Subaru rear differential leak


#1

My '96 Legacy station wagon (2.2L engine, automatic transmission, about 115,000 miles) has recently developed a rear differential leak. A few drops of gear oil appeared on my driveway after a recent highway trip (500 miles round trip @ 70-75 mph).



Upon closer inspection, I’ve discovered that the oil is coming from the TOP of the differential, running down the rear cover, and then dripping to the ground.



Is there a breather or something on top of the differential? My Haynes manual doesn’t go into great detail regarding the rear differential, and you can’t see much from under the car.



There appears to be something resembling a breather on the upper right rear corner of the differential, but I can’t get a good look at it.



If there is a breather, under what conditions would gear oil leak from it? The differential oil was changed at 80K miles. Never any leaks until now.



Why is it leaking from the top? What’s up there? Subaru experts, please help.


#2

All gear casings require some sort of vent. If there were no vent, as the gears heated up along with the fluid, pressure would build in casing and blow the seals out.

What’s probably happening is the gear oil in the differential is oxidized because of age. This causes the oil to become volotile where when exposed to heat it turns to a vapor. And this is what comes out of the vent and drips onto the ground. If you’ve never had the differentials fluids changed, it might be a good time.

Tester


#3

Oops! I see you had the fluid changed at 80,000 miles.

In that case, I’d pull the cover off the dif and see if there’s an indication of the gears getting hot.

Tester


#4

Well, I would agree, except I specified that the differential oil had been changed at 80K miles. So it’s got about 35K miles on it, tops. Does gear oil oxidize in 35K miles?

I’m sure there is a vent, I just want some confirmation from someone familiar with this vehicle, and an explanation as to why, all of a sudden, the oil is being forced out the breather.


#5

Oh, I don’t like the sound of that. Makes sense, though.

Thanks, Tester. Your always have a good answer.


#6

Well, I’m not a Subie expert per se, but many differentials and standard transmissions have a metal ‘breather’ tube somewhere along the top of the casing. A lot of times, especially on older domestic vehicles, those metal tubes had a rubber hose attached to the metal tube. This rubber usually goes upward a couple of inches from the top end of the tube to keep lube in the housing. You might have just lost the rubber tube. Or the fluid was overfilled. That, combined with high-speed operation, might have created enough heat to expand the gear fluid enough so some was lost due to expansion of the fluid. If you can, climb under there, or use jack stands for better head clearance, bring a good light with you and a rag, of course, and before wiping anything down, see if there is a much cleaner area around the top of the tube. It will be noticeable. Just less corrosion. Now look around for the rubber hose. The hose might have deteriorated at the connection to the metal tube and simply slipped off. Some of these hoses had a spring clip around them to keep them from slipping off. Look for that clip or clamp. It just might be still on the metal tube. Some hoses also have a plastic or metal retainer attached to the body to keep the hose in an upright position. Look around. If it’s simply a deteriorated rubber hose, cleanly cut it back eliminating the deteriorated parts or buy a corectly-sized piece of rubber fuel line. Loosen the body clamp (if applicable), cut off any other hose around the metal tube, slip the rubber hose back on and secure the spring clamp or hose clamp, whatever, and slide the other end of the tube back onto the body clamp. Check the lubricant and top off, if necessary, with the proper type of differential fluid as prescribed by the manufacturer, and button everything back up. While you’re there, use Simple Green or a rag splashed with keroseneor diesel fuel, (DO NOT EVER USE GASOLINE TO CLEAN PARTS!),and clean up the outside case of the differential. Should be no more leaks. DO NOT overfill the differential. Just to where you’re supposed to, usually to the bottom of the fill hole. Any extra? Just let it drip out into a container of some kind, replace the fill plug, and wipe down the casing.


#7

Thanks, Profhandy, but there’s no breather tube, and the differential was not overfilled. I’ve driven this car 30K+ miles since its last differential oil change, under a variety of conditions, with no leaks.

Now, all of a sudden, it seems to be pushing oil out the breather.