How To Flush Your Transmission & Differential (STI) 

Tannner! I’ve had my STI since brand new in 2018. I maintain it meticulously and have a pretty big handful of mods. And I’m the only person who’s ever turned a bolt on it since it was manufactured. And almost 100% of the work done was using your tutorials. Spark plugs, IAG AOS, trans and diff fluid, cyl 4 cooling mod, JDM rear spats, suspension and way more. I’ve said it a hundred times, but thank you for entertaining, teaching, inspiring, motivating, and saving me a ton of money in labor costs. I don’t have many people on maui to teach me Subie things. Hopefully someday I’ll be able to afford an engine build and you’ll be the one I hit up for sure

Love these STI maintenance videos!! Will continue to watch and support!!

I was literally googling this cause I plan on changing soon. I log onto RU-vid and the first video that popped up is yours! Talk about clutch thanks for the awesome video!

Thanks so much for what you do. As a new WRX owner it’s nice to find some reliable maintenance/ modification videos to get some reference as to what’s needed ahead of time .

You always want to make sure you can get the fill plug loose first. Once you have it loose DO NOT PULL THE FILL PLUG OUT. Remove the drain plug(s), then loosen the fill plug to adjust how fast the fluid drains and does not go all over the place.

Thank you for posting this. I seriously really appreciate your vids and explanations through your videos. You do a great job. Love your content. Keep doing it buddy!

Great video as always. I'm almost due for a fluid change, so this video is right on time!! Keep up the good work!

Best videos on the tube. Keep it up super helpful, informative and entertaining.

i just did this myself for my 2015 sti and just want to point out the washers that are needed. there are no crush washers used. both fill and drain plugs for the rear diff use the washers ending with 050. for the transmission: the fill plug uses the 040 washer and is copper. the the drain plug for the transmission uses the 060 washer. the front diff T70 drain bolt uses the 090 washer. the washers you are referencing in this video ending with 070, is not used. since the washers are not crush washers they are also reusable to a point, so if your vehicle does not have many miles the washers should be in good condition. i also want to mention that the 10mm allen bolts are really weak and i stripped the fill plug, causing me a delay. i also recommend you stick with subaru oil that you can get from the dealership unless you are tracking the car. the motul oil works best when heated and will cause very rough shifts in cold starts for anyone in the winter climates. my car has 33k miles and after the service the car shifts really smooth like it was new. i dont track my car but i do stay in the 3k+ rpm range in 3rd gear for daily street driving and coasting since that is where the car is happier at. the factory oil came out dark and the magnet plugs did their job. i am very pleased at the results and i saved a bunch of money. thanks for your video.

The strong smell that comes from the gear oil are thee extreme pressure additives which is sulfure and protects the gears at extreme tempertures . Thank you sir for the video .

Just subscribed great videos man keep up the good work, looking forward to more !

Just passed 60,000 miles on mine, need to do mine soon. Good video brother.

Thank you for this video!... Planning on doing it when I comeback from overseas. Car has low mileage but it’s just sitting there until I comeback.

Awesome work bro. Definitely doing it this weekend!👍🏼👍🏼👍🏼

May have been said already, but you should really have your car level when filling just about any fluid, except coolant. Otherwise, you will likely over/under fill... depending on where the low point is. Still love the channel, and getting the fill plug out first is still the most important thing.

Amsoil for the friction properties seems to be the census on the forums. Nascar even when sponsored by another oil company still uses Amsoil for the shear properties. In the transmission there's a cocktail Amsoil/? forget the other brand for smoother shifts. You're killing it with these videos, very informative!!! Someone fill in the subie transmission cocktail please, I ain't getting roasted asking on the forums...

Great video 👍 mines due for one and this helps.

Thanks this video was helpful when I did my 2016 wrx

Great video and explanation! I know I description box you listed part number.. how about fill plugs? And are the drain plugs same for part number too or different ? If you could please list them for me thanks

Dude thank you much. This helped me tons 🙏🏻🍻

Great video man! 👍🏽 thanks for the help

Thanks for the warning about the gear oil exploding out of the drain hole.

Fantastic DIY video.

Just had mine done by the dealership. Boy, did the cost hurt. After watching this, I'll do it in my garage next time! Side note, the recommendation is every 30k miles or 3 years they said.

Thanks for the video bro it helped a lot !

Im about to have to do this to mine as well as the spark plugs. Thank you so much for making these videos. Very informative and a trip. Good thing you werent doing firearm videos in the Army "never put your finger on the trigger why pointing at the camera BLAM!" Lol

great upload again

Live and learn bud when I did my first diff and trans flush it was messy even though I worked at a dealership 😭😭🤣🤣🤣.... Look for paper funnels that'll minimize any spills next time... keep going💯💯💯✊🏾✊🏾✊🏾

I like it man...you are pretty good of doing great videos I’m learning so much from you save money 💰 from my pocket 👍

Great video series on the STI, much appreciate you taking the time to make them. Question about the crush washers, I counted a total of 5 bolts/plugs removed, 2 drain and 1 fill for the center/transmission and 1 drain and 1 fill/sensor on the rear. Do you not need a washer for the rear fill/sensor plug, is that why you stated that you only needed 4 washers instead of 5 washers?

Just a few more questions, what was the torque specs on the rear if any, and the torque spec for the front fill bolt. And how many bottles do you need for the entire job, got 5 but after seeing this think i may need another. Thanks in advance!

You need some quick Jack's. The ones that slide under frame rails I think they work off an air compressor or hydraulic fluid. They are a live saver

Great video! You should do a video on how to flush the clutch fluid!

Great video. Just wondering if it would be better to have the car up on all 4 so it would be level to do the fluids change or it does not matter to have it inclined? Thanks.

Thanks for this!

You are the man bro

Hi there love your videos. Does the front diff and transmission use the same oil and get filled from same fill plug

Great content been wanting to do this.. next video powering steering flush/ hoses issues pls?

I don’t have a floor jack too. For rear differential oil can be come out one quart only use a ramps? Thank you

Hey Smeedia, thanks for all the uploads. I have a 2015 STI and now that I’ve watched this video I am doing my 60k maintenance early and changing out the front and rear diff oil. Now I seen you put the Motul gear 300 in the front and rear diff. “In the comments” I found that might a bit of a concern for the rear diff being that it is a Limited slip and calls for the LS... what did you put in your rear diff? If you put the gear 300 was that a mistake? Lastly, What should I put in my stage 2 2015 STI rear diff?

What are the torque specs for the drain/fill plugs on the rear differential, front differential and transmission?

This might be totally crazy, but something I like to do is put all wheels of the car up, and either jack the front of the car higher temporarily while it drains or fill it with fluid. Then run the car at 5-10mph (wheels in the air) for 2 minutes then drain again. Totally excessive here, but just what I end up doing sometimes. Oil looked good in it. Edit: also where do you jack the car up? rear diff? I see it in the manual, but I always cringe at the rubber that holds it into the chasis

Great vid man! Looks so much easier than I thought it would be. Just curious, can you do a vid showing how to do a drive belt and clutch fluid flush?

Does the differentials need any special additives for limited slip?

Got the P/N for the front diff/trans crush rings or is it the same size?

Hehehehe love the video , the last part just made my sunda lolz ,

Did it last week and the other pittsburgh pump that screws into the bottle. Works really well too. I did run into an issue with the amount of fluid that came out. The rear diff went smoothly but only 2.5 liters came out of the warmed up and level transmission. Put the same amount back in and stick read between low and high. Ever heard about this issue?

What are the torque specs for the rear diff? Drain and Fill?

About to do this on my son's 2016 sti and we located a fill hole on the top of the front differential where the dipstick used to be. I have seen another video of that being done. Is that not the correct way to fill it?

Hey great videos. You can use the same fluid for the diff and transmission? I thought they were different fluids. Please help

Do you know if you can use amsoil severe gear oil 75w90 on '17 wrx tranmission and differentail oil? I wasnt sure if they could be the same oils .

At what intervals do you change the front/rear differential oil? The manual says inspect at 30K, no mention of changing?

Thanks for the great video! I am looking for the crush washers to use for the rear diff / transmission oil change and I noticed that the part number you have in the video description is not the same as the one you show in the video (just based on the number on the little baggie). Any chance you know if part number 803926070 or 803920050 is the correct one to use?

What fluids do you recommend for a FA20 WRX 17+ like oil, diff, trans, brake, coolant and power steering?

is the crush washer the same size/style as the oil drain plug?

does the front differential use the same fill hole as the transmission? Also, does the rear differential fill plug/sensor need a crush washer as well?

Having the car leaning forward won’t make the oil stay in?

Where did you buy the crush washer? Always love this maintenance! It helps us maintain ours as well w/o having to spend a lot on the dealer or other auto shops.

is this the same process for a 06-07 sti ? thanks for the info just got my oil in yesterday

Hey wassup man, will be changing all my fluids next weekend, was planning on replacing my power steering fluid as well. Do you recommend the Subaru oem one? Or Valvoline, Redline, etc. Thank you!

Car should be flat, you won’t get all the old fluid out. Great video, it’s much easier than people think. Hardest part is squeezing the hell out of the motul bottles.

Harbor Freight has torque wrenches in sale for 19 bucks all the time. Have used min for aver five years with no issues. Bought a set for my Pop.

What are the torque specs for tightening those back down???? Im about to do mine lol!!!

😂😂😂 You got chooched on That’s why I drained the t70 first, shot straight down at least. And I’m rocking the Harbor freight torque wrench, and surprisingly it’s always been great. It’s Pittsburgh brand I wanna say 🤔

When filling the oil through the transmission fill hole, does that also fill the front differential or is there a separate fill plug for the front differential?

Awesome video. What ramps are you using?

What’s the torque specs on the rear diff drain and fill plugs you never posted them

very informative!! so im at 43k-ish miles, should i just do it early?

Does the center diff drain plug also need a crush washer? Getting around to doing this this weekend

What was the torque spec on rear diff? On both bolts

you said you needed 4 crush washers, 2 for rear diff and trany fill, and 2 for rear diff and trany drain, but there was another plug for the front diff that you didnt talk about needing a crush washer?

should the rear diff have an LS fluid different than the trans ?

So the fill plug in the transmission also fills up the front diff?

Dumb question but will the gear 300 work in an 08 Spec B 6 speed trans?

My 2011 Sti grinds when going into 4th gear sometimes. Will flushing the tranny fluid temporarily get rid of my synchro grind for the time being?

For the transmission do you keep on filling until it starts to come out the fill plug ??

do you recommend the motul gear oil on a 2015 wrx?

What all crush washers did you change? And are they all the same part number you posted? Looking on Subaru parts page I’m showing several different numbers that don’t match what you have. Gonna be doing this next week hopefully. Thanks for the video!

Dude you should definitely make a video on a coolant flush :)

Would an oil drain plug crush washer fit on the front diff plug?

Murphy's law same happened to me awhile ago except for the light part.

Great informative video. quick question, your part number for the crush washer in the video is 803920050 but listed in the description is 803926070. which is correct?

Was there any fluid leftover from the 1 qt for the rear diff? Enough leftover to make it 4.3qts with the 4 other bottles for the front? A shop was selling a combo set of 5x1qt Motul bottles so I'm curious. Love the videos, I'm starting to do a lot on my own from your channel.

Thanks again for the vid - I subscribed just cause of this. Love all your content for the STI, helps me a lot. Quick point - you left out the 17mm in the description list, lucky I remembered when I went to the shop. Also, I got the 24mm deep socket and it doesn't fit my 2010 STI, it's slightly too big. Maybe 20 or 21mm? Not sure what's going on there. Lastly, no matter how hard I tried I could not get the T70 Torx out. Can't even get close to cracking it.. any idea? I just drained the whole thing through the 10mm Hex as much I could then just overflowed it. Better than nothing until I figure out how to crack the Torx

Hey so what torque spec is the rear diffs drain plug?

Thanks for your response.... Subaru screwed me and gave me wrong crush washers. Can I reuse the old one?

Good info , under you're car looks like an operating room compared to mine !

so my car has 13k miles on it (19 sti) and i mentioned before about my 2nd gear issue. ive been told by many pple to use the motul gear oil to get rid of all the gear grind and vibration BS. was wondering if you could validate this and if im doing the transmission fluid swap, should i just do the rear diff as well? or is it too early? thanks for your videos!

Wait, shouldnt the car be tilted towards the drain ports for draining and then leveled out when filling to make sure you get the right amount of fluid?

Is the motul gear 300 LS better for the rear?

so the dif and trans take 75w90 same bottles ?

Is the procedure the same on a 2017 Legacy with a CVT? And is it easy to do?

just got my first fluid change yesterday in just local shop here in my town and guy didn’t put all the 5L of fluid on my sti only 4L, that should be fine or do i need to put all of them? Thank you so much!! (15Sti)

Awesome video! You or any other STI owners ever notice 1st-2nd gear is difficult when car is cold when 50 degrees or lower?

hey, ive seen other video, they had to take the TMIC to fill it from the top? im confused lol

So the front diff and transmission get filled up at the same time!

can i use the same oil on a 2018 sti?

I heard around were I live harbor freight has tools that can compare to actual name brand tools so look in to it I could be wrong I was going to go too shopping this week

No shit I'm doing the same thing today lol. Mine is at 72k miles. What about sticking a magnet in the drain plug to get out any shavings ? Think it would be worth it ?

Just to confirm, the fill bolt for the transmission is 12mm Allen correct? 10mm Allen for the lower pan right?