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front differential drain plug - size?


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16 replies to this topic

#1 lekmedm

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Posted 26 June 2006 - 02:36 PM

Hi all! I just wanted to confirm something that wasn't entirely clear to me from another thread...

I would like to change the gear oil in the front diff of my 1998 OBW auto. My question is: what is the size socket for the drain plug? From what I read, I think it's supposed to be 13/16", but I wanted to make sure. This seems a bit strange since the plug to the transmission pan is 17mm. Why would one be in mm and the other in inches? :-\

#2 LosDiosDeVerde86

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Posted 26 June 2006 - 02:43 PM

Why would one be in mm and the other in inches? :-\


parts made in different places, i'd imagine

#3 backwoodsboy

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Posted 26 June 2006 - 02:45 PM

I have found that there are a few direct fit conversions between metric and standard.....I believe that one of them is 13/16 to 21mm (exact fit)
Just something Ive found.:cool:

#4 avk

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Posted 26 June 2006 - 02:55 PM

The difference between 13/16" and 21 mm is less than 0.4 mm, so it's indeed an exact fit within any reasonable tolerances. Remember you need a sealing washer for that plug.

Correction made, 0.4 mm instead of previous 0.04.

#5 outback_97

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Posted 26 June 2006 - 05:35 PM

It's a minor point but I think the difference in size between 21mm and 13/16" is actually around .4mm, the standard size is smaller than the metric. But the 13/16" does indeed fit on the front diff drain plug with some minor wiggling, note post #5 in this recent thread:

http://www.ultimates...diff drain plug

Steve

Oh, I have a suggestion when draining the front: Take some aluminum foil and form it to use it as a shield for the y-pipe, which sits very close to the drain. This way you won't get the drained oil on the exhaust and you won't be smelling hot gear oil for the next two weeks whenever you warm up the car. Ask me how I know that.

#6 NiGhTeR

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Posted 27 June 2006 - 04:45 AM

The size is definatly 21mm.

#7 lekmedm

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Posted 27 June 2006 - 09:07 AM

Thanks for all your help, everyone.

You guys rock! :headbang:

#8 woodcrvr

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Posted 21 June 2012 - 11:30 AM

Hmmm... my 03 has a torx plug in it. Is this common or has it most likely been replaced at some point. If it is common, does anyone know what size it is? The rear plug was a standard 3/8" square [socket wrench] plug.

And thanks to all for the info in this forum! I'm new to the Subaru Outback and have already performed much preventative maintenance with your help!

#9 Caboobaroo

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Posted 21 June 2012 - 05:14 PM

Hmmm... my 03 has a torx plug in it. Is this common or has it most likely been replaced at some point. If it is common, does anyone know what size it is? The rear plug was a standard 3/8" square [socket wrench] plug.

And thanks to all for the info in this forum! I'm new to the Subaru Outback and have already performed much preventative maintenance with your help!


Starting in roughly 2000, depending on manual or auto, its either a 21mm like described above, or a T70 Torx. I bought one from Snap-On and the price was $50 but you can get them cheaper if you look around. The rear is actually a standard 1/2" drive size. I use a ratchet or a breaker bar if the plugs don't want to move.

#10 987687

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Posted 21 June 2012 - 08:22 PM

Eventually both manual and auto changed over to torx on the gear oil drain.

About the rear drain plugs, I have an old impreza diff sitting around in my garage that has a hex head on the plugs.

#11 Caboobaroo

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Posted 21 June 2012 - 10:44 PM

Eventually both manual and auto changed over to torx on the gear oil drain.

About the rear drain plugs, I have an old impreza diff sitting around in my garage that has a hex head on the plugs.


Ah correct. I forgot about some randomness I've seen such as this.

#12 woodcrvr

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Posted 22 June 2012 - 09:29 AM

Thanks! I did find a T-70 Torx bit (1/2" drive ratchet) at the local Advance Auto Parts store for $6.99.

Sweeeeet!

#13 vasy

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Posted 22 June 2012 - 09:48 AM

A related question. Does anyone know if the front differential drain plug uses the same size washer as the AT drain plug?

#14 ivans imports

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Posted 22 June 2012 - 09:50 AM

21 mm and new ones have a six point touqures

#15 Caboobaroo

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Posted 22 June 2012 - 10:17 PM

A related question. Does anyone know if the front differential drain plug uses the same size washer as the AT drain plug?


It does not. The diff on the auto and manual transmissions used a copper washer that is reusable unless it gets damaged. The automatic pan uses the same steel crush washer as the engine oil pan, except on some Legacys and Imprezas that have a 8mm hex plug instead of the 17mm standard plug. Also in 2010, they started in with a new 14mm oil pan drain plug which uses a different size crush washer then before. There are also some random variations out there though.

#16 vasy

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Posted 01 July 2012 - 07:57 PM

Does the old-style drain plug (21 MM) of the front diff (96 OBW auto) have a magnet on it? I've changed the fluid 3 times, all with a suction device. The plug has never been removed. If it's magnetic, I might remove it to clean it next time.

#17 987687

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Posted 01 July 2012 - 08:23 PM

Does the old-style drain plug (21 MM) of the front diff (96 OBW auto) have a magnet on it? I've changed the fluid 3 times, all with a suction device. The plug has never been removed. If it's magnetic, I might remove it to clean it next time.


Yes, it should.




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