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Replacing front/rear differential fluid

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#1
choerizo

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Just hit 18,000 miles and took the day to flush both diffs.
 
Tools needed:

  • 10mm hex socket
  • Torque wrench
  • Transfer pump to pump fluid back in
  • Breaker bar or something to break loose the plugs (they are on pretty tight)
  • 2-3L of your favorite diff fluid (I used Nismo Motul 75w140)

Specs:

  • Front diff: torque 26 ft/lb fill/drain plugs, 0.65L fluid
  • Rear diff: 25 ft/lb fill plug, 39.5 ft/lb drain plug, 1.35L fluid **note this changed from earlier years to later to avoid seal issues from too much pressure

Before I started, I wanted to pre-measure the amount of fluid I was going to need and I wanted to see how much would drain out. A quick makeshift measuring system for input and output fluids:
IMG_2727.jpg

Start by getting the car lifted up:
IMG_2714.jpg

IMG_2717.jpg

Nismo Motul 75w140
IMG_2720.jpg

---FRONT DIFF---
After removing the front undertray, you should be exposed to this (where you normally would change your oil). Note the two plugs that take the 10mm hex, one on top (fill) and one on bottom (drain).

IMG_2734.jpg

Another shot
IMG_2741.jpg
 
You have just enough clearance to get your 10mm hex socket in there with some extensions. Start by removing the fill plug first, then the drain plug. I put a funnel to catch the fluid and drain into our make shift measuring cup.
IMG_2742.jpg

Ended up draining just a little bit higher than 0.65L:
IMG_2749.jpg

Clean the drain plug well. The magnet does its job well!
IMG_2747.jpg

This fluid is the smelliest thing ever.
IMG_2750.jpg

Replace drain plug & torque to spec. Premeasure your fluid to go back in. I measured 0.65L again rather than let it drip out over the fill plug since my garage has a slight incline.
IMG_2752.jpg

Use your favorite hand pump to get it back in.
IMG_2754.jpg

Replace fill plug. Torque to spec. Replace front under tray.

---REAR DIFF---

Remove rear tray (the CF one under the transmission). It may be helpful to support with something to prevent it from falling down.

Here is a shot of the rear diff. The top fill plug has my socket inserted and the bottom drain plug is ready to be opened.
IMG_2761.jpg

Same procedure as the front. Remove top fill plug first. Remove bottom drain plug and catch the fluid. The drain plug has a magnet as well and will be dirty (be sure to clean well).
IMG_2764.jpg

After draining, I collected about 1.5L:
IMG_2766.jpg

Note the color (fresh is clear):
IMG_2768.jpg

Replace drain plug. Torque to spec. Fill using pump. Replace fill plug. Torque to spec. Replace rear under tray.

Done!


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#2
shawnhayes

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Very good writeup.  Would you prefer this to stay in this subforum or move to DIY guides?  And, would you like a link in the main area?

 

Shawn



#3
choerizo

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#4
7racer

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nice write up!!!


In7anity!!


#5
forty-two

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Thanks for DIY write up!

 

With the Nismo diff oil, I noticed my rear diff to be more clunky/binding when cold, especially when reversing out of the garage. Anyone else? 


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#6
Nodrip

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Thanks for DIY write up!With the Nismo diff oil, I noticed my rear diff to be more clunky/binding when cold, especially when reversing out of the garage. Anyone else? 

I have the same feeling, but it only hit my mind recently.

 

Maybe I reached a high transmission temperature last time i was on track, but I always got an eye on it and it never reached 130°C.

My oil has never been changed.

And sometimes i hear the same "klung" noise on track, but i have this from the beginning.

 

Don't know if something really happened or if I'm a bit paranoid!


Edited by Nodrip, 19 August 2014 - 12:12 PM.

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#7
icarus

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Great write-up, thanks for this!  In my opinion, for tracked GT-R's it is a good idea to replace the front diff fluid once every 6-8 track days, or 12 months, whichever comes first.  Rear diff I do every 18 months, same interval/time as transmission.


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#8
shawnhayes

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Great write-up, thanks for this!  In my opinion, for tracked GT-R's it is a good idea to replace the front diff fluid once every 6-8 track days, or 12 months, whichever comes first.  Rear diff I do every 18 months, same interval/time as transmission.

 

Based on fluid analysis that I have produced, this is WAYYYY aggressive.  Nothing harmful in doing it as far as I can tell, but fairly wasteful with the cost of the OEM fluid.

 

Additionally, cheaper fluids can be used in the FRONT diff with little to no adverse effects.

 

icarus, we can certainly debate this, and there are caveats to each and every different GT-R.

 

On the other hand, if your fluid is coming out looking like the fluid in THIS particular write up every 6-8 trackdays, I will suggest that it is being burned/overheated and should be replaced on your interval.  Is yours coming out looking like this?

 

Shawn


Edited by shawnhayes, 19 August 2014 - 11:27 AM.


#9
choerizo

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For reference, I have a FBO MY2010, 18000mi, and no special cooling mods. Done 6 track days in Texas between TWS, Drivers Edge, Harris Hill, COTA, and several runs at the local drag strip and a Texas Mile event (180+mph).  Track days aside, I was long overdue from both a mileage and time perspective.


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#10
shawnhayes

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For reference, I have a FBO MY2010, 18000mi, and no special cooling mods. Done 6 track days in Texas between TWS, Drivers Edge, Harris Hill, COTA, and several runs at the local drag strip and a Texas Mile event (180+mph).  Track days aside, I was long overdue from both a mileage and time perspective.

 

I'd bet you'd be surprised.  I'd bet if we sent that off it would still be okay.

 

On the other hand, one should change the first change early.  Your change included a lot of "fuzz" that I like to get out in the first 5,000 miles, but in the last 5-10 years, the diffs are doing so much better with the first change being in basically FOREVER that I grow less and less concerned the more modern fluid analyses that I do.

 

Shawn


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#11
elf_cruiser

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Good writeup!
Don't forget Amsoil ;)
I drained the factory rear diff fluid after about 10k miles and ??? Trackdays. Replaced it with Amsoil Severe Gear 75w-140 plus a tube of friction modifier. Quieter and smoother engagement of the LSD in parking lot manuevers for sure.
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#12
icarus

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Based on fluid analysis that I have produced, this is WAYYYY aggressive. Nothing harmful in doing it as far as I can tell, but fairly wasteful with the cost of the OEM fluid.

Additionally, cheaper fluids can be used in the FRONT diff with little to no adverse effects.

icarus, we can certainly debate this, and there are caveats to each and every different GT-R.

On the other hand, if your fluid is coming out looking like the fluid in THIS particular write up every 6-8 trackdays, I will suggest that it is being burned/overheated and should be replaced on your interval. Is yours coming out looking like this?

Shawn


My first front diff fluid change the fluid was super dirty and lots of residue on the magnetic plug. I have been running Motul ever since mostly because I find the Castrol harder to get ahold of. Subsequent fluid changes the fluid is much cleaner. Maybe because Motul, maybe because more frequent changes, maybe both. Since I'm usually changing the engine oil at the same time I do the front diff too, since it's less than a quart.

I don't have any reason to believe you're wrong, my first fluid change just made a strong impression on me.

My first change on the rear diff, the fluid was cleaner and less residue on the plug than on the front diff. So I go with longer intervals on that, do it the same time as the tranny.
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#13
shawnhayes

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My first front diff fluid change the fluid was super dirty and lots of residue on the magnetic plug. I have been running Motul ever since mostly because I find the Castrol harder to get ahold of. Subsequent fluid changes the fluid is much cleaner. Maybe because Motul, maybe because more frequent changes, maybe both. Since I'm usually changing the engine oil at the same time I do the front diff too, since it's less than a quart.

I don't have any reason to believe you're wrong, my first fluid change just made a strong impression on me.

My first change on the rear diff, the fluid was cleaner and less residue on the plug than on the front diff. So I go with longer intervals on that, do it the same time as the tranny.

 

On the first change, I certainly agree.  Super dirty.  But, it appears that manufacturers account for it when they are planning "break in wear" and manufacture the diffs accordingly.

 

Since you are using Motul (regular I presume), the price argument is basically non-sensical.  That is a very affordable fluid.  The Nismo Motul is quite expensive, as well as the OEM Castrol.  So, it isn't such a big deal for you to change it - but it still can be pretty wasteful.  What it takes to make a quart of synthetic gear oil in 2014 is a whole lot of energy and additives, and I say why waste what you paid for.

 

I have, and stand by the fact,  I have used Mobil-1 75W-140 in the front diff, albeit with some limited slip additive - but that is probably unnecessary in the front diff.  The analysis came back perfect.  That fluid is super cheap, and can be purchased at Advance Auto easily.  Little reason to be super stingy there.

 

I would say that you can probably extend your front diff drain interval.  No reason to if you are happy other than conservation of money and time, but you should be okay unless, as above, your fluid is coming out like in the thread above.

 

Shawn



#14
icarus

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Thanks Shawn that is good info, and I'll likely take your advice. I'm so desensitized to fluid costs because the dang tranny fluid costs me nearly $500 every 18 months.
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#15
AP@AMSOIL

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Thanks Shawn that is good info, and I'll likely take your advice. I'm so desensitized to fluid costs because the dang tranny fluid costs me nearly $500 every 18 months.

 

 

Then use this and save the delta money to go on vacations :)

Talk to elf cruiser he has been racing with this fluid.

 

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#16
awdtt

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Choester, thanks for taking the time for the writeup.  I'm getting ready to do my own fluids, including diffs, and have a few questions.

 

It looks like there's always going to be a small amount (an ounce or two) of residual of dirty gear oil left, since the drain plug is side-mounted.  Is there a recommended way to mitigate that?

 

In looking around at what people are using, I've seen 4 different gear oils mentioned with some degree of regularity:

  • NISMO Competition Oil 2189E 75W-140
  • Dodson High Performance differential oil
  • Amsoil Severe Gear 75W-140
  • Mobil 1 75W-140

Since the OEM-specified 2189E oil seems to be harder to get, what would be the next best choice from the list?

 

Thanks,

 

Bob


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#17
choerizo

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Choester, thanks for taking the time for the writeup.  I'm getting ready to do my own fluids, including diffs, and have a few questions.

 

It looks like there's always going to be a small amount (an ounce or two) of residual of dirty gear oil left, since the drain plug is side-mounted.  Is there a recommended way to mitigate that?

 

In looking around at what people are using, I've seen 4 different gear oils mentioned with some degree of regularity:

  • NISMO Competition Oil 2189E 75W-140
  • Dodson High Performance differential oil
  • Amsoil Severe Gear 75W-140
  • Mobil 1 75W-140

Since the OEM-specified 2189E oil seems to be harder to get, what would be the next best choice from the list?

 

Thanks,

 

Bob

 

 

Bear in mind I've only done a few flushes in comparison to some of the other guys on the forum, but I'm happy to provide my input.

 

First, I am not sure that small amount of residual fluid will make a huge difference but I suppose you could "flush" some more of the insides with fresh fluid and let it dribble out (keep drain plug open while filling). I think of it similar to changing the transmission fluid -- if you use the OEM drain port, you're still going to have some (quite a lot) fluid remaining in the trans unless you take the pan/filter off (even then some will reside in the DCT cooler lines if you have one installed). I recall seeing someone install an inline bypass that would purge all the old fluid but it's all about how anal you want to get with it. Heck people change engine oil without even removing the filter sometimes.

 

Having just gone through a diff debacle and looking back now my advice would be to change the front diff fluid often especially if you are tracking it (I have another thread where my front diff was making whining noises probably due to insufficient fluid changing). I would fill the front diff with the most inexpensive option that still provides sufficient protection (Mobil1).  The other fluids probably have more additives that can provide longer intervals between changes but will cost more. I ran Mobil1 in the front diff and couldn't tell a significant difference from the Nismo fluid. Get your old fluid tested if you are concerned. 

 

That being said, I wouldn't run Mobil1 on the rear diff. I believe any of the others you have listed will be fine but I'm sure Shawn (aka. Dr. Fluid Expert) can probably chime in with more technical details.

 

Good luck! It's not too hard but hella messy and stinky. Check your drain plug magnet to make sure it looks good too.


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#18
shawnhayes

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Choester, thanks for taking the time for the writeup.  I'm getting ready to do my own fluids, including diffs, and have a few questions.

 

It looks like there's always going to be a small amount (an ounce or two) of residual of dirty gear oil left, since the drain plug is side-mounted.  Is there a recommended way to mitigate that?

 

In looking around at what people are using, I've seen 4 different gear oils mentioned with some degree of regularity:

  • NISMO Competition Oil 2189E 75W-140
  • Dodson High Performance differential oil
  • Amsoil Severe Gear 75W-140
  • Mobil 1 75W-140

Since the OEM-specified 2189E oil seems to be harder to get, what would be the next best choice from the list?

 

Thanks,

 

Bob

 

 

Ignore the extra few ounces that you can't get out.  Not worth "flushing" it.

 

All the fluids you have listed are fine for the FRONT diff.  Do NOT use the mobil for the rear diff.  It will protect the diff, but it will chatter like hell.  It lacks adequate anti-chatter for limited slips.

 

You also didn't mention the fluid most often used on this board, the maker of the Nismo competition oil, Motul.  The Motul 75W-140 is FABULOUS for this application.  The castrol from the OEM is a BITCH to get, but is the factory fill, and is great.  Redline 75W-140 is also great for this diff, and works well.

 

Pick whichever you prefer for the front (but as our friend choerizo points out) change the front early once, and then once every one-two years after that.  Six trackdays only would be a little early, unless they occur over a year.  Twelve trackdays over a year is about what I do, and the fluid analyses come back fine.

 

Shawn


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#19
shawnhayes

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Having just gone through a diff debacle and looking back now my advice would be to change the front diff fluid often especially if you are tracking it (I have another thread where my front diff was making whining noises probably due to insufficient fluid changing). I would fill the front diff with the most inexpensive option that still provides sufficient protection (Mobil1).  The other fluids probably have more additives that can provide longer intervals between changes but will cost more. I ran Mobil1 in the front diff and couldn't tell a significant difference from the Nismo fluid. Get your old fluid tested if you are concerned. 

 

That being said, I wouldn't run Mobil1 on the rear diff. I believe any of the others you have listed will be fine but I'm sure Shawn (aka. Dr. Fluid Expert) can probably chime in with more technical details.

 

Good luck! It's not too hard but hella messy and stinky. Check your drain plug magnet to make sure it looks good too.

 

Thanks for the Moniker.  Bachelors was UVA, chemistry 1991.

 

That being said, can you comment on your front diff whining and change intervals?  How long and how many miles before the first one, and which fluid was in when it whined, and whether or not replacement was required?

 

Shawn



#20
awdtt

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Ignore the extra few ounces that you can't get out.  Not worth "flushing" it.

 

All the fluids you have listed are fine for the FRONT diff.  Do NOT use the mobil for the rear diff.  It will protect the diff, but it will chatter like hell.  It lacks adequate anti-chatter for limited slips.

 

You also didn't mention the fluid most often used on this board, the maker of the Nismo competition oil, Motul.  The Motul 75W-140 is FABULOUS for this application.  The castrol from the OEM is a BITCH to get, but is the factory fill, and is great.  Redline 75W-140 is also great for this diff, and works well.

 

Pick whichever you prefer for the front (but as our friend choerizo points out) change the front early once, and then once every one-two years after that.  Six trackdays only would be a little early, unless they occur over a year.  Twelve trackdays over a year is about what I do, and the fluid analyses come back fine.

 

Shawn

Well, I ended up getting 2 liters of Motul Gear FF Competition 75W-140.

 

Other fluids:

 

6 liters Motul 300V 15w150 engine oil (which may be irrelevant if I swap motors next month)

2 NISMO 11208-RN011 oil filters

14 liters Motul Multi DCTF

2 cans Endless 650 brake fluid

 

Interesting development with motor swap.  The engine builder insists on Amsoil.  I might have to use it in order to have a warranty.  With a Bill@SIR tune, it'll make 750 HP on pump gas.  Details when everything is finalized.


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