Mobile 1 in a Subaru Manual transaxle?

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Aberdeen washington USA
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Well Bob: I have an odd question: I was told by the master mechanic that rebuilds trannies to use Mobil 1 0-50 synthetic motor oil in my Dodge Cummins NV4500 instead of gear lube: was told it runs cooler and lubes better. So I did it.. and the transmission ran quieter and has been problem free for about 25,000 miles.. The Question: does anyone know if this can be done with a Subaru manual transaxle? Thanks
 
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12,873
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ROCHESTER, NY
Welcome youoldguy! laugh Hopefully someone or many will chime in and answer your question. But most likely the answer will be to use whatever Subaru recommends. Another old guy, CB
 
NO! Not if you want it to last. Subaru transaxles are shared-lube on manual trannies, meaning you've got the clutches, shift forks, and hypoid gears sharing the same lube. You need a gear lube as it is designed for; Amsoil, Motul, Redline, and even Mobil all make lubes that meet the specs; why take the chance... do you think your "master mechanic" knows better/has more experience than either the Dodge or Subaru engineers, or is it more likely he's recommending this because he knows it will generate him more business? Not attacking you, and welcome to the board... but if somebody told me this and claimed to be a "master" I'd be hauling donkey out of his shop. JMO.
 
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15,001
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Upper Midwest
Originally Posted by someoldguy
I know he is a GM Certified Master Mechanic.. and has rebuilt thousands of transmissions...
Thousands? That's pretty amazing. I too would use what the manufacturer specifies, rather than one person's opinion about a different transmission in a very different vehicle. In the end it is a GM mechanic giving out advice on a Dodge transmission which you wish to extrapolate for a Subaru. What could go wrong?
 
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14,185
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Central NY
I would in the NV - they can't use any sort of gear lube but use some sort of prorpietary less viscous fluid. I'm sure it interchanged with engine oil though. It's also popular for some of the FWD manual transaxles.
 
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9,912
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Jupiter, Florida
In some cases, Mobil 1 ATF is a wonderful manual transmission fluid. However, those cases are generally conventional FWD transaxles or conventional manual transmissions. The M1 ATF can be used to replace a conventional 5W-30 motor oil transmission fluid and is generally superior. In your case, the somewhat unusual configuration of ring and pinion gears in a FWD transaxle, require a specific type of lubricant to ensure adequate gear life.
 
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6,819
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California
XOM does make a dedicated MTF for HD trucks, Delvac SAE50, but in your case any GL-5 75W-90 is sufficient. Subaru manuals share oil with the front diff and transfer gear/center diff. If you have a LSD center diff, some swear by OEM Extra-S, others will say Amsoil or RL is fine.
 
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5,301
If you use anything but a non-LSD GL5 gear oil in a Subaru manual transmission the syncros won't hook up right and shift quality is going to go downhill and get notchy. Non-LSD means it doesn't contain friction modifiers. Gear oils for limited slip differentials contain friction modifiers and you don't want that in a Subaru manual transmission due to the syncros. I owned a manual transmission Subaru Forester for 10 years. I did oil changes, rear differential lube changes, and manual transmission oil change (which includes the front differential-- shared lube) myself and I abided by Subaru's recommendations religiously on fluid specs. The car never gave me any big problems and drove as well the day I traded it in as it did when new. But it only had 67,000 miles so there's that. Anyhow, use a GL5 75W90 gear lube containing no friction modifiers, in your Subaru's manual transmission that really is what needs to be put in it. I used a 75W90 non-synthetic GL5 gear oil by ENEOS which worked well. I see from checking their US web page that they no longer offer it in non-LSD though, only LSD friction modified form so it's a no-go now for Subaru manual transmissions. Subaru Extra S GL5 75W90 gear oil would be the best choice. Back in the day a Subaru dealership used to sell it online, I think it was Fred Bean (?) Subaru.... maybe. Been awhile.
 
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3,491
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Occupied Virginia
Originally Posted by nthach
If you have a LSD center diff, some swear by OEM Extra-S, others will say Amsoil or RL is fine.
Diff type really has nothing to do with it, it's keeping the manual transmission's synchros happy is the problem. Subaru's own Extra-S was the best thing I ever put in mine but I don't believe they make it anymore. I think Subaru has a generic MT/center diff oil now and it's not Extra-S. Problem is once you 'contaminate' the guts with a lube it doesn't like it never seems to be the same afterwards.
 
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The exceptions to the rule where GL-5 should not be run in a manual transmission besides the forementioned NV4500 or any transmission calling for a MTF are Toyota, Tremec, Honda and Mazda gearboxes. Toyota wants GL-4 fluid safe for yellow metals, as the organosulfur compounds in GL-5 fluids affect them. Tremec and Mazda call for ATF, and Honda wants their own fluid, in the past they said 10W-30 motor was fine until the API specs were updated to SM/SN.
 
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5,301
Originally Posted by Bottom_Feeder
Originally Posted by nthach
If you have a LSD center diff, some swear by OEM Extra-S, others will say Amsoil or RL is fine.
Diff type really has nothing to do with it, it's keeping the manual transmission's synchros happy is the problem. Subaru's own Extra-S was the best thing I ever put in mine. Problem is once you 'contaminate' the guts with a lube it doesn't like it never seems to be the same afterwards.
The center differential in manual transmission Subaru is a viscous type, is a sealed unit, and does not share the gear oil that's shared between the manual transmission and the front differential. Confused yet? It's Subaru, they're weird. Cool as heck and great vehicles, but a little different from the norm !!
 
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3,491
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Occupied Virginia
Originally Posted by LoneRanger
Subaru Extra S GL5 75W90 gear oil would be the best choice. Back in the day a Subaru dealership used to sell it online, I think it was Fred Bean (?) Subaru.... maybe. Been awhile.
Yes, Fred Beans in Doylestown PA. They would sell Extra-S in unmarked quart bottles because there was no market in selling it in the 5 gallon buckets it came from Subaru in.
 
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3,491
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Occupied Virginia
Originally Posted by nthach
Honda wants their own fluid, in the past they said 10W-30 motor was fine until the API specs were updated to SM/SN.
I made the mistake of putting Mobil 1 in my '94 del Sol transmission a long while ago, thinking I was doing it a favor. It hated it and hated me for doing it. 2nd gear was never the same. frown
 
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8,074
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New England
I had good luck with Redline 75W-90 NS in my STI. Redline support recommended this to me for that application. I had tried Motul Gear 300 75W-90 GL-4/5 before that and after the FF and found it didn't enhance the feel the MT. The Redline did, though it still remained very notchy. Note: I had driven other STI's with the same MT and OEM fluid and they were much less notchy than mine.
 
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6,819
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California
Originally Posted by LoneRanger
The center differential in manual transmission Subaru is a viscous type, is a sealed unit, and does not share the gear oil that's shared between the manual transmission and the front differential. Confused yet? It's Subaru, they're weird. Cool as heck and great vehicles, but a little different from the norm !!
Wait, I thought the LSD center diff used on STI models shared fluid with the trans/front diff, and the viscous coupling/MPT center diff used on the rest was sealed?
 
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5,301
STi could be different since STi allows variable torque to rear differential, I'm not up on STi dynamics but I think driver can select to change the torque bias from, say, 50/50 front/rear to, say, 30/70 front/rear? Not saying those figures are accurate, simply an example to illustrate the capability of torque vectoring on demand by driver input. So clearly the center differential on STi is not same as the regular manual transmission driveline which is locked to a 50/50 front/rear axle torque distribution.
 
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