Gear Oil Questions

[Bluestone]

Gonna change my 2000 Legacy GT wagon's gear box(manual tranny) and differential oil. If I use Red Line oil, is it 75/90 gear oil in the gear box, and 75/90 NS gear oil in the differential?

If I just use regular 75/90 GL-5 rated oil, do I need to put a limited slip additive in the differential?

What size sockets do I use for the drain plugs?

[porcupine73]

You don't need limited slip additive for that LS diff. It is a silcone oil viscous type that the gear oil doesn't actually get to the limited slip part.

 

Maybe someone else knows what exact type redline gl-5 gear oil works good in the Subaru MT's. I think it might be the NS but I dont' have an MT so I'm not sure.

 

The drain plug size for the rear diff should be a 1/2" pipe plug. A 1/2" drive breaker bar will fit in there, or you can get actual pipe plug sockets. Not sure about the MT drain; common Subaru sizes would put it probably at 17mm, 19mm, or 22mm.

[powderhound]

The Redline NS goes in the gearbox. I've had it in for 65K...initially helped the synchros but now seems to need replacement. There are as many different recs for gear oil on here as there are members...some say the redline doesn't last long. Mobil 1 in the diff will work fine.

[Bluestone]

.....Mobil 1 in the diff will work fine.

 

Mobil 1 in the gearbox, too, ya think? It's an LS rating but there's no non-LS Mobil 1 gear oil available, as far as I can tell. And the specs say it's for applications where a GL-5 rated gear oil is called for, as well as non limited slip use.

What sayest thou?

[bulwnkl]

Don't use the M1 in the gearbox. I liked Red Line 75W90NS in my XT-6 tranny. There isn't anything that's positively beautiful in a Subaru MT, but the NS is about as good as it gets for us. You'll probably have to change it every 30,000 miles to maintain best feel, but protection-wise, it'll last super long.

[edrach]

I'm embarassed to admit this but I installed the 75W-90NS Redline in my '91 Legacy wagon at 93K miles when I bought the car about 5 years ago. This past weekend, I had it replaced while having other work done on the car (new GR2's all around:banana: ). Anyway, the mechanic pointed out to me that gear oil should be changed every 30K miles. I currently have 192K miles on the car. Gearbox works just fine and is missing the 2nd gear synchro crunch it had when I bought it.

[porcupine73]

You can use a GL-5 gear oil that says it is OK for LS diffs in the differential. It doesn't need the LS additive but it doesn't matter if it has it.

 

It is not suggested to use Mobil1 gear oil in the Subaru MT. There were issues in the past with it's high sulfur (a great antiwear) eating up various parts.

[Bluestone]

Ok then....it'll be Redline 75/90NS in both the gearbox and the diff. (Strange, but there are only two vendors that I could find around here that carry Redline gear oil and both only stock the NS version).

I'd go for Redline motor oil too, but at $9-$10 a quart, it's just too expensive for 5000 mile oil change intervals. I couldn't find Mobil 1 gear oil(for the diff) anywhere around here, so it'll be Redline.

Thanks, everyone, for your helpful replies.

[powderhound]

you probably don't want to use the ns in the rear diff...that is not its intended use. the ns means it has friction modifiers that would not be needed and perhaps be harmful to the rear diff. Can't find mobil one gear oil?! I'm sure they have it at walstarmart. And yeah when i bought the ns in the minneapolis area i was in a sketchy back alley shop that was the only supplier around...it was weird to say the least.

[bulwnkl]

you probably don't want to use the ns in the rear diff...that is not its intended use. the ns means it has friction modifiers that would not be needed and perhaps be harmful to the rear diff.

 

WRONG. The NS does not have the FMs that the "regular" stuff has, and there will NOT be any harm to the diff.

[jomo12]

So I have a question too about gear oil. I have a 02 legacy, 5speed. The transaxle was just replaced by with a unit that has (so they say) 27k miles on it. It was replaced due to a bad center diff, had hell of torque bind. Now, the new transmission shifts much harder than the old one. It's not like bad syncros, it's just notchy as all f-out, it's even chunky pushing it into 1st or reverse from a dead stop.

 

This was a ford dealership who did the work, and they put in Motorcraft 80-90 oil -- from the part # I can tell that Ford sells this as "premium rear axle oil".

 

Should I change the oil? (and to what, of course?) This thing is no fun to drive.

[Bluestone]

I was just looking through a Subaru factory service manual and in the entry regarding filling the rear diff, it says when reinstalling the filler plug, "CAUTION: Apply fluid packing to filler plug before installation. Fluid packing: Three Bond 1105 or equivalent."

I'm assuming that it's saying to lubricate the threads on the filler plug, but why specifically "Three Bond 1105(whatever that is???) or equivalent"? Why not just some of the gear oil or any other oil? And why does it caution to apply lubricant to the diff's filler plug, but no mention of doing the same to any of the other filler plugs? Might there be a particular issue with the diff's filler plug only? Puzzling.

[forester2002s]

"Three Bond 1105(whatever that is???) or equivalent"?

 

It's a silicone sealant:

http://www.threebond.co.jp/en/product/series/sealants/1100list.html

[bulwnkl]

Yeah, it's a sealant not entirely unlike teflon tape or even packing like you use on water valves, etc. It's used there because that plug is just pipe thread whereas all the others have a seat.

 

Regarding the "new" tranny not shifting well: Is it possible that the clutch is not properly adjusted? If I was confident of proper clutch adjustment, I'd probably swap out the fluid (but that's just me).

[Bluestone]

Wonder why Subaru doesn't just use crush washers on the diff's plugs?

Anyway, I got a tube of "Ace" brand Pipe Thread Compound TFE Paste for a couple of bucks at a local Ace Hardware; it's non-hardening, compatible with oils, lubricates as it seals, and withstands temps of up to 500˚F.

That should do the trick.

[porcupine73]

Application: Differential oil drain plug, bearing cap #5 (Impreza only), oil pressure switch, etc.

Recommendation: THREEBOND 1105 (also referred to as FUJI BOND “C”) SOA part number #004403010

Equivalents: 3M T-3 Silicone (black) #08670

 

Threebond products are very common and obtainable in japan. Not so much in the U.S., though many ATV dealers will have it.

 

I've used pipe dope before too and it works fine. It needs a sealant because it is a tapered thread and there is a leak path between the crests and roots. I don't know why they use this style plug, but it is a fairly common style on the rear diffs of many automakers.

 

New tranny not shifting well: get that ford oil out of there and put in some redline NS or something that is going to be a little smoother. Also, it is possible the ford dealer doesn't know a lot about subaru's and how to make sure everything is lined up for the shifter, bushings, etc.