Amsoil Severe Gear 75w90 - 50,000 mile drain

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mvw2

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Jul 6, 2008
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Minnesota
Well, it's been around 50k miles and a few cold winters since I threw some Amsoil Severe Gear 75w90 in the tranny and rear diff of my Subaru Forester. I must say I've loved every day of it. The Subaru 5-speed tends to be a little picky with slipperiness and good syncro function, and it just loved the Amsoil.

I started to drain out the old oil for some fresh stuff. I've only got the rear diff so far and will pump out the tranny fluid tomorrow. I say pump because the drain plug is apparently not going to budge, at least didn't last time at the auto shop.
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I recently boiled the rear diff a little after a rally-x and having to run mismatched tires for a 50 mile drive home. God the center diff hated it, and the rear diff got a little too hot with the constant load. I got a lovely decel whine out of it too, not horrible but not going away either... Everything functions normally though, so probably just some roughness on the back sides of the teeth. They've never gotten used under load before, lol.

Wear was minimal on the rear diff, gears looked fine, very little metal on the magnet. The diff oil came out a bit black but didn't seem completely destroyed and probably still usable. I expect similar, well a little better, with the tranny fluid.

I auto-x, rally-x, and ice race the Forester a decent amount, and I make the 2.5L NA work hard not to mention the diffs. The Severe Gear has help up flawlessly and feels as good as it did the day I put it in a few years ago.

I'll see if I can get an oil analysis done on the tranny fluid. There's a local lubricants guy who handles a good portion of the Midwest's commercial needs. I'll probably chat with him tomorrow and ask about the procedure. I know he does it quite a bit for fleet vehicles and his own oils. I want to get my motor oil checked in 1k miles or so too. I've been running M1 0w40 year round, swapping probably a bit too often according to some threads here at around 3-4k miles, PureOne filter too. I wouldn't mind bummping that to 5k or longer if I could easily get away with it at zero side-effects. I just know I'd have to dump in at least half a quart or more if I was doing an extended drain interval. I've run 0w30 and 0w40 with very little difference in loss, so I'm not certain exactly where it goes. I've had the Forester since 26k and now has nearly 80k. It's behaved about the same always. I may try Amsoil 0w30 or 5w40 in the future, but that discussion is another forum section, lol. I'll get tranny oil impressions and an analysis up whenever I can get that done and back.
 
It's not that simple. The oil did fine. I can't even tell you what gear(s) the whining is coming from. I want to say it's not even from the rear diff. Visually, the diff gears look good.

Basically, the only reason why the whine exists is because I had to run unequal diameter tires home from a rally-x. 50 miles plus constant load from the center diff does not equal good times and is above and beyond what I would expect any gear oil to nicely handle.

The whine, whatever it's from, is only on decel, i.e. load on the back side of the gears. Normal operation is, well, normal and silent. The transmission works fine and with zero ill effects, and the diffs seem to function happily. The front and rear are a simple open type and the center a sealed viscous type.

Metal shavings from the rear diff were very minimal, even after a slew of auto-x, rally-x, and ice racing and the unkind limp home.

I just swapped out the transmission fluid, and it looks and smells a bit better than the rear diff did. It's not quite so black and with zero burnt smell. The rear diff fluid was darker and with a little bit of burnt odor too it, still not as bad as some well used engine oils I've drain in my youth. I'm sending some off for analysis, and I'll see what I get back for the results. I didn't remove the drain plug, so I have zero comments on metal shavings. I figure the oil will show any wear indicators anyways. The oil appeared and smell like it was still in good condition. I would venture to guess I could get a good number of more miles out of it, but I'll see what the tests show. The transmission houses the full gear set plus the sealed, viscous center diff and open front diff.
 
I just switched to the Severe Gear as well this past weekend and I love it.
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So far I feel it's the perfect combination of ease of shifting and friction for the synchros. I put 75W110 in the rear.

What did you use in the rear? For those conditions, definitely go with at least 75W110 or probably even 75W140.
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Mis-matched tire sizes are bad in a Subie, but you know that.
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-Dennis
 
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Yeah, I really, really, really hated driving back home like that. About 10 miles from home the rear diff got so hot it started to burn the rubber bushings supporting it. Things are getting a little toasting if you can get something nearby up to 300-400F, lol. The oil was a little burnt but wear remained minimal, so I'm happy. I just hope the whine goes away in 10k miles or so as the rear gear face smooths off a little. Interestingly, the center diff never seemed to degrade through the entire drive. It always seemed to get heat in it and just work.
 
Originally Posted By: lumpy_grits
Hi mvw2, I hate to say this. IF your Subaru has a limited slip in that rear diff, you may have very well "smoked" the clutches because of the two different tire O.D's.
Respectfully,
LG


I agree and even if it's an open diff, the strain was on the diff itself, not on the R&P. If it got as hot as you say, my money is on it having a clutch type limited slip (LS) because continuously slipping those clutches would create mondo heat. An open diff would be spinning pretty hard but wouldn't get all that hot. If a LS, I'd guess the black in the oil was probably as much from about 50K miles of clutch lining burnt off as much as burnt oil. All that lining material in the oil could have a deleterious effect on all hard parts and perhaps that's the root cause of the new noise.

On a part time 4wd rig (or by disconnecting the rear driveshaft on a full-time system) you can do a quik & dirty test by lifting one tire and trying to spin it. If it spins (and you'll see the pinion yoke spin too), you either have an open diff or your LS is smoked. Some LS are tested by the amount of torque it takes to spin the lifted tire. Not sure how Subaru tests theirs. When you wear out a LS, it reverts back to an open diff so unless there are other issues, you may not have a screaming emergency. Obviously, I've wasted our time here if the Sube has an open rear diff but this was a good segue for the info. Hope it turns out well!
 
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Hmm...looking into it further, it appears mine might actually have a limited slip rear diff. Oddly, pretty much all old documentation I've seen in the past never pointed to a lsd as an option nor available for the Forester. However, digging around specifically for the Forester and lsd, I did manage to come across more than one listing of a rear lsd being included with the "winter package" which included heated seats, mirrors, and wipers...which I have.

Oddly, I've never noticed, lol. I've also never used any lsd slip modifiers in the rear diff and have never had any chatter. I've also gotten stuck a couple times after getting one rear tire on ice while the rest were in the snow. This would be normal for an open diff, but a lsd type should get me unstuck or at least the other rear tire spinning. I really can't say how worn it is, if there is one. I got the car with 26k on the odometer and have nearly 80k now. The awd system hasn't really ever noticeably changed, yet, I don't really get to test it out except winters and for the most part, the symmetrical design takes care of most things well enough.

Now in terms of putting wear on the rear diff, if lsd type, I did run the same diameter tires on the rear as well as the same diameter tires on the front, 215/65/R16 front, 215/60/R16 rear. The only difference was between the front and rear which should focus everything on the center diff. The front and rear diffs should not be working, just simply have stress on the main gearing.
 
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Hi, don't know what to tell ya, but I have a real strong feeling your rear LSD clutches are toast. One end of your Subaru was turning faster that the other was, and the rear LSD was the "weak-link".
The next time you are in that same type of stuck. As you give power VERY lightly add some brake and release, you may have to do that a couple of times. That will "fool" the LSD into sending power to the wheel with grip. Always works for me anyhow.
Respectfully,
LG
 
Well, lifting up the rear end, the tires spend pretty freely. I can't say I've ever had it not.

My gripe with your thinking is that in order to even use the lsd at all, one needs to spin the rear tires at different speeds. If this never happens, the diff never operates. The tires never slid. The center diff just stayed [censored] off the whole time. Being a viscous type, it just gives. I'm running 245 wide RE01R tires on the car. It takes a bit to get them to slide, lol. This is why I don't get how I could burn it out, if it does have one.
 
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mvw2: I may have misunderstood your original post. I thought you had different size tires side to side. If the difference was front to rear, then you are right, the center diff would take the hit (and the heat). What accounts for the melted rubber diff mounts, though? There's 1/2 tp close to an inch difference in diameters, which is significant.

Did you read my post and do the test exactly as I said? If you lift both wheels, that doesn't count. One must be on the ground and the rear driveshaft must be able to turn free (no center diff). The clutches in the LS essentially connect the two axles together but enough torque will slip the clutches. Or it could be an open diff.

RE the VC: If you can lift one rear tire and spin the wheel with your driveshaft connected, then your viscous coupling is toast. That was the test we used back in my Factory Trained Land Rover Tech days. With an open diff and one wheel on the ground, the pinion HAS to turn. If it turns freely, then the viscous coupling isn't working. With a good VC, it should turn but with effort. I

What year is your Forester? I have some Subaru dealer data books from the '90s and early 2000s. I could look it up. Or I could sell you the books and let you look it up! PM me.
 
It's an 02 S model. Apparently the S either came or had available the winter package which included a rear LSD.

If I lift the rear end off the ground, front still on the ground, I can spin one rear tire and the other would spin opposite pretty freely. A clutch type limited slip should provide some resistance I would think.

The center diff never seemed to stop working. All the way home it would always blatantly resist and bind the drivetrain. If I ruined it, I would expect it to stop functioning or lessen, but it never seemed to.

Other than the audible whine on decel, everything seems to function normally, at least as normal as I'm aware of. There just aren't any indicators of damage or non-function. I could probably give a quicker estimate if there were snow on the ground or if I took the car on some gravel roads. However, even then, my current suspension setup is new, and I have yet to run it aggressively on gravel yet. I wouldn't have a base point for its behavior. As well, with the symmetrical design, it is not so easy to simply spin up a tire. About the only thing that ever freely spins up is the front, inside tire during hard cornering, but that's an open diff anyways. The rear end has always broken away together, irregardless of surface as long as it was of an even type.
 
Hi, IF I understand how a Subaru AWD works(have an 03 & 07, both w/LSD re.)It maybe possible for the front end, with the different size tires,and center diff. to "over drive" or make the rear LSD clutches slip on both sides of the carrier. I seem to remember reading that the torque split from front to back was a 60%rear/40%front, BUT not sure about this at all. mvw2, your burned rear diff. bushings would seem to bear this out.
Now here is the weird part mvw2. You stated that when you lift the rear and turn one rear wheel the other turns in the opposite direction. FWIW: every, in good working order, LSD I have installed or rebuilt they would do this and they are
supposed to. In fact that is a way to check to see if you have an LSD. And that other wheel WILL turn freely. You need to have someone hold that wheel and see how much it takes for you to over come that stopped wheel. It should not take allot with the small Subaru diff.
Respectfully,
LG
 
Originally Posted By: lumpy_grits
Hi, IF I understand how a Subaru AWD works(have an 03 & 07, both w/LSD re.)It maybe possible for the front end, with the different size tires,and center diff. to "over drive" or make the rear LSD clutches slip on both sides of the carrier. I seem to remember reading that the torque split from front to back was a 60%rear/40%front, BUT not sure about this at all. mvw2, your burned rear diff. bushings would seem to bear this out.
Now here is the weird part mvw2. You stated that when you lift the rear and turn one rear wheel the other turns in the opposite direction. FWIW: every, in good working order, LSD I have installed or rebuilt they would do this and they are
supposed to. In fact that is a way to check to see if you have an LSD. And that other wheel WILL turn freely. You need to have someone hold that wheel and see how much it takes for you to over come that stopped wheel. It should not take allot with the small Subaru diff.
Respectfully,
LG


The test is different for a Torsen-type vs. clutch type. If you do the simple one-wheel spin on a Torsen it will act like an open diff. A clutch-type should not spin the other wheel in the opposite direction IIRC but instead attempt to spin the driveshaft so it may be difficult to turn.

I had a vehicle (Porsche 968) where some model years had ZF clutch type LSDs and later models had Torsen LSDs and although it's been a couple of years I remember these test differences. The torsen test was to pull onto grass and stomp on it and look for TWO ruts behind you.
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Well, I just happen to have the '02 Subaru Forester press kit and it lists the rear diff as a "viscous limited slip differential." As you said, it comes with the "All-Weather Package." I just did a search and find that the viscous LS are very much like a clutch type LS but they use sealed a viscous coupling in the carrier instead of clutch packs to provide the braking action. I think my test will still apply, but instead of not being able to turn it at all (or have to use a bar), you'd just feel resistance, kinda like stirring honey.

mvw2: Something you said just hit me. If you raise both wheels in back, spun one, and the other spun in the opposite direction, and the driveshaft didn't turn, that indicates an open diff. If you had clutches of any type in the diff, the only way they both could turn is in the same direction because they are coupled together to the diff case, but if you turn the case, you have to turn the ring and pinion as well and the driveshaft would have to be turning as well. Which can't happen if your center viscous coupling is holding the driveshaft (and therefore the ring and pinion) still. On an open diff, the side and pinion gears could still turn inside the case, but the wheels would have to turn in opposite direction because of the way the diff gears change direction. If there were any type of operational clutches, you wouldn't be able to turn the wheels at all, or only with effort. So, if they turn in opposite directions, either you have an open diff or your axle diff viscous coupling has failed and the unit has reverted to an open diff. Your diff should have a sticker on it indicating a LSD. Go here for some pics:

Subaru LSD

lumpy Grits: If you think about your comment above, "... to 'over drive' or make the rear LSD clutches slip on both sides of the carrier." you'll realize that's impossible. With a clutch type limited slip, which are essentially open diffs (with the usual spiders and side gears) but with clutch plates. The clutches merely provide "brakes" on each axle shaft to provide a certain amount of "artificial traction" on the low traction side so some torque will transfer to the higher traction side. Remember the basic rule of differential operation, "The average speed of both axles is always equal to the speed of the ring gear."
 
Hi, Jim YOU are CORRECT. That was MY error on the LSD check! And I am sorry for that! Long days and little sleep. Have had some sick grandkids and now I think I have it too. YUK!
Jim, IF mvw2 was on a "winding" road or making lots of tight turns that would "cook" The LSD with the different tire speeds due to mis-matched tire ODs. IF he had an LSD to start with. One thing for sure is that's it an "open" diff NOW!
Jim you are correct and I should have said it "more better" about the rear diff. clutches slipping at the same time. Just remember, " If you can correct me.....Then you know what I meant :)"
Respectfully,
LG
 
lumpy: No worries and no need to apologize. The only thing I see as getting roasted in the mismatched tire scenario is the center diff (viscous coupling). The rear diff won't know any different but that center diff will be constantly churning, even on a straight line. I hope mvw2 give us an update. This post caused me to learn a whole bunch more about Subes than I knew. Had most of the resources right here but never needed to use them until today. Now I wanna know, a) does it have a LSD, b) is it toasted, c) is the center diff toasted or d) is all cool? I hope "d" is a resounding yes!
 
lol, I'm not particularly light on my car. It's seen a lot of back roads on heavy throttle and not exactly pointing straight ahead. It also sees several auto-x, rally-x, and ice racing throughout the year. I really don't expect the diffs to last long, and agree if the rear was limited, it probably no longer is and probably hasn't been for quite some time. I may look at a rebuild in the future when I have a chunk of change in my pocket and nothing to spend it on. If it's open, I may add a limited version at some point, wouldn't mind one on the front too.

In terms of slipping, I'll state that the rear end has never "slipped" on me. The weakest point has always been the main clutch. On launch, it is the only thing that slips. If I were able to slip the rear lsd vai torque loading, it would happen often and noticeably so. I would easily be able to feel the power loss through that. This of course doesn't happen.
 
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