how dirty does rear diff gear oil get?

[matt167]

I've changed lots of rear differentials in various vehicles, but only one other Subaru and that came out a dark honey color.. I just changed the gear lube in my Forester because I'm starting to think it's gear whine and not a wheel bearing.. The plugs were corroded shut so I had to use the jack on the socket wrench trick.. The oil came out clean and light colored. the magnent had a bit of crud on it but not too much. I'm thinking that oil was very fresh because someone else came to the same conclusion and tried the same thing.. I filled it back up with 80W90 GL5 conventional. store didn't have 75W90 and I know in my 230k mile car it's not going to make much difference anyway..

 

Now comes the question. If it is gear whine and I need a new differential. what is the gear ratio for a 2001 Forester S 5spd?  I was thinking it was 4.44 but I want to make sure, and what models I can get one from. The local U pull has plenty of Subies that as long as it does not need to come from a 5spd Forester I should be able to grab one.. There like $50 OTD

[Fairtax4me]

Manual trans forester should be 4.11.

 

Rear diff failure is rare. Wheel bearings, much more common.

 

The best way to check wheel bearings is to remove the wheel and brake rotor, and push the axle out of the center of the hub so you can spin the hub by hand. Can be easier said than done if the car is in the rust belt or has a lot of miles on it.

[idosubaru]

what he said - rear differential failure is rare.  they're often replaced only to still have the same issues because the rear diff wasn't the problem to begin with.

 

i like to sit in the rear cargo area while someone drives - if the sound is left/right then it's hub related (bearing for instance).  

 

of course it can happen but it's rare in Subarus.

[golucky66]

I've changed a fair bit of subie rear diff oil. And in my own experience, I've rarely seen the fluid come out darker then a dark honey color like you've explained. (unless internal damage is occurring) not to say it will always be lighter colored. But I don't see subies getting really dark like most cars.

[forester2002s]

In my experience, diff oil gets slightly 'cloudy', with some discoloration but not much.

And it's normal to see some accumulated grey 'fuzz' on the drain-plug magnet.

[matt167]

Cool, guess I'll inspect the other wheel bearing closer or just change it, it's probably the last thing the car needs for a while. It doesn't cost me much to operate and that's how I like it

[lvsarge]

Different vehicles and differentials, but when I took my brat in, the oil in the rear dif was so coagulated, it didn't even drip off the plug, it was almost like a gel, and the color was pitched black, with a slight green tinge. The poor dif was due for an oil change years before I owned it. Despite that, she still ran fine, and does today.