You changed it already when you did the transmission.

 

So the front, center, and transmission all share the same oil? Interesting. I was wondering why I never noticed another differential in the "middle" ... similar to a transfer case on a 4x4.

 

Right, our center diff is built into the transmission with the front. However I use different gear oils front to back, no friction modifiers in the transmission.

 

Friction modifiers are usually for clutch/plated LSD. We don't have any of those ;-(

I do recall that diffs can benefit from extreme pressure additives (usually the stuff that makes it smell sulphury) but those additives are not always the best for synchronizers in a transmission.

I am looking forward to changing out for the extra-s soon.

 

I used the same stuff front and rear ... Extra-S 75-90. Noticeably smoother in the shifting. What'd you use up front?

 

I am using motul in the rear and trans and can feel a big difference especially in winter

 

Redline 75w90NS in front, 75w90 in back.

 

i used extra-s in the tranny and rear diff. as said previously,the tranny and front diff are all the same drain and fill tube. the extra-s shifts soo nice even in the coldest winter days.

 

I jumped the gun a bit and did the switch at only just shy of 30k miles. Probably could have saved some money and waited on the rear diff since that's not something I'll notice a difference with, but doing the trans/front was definitely worth it.

 

Can anyone tell me what tool I will need for the rear diff AS WELL as the front transmission bolt? My 05 STI buddy told me he had to buy a T70? or T60? I forget..

 

Looks like T-70 Torx for the front diff/transmission drain. Rear diff is a square female that either a 1/2" or 3/8" drive wrench or breaker bar will fit (I don't remember which size, but both are common toolbox items). When doing the rear, remove the top/fill plug FIRST. Just in case - if you can't get that out and need help, but you've already drained the rear diff, the car's pretty much stuck where it's at unless you tow

 

its a t70 bit. i bought one off ebay for like 8 bucks. the rear diff is just a 1/2 square drive extension opening.

 

^^ and ^

Wow, it took me an hour with a 20 minute break because of sudden rain for the whole thing. Tranny fluid and rear diff. Thanks so much for the fast responses. I recommend doing this for anyone reaching 30-36k miles ! I can definitely feel the smoothness in the gas pedal and clutch. Especially when accelerating and shifting up..

Next, I think I'm going to do a kartboy ss and shifter bushings.

 

^^ and ^

Wow, it took me an hour with a 20 minute break because of sudden rain for the whole thing. Tranny fluid and rear diff. Thanks so much for the fast responses. I recommend doing this for anyone reaching 30-36k miles ! I can definitely feel the smoothness in the gas pedal and clutch. Especially when accelerating and shifting up..

Next, I think I'm going to do a kartboy ss and shifter bushings.

the fluid change really helps with the smoothness of shifting. i can downshift into first coming to a stop now. before it was almost impossible to get in gear.