Hello fellow Legacy 2.5i owners, this guide will show you how to change your front differential fluid. Doing this maintenance yourself will help you learn about you car, understand the importance of keeping your fluids fresh, and save you a lot of money over the life of your Subaru.
Safety First!!! If you are not mechanically motivated or not even in the same field as mechanical prowess exists, scared to get under your car, scared to touch your Subaru, no idea how to put it on ramps or stands safely, or are just plain not comfortable with this THEN DO NOT DO IT! I take no responsibility for you F-ing up your car.
This is a 3/10 on the scale of difficulty only because you have to put your car on jack stands or ramps, the other aspects associated with this maintenance are easy. (if you have access to a lift then this will be very easy)
I use Super Tech 75w-90 it is really good stuff, not too expensive and exceeds the requirements for many transmission manufacturers including our own Subaru gearboxes. You can however use what ever fluids you have had the best success with( Subaru Extra-S, Castrol, Royal Purple) as long as it meets or exceeds the 75w-90 requirement set by SOA.
Side note on gear oil "weights":
The 75W pertains to how the oil performs in colder temps and the 90 pertains to the way the oil performs at 100C (that is the standard engine operating temp per SAE) So.... the 75w will still lube well in the cold temps but it will always perform like a SAE 90 at normal operating temps. I know some guys want to run 75w-140 but it is really not needed unless you tow heavy loads (doubt that with a EJ253) or your gearbox operating temps climb high (if you drive your 2.5i hard).
Q. Well GEE OTTO I heard you never have to change your diff fluid, so what's the deal Yo?
A. Well you don't have to change your fluid ever but your gearbox will suffer and functionality will decrease.
Q. What does fresh fluid help?
A. Fluid breaks down as the miles roll past, your synchros are like little clutches for all the forwards gears. They keep each gear spinning at or near the same speed as the layshaft so you get smoother shifts, without them you would have to double clutch every shift to get the gearbox up to speed with the engine.
Old fluid doesn't lubricate the synchros optimally and they spin slower, when you try to shift the difference in speed is then forced on the synchro causing it to come up to speed and allows the shift. When this happens you get that nasty "grind" and also accelerated wear. Fresh fluid also lubricates your shift forks and more importantly for us 5MT guys the Front differential! You synchros WILL wear out at some point no matter how great of a driver you are but performing this service will add a few thousand miles to their lives
Q. GEE OTTO I want to run Shock Proof SAE 140
Q. I hear the "transmission cocktail" is the shizz, what say you?
Q. How often should one change their gear oil?
A. I stick to 30k miles intervals, however if you auto-X or race or goose your car around a lot then your fluid will break down at a faster rate and you can determine your own change interval. If you drive on the calmer side of the scale you may not have to change it but every 60K miles.
Q. Can i use SAE 90 gear oil ?
A. Well this is a odd question but No you shouldn't cheap out and buy a 5 gal. pail of Coastal SAE 90 gear oil. It isn't a multi grade oil and it will not perform the same in colder weather.
What you will need to do this job:
4 quarts of 75w-90 Gear Oil
10mm and 14mm sockets
3/8" Drive ratchet
Flat head Screw Driver
3/8" clear tubing
Beer or Soda YAY!
1.First you will want to put your car on ramps or jack stands, make sure the hand brake is engaged, chock the rear wheels, and raise your hood. SAFETY FIRST!!!
2. Now that your car is in the right position lets tackle the topside. First remove the intake piping, filter and MAF housing. If the filter box seems stuck make sure to unclip the the hose on the side.
3. Next remove the 10mm bolts that hold the air chamber inplace, and the two breather hoses on either side that are held in place with simple squeeze clamps.
4. You can now flip the air chamber up and rest it on the intake manifold. If it wont move enough simply unhook the third breather hose on the front of the air chamber connected to the white sensor to the right of my finger in the picture.
5. Remove the bracket that holds the two connections leading into the transmission tunnel with the 4" extension and the 14mm socket. This bolt is long and in there tight because it is used to hold the engine to the gearbox. Do not worry your engine and gearbox will not come apart while this bolt it out
6. Now take your transmission dip stick out to better drain the fluid.
7. Now get under your car with your 3/8" drive ratchet, 4" extension, drain pan, T70 bit, and some paper towels.
8. Find your T70 style drain plug just behind the transmission cross member. This plug may be in there tight so if you must, use a longer handle ratchet to help you break it loose.
9. Now that your plug it out let it drain for about 10 minutes and in the mean time you can clean up you plug and hands as they both may be covered in gear oil. You will also want to inspect the plug, as it is magnetic, it will attract any shavings in your fluid. You will want to wipe it off clean and make sure the crush washer is intact ( it should be if this is your first or second change if not you can buy another one for pennies)
10. Now that all your gear oil has drained it is time to reinstall the plug. Now that T70 bit is a 3/8" for a reason and that reason is that you don't have to put 100ft/lbs of torque on it to get it secured. 33ft/lbs will do the trick
11. Now that the bottom is buttoned back up lets move back topside.
12. If you are on ramps or jack stands take your car off of them. This is to ensure the most accurate dipstick reading when refilling your gearbox
There are two methods I have tried in the past the tubing method and the direct fill method (this is the same as using a long funnel)
Now using the tube can be slow because the new gear oil doesn't flow like water, but it can be cleaner and it can save you from the first few steps, But I like to see what I am doing so I use the direct method.
13. Clip the ends off your gear oil of choice (if it comes in the standard type bottles with the nozzle) Place your finger over it then position it over the fill hole of the gearbox, then take you finger off and squeeze the new fluid in.
14. Repeat that 3 times then MEASURE. I have NEVER used 3.8 quarts to refill my gearbox and. The book says 3.8 quarts but you will more than likely be at or very near FULL after 3 quarts. My Legacy took 3.2 quarts to refill.
15. Once you fill it up replace that long bolt that held the bracket to the bell housing.
16. Reinstall the air chamber and ALL breather hoses to the original locations. After that reinstall the intake tract, tighten all clamps and make sure your MAF sensor is plugged in. Inspect the engine bay for any sockets, tools, etc.
17. Take you car out for a drive you should notice that the the gears engage much easier while stationary, especially reverse. If you had grinding this should help to reduce the occurrence of that as well due to the synchros being better lubricated and able to spin up to match gear speed more effectively.
18. As a final step when you return from the test drive, allow your car to sit for 15 minutes. Our gearboxes are splash lubricated so it will take a few minutes for all the fluid to collect off of the layshafts. After it has sat for a bit, check the fluid levels they should read at or over the F line. Check under the car for leaks, if you see some oil around the plug wipe it off wait 10 min check again if it is wet again then you need to tighten your plug or loosen it a bit as it can be over tightened.
And you are done and it is time for :