2.5i 5MT Front Differential Fluid Change Tutorial

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

A. No.

 

Q. I hear the "transmission cocktail" is the shizz, what say you?

A. No.

 

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

4" extension

T70 bit

Flat head Screw Driver

Drain pan

 

Optional:

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.

 

http://i144.photobucket.com/albums/r182/GEE-OTTO/intake.jpg

 

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.

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/c2210c58.jpg

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/995cb18e.jpg

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/2d16860a.jpg

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/414a605f.jpg

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.

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/18fcdaa0.jpg

 

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

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/5256c07f.jpg

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/09c21c65.jpg

WHOA!

6. Now take your transmission dip stick out to better drain the fluid.

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/d3a857dc.jpg

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.

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/cff8e9d0.jpg

 

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)

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/8e289bcb.jpg

 

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)

 

Tubing

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/b6e13e04.jpg

Direct Fill

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/a91e64d8.jpg

 

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.

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/4e494b74.jpg

WHOA!

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 :

http://i144.photobucket.com/albums/r182/GEE-OTTO/Modifications/36629358.jpg

Excellent writeup, however I think it should be noted that this is a tutorial for the 2.5i 5MT gearbox fluid change - the front differential just happens to share the lubricant for the transmission! Might alleviate some confusion to some that think they are separate. (As they are on the 5EAT)

 

That said, I think you removed a littttle too much and made it harder on yourself! The airbox torque chamber doesn't need to be removed, nor does the long transmission mounting bolt. All you have to do is remove the rubber air intake hose (2 clamps), place a flexible funnel in the dipstick hole and pour away!

I didn't remove anything from the top side, just used a flexible funnel... but that seems like an easier way to get at the dipstick to check your levels.

Yeah I buy a 2ft section of clear plastic tube at home depot, slap a funnel on top, take out the dipstick, and stick the other end of the tube in the dipstick hole. I appreciate the walk through, but I think taking out the intake plumbing is unnecessary.

PS: what kind of beer? (it affects shift feel!)

great writeup...at what mileage is this recommended at?

I believe that manual calls for every 30k, which is the only time I've done mine.

The write up for for the first timer that WANTS TO SEE IT CLEARLY! Yes i know it can be done easier and I use clear tubing and a funnel but some people feel more comfortable ( a novice owner doing this the first time) if they see where the fluid goes etc.

 

The beer was a Bud Light I typically drink Molson XXX but that is too stout for car maintenance

curiouse, im at 30k now and am planing on doing this when i do my oilchange new week. I want to change it out with royal purple though and they do not seem to have a 70w 90 oil.. they have MAX GEAR and Syncromax.. are either of these equivlent to 70w90 or no? also can you use any 75w90 in the transmission, i know some where some one used redline 75w90ns for the tranny and regular 75w90 for the rear diff. whats the difference? this is the first car i drove that ddi not take ATF (auto and stick).

 

BTW STICKIE THIS PLEASE!!!! it took me forever to find a tutorial on this. i know its the same for the 2.5i as the GT but still it would be nice to have this some place easly accessable..

Good write up. I wish I would have found this a week ago. I just had a high end service shop my friend works at do all the fluid swaps for my 60k service (tranny, rear diff, brake fluid, coolant flush). They do really good work and don't charge too much. I'll keep this in mind 30k down the road.

 

It really is worth doing every 30k miles. The manual says to Inspect/Replace if Necessary but both at 30k miles and just now I notice a huge difference in the shift quality. Especially if you've gotten stuck in the snow a couple of times (as I have driving through too deep of snow) and tried to rock yourself out, it's stressful on the fluids.

Dont use GM Synchromesh fluid and don't use Fluids with friction modifiers as those are for real AWD systems not open diff subbies

 

I have used Extra-S and now Super Tech both are 75w-90 as specified by SOA for use in our vehicles. You could use any brand 75w-90 you like. That Royal Purple is expensive stuff but im sure it does the job nicely, I have had such good results with the Super Tech that I dont think ill ever switch back to Extra-S or other costly fluid unless I get Pre 2010 6MT

Don't waste your money on Royal Purple Jmhm17, it's expensive and overhyped for what it is. Just go with the basics, Valvoline 75w-90, the Supertech, or even Mobil1 Synthetic. The Redline 75w-90NS would be nice, but I think its something like $12 a quart!

Mobile 1 across the boards gets bad reviews but here and there a good review. The factory stuff (what my dealer would install) is Pennzoil but in the end if you look under most major brands there is a WPP stamped on it.

yeah i use mobil 1 oil and was thinking if you guys said no on the RP I would use mobil 1's gearoil as well. I hate the negative reviews I have used the stuff in every car i have owned and had no problems. the only other motor oil i have used is Royal Purple and it was a significant difference over M1 but it was exspensive and worth the money in the car i was using it in. I was thinking the gear oil would be woth the extra money since your only changeing it every 30k miles. ill mostlikly see if i can get my hands on Mobil 1 75w90 and go from there. Makes me feel better when all the oil in my car is the same brand

 

also i dont think there is any harm in putting friction modifier in an open diff, your just going to pay more for oil with it added in.

 

thanks for the help g and burnout.

 

also i dont think there is any harm in putting friction modifier in an open diff

 

 

NO you do want to put friction modifier in a Open Diff gearbox like ours. There are no other ill effects of Redline Shock Proof, it is good stuff, not too expensive but the it wont produce the optimal hydrostatic force to make your synchros operate right.

 

It is more like our gearboxes aren't good enough for Redline Shock Proof not the other way around

Mobile 1 across the boards gets bad reviews but here and there a good review. The factory stuff (what my dealer would install) is Pennzoil but in the end if you look under most major brands there is a WPP stamped on it.

 

Interesting, this brings back memories of NASIOC stories saying not to use Mobil1. I know in other makes and models people swear by the M1 gear lube because it makes their shifts silky smooth, but different transmissions use different metals in the gearsets and react differently to different gear lubes

Yeah my first choice was Mobile 1 but many people gave it the Nay No:lol: so I went to Extra-S then saw the light that Extra-S isn't that good in the cold (for me) and now its Super Tech

How is this process different on the 4AT? Based on an earlier comment, the front differential shares fluid with the transmission (i.e., they both pull from the same source / reservoir), so no need to perform a separate flush for both, yes?

4EAT uses two different fluids, one for the differential and one for the transmission

4EAT uses two different fluids, one for the differential and one for the transmission

 

OK... so I need to change the transmission and two separate differentials (front and rear)?

oh dang i am at 40k already...i better get a move on it and spark plugs as well...yikes

Yeah my first choice was Mobile 1 but many people gave it the Nay No:lol: so I went to Extra-S then saw the light that Extra-S isn't that good in the cold (for me) and now its Super Tech

 

yeah i've heard that mobil 1 synthetic gear lube destroys Subaru gear sets for some reason. bizzare, i went Havoline, haha.

OK... so I need to change the transmission and two separate differentials (front and rear)?

 

I'm pretty certain the front uses it's own fluid but maybe it was only like that on the older 4EATs? Take a picture and I'd be able to tell you for sure.. Some new cars use atf in differentials so maybe they switched over.

 

I did a search on this and wasn't able to find a clear answer

Subies use good old Dextron or Dexron w/e ATF nothing fancy there and Regular 75w-90 gear oil in the rear

So the front diff shares the ATF with the transmission then?