I was out doing some firewood and while going up a hill on my 85 BIG RED I felt an interruption/skip in power and heard a clicking noise. This only lasted a second and then power was restored and the clicking noise was gone. The first thing I thought was that the rear wheel hub splines were worn. I took it easy and got back home with a little more clicking and power loss. I went to drive the big red up on the Handy lift and then I lost all power to the rear wheels and it wouldn't climb up the small ramp. Upon further inspection I found that the rear axle wasn't spinning while in gear and under load so I knew it wasn't the wheel hubs. Normally if its wheel hubs only one will go so you can still move (power to just one wheel) but you will hear a clicking noise. HERE is a link to a worn wheel hub post. I jacked up the rear end and the tires would spin but as soon as I applied some resistance to the tires they stopped and I heard the same clicking noise. The clicking was coming from the differential area. I proceeded to remove the rear axle and found that the splines that connect the rear differential ring gear and rear axle were worn.

Worn differential splines

Worn rear axle splines at differential location

Next I needed to disassemble the rear differential to replace the ring gear splines. Since I have the differential open I will do a good inspection and rebuild if necessary.

The good news is that I found the rear differential was in good shape. It's also good that the sleeve with the worn splines can be pressed out of the ring gear.

Images showing the sleeve and ring gear fit.

I had an ATC250SX rear differential that had a bad ring and pinion but the ring gear sleeve had good splines. I'm glad I hung on to that. The 85 250ES and 85 ATC 250SX use the same ring gear sleeve. I used a shop press to remove and install the sleeve in the ring gear. It's not a really tight fit and it doesn't take much press pressure to remove and install.

Using shop press to install ring gear on sleeve.

Splines are used but are in good shape. I will replace the rear axle with one that has good splines.

I put everything back together and my daily BIG RED is back in service.