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What you need for a rear differential fluid change

55K views 99 replies 42 participants last post by  non-ricer  
#1 · (Edited)
K0305Y0900 - LSD (75W-90 GLS), previously K0904AA080
004403010 - Three Bond 1105 (liquid gasket)
Large adjustable wrench or corresponding socket (not sure on size)
1/2" breaker bar
Hand Pump
Fluid Extractor (optional)
Torque spec on plugs: 49.0 N·m (5.0 kgf-m, 36.2 ft-lb)

I drove the car up on ramps in the front, jacked the rear diff until the car was about level, and put the back on stands under the side jack points. Clean off the area around the plugs to keep any debris out of the diff; it will also make it easier to find any leaks. I pulled the top plug first (pull the sensor harness first) to make sure it wouldn't give me any trouble. Use a large spanner, adjustable wrench, or properly sized socket (I didn't measure). Some oil poured out (probably wasn't a 100% level), but not much. Put the plug back in so the oil wouldn't run into the bottom plug. I pulled the bottom plug (1/2 drive breaker bar) and drained the fluid.

The fluid was BLACK (30k miles) and there was a fair amount of metal on the magnetic drain plug. I pulled a tiny bit more oil out of the bottom with the fluid extractor - not much though really. Replaced the bottom plug (with liquid gasket on the threads), pulled the top, and put the pump tube in. I got a pretty decent one that has some teeth to hold onto the threads in the diff. Pump like a madman. Mine took about .9liters before it started running out of the diff. Replaced the top plug (with liquid gasket).

NOTE: At least 2 people have broken their top plug with the sensor. I am not sure what the cause of these failures actually was, but make sure you do not over-apply the liquid gasket and then over torque the top plug. The gasket acts as a lubricant and WILL affect the torque wrench to some extent. Covering the threads from the halfway point to the head of the bolt is probably sufficient.
 
#2 ·
Do you think it would be worth while to say run on that oil for a 100 miles or so, then change it again? That might make sure you flush out all the old oil and filings. Just a thought.
 
#8 ·
Singletrack said:
K0305Y0900 - LSD (75W-90 GLS), previously K0904AA080
004403010 - Three Bond 1105 (liquid gasket)
Large adjustable wrench or corresponding socket (not sure on size)
1/2" breaker bar
Hand Pump
Fluid Extractor (optional)
Torque spec on plugs: 49.0 N·m (5.0 kgf-m, 36.2 ft-lb)

I I pulled the top plug first (pull the sensor harness first) to make sure it wouldn't give me any trouble.

How does that sensor get pulled :confused:
 
#10 ·
qingshan said:
:) Thanks - I got it done Mobile Syn in the diff, trans lube next with my Kartbot ss install
The rear diff requires a 90 wt. LSD oil, which Mobil does not make, so it sounds like you put the wrong stuff in. You need to use Subaru 90 wt. LSD oil or Motul 90PA LSD oil which is an equivalent.;)
 
#11 ·
Nice post Singletrack

I just got done reading this and the trans thread and wanted to say thanks for the heads-up on the gasketsfor the trans, along with pointing out the appropriate liguid gasket. I did some checking and was a bit surprised that the Three Bond Subaru recommends for the rear diff is not the same as Permatex ultra grey. Glad you brought it up otherwise I am certain I would have used the wrong stuff without having any clue.

I know there will be people saying no big deal, and they may be right, but why risk it when Subaru specifically endorses Permatex ultra grey as an appropriate substitute for a host of other applications, just not for the rear diff.

Thanks again. (no, I am not posting appreciation in both threads) :)
 
#13 ·
solbergfan said:
The rear diff requires a 90 wt. LSD oil, which Mobil does not make, so it sounds like you put the wrong stuff in. You need to use Subaru 90 wt. LSD oil or Motul 90PA LSD oil which is an equivalent.;)

Just to kind of piggy-back what you said. You can use Silkolene BOA90 LS as well. I like both Motul and Silkolene.
 
#14 ·
Just a quick FYI. These "plugs" referenced here for torque specs is incorrect, there should only be ONE plug with that spec and its the 1/2" drive one (drain).

32.6 breaks the temp sensor plug. I dont know if this is common knowledge in this thread, but i certainly feel like an idiot now :/
 
#15 ·
Arcticsun said:
Just a quick FYI. These "plugs" referenced here for torque specs is incorrect, there should only be ONE plug with that spec and its the 1/2" drive one (drain).

32.6 breaks the temp sensor plug. I dont know if this is common knowledge in this thread, but i certainly feel like an idiot now :/

Good point! I hope you didn't break it.
 
#16 ·
Yea, i broke it, the threads are stuck into my diff, so I gotta take it to the dealer on monday. Stupid on my part, i went 1/2 a turn too much :(.

To make matters worse Im currently at a little car meet in chicago and i backed into my friend at a gas station earlier today, Gonna need a new bumper
 
#19 ·
I changed the rear diff oil last weekend using the genuine LSD fluid.What came out was so nasty,have no idea what it was.Was very thin & black.The new fluid is like thick honey.The rear diff acts a lot better also.
 
#20 ·
I am changing the diff fluids next weekend with Amsoil Severe Gear 75W-90 oil.

It is much cheaper than the $19/L that someone was talking about and I hope it is better.
 
#26 ·
BHazel said:
I am changing the diff fluids next weekend with Amsoil Severe Gear 75W-90 oil.

It is much cheaper than the $19/L that someone was talking about and I hope it is better.
You must use one of the three fluids listed above for the rear LSD diff.You need to use Subaru 90 wt. LSD oil or Motul 90PA LSD oil or Silkolene BOA90 LS.If you dont your rear diff. will lock up at strange times or be noisy.