My Sunbeam leaks oil from the engine, transmission, and rear axle. Hence, I expect to post several articles on my attempts to lessen the puddles that accumulate on the garage floor. I will start at the back.
To the right is an internet image (ie, not from my car) of a Sunbeam rear axle. In short, the axle connects the engine through the transmission to the rear wheels. Gears inside the axle transfer the engine’s rotating force 90 degrees and allow the left and right wheels to turn at different speeds.
The axle is filled with a special oil to lubricate 
gears and other moving parts. Three rubber seals are meant to keep the oil in, but they can deteriorate over time and leak. My Sunbeam has been dripping oil from the seal where the transmission connects to the axle (green arrow above). This is called the pinion, named for the gear behind the seal.
The Sunbeam’s rubber seals are held in place by metal rings. To the right is the old seal that did not come out without a fight. Seals are press fit into the axle housing and, after 50 years, can be very difficult to pull out. The red arrow points 
to a bit of hardened rubber. You can also see a piece of spring that originally pressed the rubber against the shaft.
With the old seal out, I looked inside the axle. To the right is the pinion shaft in the center of the picture. A roller bearing (not shown) holds the shaft in place, and the seal fits inside the axle housing. I happened to notice a shiny piece of metal in the bottom of the housing. It looked out of place, and I used a magnet to fish it out for inspection.
It turns out that the unidentified object
is part of a shim (green arrow). Its other half was nowhere to be found, and I decided to ignore this fact and hope that it will not get caught in any gears.
Shims are used to set the position of the pinion gear and its roller bearing. According the to the workshop manual, one adds or subtracts shims based on the force needed to turn the pinion shaft. If the shaft is too tight (hard to spin), then more shims are needed. I removed six shims from the roller bearing and measured their total thickness with a Harbor Freight caliper (blue arrow). I didn’t care about accuracy but precision: I needed only to reproduce the total thickness with a combination of old and new shims, of course without the broken one.
Fortunately, I was able to buy a few new shims and find a combination that seemed to provide the correct clearance. But I was still left with the question, ‘why did the shim shear in half?’ One possibility is that the nut holding the bearing in place was loose when I removed it. According to the manual, the pinion nut should be torqued to 110 foot pounds, a setting that is hard to remove. I remember that the nut came off surprisingly easily.
The manual calls for 4-8 inch pounds of pressure (torque) and helpfully recommends using a fish scale
and string to measure the pressure. Wrap a string around the pinion yoke (above left), attach the string to the scale, and pull. If the scale reads in the specified range, you have the right shim spacers. For those technically inclined, this trick works because the yoke is almost exactly 2 inches in diameter, or has a 1 inch radius. The fish scale measures force at 1 inch from the center of the shaft.
Did I cure this leak? Time will tell.
Sunbeam 