten times too much for parts that BMW does not manufacture.

Ah! I do have oil soaked breaks so maybe the seal is Ok!.
I have a much larger problem righ at the moment. I took off the exast headers yesterday night and when I emptied them into the trash sun flower seads fell out? O No? Anyway the left side was perfect but when I cracked the head on the right I discovered a mouse had made it's home years ago and the cylinder and piston is stuck. I now have the frame and engine on its side with PS Blaster covering the whole piston. Hopefully everything will clean up Ok? My fater and I restored a 1908 Thor and the bore looked a lot worse than this and it was fine so I'm sure this will be ok too.