Blacky's been a faithful draft horse for many years. Of course aside from preventive maintenance, some repairs must be expected, eventually. At 19 years old and 273k miles the rear axle started leaking oil.
It wasn't leaking from the fill/check plug as that pic might suggest. The problem was corrosion. That rear cover was rusted to the point of perforation. The leak was caught early, so it didn't lose much oil, fortunately.
Thanks to online forums I found others had experienced the same problem. Many tried plugging pinholes with JB Weld (epoxy). It's a bandaid type fix. Not surprisingly, success was limited. What I liked better was how one guy modified a replacement cover. Instead of welding on the cover, as the factory made the original, he threaded holes into the axle housing. His new cover bolted around the edges. He sealed the interface with RTV silicone for a custom gasket.
Toyota made the rear cover permanent. Internal gears are accessible from the front/shaft end. Just unbolt and remove the ring & pinion carrier as a unit. I liked the idea of the new cover being removable for inspection.
The old cover was removed with a cut-off wheel. The old lip/rim was ground flat enough. Exposing the internals helped inform modification of the new cover. The fill hole was drilled larger with a hole saw. A simple guide upturned about 45 degrees made the hole elliptical.
A threaded coupler was welded into the cover both inside and out. Upturning the fill port is not only more funnel friendly. The angle was chosen for a clear path to the bottom of the axle housing. So it'll be noninvasive to periodically swab it with a telescoping magnet to remove any wear material.
A second threaded hole was added for a site glass. That way instead of crawling under the truck with a wrench (and risk getting dirty, gasp!) the oil level could be checked visibly at a glance. Of course being so trivial, oil level can monitored much more regularly. To me that's great Murphy Insurance for keeping the truck healthy.
To finish the project, with the axle removed from the truck the housing was wire wheeled to remove rust. Both housing and cover were Rustoleumed. First primed with Rust Reformer. Then painted with Rubberized Undercoating.
The rear brakes also got a complete overhaul: new drums, shoes, springs etc, parking brake/adjuster mechaninism, even brake lines.
What a project. It was budgeted for: time and cost. And the leak made sense given the truck's age. The first eight years of its life were spent in snow/salt states.
Also, I learned something while researching the issue. On one forum a nice guy shared how his mechanic found the axle vent clogged. While only a $10 part, easily replaced, mine only needed cleaning. Moreover! I suspect that clogged vent observation was key. If moisture from condensation could not escape the axle housing, where would it collect? Oil is lighter. Water is heavier. That explains why pix of other leaky differentials were worst on the bottom.
Take away: also check that axle vent periodically!
Overall, this project was quite satisfying. It improved my confidence in Blacky providing reliable service for the foreseeable future.
