I started with the rear differential- and I used Mobil1 Synthetic 75 90

You don't need to jack the car up for the rear. I laid on the ground and loosened the lower drain plug, then the upper fill plug. Taking both out allows the old oil to drain faster. Give it a few minutes to fully drain.

Note: I was aware that the rear differential plugs were tight, but mine were really tight. I'm pretty strong, but there was no way these would move for me. If I'd had the car jacked up, I may have been able to get in a bench press type of position and turned them, but I just put the ratchet in and used my jack on the handle to get them to turn.

While you're wating for the oil to drain, take the plugs and clean them up- this is what they look like (Notice the bottom plug has a magnetic end to collect any metal particles floating throughout the differential. Make sure there aren't any large pieces, or you may have an issue brewing! IMPORTANT: Make sure to put the magnetic differential plug on the bottom (IMG:style_emoticons/default/wink.gif) ): EDITED by Sube, the moderator with class. (IMG:style_emoticons/default/cool.gif)

Put the lower drain plug in and torque to 36.2 foot pounds (A torque wrench is needed). In order to fill the rear differential, I used this handy little pump.

When the oil starts to run out of the fill hole, your differential is full- put the upper plug back in and tighten to 36.2 foot pounds. Don't forget to wipe off any oil from the differential.

Next, it was time to do the transmission- mine is a manual gearbox- the autmoatics are a little different. I used the good stuff, touted on this site by MisterX, NEO synthetic gear oil- also in 75 90. You'll use most of a gallon to fill your transmission.

Click here for the link Jedi's Review of the NEO synth gear oil

For the transmission, you'll need to jack the car up, support it with jack stands and crawl under to get at the transmission drain plug. Don't mistake this with the engine oil drain or you'll be doing an oil change as well. Once you have the drain plug out, lower the car to allow the old transmission oil to drain- give it a few minutes- you can wash the plug while you wait. The plug has a magnet in it to catch metal filings from when you grind your gears. Clean all that gunk off.

Once the old transmission oil is drained, jack the car back up, support it with jack stands, and reinstall the plug- torque it to 32.6 foot pounds.

Save yourself the headache of removing the intercooler to fill the transmission by getting a flexible funnel like I have shown here- it was only a couple of bucks.

Don't forget to recycle your oil- I used some old bottles because their mouths were larger than the ones on the bottles my new oils came in. Check your tranmission oil to make sure it's full. Now, go out and enjoy your smooth shifting WRX. Before doing this little "mod", a smooth shifting WRX was a contradiction.

Very helpful Jedi! Nice post. I want to switch all my fluids to better brands soon. I'm only at 4k miles though. Is that too soon to change tranny fluids or does it not matter? I have an auto, I think it's a bit more tricky. Something about dropping plates. I'll have to read up on it. It's either that, or the coolant (which I want to do too and put in Water Wetter) that has the plates.

I'm not 100% sure about the procedure for the autos. So I'd better not comment- I guess you could change at 4K though. I'm going to go for synthetic mtor oil too- but I'm not sure if it's acceptable at 15K or if that's too late.

You mean there is a point where your engine gets accustomed to petoleum motor oil and you shouldn't switch to synthetic. I already switched, but I didn't think there was a "point of no return".

15k is not too late at all. switch now.
did you run the car without any oil in the diff for a while to make sure you got most of it out? (IMG:style_emoticons/default/smile.gif)

Nice job, Jim! Thanks.

Jedi,
A nice EDIT to this DIY would be an explanation of the costs you spent doing the mod, where you bought your materials, and amount of time spent. I think all of those things should be included in DIY's from now on. Helps the newbies!

As if the pics and the step by step (plus little tips) wasn't enough!!! Jees Tubbytreats, you have some high standards! (IMG:style_emoticons/default/neener.gif)

Thanks Jedi, I will be doing this very soon. I'm kind of wondering if you've had enough time to drive with the synth in? Was there an immediate difference?

EDIT: found the review for NEO and added link to Jedi's post!