Developed a terrible vibration from the rear end on Friday (4/1) on my way to work in the morning. Pulled it onto the rack and verified vibration was coming from rear differential. Pulled it back outside so I could work and spent the rest of the day thinking about my options.

Pulled the 4Runner back on the rack that afternoon. Drained the diff fluid and checked the fluid for color and condition. Fluid looked brand new with hardly any metal flecks in it so I decided to gamble and replace the side bearings. Ordered the carrier bearings (9036650007) Friday from Toyota dealership next door. Picked them up Saturday, but the bearing puller I ordered from Amazon didn't get delivered until late Saturday.

Pulled the rear diff on Sunday, and checked the backlash/preload before disassembly. Backlash was 7 thou and pinion preload was around 30 in/lb to start (very high) but was around 7 in/lb once it was spinning. Pinion bearing felt notchy as well. Not a good sign, but I couldn't return the carrier bearings since they were special ordered. Old carrier bearings felt and looked fine.

Went ahead and replaced the carrier bearings. Final backlash was 5.5 thou. Spec is 5-7 thou. Reassembled and test drove it on the lift. The noise from the rear end was still there, but the vibration was gone. I'm not sure what happened or why, but I highly doubt it was replacing the carrier bearings that fixed it.

Since I'm retarded not rich I'm going to keep running this rear diff until the vibration comes back.