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Guest Message by DevFuse

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How to change rear diff fluid?

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8 replies to this topic

#1 Draco


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Posted 07 April 2004 - 03:48 AM

Well I thought I should change the rear diff fluid on my '97 Legacy 5spd GT, I got a 1/2" ratchet to take out the plugs but man they are in there really hard! Do I need some kind of penetrating lubricant or do I need like a 2ft extension? Doesn't seem like it should be that hard but I couldn't get either the drain or fill plug to budge.Any suggestions on how to get them out would be great.

When I put them in what are they supposed to be torqued at? (never saw that in my book)

Also what oil do you guys use in the rear diff? I had some Castrol Syntec 75-90 I thought I'd use, wondering if there is anything better or a majority opinion of what to use. I use Mobil 1 in the engine and plan on using a dino gear oil in the trans as I have heard synthetics don't work well in MT.

#2 hawksoob


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Posted 07 April 2004 - 04:40 AM

I tugged and pulled and pulled and tugged on mine with absolutely no luck. Was all ready to buy a breaker bar or even air tools just so I could do it myself. I finally decided to take my bottle of Valvoline 75W90 GL-5 to my mechaninc and he did it for me for 10 bucks. Nice to do stuff yourself, but this time, I figured it was worth the 10 bucks to just get it done. I mean, the 1/2 inch adapter for my socket wrench cost about $5, the breaker bar would have been about $20+. Then there's the convenience of a pump to get the stuff in - extra cost. $10 was a bargain.

I recall reading in Haynes that the proper toque on the plugs is like 37 ft/lbs.
Not sure if they get extremely overtorqued when they're put in at the manufacturer or if they seize up over time due to extreme heat sort of welding the bolt to the casing, but it seemes as though EVERYONE has a difficult time getting them out with hand tools.

#3 aba4430


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Posted 07 April 2004 - 05:01 AM

The plugs can be real tough to loosen. You can fit a 1/2" ratchet head to the plug and place the end of the handle on a jack. Then lift the jack carefully. A couple of strokes should do it. I use Castrol Syntec 75W-90 in my Nissan Altima and front diff. on our 4WD Expedition with good success.

#4 99obw


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Posted 07 April 2004 - 07:17 AM

I always coat the outside of the plug with never sieze after I am done, never have any troubles getting them out. I don't coat the threads of the plug before assembly because I am worried about contamination of the gear lube. Be sure to clean off the old never sieze before removing the plugs. Always remove the fill plug first.

Synthetic gear lube is awesome, so much better than conventional. I used the Valvoline for a while. It isn't bad, but I think Mobil 1, Amsoil, and Redline are much, much better. The Valvoline would discolor significantly in a year of use. The Mobil 1 looks brand new when I drain it. I am going to give the Amsoil 75w-90 a try sometime soon.

#5 hklaine


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Posted 07 April 2004 - 06:54 PM

aba4430's jack method works well. The biggest PITA with this job is refilling the rear. I use a large "syringe", w/o the needle of course. I am running RedLine 7590NS and it works great in all weather.


#6 sprintman


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Posted 07 April 2004 - 06:58 PM

Schaeffers, Amsoil Series 2000 and Redline are about the best. Hard to go past Redline 75W90 in diff and 75W90NS in manual trans, well in an Outback anyway (GL5).

#7 frag


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Posted 07 April 2004 - 08:14 PM

I use my regular 18 inch breaker bar to remove the plugs on my 96 and it's not difficult. Pumping the new gear oil in there is another story.

#8 Chip Hedrick

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Posted 07 April 2004 - 08:22 PM

The rear diff plugs are difficult to get out. I bought what I call a Craftsman "breaker ratchet" just for the job. It has a ½ ratchet head, but the long handle of a breaker bar. It gives you better maneuverability in a tight place (e.g., under a car that’s on jack stands) than a fixed breaker bar, but it gives you much more leverage than a standard ratchet. The tools is great for other things too, such as loosening lug nuts. It’s only about $25.00 or so.

I agree with 99OBW that you should always remove the fill plug first. You’re in trouble if you drain the diff and then can’t get the fill plug out.

As far as getting the gear oil in, both NAPA and Pep Boys (and probably other auto parts stores as well) sell inexpensive flexible tubes that thread onto the top of gear oil bottles. They also allow you to turn the flow on and off. They’re also great to use when putting gear oil in a manual tranny.

#9 99obw


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Posted 07 April 2004 - 08:22 PM

I have been using the 1 quart squeeze bottles to put it in. I just keep filling up the same bottle to keep it as full as possible, and sqeeeeze.

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