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Discussion Starter · #1 ·
Hey guys, I am wanting to replace the fluid in my t-case and differentials. I am looking for your opinions on what to put back in them.

Thanks
 

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For the front and rear ends, any high quality synthetic 75w90 will do. If you have one that doesn't have the limited slip additive in it already, you may need to add it.

I used Amsoil on my 05 and didn't have any issues. I just changed the 09 to Amsoil before I traded it in (long story) and I have Amsoil in the Excursion too. I like it and it works well. It really smoothed things out in the Excursion.

If Amsoil isn't your thing, Mobil 1, Royal Purple, or Red Line will also work.

For the T case, you are going to get some varied answers on this. Some guys like to run a light weight motor oil in it as opposed to ATF. Personally, I like to keep my Tcase and Transmission the same so I switched everything over to Amsoil Torque Shift when the time came. You can also use Transynd or Dex or whatever you prefer.

My 15 is still running all factory fluids but I'll slowly make the change as the service intervals approach.
 

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Synthetic only

Mobile One synthetic ATF in the transfer case. Recommended gear lube in diff's in synthetic also.
 

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ATF or 5w-30 synthetic engine oil in the tcase, & synthetic (GL-5) 75w-90 gear lube in the diffs. Any brand will do.
 

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Valvoline SynPower 75W-90 Gear Oil in the differentials and Valvoline Dexron VI ATF in the transfer case - easy to find at all part stores.
 

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Ft&rr diffs...Mobil 1 75/90 synthetic $50
Transfer case...Mobil 1 5w30 synthetic motor oil $15
Transmission...Castrol Transynd $190
Engine...Rotella T6 5w40 synthetic $45

All of which are super easy to change on your own. I can only imagine how much this would cost to have a shop do it With using the double drain and refil plus filter for my trans I have a total of $300.00 by doing it myself.
 

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At what mile marker would you suggest changing these fluids out at?
 

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Me, 3 years maximum for the brake fluid, synthetic power steering fluid 3 years maximum give or take some months is my range. Friction modifiers for the G-80 differential, not sure your supposed to use it.
 

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The 2015 Maintenance Schedule has brake fluid replacement at 45,000 miles or 3 years.
 

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Well...guess ill be doing my break fluid swap this week too. Good lawd ive changed a lot of fluids in the last month!!
 

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Well...guess ill be doing my break fluid swap this week too. Good lawd ive changed a lot of fluids in the last month!!
Don't feel too bad. I changed all the fluids in the 09 I had just so I could trade it in. Grr.
 

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Oh no!! That sucks. Im thinkin this will be the last truck I buy for quite a few years. Its low miles (25k) plus we dont drive her in the winter plus all the goodies I am and want to throw at it. Can you say CP3 conversion=next mod...I hope.
 

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Oh no!! That sucks. Im thinkin this will be the last truck I buy for quite a few years. Its low miles (25k) plus we dont drive her in the winter plus all the goodies I am and want to throw at it. Can you say CP3 conversion=next mod...I hope.
Yeah, the 15 is hopefully the last truck I'll have to buy. Gonna do my best to take care of it and keep it happy, with a few sensible mods here and there.
 

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Exactly. Ive been combing through the cp4 delete to a cp3k or a stroker pump. I truely believe by deleting all the emissions crap (my exhaust is done) and changing this pump these lml trucks will last forever only having to keep it properly maintained.
 

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Discussion Starter · #16 · (Edited)
I have some Mobil ATF D/M at work for cheap. Says it's Allison rated. Think I'd be good to go with this for the transfer case? Or GM auto-trak ll?
 

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Discussion Starter · #17 ·
Yes I plan on doing the brakes and powersteering as well, but one thing at a time.
 

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I have some Mobil ATF D/M at work for cheap. Says it's Allison rated. Think I'd be good to go with this for the transfer case? Or GM auto-trak ll?
Don't use Auto-Trak fluid in your transfer case. You have a manual case. Use Dexron VI as previously mentioned.
 

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Front and rear diff - Mobil 1 75X90
Transfer case - TranSynd.
 

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^^^ He's in Nebraska, Transynd will work great.
 
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