Best fluids...

[BAC5.2]

Ok, I've GOT to do my diffs and tranny at some point soon (along with brakes, lol).

I know the best brake fluid, but not the best other fluids.

What are your preferred Diff and Tranny fluids (5MT)?

Anyone got any tips on doing these fluid changes? I'm not EXACTLY sure on how to do it, so I guess I'll go digging for my Haynes Manual, lol.

Thanks!

[scottzg]

redline fluids all around.

Trans- open the big bolt in the middle of the bottom of the trans case. Be sure not to have your face under it! (heh) Fill with the tranny with the dipstick hole that is behind and to the right of the engine as you're facing it. 5 quarts, i think.

Diff- use an oil pan again, open the top bolt on the diff, then the bottom, using a 1/2" ratchet end. Close the bottom one when it empties. Take a piece of hose, stick it in the top hole, and put the other end to your bottle. When its full, close the puppy up. Both are pretty painless jobs.

[vrg3]

There's a lot of disagreement about the best transmission gear oil -- just do a quick search on NASIOC and you'll see what I mean. A lot of people use some certain type of oil and either have difficulty shifting or get grinding when they try to shift.

Our cars definitely tend to have some shifting issues. I personally think it's a combination of some not-great synchronizer design and a requirement for extreme pressure additives in the gear oil. Here's what I've managed to gather from various readings and discussions with very smart people:

Apparently they redesigned the synchros somewhere along the line, so current Subaru synchros are better than the ones most of us have in our cars.

Our transmission lubrication requirements differ from almost every other car out there. The manual transaxle contains the transmission and both the front and center differentials, all of which share the same lubricant. These differentials both have hypoid gears, so proper lubrication requires extreme pressure additives in the oil; without EP additives the sliding friction between the hypoid gear teeth would shear the oil and allow for metal-on-metal contact.

But, EP additives are typically sulfur based, from what I understand. And these sulfur compounds typically react badly with yellow metals like brass and bronze. Our synchronizers are made of yellow metals. Put simply, that means that EP additives are bad for synchros.

I know when I drained out my gear oil (conventional Castrol GL-5 that was only around maybe 15,000 miles old), I could see clouds of yellowish-goldish metallic stuff floating around in it, glinting in the sunlight. I know that's not a chemical test or anything, but it certainly looked like synchro material.

Apparently it's possible to make EP additives that are inert with respect to yellow metals, but it's cheaper or easier or something not to, so most manufacturers don't.

Most cars out there don't have any trouble with this stuff.

Front-wheel-drive transaxles have everything lined up neatly so they don't need to use hypoid gears. So they can use gear oil with less EP additives and things'll be dandy. This is typically an API GL-4 oil.

Rear-wheel-drive cars use separate fluid for the transmission and differential. The transmission can use the same kind of low-EP oil that FWD transaxles use, and the rear end (which typically does use hypoid gears so that the driveshaft can be mounted low enough not to impinge on passenger compartment space) can use the high-EP additive stuff happily, since it has no synchronizers or anything. The high-EPI oil is typically an API GL-5 oil.

So our cars are an exception to the rule. The kinda-conflicting requirements mean it's hard to get things right, and most people have problems shifting at least some of the time. Even without this conflict you still have the standard bearings-vs-synchros conflict; synchronizers require friction while bearings of course hate it, so any manual transmission fluid has to find a compromise between the two. The EP-additive issue just makes it that much more complicated.

So... there's a nice long thread subyluvr2212 started a long time ago that you should read about this. I think his conclusion was that Castrol conventional GL-5 worked the best for him. mile hi strongly recommended using BG Synchroshift (a GL-4 oil, though I don't think he realized that), which has a huge following among the FWD crowd. I think MK actually said he liked how the transmission worked when he put 10W40 motor oil or something like that in it, which scares me since it has, like, no EP additives at all.

What am I using in my car? Well, my car has always had synchro issues ever since I got it, especially 2nd gear's and to a lesser extend 3rd's. Like I said, I did change in some Castrol GL-5 like subyluvr2212 suggested, and it definitely felt like an improvement in shifting, and seems like it would provide good protection for the bearings and gears. But then one day I lent my car to my dad. When I got it back I couldn't even get it into 2nd gear.

So I cajoled him into buying me some Redline MT-90. It's a synthetic GL-4 oil. Redline says it's meant to provide superior bearing and gear surface protection and also protect the synchros. It's also designed to somehow make shifting easier.

GL-4 oil has about half the EP additives that GL-5 oil has. I figured that probably means that brand new high-quality synthetic GL-4 wasn't going to kill my differentials, considering that there are plenty of people out there who, like, never change their differential oil on 4EAT Subarus, or who, like, never change their gear oil on 5MTs. Brand new MT-90 probably isn't that bad compared to 150,000-mile-old GL-5 dino oil. And Subaru differential failures aren't very common. So I put it in.

Wow! Shifting is soooooooo much better.

I will say, though, that sometimes I feel like I can hear a little more noise from the differentials than I used to. It may just be my imagination since I'm just more aware of what's going on there since doing the above research, but I don't know.

But I feel very happy with MT-90 in my car. I wish I'd put it in the day I took ownership.

It's worth noting that Redline also makes an oil that meets Subaru's specs for our cars: Redline 75W90NS. That's what they recommend for our cars. It may be a better choice, since it would provide more EP protection. And it sounds like maybe they are using the intertificated sulfur compounds, since even 75W90NS is meant to help with shifting.

I guess I just talked a lot there without giving you any answers. Sorry.

As for the rear end, just use a good quality GL-5. There are no compromises to worry about there. Mobil 1 would be my choice.

Both fluids are fairly straightforward to change.

The manual transmission drain plug has a 21mm head on it; it'd be hard to miss it. I think I just used a spark plug socket to get mine off. You just drain it all (pulling out the dipstick helps it drain faster), wipe the drain plug and its mating area clean, put the plug back in with a new gasket (part number 803926070, or I think any 26mm copper washer would do), and then fill it through the dipstick hole.

I haven't done the rear differential oil change myself, but here's what I know:

The rear differential has two plugs on the back that take 13mm male square sockets. A 1/2" drive wrench with no socket on it fits very closely. The upper plug is the fill plug and the lower one is the drain plug. So remove the upper plug first, and then the lower one. It usually takes a lot of torque to break them loose if it's been a while. After the oil drains out of the lower hole, clean the drain plug off and put it back in (I think technically you're supposed to put new thread sealant on the threads or something, but apparently nobody actually bothers -- maybe Teflon tape would be good though). Then fill it through the fill plug hole until it spills out. Then put the fill plug back in (after cleaning it too of course).

[BAC5.2]

OK, so what it looks like is using Redline 75W90NS for the tranny/front/center diffs, and some form of GL-5 for the rear end (Mobil 1 or Redline).

Sweet. I can probably do this right after I get back from the Bank. Sweet

Thanks guys!

[professor]

my experience has been that the Redline products are the best I've ever used for manual transmissions. On several occasions, slight synchro grinding was improved, and there is no question that synthetic gives much better cold-start performance; your shifting will be much more like it is on a warm car on cold morinings. I've had several cars where the shift into 1st, 2nd or reverse was very tight and difficult in the cold (especiallt Pittsburgh cold), and the Redline would fix that right up. I did some work in college showing that synthetic lubes have a much flatter viscosity vs temperature curve than conventional, so they are much more consistent. Conventional oils become very thick at cold temps.

So, definitely the Redline in the gearbox.

My experience with Redline in differentials has been, well, different. In a couple of vehicles, I experienced groaning around tight corners that did not exist before. These were limited-slip diffs so your experience may vay. In those cases I took the Redline back out and replaced with conventional, and the problem disappeared.

For any of this work, go out and get yourself one of the plastic pumps / tubes that are a direct fit for the cap of gearbox lube bottles. It is often impossible to fill gear cases by gravity, and trying to squeeze the bottle sucks also. The little pumps are a revelation, making this hassle go away.

One final thought...if you have leaks, with synthetic you'll leak more

[BAC5.2]

Yea, that's my fear with Synthetic. The car has so many miles on Dino, that the seals are nicely varnished over (well, not nicely, but varnished over). I'd rather not use synthetic because of the possibility of removing that varnish and exposing leaks and rotted seals.

[tris91ricer]

mm.. i need to take all this in, as my new legacy will need its fluids changed..

i put this entire thread into my palmpilot...hehe

-=tristan

[kelley]

i've said it before and I'll say it again, I wil only use neo period. I have seen a subaru motor with 200k on it that had neo in it since day one that has never leaked oil and has never had a seal wear out. the neo keeps the seals pliable so they don't crack.
it is expensive but worth it imho.

[BAC5.2]

Where do I get it Kelley?

[vrg3]

Oh yeah, Jason Grahn also swears by Neo. I believe he recommends the RHD (racing heavy duty) variety.

Most of us would probably have to mail order it: http://www.neosyntheticoil.com/where.htm

I'm no expert, but I don't think leaking synthetics are as much of a problem in the transaxle and rear end as they are in the engine. Stuff just doesn't get as hot inside a transmission or differential, so the oil doesn't thin out so much. There are only a few seals and they all seem pretty robust to me.

[evolutionmovement]

I've never changed gearbox oil and I don't even know what's in it. The only shifting issue I have is with some bushings that very occasionally get skewed a certain way and make it difficult to shift gears.

Steve

[kelley]

Where do I get it Kelley?

www.perfectionmotorsports.com

[elkaboom]

I have 75W90 Amsoil series 2000 ( synthetic racing formula) in both my front and rear diff. In the tranny (4EAT), I use Amsoil synthetic.
It's unlikely that you'll experience any leaks in your diffs if you already don't have them and it's arguable that any will develop there if you start using synthetic fluid in place of petroleum based products. I switched to full synthetic all around: crankcase, tranny, diffs and haven't experienced a leak anywhere -it's been well over 30k where engine oil is concerned and close to 15k in the diffs and tranny.
Redline is a superior product to be sure (particualrly where their gear oils are concerned), but the there are a lot of guys on the various oil/engine lubricant forums that dispute Redlines claims about it's ability to hold up for extended periods of time; one of the reasons people switch to synthetic is the longer drain intervals in addition to superior extreme temperature performance, oil film shear strength, etc, etc...
I've used Redline myself and I personally have nothing bad at all to say about it. In fact, when I sent my oil analsis to Blackstone labs, the oil showed almost no signs of degradation and the trace metal analysis was extremely good.
However, at $8.00 a quart (you can't get it cheaper btw) it's damn expensive. Mobile 1 supersyn is very good oil, and for the best all around value (in addition to having been tested, used and sworn by by many, many of it's users, at least in my opinion, is Amsoil.
I've experienced exceptionally good results with both the series 2k gear oil and the tranny fluid -several of my shifting issues disapeared with the conversion to Amsoil tranny fluid .
Also, Amsoil is slightly less expensive than Redline and arguably a little easier to find.
You can look into Royal Purple as well -they make a complete line of synthetic lubes (motor oil, gear, tranny, etc...).
Swapping the diff fluid is easy in the front -just do like you're changing your engine oil (same side, but just behind the oil pan -you can't miss the drain plug); let it drain (do it when it's warm obviously), replace the plug and fill it with a narrow nosed funnel. It's takes a litle over a quart... 1.5 or 1.8 quarts, I think.
The rear is easy too, but if possible, try to find a lip where you can back the car up to so it's easier to get under the rear of the car -it's also a good way to get better leverage when breaking free the drain plug -I used a breaker bar with a pipe on the handle as a lever 'cuz the plug was seriously overtightened.
Rear diff takes a little less than a quart incidentally -you need to eyeball it, but it's about a quart.
Filling is a little more difficult, but a long length of flexible plastic tubing might help -if you can attach it to the end of a funnel and run the tubing to the top filler hole, you can prolly fill the diff without having to lie at an akward angle with a bottle of gear oil -it's tight at that angle.
Anyway, it's all pretty straight forward, but I'd seriously consider Mobile 1 if you're budget conscious -it's good. Otherwise, go Amsoil or Redline -assuming you're converting to synth.
Good luck!

[Legacy777]

I actually have something to input on this thread now

I did very minor research on oils, and just stuck valvoline 75w90 gl5 in. Shifting is notchy, and not all that smooth. My nissan pickup is smoother.

I talked with Richard buckner about oils. he recommended some form of synthetic, but said to wait on the transmission since synrcos were new and to give it some miles. Drain and put synthetic in.

He also said that Neo is awesome shit, price is the only drawback.

I heard too many stories/problems with redline 75w90NS oils.....so I'm probably going to stay away from those. Interestingly, Richard said to stay away from mobil 1.

Some of the guys on nasioc have been running tranny cocktails. A quart of pennzoil synchromesh, qt of something else, and then just regular 75w90. I'm tempted to try that, but I'm not sure.....

I will probably do some more homework/research, however I am leaning towards trying some of the NEO gear oil

[Legacy777]

There seems to be three different kinds of neo oil that would work.

75w90 EP
75w90 HD
75w90 RHD

The HD probably looks to be the best option, however I haven't read things too closely.

Kelley, what do you charge per qt or gallon...however it's sold.....and which kind do you sell/use?

[entirelyturbo]

Lemme throw in my .02 again...

I will actually challenge some of your guys driving styles, as I really see no need to slam gears around. I think we can all agree that stock Subaru flywheels are especially heavy, as I've never seen another car that takes so long to change RPM's. So you're coming out of 1st gear at redline, and you slam 2nd as fast as you can, for what? To wait for the engine to come back down in RPM's, or to dump the clutch, trying unsuccessfully to chirp an AWD car, and doing lots of damage, with NO acceleration increases at all. I say get in touch with your tranny, feel through the shifter what the transmission is doing. When the gear is ready to engage, let it, and I'm sure the engine will be in the right RPM range to engage the clutch and go again.

Boy I sounded like an old man saying that!

I drove the Dragon like this, never ground gears once, and for a 130-hp 14-yr-old car, I was haulin!

Drive like me and dino oil will suit you just fine.

But if you insist, then yeah, Redline MT-90 is probably your best bet. As Vikash said, it's probably not best for the gear-meshing action in the tranny and diffs, but the synchros seem to like it. Just be aware, that if you're in a hot climate like me, it might just get too thin to work properly and grind no matter what, unless you double-clutch.

The synth with old seals doesn't seem to apply to trannies. I didn't leak any when I used it in the Legacy.

As for rear diffs, I do use Redline 75W90, no NS. A very serious suggestion on changing rear diff oil. Loosen the top plug FIRST!!! It's going to be very hard to get it loose, needless to say. But it just might happen that you can't get it loose. I've come close to stripping out the inside of the plug. So let's say you loosened the bottom one first, and then you can't loosen the top one. You've just drained all the oil out of your diff with absolutely no way of replacing it! The car is stuck there...

Ultimately, you have to experiment. It all depends on how you drive, what condition your gearbox is in, blah blah blah...

[vrg3]

Well, I've driven several older Subarus in which it was very hard to shift into 2nd gear at all[ without grinding, even with the gentlest driving style. The synchros were worn to the point that it was just a very weak dog box. When I got my car back from my dad, even when double clutching it was hard.

I disagree with your recommendation to use Redline 75W90 in the rear differential. It contains friction modifiers, which are at best unnecessary for our rear diffs. Redline 75W90NS doesn't have the friction modifier.

Kelley - I'm also curious about how much Neo fluid would cost. I'd prefer to get good shifting from a GL5 rather than a GL4.

[entirelyturbo]

Hell, I really don't remember what I use, it's been so long since I've changed gear oils in my rear diffs. I seem to recall a big discussion on the USMB about using NS in the gearbox and no NS in the diff...

[vrg3]

I think the old-school clutch-type rear LSDs need the non-NS stuff, which would explain that discussion on the USMB.

[BAC5.2]

Subyluvr - Your comment about fast shifting does not apply to those of us (like me) with lightweight flywheels. If I DON'T shift fast, the revs fall to far and I HAVE to double clutch the shift. Double clutching is slow, shifting quickly is fast, and I've got a flywheel the allows it.

I just want a tranny fluid that helps smooth things out a bit.

[evolutionmovement]

Try the older Subarus for big-ass flywheels. I felt like I had an F1 car with the way the revs fell after moving from the EA81 to the Legacy!

I also shift slow and deliberate. I know, I know, I'm on my second gearbox ... I'm telling you it was the J-TURNS!

Steve

[Legacy777]

I don't consider my shifting "slamming" gears. I just want the shifting to be better then it is. It's not smooth. As I may have mentioned. My 95 nissan pickup shifts smoother through the gears then my subie does with new synchros.

I'm planning on calling neo to talk to one of their techs/engineers about our(subaru's) transmissions, and out of their products....what would work best.

[entirelyturbo]

I wouldn't be surprised, Josh. Nissan probably built the transmission to take more abuse than Subaru built ours.

My grandfather's 92 Isuzu p'up shifts a hell of a lot better than either of my cars, and that truck is beat to shit...

[kelley]

i'll find out for you josh. i can't remember what i put in.
the last one I did was the 6 speed and I think that was differant than what is in my legacy.
it definately does shift smoother than any other fluid I have used. I know some people that find it too smooth. perfect imho.
but yeah, you still shouldn't slam the gears no matter what fluid is in if you wan't your tranny to last.

[Legacy777]

I talked with a tech at baker precision, which is apparantly who makes or runs the neo synthetic site and has contact info.

Anyway, they recommended the 75w90 HD
http://www.neosyntheticoil.com/75w90hd.htm

Baker sells it for $10.95 a qt, or $38.95 a gal.
http://www.bakerprecision.com/neocirc.htm

I also talked with Richard Buckner, and he recommended the HD as well.

I haven't called around to check prices, but I'll probably see if anyone locally carries it.

kelley, can you see what you can get the 75w90 HD for?

thanks