Does the Sterling 10.25 rear diff have a vent tube? If so, where does it exit the case? I cannot find a vent tube on mine.

Reason I'm asking is that I accidentally left my rear air locker on for about 40 minutes and 40 miles on the interstate. Stopped at a rest area, walked back and found a puddle of gear oil coming out of the downhill brake drum, and heard air and oil spitting through the seals on both sides. Air leakage from the locker (and some slow leakage is normal) overpressurized the case and vented out the axleshaft seals.

I quickly turned off the locker and loosened the fill plug to vent pressure. There was enough pressure to stream oil 3' from the plug. Once pressure dropped, I tightened the plug and drove home. No sign of rear brake grabbing or slipping, so I may have gotten lucky and not had any significant oil on the braking surfaces. I also don't see any signs of additional leakage out the seals.

I figured the reason that air and oil vented out the axleshaft seals was that the vent tube was blocked and needed cleaning but I can't find a vent tube. Is there a vent somewhere, or is the rear differential fully sealed?

 

It should. Slide under from behind, driver's side, find where the brake lines come together in a block attached to the axle tube. That block does double duty as the axle vent. Rubber hose clips to the frame. When we bought our '85 IDI last year, the hose coming off it was cut and plugged with dirt. When I took it off, it hissed off pressure for several seconds. Caught it before it leached anything out the end seals. Sounds like you dodged a bullet just like I did.

 

Thank you- I mistook the whole assembly for all brake lines.

Problem was a big "grease" clog in the hose nipple screwed into the block on the axle tube. Case was still pressurized (3.5 days after being driven!), and the clog held even after digging some out with an awl AND putting over 25" of vacuum on the nipple. Cleared it with a small drill bit in a pin vise- basically drilled out the gunk. Used the pin vise so I didn't drop the bit into the tube.

The gunk looks like old-fashioned brown "cake" grease.

Also, the vent hose was a bit restricted.

The differential is going to get re-filled, so I'm going to spray degreaser into the detached vent hose, followed later by air. I'll spray some degreaser into the nipple, drain the case, follow up with some used gear lube and then air through the nipple to flush. And then I'll refill.

 

No surprise there. When this happened with my '85, it had been parked for probably a month and still vented quite a bit of pressure.