DIY: Rear Differential Fluid Change
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This is a discussion on DIY: Rear Differential Fluid Change within the Powertrain forums, part of the Tutorials & DIY category; Alright, just in case anyone was wondering how to change your rear diff fluid, here is a write up on ...

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    DIY: Rear Differential Fluid Change

    Alright, just in case anyone was wondering how to change your rear diff fluid, here is a write up on how it's done. It's a pretty simple job, and is better (and probably cheaper) to do it yourself, rather than taking to a shop of the dealership.

    ***Extra Information from YBnormal07***

    Equipment Needed:

    1/2" ratchet (breaker bar is probably better)
    1 quart of rear diff fluid (75w90)
    1 oil pan (at least 1 quart capacity)

    Step 1: Make sure your car is on level ground, as to properly fill the differential case. There is enough room to get underneath the rear of the car without jacking it up. Put the car in gear, pull the E brake up, place an oil pan under the diff, and you're ready. You can jack the car up while loosening and tightening the plugs, just make sure that when you fill and drain the diff case, that the car is leveled.

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    Step 2: As you can see in the picture, there are two plugs... the top one is the fill plug, and the bottom one is the drain plug. Both of these plugs are in there pretty tight, and removing them is definitely the hardest part of the job… don’t be afraid to use force. First, you’ll want to remove the “fill plug”, to relieve pressure in the tank. Place the ” drive of the wrench into the square indentation on the plug, and twist it out.

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    Step 3: Once the “fill” plug is removed, remove the “drain” plug the same way, and let the fluid drain out. There isn’t much pressure behind it, so it won’t really “splash” out or anything like that. If you want, you can put an air compressor up to the “fill” hole and blast a lot of the gunk out of the bottom of the case, but keep in mind, this is EXTREMELY messy.

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    Step 4: Once both plugs are removed and the oil is drained/draining, clean the surface of the two plugs. The “drain” plug has a magnet to collect any metal particles, and keep the gears safe. Make sure to clean both plugs so they look at least as good as the ones in the picture. When cleaning the plugs, look for any metal shavings. Small shavings here and there are normal, but if you find any pieces more than a few mm across, it could be a sign that your differential is shot, and you should have it looked at. Also, make sure to clean the threads of each plug and plug hole to get rid of more grime and ensure that it seals the hole properly.


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    Step 5: Once the oil is finished draining and the plugs are cleaned, replace the drain plug, leaving the fill hole open. Take the differential fluid and pour (or squeeze) it into the fill hole until oil starts to leak out. The case only takes .8 quarts, so you should have some leftover fluid. To make things easier, you can buy a siphon hand pump, allowing you to pump the oil into the case, which is much easier than trying to squeeze it in, as space is quite limited.

    Step 6: When the case is filled, put the fill plug back into the hole, make sure both the drain and fill plugs are tight, and you’re done. It is extremely important not to over torque these plugs! Best bet is to measure the force to break them loose with a torque wrench, and apply that same force to tighten them back up.
    Last edited by nocturnal_wrx; 05-30-2007 at 12:04 PM. Reason: New insight from YBnormal07
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    Registered User rr1911's Avatar
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    nice write up
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    Quote Originally Posted by rr1911 View Post
    nice write up
    +1. Sticky?
    As far as getting the leftover fluid out, I just stuck my finger in the hole. What?!
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    Moderator YBNormal07's Avatar
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    Good write up. Mind if I add a few thoughts?

    1. They sell an oil transfer hand pump for about 5 bucks at most auto shops. Makes the insertion of the new oil much easier. This is also a very handy item for many other fluids so I highly recommend it (they are also called "siphon" pumps).

    2. The drain and fill plugs are alumimun. DO NOT OVERTORQUE THEM!!! Pay attention when you break them loose and try to apply the same force when tightening. If you have a torque wrench, monitor the breaking force and do not exceed it when re-torquing. I'd give the torque specs, but I don't have them.

    3. Don't foget to also clean out the drain/fill plug hole threads, especially the drain hole.

    4. After removal of the drain plug, carefully wipe off the magnet on a clean shop cloth or napkin and inspect what was wiped off. If there are metal filings/shavings present, rub some between your finger and thumb. If you feel anything larger than bb, you might want to consider having our diff looked at. It is normal to see what appears to be large amounts of filings/shavings in the shape you can get when using a magnet so don't let this worry you. Once they are wiped off onto a towel you'll see the amount is insignificant.

    5. It isn't necessary to remove the fill plug when draining, but since it has to come off anyway, it's just practical to remove both at the same time.

    6. For those who don't want to twist around under the back of the car, you can jack it up and just lower it when draining and filling.
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    Thanks YB, i will incorporate that information back into my original post as to make it more straightforward to anyone trying to follow these directions, if thats ok by you.
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    Quote Originally Posted by nocturnal_wrx View Post
    Thanks YB, i will incorporate that information back into my original post as to make it more straightforward to anyone trying to follow these directions, if thats ok by you.

    No prob. Glad you did it that way. BTW..made this a stickey. Should've done this a long time ago but I always forget about basics like this.
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    what kind of fluids do you use for the rear differential and tranny anything will help thanks
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    I have a 2002 shop manual. It says both the drain and fill plugs are to be tightened to:

    49.0 N-m / 5.0 kgf-m / 36.2 ft-lb

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    where did you get that shop manual at?
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    Quote Originally Posted by Warts View Post
    I have a 2002 shop manual. It says both the drain and fill plugs are to be tightened to:

    49.0 N-m / 5.0 kgf-m / 36.2 ft-lb
    The diffs for an 02 WRX are different than for an STi. What model is the maual for?
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    I should have been clearer. It is a Factory Service Manual for 2002. It does not cover the STi.

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    torque specs for 07 STI

    I talked to my service guy (very cool) and he looked the specs up for me. back plugs (rear diff) 32.5 .. front oil plug 32.5 and clutch plug 51.6. Not sure if they apply to any other year but when in doubt ask

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    How long a ratchet/breaker handle will fit between the drain plug and ground and still give enough leverage? I've got a 14in breaker bar and it doesn't look like it will fit, even with the car up on jack stands.

  15. #14
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    Quote Originally Posted by BarryG View Post
    How long a ratchet/breaker handle will fit between the drain plug and ground and still give enough leverage? I've got a 14in breaker bar and it doesn't look like it will fit, even with the car up on jack stands.
    You won't need a breaker bar. A regular ratchet gives plents of torque.
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    Wow... So, I spent a half an hour under my car trying to get the fill plug to budge... No dice. Using a pretty big Craftsman 1/2" drive... Turning counterclockwise, can't get it to move at all. Any ideas? Thinking about getting it up in the air to get some more room to work. Do I need something bigger/better?
    2005 Subaru Impreza WRX Wagon - 3" TBE w/ SPT Catback, Cobb Stage 2 91 Octane map...

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