Cleaning One's Rear End

Of course it's not what you think.  I cleaned up the rear differential I bought last year along with the bounce house bonnet.

I want to lower the RPMs while cruising at highway speeds.  One way to do that is to change the final drive ratio at the differential.  (The other way is to change the transmission, but that's becoming prohibitively expensive.)  With a 4.22 final drive ratio, I'm running over 4500 RPM at 70.  It sounds like a swarm of angry bees, which is neat in short bursts but not fun for 50 miles, or even 10.  So I found a 3.90 final drive differential, which should lower the RPMs by about 10% and be more tolerable.  The only problem is, it's filthy dirty having sat in a breaker yard for who knows how long.

Here's what I got.  The outside is pretty gnarly, but the innards are actually pretty clean.

 

I pulled the flange off the front and ewww.

 

After a good scrubbing and some parts cleaner on the innards, I got this.  Notice the new oil seal in the pan.

Having cleaned everything as best I could, I stood it on end and ran some synthetic oil through the bearings and gears to flush out whatever else I could.  After a couple passes it came out pretty clean, and once it's in service I'll change the oil after a few miles to finish the job.

That 10-39 number is what I'm after.  10 teeth on the pinion, 39 teeth on the crownwheel.

After sandblasting, fixing and painting the flange and dust cover, it's time to reassemble.

 

And now it goes on the shelf with everything else until I can use it.