I replaced the manual transmission and differential oils the other day in my 2003 Baja.

 

The Haynes manual said to use GL-5 in the transmission. I was like "What, HUH?".

 

I thought GL-5 was a no no in the transmission because the additives are bad on "yellow metals". In other words it would eat the brass syncros up. Unless the transmission oil was not "EP" but still classified as a GL-5.

 

I've owned numorous older Fiats that call for GL-1 90 which is a straight weight mineral oil with no additives. Allot of idiots would use GL-5 instead of GL-1 and just about every Fiat I've purchased had problems with the sycrnos. Although GL-1 is not readily available at most autopart stores, is actually cheap if you know where to find it. Like Tractor Supply at $13 for 2 gallon jug.

 

So I checked the owner's manual just to confirm and it also said to use GL-5. I forget the weight but I used the correct weights based on what the owner's manual said to use.

 

I got my oils from O'Reily's. I got by with conventional oil for the differential at $5.00 a quart but they guy said the transmission oil was only available in synthetic at $10 a quart.

 

I don't recall the bottle mentioning anything about "EP" which is what you are supposed to use in a typical hyploid differential but not the transmission. I'm not sure what type of differential the Subaru uses. If it's a typical hyploid type or something different. I'd imagine it's not like a typical RWD differential being AWD.

 

 

 

 

 

 

i'm not familiar with that except to say i've always followed the owners manuals for 20+ years on Subaru differential fluids and GL-5 is what i've always used.

There's a hypoid diff in the transmission, so you have to use GL-5. I've always wondered if this is why subaru synchros are crappy. Because, yea, coming from anything else putting GL-5 in a transmission is a major red flag.

80w-90 Gl-5 is what all of the older models use. Newer stuff Subaru came up with their own fluid that is supposed to allow easier synchro engagement.

 

These run for hundreds of thousands of miles with GL-5, so the issue isn't that the fluid damages the synchros. The synchro issue is nothing compared to eating up the front diff, which will happen very quickly by using the wrong fluid.

Edited May 3, 201510 yr by Fairtax4me

Yea, other things usually get to the manual transmissions first. Input bearing failure, the input shaft nut backing off, etc.

80w-90 Gl-5 is what all of the older models use. Newer stuff Subaru came up with their own fluid that is supposed to allow easier synchro engagement.

 

These run for hundreds of thousands of miles with GL-5, so the issue isn't that the fluid damages the synchros. The synchro issue is nothing compared to eating up the front diff, which will happen very quickly by using the wrong fluid.

 

Dumb question but on manuals, isn't the front differential built into the transmission (uses the same oil)?

 

Where on automatics, they use a separare front differential?

 

The owner's manual indicated that on automatics there was a front differential but only mentioned a rear on manuals.

its the transmission fluid on manuals, but same thing. Even has same dipstick. The autos have the diff sealed from the rest of trans

See: ~► https://www.lubrizol.com/DrivelineAdditives/AutomotiveGearOil/GL5.html

 

Despite that GL-6 existed, it is inactive nowadays.

 

Kind Regards.

... The autos have the diff sealed from the rest of trans

 

Not all of the Automatics are like that, see:

 

~► http://www.ultimatesubaru.org/forum/topic/148220-automatic-transaxle-lubrication-the-differential/

 

Kind Regards.

Dumb question but on manuals, isn't the front differential built into the transmission (uses the same oil)?

 

Where on automatics, they use a separare front differential?

 

The owner's manual indicated that on automatics there was a front differential but only mentioned a rear on manuals.

I don't think the owners manual specifically says they are built into the same case. Its kind if of vague on some (most) things.

Yes, the manual shares the case with the front differential, as well as the center differential on AWD models. If you search here for "easy transmission front seal replacement" (or something to that effect) that thread has good pics of how all the guts are arranged inside the manual trans.

I've been using Mobil One 75w-90 GL-5 synthetic in my 97 Nissan Pick Up's transmission and haven't had a problem yet.  194k miles.