Panthasoccer4 Posted June 7, 2004 Share Posted June 7, 2004 Im thinking about changing my gearbox and rear diff oils. Any special oils or favorites anyone uses? Is the operation pretty easy, or something to avoid? Quote Link to comment Share on other sites More sharing options...
hohieu Posted June 7, 2004 Share Posted June 7, 2004 I refilled w/ Mobil 1 75W/90, and noticed smoother shifting. It's a good synthetic that is readily available. Just pull out the drain plugs on both the front and rear - some people jack up the front of the vehicle to drain all the old oil from the rear differential. Subaru recommends a Three Bond thread sealant for the rear plug, but you can use teflon tape or Permatex thread sealant, which is also readily available. You could also replace the washer on the transmission plug, but I did not and have had no leaks. You will need a long funnel to refill the transmission, and refill through the upper plug on the rear differential. Rear plugs can be removed w/ 1/2" ratchet, but I can't remeber the size of the metric front plug. Take care Quote Link to comment Share on other sites More sharing options...
Commuter Posted June 7, 2004 Share Posted June 7, 2004 I have no personal experience, but I've heard a lot of good things about Redline oils. You might want to check into their products if you are looking for a top line synthetic. It seems that it can be a bit tricky to figure out exactly what grade of their products is appropriate for your vehicle, so it is probably best to contact them directly. Commuter Quote Link to comment Share on other sites More sharing options...
sprintman Posted June 8, 2004 Share Posted June 8, 2004 I use RL 75W90NS in the trans and 75W90 in the diff. Don't make the mistake of putting 75W90 in the trans as it's too 'slippery' and syncro's crunch. Also use RL D4ATF in the p/s. Good stuff. Quote Link to comment Share on other sites More sharing options...
Chip Hedrick Posted June 8, 2004 Share Posted June 8, 2004 My practice is to use inexpensive NAPA ($1.99/quart) or Castrol Syntec ($2.99 +/-/quart at Wal-Mart) gear oil and to change it once a year or every 15,000 mi, whichever comes first. This is more frequent than what most people do, but I want my transmission to last 200,000-250,000 mi. I’m not saying there’s anything wrong with synthetic gear oil, but at $9.00-$12.50/quart, it’s much more expensive. I have opted for frequent gear oil changes over the long change interval that synthetics offer. In my opinion, if you go to the effort of checking the gear oil, you might as well go to the effort of changing it because it’s not that much more work. I like the idea of draining my transmission and rear diff of metal particles and other contaminants once a year rather than leaving the oil in there for a longer period. You will need 5 quarts to change the oil in both a manual transmission and rear diff (the manual transmission cars do not have a separate front diff, the automatic transmission cars have front and rear diffs). I think the socket size for the manual transmission drain plug is 22mm. I agree that you will need a long funnel for filing the transmission. I remove the “air box” attached to the throttle body at the top rear of the engine for easier access to the manual transmission dipstick/fill tube. What I find works even better than a funnel is a clear, flexible plastic tube that threads onto the top of a gear oil bottle. They are available at Napa (and I think Pep Boys) for a few dollars. The advantage of the flexible plastic tube over a funnel is that it will help you fill the rear diff, which the funnel will not. A length of pipe placed over a breaker bar will make easy work of loosening the rear diff plugs (I actually use what I call a “breaker ratchet” for the job). It’s a long-handled ½ socket wrench—Craftsman makes one. It allows you more maneuverability than a breaker bar when your car is on jack stands and you have limited room to work on the rear diff plugs. I torque both the transmission drain plug and the rear diff plugs to 25-30 lbs.-ft. NAPA makes a high temperature thread sealant that’s available in a small tube for a few dollars. Use it sparingly, a little bit goes a long way. The instructions said coat ¾ of a thread length. I coated a 1 ½ thread lengths. I should have adhered to the instructions. Quote Link to comment Share on other sites More sharing options...
99obw Posted June 8, 2004 Share Posted June 8, 2004 My $0.02 I have been using Mobil 1 75w-90 changed every year, which is every 30k miles. My experience in the past was that conventional gear lube severely discolored by 30k, so I use synthetic, which darkens very little. I know, I know, color doesn't mean anything, but I prefer the synthetic. I don't believe any of the BS about synthetic gear lubes being good for 100k or the life of the vehicle. My experience has been that sealant isn't needed if the plugs are properly torqued. YMMV Quote Link to comment Share on other sites More sharing options...
Setright Posted June 8, 2004 Share Posted June 8, 2004 I have tried all the oils mentioned, and whilst M1 and Redline are good. I have found something better: Castrol TAF-X ! Best shift yet in a Subaru box, and let's face it, they are stubborn! Quote Link to comment Share on other sites More sharing options...
hohieu Posted June 8, 2004 Share Posted June 8, 2004 My $0.02 I don't believe any of the BS about synthetic gear lubes being good for 100k or the life of the vehicle. YMMV I was wondering if you could elaborate. I never changed the factory gear oil in my '85 Accord and had absolutely no transmissions problems up until I gave it away at 220 K miles. I only changed the trans.+ rear diff. oil when I bought my Forester at 72,500 miles, because, well, I wanted to baby it w/ M1 75W/90. The owner's and service mauals recommnend only inspections of gear oil under "normal operation" (whaterever this means) at 30K-mile intervals. I never felt inclined to change the gear oil in previous cars because, as I see it, transmissions never reach the extreme temperatures found in engines and there are, of course, no blowby gasses in the the transmission. Covnversely, there is also no filter on the manual transmission. On another note, would anyone use a 75W/140 synthetic gear oil? It has the same cold viscosity as the recommended 75W/90 and I would think that a thicker oil at 100 degrees would stay on the gears and reduce wear when cold. I look forward to reading your thoughts. Quote Link to comment Share on other sites More sharing options...
99obw Posted June 8, 2004 Share Posted June 8, 2004 Well, I don't have any scientific data, only opinion and anecdotal evidence. In general gearboxes and differentials don't have a filter. Any metal (minus what the magnet can hold) or other contamination is going to stay in the lubricant until the lubricant is changed. The metal particles tend to be large and I think as a result that they are very abrasive. I live on a dirt road, and drive in heavily salted western NY, so contamination from dirt and salt is a concern for me as well. I have drained gearboxes and diffs after 50k or so to find a lot of metal, more than the magnet could hold. I often find a lot of metal suspended in the lubricant in gearboxes, giving it a metal flake paint appearance. I think periodic fluid changes are relatively inexpensive based on the small capacity, and good insurance based on the contamination I have seen. Plus it gives me that warm fuzzy feeling knowing my gears are bathing in a fresh bath of the finest synthetic. Quote Link to comment Share on other sites More sharing options...
hohieu Posted June 8, 2004 Share Posted June 8, 2004 I live on a dirt road, and drive in heavily salted western NY, so contamination from dirt and salt is a concern for me as well. I guess you would not qualify for "normal operation." I think periodic fluid changes are relatively inexpensive based on the small capacity, and good insurance based on the contamination I have seen. Plus it gives me that warm fuzzy feeling knowing my gears are bathing in a fresh bath of the finest synthetic. Yes, yes ... you are an admitted "oil nut" and science cannot quantify the emotional fulfillment derived from automotive maintenance. Thanks Quote Link to comment Share on other sites More sharing options...
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