What you need for a rear differential fluid change

Singletrack · Nov 7, 2005

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.

Mykl · Mar 8, 2007

005sti said:
anyone care to comment on this?

I don't use sealant on my engine drain plug.

005sti · Mar 9, 2007

Mykl said:
I don't use sealant on my engine drain plug.

...was referring to the rear diff, not the engine oil drain plug.:lol:

Mykl · Mar 9, 2007

005sti said:
...was referring to the rear diff, not the engine oil drain plug.:lol:

But they both hold oil. Engine oil is thinner than rear end oil and the drain plug on my engine keeps the fluid in. So why should I think it'll leak through the plugs on the diff?

005sti · Mar 9, 2007

because there are no crush washers for the rear diff. the crush washer for the oil pan drain plug expands when hot and prevents leaks.

Mykl · Mar 9, 2007

Then use a bit of copper RTV.

005sti · Mar 9, 2007

thanks, it just so happens tha the friend whose lift i will use has some rtv

Mykl · Mar 9, 2007

That's what I used for the gearbox drainplugs... I don't think it's leaking.

scoob · Mar 10, 2007

005sti said:
because there are no crush washers for the rear diff. the crush washer for the oil pan drain plug expands when hot and prevents leaks.

I just changed my rear diff fluid an hour ago & I didn't use sealant (dealer didn't have it). I drove the car around for 15 minutes to give everything time to heat up then came back & checked for leaks and its fine. There are a lot of threads on the plug so I don't see why it would leak if the plugs are torqued correctly. I'll check it daily over the next week to report if anything changes though.

scoob · Mar 10, 2007

005sti said:
because there are no crush washers for the rear diff. the crush washer for the oil pan drain plug expands when hot and prevents leaks.

I just changed my rear diff fluid an hour ago & I didn't use sealant (dealer didn't have it). I drove the car around for 15 minutes to give everything time to heat up then came back & checked for leaks and its fine. There are a lot of threads on the plug so I don't see why it would leak if the plugs are torqued correctly. I'll check it daily over the next week to report if anything changes though.

On a side note, one of the sales guys saw me leaving with the fluid and asked me if I was changing it myself. When I told him I was, he gave me a

like it was a serious issue. Weird.

005sti · Mar 10, 2007

thanks for the info. i'm changing mine today. not sure if i will use sealant.

005sti · Mar 10, 2007

thanks for the info. i'm changing mine today. not sure if i will use sealant.:lol:

Mykl · Mar 11, 2007

Eh, if you've got some copper RTV sitting around you may as well. Can't hurt anything.

005sti · Mar 11, 2007

i decided not to after i took it out to drop the fluid because it was pretty hard to remove and 33 ftlbs made the bolt feel pretty damned snug. i didn't want to be stuck trying to remove it next time. i'll post here if i notice any leaks

Digitalfiend · Mar 16, 2007

Add this thread to the "Drivetrain Threads of Interest" thread. Good info.

005sti · Mar 17, 2007

005sti said:
i decided not to after i took it out to drop the fluid because it was pretty hard to remove and 33 ftlbs made the bolt feel pretty damned snug. i didn't want to be stuck trying to remove it next time. i'll post here if i notice any leaks

no leaks since the change over 1 week ago, although i checked my tranny again today and it was a quart low. don't know why it read full before. oh, well. just topped it off.

hulk252 · Apr 4, 2007

Nice thread. lots of good info.

effect · Apr 22, 2007

dont remember who said it that Rolal Purple does not make GL-5 approved Oil.
for the Rear Diff.. here's a link to their site..

http://www.royalpurple.com/prodsa/mgeara.html

S1MPSONS · Jun 15, 2007

Chris05STi said:
Anyone know where I can pick up Motul 90PA? I heard their stuff is great and want to change the rest out since I am using it for the brake system. Motul 90PA is for the Rear diff correct? What Motul product would be for the trans, and where could I get them all? Also, how much is required for the Diff and Trans (liters?). Thanks!

Arcticsun said:

Motorspot.com i believe. I got mine from there, very fast and good price! 25 bucks shipped for 2L (subaru's is 19.95 for 1L). you only need 1L to fill it up.

Click to expand...

What do I buy from them for my trans/center diff? How much? 4.5 Qts?

Good2Go · Jul 7, 2007

Am I reading correctly that the tool needed to remove the drain plug is a 1/2" square drive found on a common ratchet wrench. I took a quick glance under the car and I noticed a square drive and no hex on the plug. I want to make sure I have the right tool for this.

arkleseizure · Jul 7, 2007

Good2Go said:
Am I reading correctly that the tool needed to remove the drain plug is a 1/2" square drive found on a common ratchet wrench. I took a quick glance under the car and I noticed a square drive and no hex on the plug. I want to make sure I have the right tool for this.

That's what I used to remove that drain plug...worked fine for me (with the requisite effort, naturally).

Chris05STi · Jul 7, 2007

Yup that is exactly what you have to use!

Engmus · Jul 8, 2007

Wait wait wait. As I read over this whole thread at first everyone is saying a straight 90weight only. Not to use a multiweight oil.

Now were back to multiweight?

To me it seems like the only diff oils that people recommend are the Motul 90PA

And the Fujutsu heavy industries lubricant.

---

(Posted this in the amsoil thread as well)

Time to be the monkey in the wrench.

I talked with a upper Amsoil Engineer. He looked up the technical specifications on the 04\05 STi and got back to me over the phone.

He came to the conclusion that for the front diff\tranny to use...

http://www.amsoil.com/storefront/fgr.aspx?zo=515729

and for the rear diff to use

http://www.amsoil.com/storefront/svg.aspx?zo=515729

He said that would be the best that amsoil has to offer.

Thoughts?

---

Good2Go · Jul 16, 2007

arkleseizure said:
That's what I used to remove that drain plug...worked fine for me (with the requisite effort, naturally).

Thanks for the info on the tool. Got this done this past weekend along with a tranny and coolant change.

I found the greatest deal on a 1/2" monster breaker bar (25") from Harbour Freight for $8 with a coupon. Better hurry though, the coupon is only good for 2 more days. This could easily cost $60 or more from Sears. Here is the link to the part and the coupon. This made the job super easy (almost no requisite effort).

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=30395
http://www.harborfreightusa.com/html/emails/28/RetailB/Images/11.gif

I also got a suction tool from Ace Hardware for like $5 that looked like a thin necked turkey baster that was perfect for getting the last bit of old oil out of the diff.

non-ricer · May 30, 2008

thnx for the writeup... i just finished and so far so good!

What you need for a rear differential fluid change

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