Hi,

    I recently noticed that the rear diff is leaking some fluid but the leak appears to be coming from the top of the housing and not from the stub seals or plugs. 

 

I read that there is a small port in those diffs which allows fluid to drain in case of an overfill (esp. when the car is on a steep incline)...other than that I can't guess why it would be leaking.

 

 

Any ideas?

 

 

Thanks...

 

--Damien

 

 

 

If it's just a little bit of dark dust/crunge stuck in place, that's just normal hot oil mist/vapors from the vent condensing on the outside of the housing.

probably OK, but, if the car has been driven through extremely high water, might be a good idea to do a drain/fill.

   Guys need to learn about running the vent tube up into the cab

So there is such a port hole?  I just got my winter tires off...and the wear on them is slightly uneven.  So when they are on the rear wheels they probably cause the RPM diff which causes that whatchamacallit component to spin wildly generating heat and a vapor mist. 

Heat and vapor mist are a normal part of operation, just a tiny bit but over long time frames a little builds up.

Oh I get it.  There's a breather on the top of the housing.

 

 

Yeah, I recently took a couple of long trips on snow tires...I'm sure it caused the fluid in there to heat up, build a vapor and overflow.

 

 

It doesn't look like a biggie and 'the man' in the shop wants 80 bucks to change the fluid so I'm thinking...'screw it'.

 

 

--Damien

I took it in and sure enough the level was down about halfway. 

 

 

Drivers who notice that symptom may want to take it in anyway...

"down about halfway"....how did they know?  the fluid level is sort of ambiguous and difficult to "check".

 

fluid loss suggests something is wrong other than unevenly warn tires, though i see that is your suspicion.  folks drive with mismatched tires and don't have this symptom.  very strange.

 

the rear tires are intended to turn at different rates - that's what allows you to go around a turn.  see this video posted today with a subaru rear wheel spinning on rollers while the other is stationary demonstrating this fact (same thing thaat happens when a Subaru's gets stuck, high centered, etc): http://www.ultimatesubaru.org/forum/topic/136943-awd-system-comparison-video/?do=findComment&comment=1153547

 

the AWD systems are robust and tires don't easily mess with the drivetrain.  by the way some folks talk one might think stones caught in the tire tread would affect resistance so much the drivetrain will explode so beware if you live on a gravel road. LOL. take those comments with a grain of salt.

 

you never mentioned vehicle/make or whether it's VLSD or not?

Oh yes...it's a '98 OBW.   No it's not ambiguous...I take it into a different shop when they want 100 dollars for a simple job.  Maybe where you're from the tax system works differently?

 

 

Well ok...maybe not halfway...but about a third of a full bottle of gear old had to be replaced. 

tax comment makes no sense but i assume means discussion not wanted.

 

by amibiguous i only meant there's no measuring device/dipstick and fluid level may or may not mean anything.  that may have been the amount of fluid it was refilled with at the last change, those rear diffs are easily mis-filled depending who/how it was done.  i'm curious because i've never heard or seen mismatched tires cause that.

did any 98s have a rear LSD?

did any 98s have a rear LSD?

No.

Really...well, Gary, if you want to talk about 'that' we'd have to find a secure channel cuz...the enemy is listening.

 

 

Otherwise, to the best of my knowledge those rear diffs are outfitted with a breather to keep internal pressure from blowing fluid thru the gaskets and seals.

 

 

Fitted tires that have uneven wear cause the diffs to generate a lot of heat...I guess with some fluid types/brands it's probable that they may be more susceptible to evaporation, anyway.

 

 

It's possible you may never have seen a problem like that before...in spite of all your years of experience.

 

 

Could have just been an unlucky batch of barrels of gear oil in the factory...who knows?  I've seen stranger things... :-D

 

 

--Damien

It's possible you may never have seen a problem like that before...in spite of all your years of experience.

indeed, if that is anecdotal then a simple search of Subaru forums comprising 10's of thousands of owners, mechanics, dealer service technicians etc, shows little, or no results.  and yet mismatched tires are common.

Have you ever tried driving with the supplied tire?  That happened to me once.  I had to drive for nearly 10 miles on that bicycle wheel.  When I got to the shop I took a look at the differential and sure enough it was smoking and the fluid was seeping thru the gaskets it was so hot. 

 

Maybe water gets into the sump somehow and causes some kind of boiling over...maybe there's a hairline crack somewhere...

 

I won't know absolutely for sure until all the facts are in but I'll keep you updated.

 

 

Cheers!

 

--Damien

this would be easily missed - lots of people don't look at their rear diff.

 

Have you ever tried driving with the supplied tire? 

many times.  hundreds of miles on road trips. 

at least you figured yours out and know to keep an eye on it.  this topic will come up again some day, we'll see what happens then, no one else seems to be seeing this thread.

I don't know...it can be a Middle-earthian metaphysical nightmare then.

 

 

 

All riddle...and no middle, ya know?

 

Over and out,

--Damien