Front/Rear Differential Fluid Change

I drove it earlier about 8 miles. Do you think I did any damage to the front diff?

Highly unlikely you did any damage. The probable short-term result was thoroughly foaming the fluid, which reduces its lubricity (i.e. air makes a poor gear lubricant). Removing the "check" drain plug should be all you need to do at this point, but I'd let the car sit overnight beforehand to allow the fluid to de-foam itself.

You filled the front differential incorrectly. It is now overfilled.

 

You don't fill until oil flows out of the fill hole. There is a separate "overflow drain plug." To quote from the Factory Service Manual, page CVT(TR580)-46:

If you're going to be doing maintenance stuff like this yourself, which I highly support, you really need to get a copy of the Factory Service Manual.

Thanks again for your insight.

Matt,

 

You didn’t do any damage. As a rule of thumb, I’ve always filled a diff to the point where it starts to just trickle out the fill hole. Apparently the Subaru method is different.

 

Anyway, just do as you mentioned with the check plug and let the excess drain out.

 

If you like, PM me and I will get you an FSM for our cars.

 

Good on you for actually turning a wrench and not making a post about LED lights and spoilers.

Thanks for the reassurance that I didn't damage anything. I opened the overflow plug and drained the excess fluid until it became a steady stream, then put the plug back. Done IAW the FSM which I did find and download. Thanks for the offer to get FSM to me.

Highly unlikely you did any damage. The probable short-term result was thoroughly foaming the fluid, which reduces its lubricity (i.e. air makes a poor gear lubricant). Removing the "check" drain plug should be all you need to do at this point, but I'd let the car sit overnight beforehand to allow the fluid to de-foam itself.

my differential in my 14 was cracked at the dealer and I drove it 1500 miles while the fluid slowly leaked out... by the time I got home the from the trip the fluid had re-leaked out and the front differential was TOAST with metal shavings like glitter in said fluid.

my differential in my 14 was cracked at the dealer and I drove it 1500 miles while the fluid slowly leaked out...

I'm not sure how that's relevant to Matt_75 driving his 2016 Legacy 8 miles with excess fluid in its front differential.

I'm not sure how that's relevant to Matt_75 driving his 2016 Legacy 8 miles with excess fluid in its front differential.

Since no one has posted a pic of the rear diff I thought I would add one to this thread. As mentioned previously the rear is easy peasy!!

10mm allen loosens both fill & drain plug.

Just a reminder, always loosen the FILL plug first!!

I went with Royal Purple as I had some left from other vehicles. Manual states .8 qt.

Good Luck!!

OP, is the fluid you used full synthetic? I have almost 38K miles and feel like I should probably do this and I he cvt fluid. I'd like to use full synthetic gear oil in all of these parts for long lasting parts.

I used Royal Purple, leftover from other vehicles. I always use synthetic.

I currently have 53,000 miles on a Legacy 2.5. According to the dealer, maintenance is needed soon on my front and rear differential. I have never towed, and do not consider my vehicle used under severe conditions.

Is it necessary to change the differential fluid to prolong the life of the front and rear differential, or is it an unnecessary expense?

Is it necessary to change the differential fluid to prolong the life of the front and rear differential, or is it an unnecessary expense?

"YES" and "NO"

For those of you that have done this, can you share what tools you used to get the front fill plug off? I had a heck of a time trying to get it off. First, I tried the 8mm hex with a 9" extension, but it ended up hitting the brake line. So I tried to go from the bottom of the car with just the hex and no extension but couldn't get the plug to budge. Maybe I need a wobble extension to clear the brake line?

The rear was pretty easy. I did mine today at 44k, and the fluid looked pretty nasty and dark. Next time, I will do it at 80k and see how the fluid looks. I used Mobil1.

I'm not sure how that's relevant to Matt_75 driving his 2016 Legacy 8 miles with excess fluid in its front differential.

I am sure that if a car can make it 1500 miles with little to no fluid, his car would be fine...with excess fluid