2000 subaru trans and diff change

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Just changed out the transmission and rear differential gear fluid on my impreza. Didn't know what was in there before, but I put in supertech 80w-90 conventional. It's GL-5 and "safe for copper and bronze". I plan to leave it in for 25,000 miles. Comments?
 
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Yeah I would use a high-quality 75w90 to improve efficiency and reduce temps / wear. I used two bottles of Amsoil SVG 75w90 in the 2002 Forester. Next time will likely use Motul Gear 300 75w90 as it's the highest VI gear oil that I can get my hands on.
 
Can't use most gear oils in subaru transmission because it shares fluid with the front differential. Subaru also recommends not to use synthetic gear oil. The fluid has to be safe for the synchros and suitable for the hypoid gears.

Side note: The trans dipstick is reading slightly overfilled. I put in 3.7 quarts which is what the owners manual says. Any cause for concern about it potentially being a little overfilled?
 
Originally Posted By: jimwards17
Can't use most gear oils in subaru transmission because it shares fluid with the front differential. Subaru also recommends not to use synthetic gear oil. The fluid has to be safe for the synchros and suitable for the hypoid gears.

Side note: The trans dipstick is reading slightly overfilled. I put in 3.7 quarts which is what the owners manual says. Any cause for concern about it potentially being a little overfilled?


That's different in the MT vs AT.
 
I chose Mobil 1 75/90 IN MY 2000 Forester. There was no measurable difference in fuel mileage after switching to synthetic gear oil. I ran the synthetic gear oil in my Forester for over 100,000 miles and changed it out at ~ 30,000 mile intervals. You will do just fine with the 80-90 gear oil. I would be interested in seeing a copy of a Subaru statement that states we should not use synthetic gear oil in our transmissions.
 
Originally Posted By: dparm
That's different in the MT vs AT.

Correct. The AT has the front diff separate from the transmission so you can use a dedicated GL-5 for the diff.
 
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