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S401 Drivetrain Oil Change

The last thing left in my maintenance overhaul of the S401 was to do the oils for the transmission and differential. I decided to take advantage of having access to a hoist and decent tools whilst at work today, and changed them.

Considering the rest of the car and its neglect in the past, I had no faith in the rest of the oils.

At the recommendation of an old friend who seriously knows his Subarus, I went with Castrol Syntrax Universal Plus 75W90. It’s also what Castrol recommends for V7 onwards STI, which use a similar gearbox to the S401 (same box but with different ratios and front diff). This oil is also recommended for running in the rear differential too. The front differential (which is in the gearbox and shares its oil with that) is of a SureTrac torque sensing type, and the rear is a standard viscous style, which means neither need special friction modifiers to keep them happy (unlike the M3 plate diff).

I started with the gearbox, which is actually easy. There are two drain bungs, one for the oil pan and one for the front diff (two drains, but they share the same oil so don’t need separate filling). The differential drain is 21mm (although apparently later model STIs went to a huge T70 torx), and the pan is 14mm. When I pulled my plugs I was really surprised at how clean the oil actually was. May not have been that old? Even the plug magnet had only a little sludge on it.

The 21mm was really hard to get off, and we ended up having to use a 1/2″ beast of a rattle gun to shift it. Once drained, I torqued both up correctly. 14mm to 33ftlbs, and 21mm to 52ftlbs. New genuine crush washers were used, and I did note that the diff housing washer has been superseded from a standard copper washer to a composite washer with fibre coated aluminium.

Once they were torqued I dropped the car down and using a long, narrow funnel, I poured 4L of oil down the dipstick tube. The gearbox should take about 4.1L, but to be sure I had enough for the diff (as I ordered 5L), which takes 0.8L, I under filled the gearbox initially. The dipstick tube is on the RH side, tucked down under the intercooler.

The diff was much the same to do. There is nothing in the way, but having either a bottle you can squeeze, or a pump to fill it, will help a lot. MAKE SURE TO CRACK AND REMOVE THE FILL PLUG FIRST. My fill plug was very tight, but using a 1/2″ power bar it eventually came out. This had a much different result to the gearbox though, the oil was very dark and a little cloudy, and there was a fair bit of sludge on the magnet, and in the bottom of the housing (which I scraped out with my finger). Also no chunks though, so this is normal.

Clearly this was another case of “good enough” servicing 😣 Thankfully no chunks, so we are still OK.

Once drained, I refitted the drain plug and begin pouring oil in. Sure enough I got to about 800ml before it started to run out from the fill hole (which is the sign its at the correct level). I let it drain back until it slowly dripped and then put the fill plug back in. I didn’t torque these, but tightened them firmly. There is a need for caution though, as they are a tapered plug and over-tightening can result in a cracked diff cover. I returned to add in another 100ml to the gearbox, which brought it to the full level.

The results aren’t huge, as the gearbox was pretty good to start with, but on the drive home (once out of the 1-2nd gear start stop traffic) i did note it is smoother, and it takes less force to get into gear now. It’s an interesting box, it has a very firm feel, and sort of pops into gear. It’s great to use, much better than the 5 speed boxes. It’s probably a placebo, but it also seems a bit quieter under heavy acceleration. Still worth it knowing it’s been done, especially with how the rear diff oil looked.

I have also been amassing a few odds and ends for the car that were missing when I got it. The first part is an ash tray. Although I don’t smoke, there was a horrible gaping hole in the dash where it should have been. At night the ash tray light would cast a green glow from in the dash.

You can unfortunately see in that photo what im dealing with on the interior trims. Horrible sticky “soft touch” coating that is easily, and badly scratched. My plan is to clean all that rubbish off, and plasti-dip all the trim, and return it to factory look (but hopefully more durable).

The other, far more important part I obtained is a boot tool kit, so in the event of a flat tire I can actually get the wheel off and put my huge space saver wheel on. Sadly as mentioned, someone has removed the STI “Snap-On” tool kit in the past, so I have to make do with a normal Subaru kit. Being a used kit there are some oddities, like a couple of the parts being BMW parts, but hey, they will still work and they are in decent condition.

This is the missing STI toolkit, that I am very unlikely to ever obtain. My only chance is to get one from another S401, as you cannot buy it new.

Oh well.

Speaking of other cool things that are rare about the S401, it is the only BE5 Legacy to not say Legacy anywhere on it. Even the rear garnish between the tail lights doesn’t say it, instead it says SUBARU (all other Legacys say LEGACY).


It’s the little things that make this car so special.

So anyway, when I got home from work I put the tool kit in the boot, and noticed how filthy the number plate lights were, so undertook a mission to clean the lenses and convert to LED. This is what I started with,

Theyre bit of a shitty design, because the bulbs don’t oppose each other like a lot of other cars (so the light isnt symmetrical), and the holders are a three-piece setup, with the lens, a gasket and then the housing. The two screws go through all of this and then also secure it all to the car. 😑

This is one before and one after

And then both done, and lit. Not sure how good they will be at night with that style LED, but ill check soon and maybe change to a different style if needed. There is limited space though, so it has to be a fairly short LED.

Once I was done with that, I moved to another thing that’s been bothering the crap out of me recently. I tend to use windscreen washer jets a lot, because i like a nice clear view, but the jets on this were just terrible. It’s the old style with two nozzles per jet, which just fire a jet of water at the glass.

On the passenger’s side, of the two nozzles, one was blocked and didn’t work, and the other was pointing up and too far left, outside of the sweep of the wiper. On the driver’s side it wasn’t much better, one was too low and under the sweep, the other was shooting over the car.

I unblocked and adjusted all of the nozzles to point where they should (as per the workshop manual),Washer jets

I didn’t measure it, because im not that pedantic (and I couldn’t be bothered getting my tape measure), but the general idea is there. I used one of the little “T” pins I got off eBay a while back.

I also adjusted the rear, which was a bit of trial and error. At one point I had it shooting right over the car, hitting the bonnet!

But now it all works perfectly, and its great. I do need to change the refills in my wipers though, they streak a bit. I don’t want to change the whole blade, because I have these mint PIAA aero blades.

So that’s that, more work completed, a much nicer car to live with. Every little bit helps.

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7 years ago

You may be correct that its the only _legacy_ to have ‘Subaru’ on the rear garnish, but all AUDM Legacies (known as Liberty in Oz) do, too.