Rear Differential Fluid and Timing Belt questions...
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This is a discussion on Rear Differential Fluid and Timing Belt questions... within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; I'm at 58,000 on my '05, and getting ready to change the rear diff fluid myself, since the dealer wants ...

  1. #1
    Wrinklechops

    Rear Differential Fluid and Timing Belt questions...

    I'm at 58,000 on my '05, and getting ready to change the rear diff fluid myself, since the dealer wants to charge an arm and a leg to change it (along with my timing belt).

    I have a few quarts of Redline 75W90 from my transmission fluid change, so that will do just fine right? What about that Lightweight Shockproof stuff?

    Any tips/tricks for the rear diff change? I've never done it... I'm reading that you just take both of the plugs out, let it drain, then put the bottom one on and fill it up until it's spilling out of the top hole?

    I feel bad because I don't think the rear diff fluid has ever been changed. At least, not since I've had the car with 30,000 miles on it.

    And lastly, what's the general consensus on timing belts? I hear the stock one on our WRX is pretty weak, and people upgrade to like, the STi one, Cosworth, or something else that's stronger? But then again, I had a local tuning shop here tell me that the stock belt is good to 100,000 miles and I shouldn't even bother with spending $ on an upgraded timing belt?

    And obviously, you can't do the timing belt replacement at home, eh? Not for the mediocre mechanic with *almost* all the tools to get work done on the car.

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  3. #2
    The Default One SeattleJeremy's Avatar
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    There is lots of information about gear oils in this thread.
    >>Tranny Fluid Info and Experimenting Thread<< (Amsoil, Redline, USC, etc.)

    I ran Royal Purple in my stock 05, trans and diff, from 15k miles until I sold it at 56k. But you should make your own judgments.

    As for timing belts, the stock one works great, and only needs to be changed by 105k miles. The STI one Subaru sells has a recommends it be replaced every 62,500 miles.

    Here is a thread of replacing the timing belt.
    Timing Belt and Water Pump Replacement

    Cosworth doesn't make a timing belt for our cars, they only make a "Billet Timing Belt Guide".

  4. #3
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    Stock belt is fine.

    Don't use the shockproof. I just put Castrol Synthetic 75w90 in mine 2 days ago.

  5. #4
    Wrinklechops
    Quote Originally Posted by jeremy96gase View Post
    There is lots of information about gear oils in this thread.
    >>Tranny Fluid Info and Experimenting Thread<< (Amsoil, Redline, USC, etc.)

    I ran Royal Purple in my stock 05, trans and diff, from 15k miles until I sold it at 56k. But you should make your own judgments.

    As for timing belts, the stock one works great, and only needs to be changed by 105k miles. The STI one Subaru sells has a recommends it be replaced every 62,500 miles.

    Here is a thread of replacing the timing belt.
    Timing Belt and Water Pump Replacement

    Cosworth doesn't make a timing belt for our cars, they only make a "Billet Timing Belt Guide".
    Thanks for that thread man that is really helpful!

    And check out the COSWORTH Timing Belt for our car:

    COSWORTH Timing Belt EJ20

    Will that not work?

  6. #5
    Wrinklechops
    Quote Originally Posted by brfatal View Post
    Stock belt is fine.

    Don't use the shockproof. I just put Castrol Synthetic 75w90 in mine 2 days ago.
    Right on, yea I heard the Shockproof was for some serious racing or something... I'll just stick with my Redline 75W90 I have in the garage lol

  7. #6
    The Default One SeattleJeremy's Avatar
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    Hmmm, wonder why I couldn't find that when I looked.
    Make sure to find out what the service interval is on the Cosworth one before buying it.

    Dunno, I'll be sticking to the stock one when it comes time

  8. #7
    Registered User gprwrx's Avatar
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    I have to do my diff fluid soon!!
    02PSMWRX VF39'd STI Killer
    Wingl3ssAlli@nce#27

  9. #8
    DUB
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    Quote Originally Posted by lundholm08 View Post
    ...I have a few quarts of Redline 75W90 from my transmission fluid change, so that will do just fine right? What about that Lightweight Shockproof stuff?
    Either one of those is just fine for the rear diff.

    Quote Originally Posted by lundholm08 View Post
    Any tips/tricks for the rear diff change? I've never done it... I'm reading that you just take both of the plugs out, let it drain, then put the bottom one on and fill it up until it's spilling out of the top hole?
    That's it. A tip: Remove the top plug first. The reason? If you remove the drain plug first and then can not remove the fill plug (seized threads, stripped flats) you will be left with an empty diff with no way to fill it.

    If you wanna do it right get this, as it is the proper tool: 13mm Subaru & Nissan Drain Socket Otherwise, just use your 1/2" drive breaker.

    Quote Originally Posted by lundholm08 View Post
    And lastly, what's the general consensus on timing belts? I hear the stock one on our WRX is pretty weak, and people upgrade to like, the STi one, Cosworth, or something else that's stronger? But then again, I had a local tuning shop here tell me that the stock belt is good to 100,000 miles and I shouldn't even bother with spending $ on an upgraded timing belt?

    And obviously, you can't do the timing belt replacement at home, eh? Not for the mediocre mechanic with *almost* all the tools to get work done on the car.
    You are well ahead of the factory recommended replacement interval of 105k miles. But, if you want to go ahead and replace it now with an upgraded part, go for it.

    If you have to ask if you can do it, you can't do it. Take it to a mechanic and save yourself a disaster.

  10. #9
    Wrinklechops
    Quote Originally Posted by DUB View Post
    Either one of those is just fine for the rear diff.



    That's it. A tip: Remove the top plug first. The reason? If you remove the drain plug first and then can not remove the fill plug (seized threads, stripped flats) you will be left with an empty diff with no way to fill it.

    If you wanna do it right get this, as it is the proper tool: 13mm Subaru & Nissan Drain Socket Otherwise, just use your 1/2" drive breaker.



    You are well ahead of the factory recommended replacement interval of 105k miles. But, if you want to go ahead and replace it now with an upgraded part, go for it.

    If you have to ask if you can do it, you can't do it. Take it to a mechanic and save yourself a disaster.
    Thanks for all your info. That bit about the special diff tool really helps. Glad to know that before I crawl under there tomorrow.

    And yea, I think I'm going to stick with the stock timing belt, since there's no need to replace it right now. If I was doing some major engine work/repair that might be a different story I suppose... but since I practically have a new engine (er, half of a new engine) because Subaru put a new short/small block in my car (cuz it kept "throwing a rod" and getting metal in the engine somehow), I think I'm OK...

  11. #10
    Wrinklechops
    Quote Originally Posted by DUB View Post
    Either one of those is just fine for the rear diff.



    That's it. A tip: Remove the top plug first. The reason? If you remove the drain plug first and then can not remove the fill plug (seized threads, stripped flats) you will be left with an empty diff with no way to fill it.

    If you wanna do it right get this, as it is the proper tool: 13mm Subaru & Nissan Drain Socket Otherwise, just use your 1/2" drive breaker.



    You are well ahead of the factory recommended replacement interval of 105k miles. But, if you want to go ahead and replace it now with an upgraded part, go for it.

    If you have to ask if you can do it, you can't do it. Take it to a mechanic and save yourself a disaster.
    Last question: will putting the rear up on some ramps to give me some room to get under there to change the rear diff, will that throw off the draining of the old fluid, etc? Cuz it'll be angled?

  12. #11
    Wrinklechops

    torque specs?

    I don't suppose anyone knows what torque spec I should tighten the rear diff fluid bolts back up with do you?

  13. #12
    DUB
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    I used an 18" long 1/2" drive breaker bar on the plugs and there wasn't enough room under there with the car on the ground. So, yes, you're probably gonna want to raise it up. I would raise the whole thing to get as much of the old gear oil out as possible.

    The spec for both plugs is 36.2 ft-lb.

    You should also use some thread sealant on the plugs to avoid leaks. The factory service manual recommends THREE BOND 1105 or equivalent. When I did it, there was quite a bit of left over sealant from the factory so I skipped it and remain leak free.

  14. #13
    Wrinklechops
    Quote Originally Posted by DUB View Post
    I used an 18" long 1/2" drive breaker bar on the plugs and there wasn't enough room under there with the car on the ground. So, yes, you're probably gonna want to raise it up. I would raise the whole thing to get as much of the old gear oil out as possible.

    The spec for both plugs is 36.2 ft-lb.

    You should also use some thread sealant on the plugs to avoid leaks. The factory service manual recommends THREE BOND 1105 or equivalent. When I did it, there was quite a bit of left over sealant from the factory so I skipped it and remain leak free.
    That's awesome thanks for the info. I don't have any THREE BOND so we're gonna use PIPE DOPE? Hope that works. I won't be able to torque it exactly because that whole 1/2in socket is too loose in the plug. It took me and my friend two trips to Home Depot and a torch, an angle grinder, 4 hours, and a few headaches to make a piece fit in there just right, with a pipe wrench. No way to get a torque thing on that I don't think....

    Guess I should've bought the special gay tool Subaru sells for that.

    I'm still trying to think of how to do it though...

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