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What Synthetic To Use For Diffs And Transfer Case?

ATF in the TC

and 90W in the diffs. Brand is your choice...

Royal Purple, AMSOil, etc...
 
I used Royal Purple 90w front 140w(?) in the back.
 
MOUNTAINGARAGE said:
I use Mobil1 or Redline 10W 30 in my NP231's

ATF evaporates out of the vent tube over time.

Never heard of the evaporation.... Check mine every other oil change and never need to add any.

I use all Mobil 1
 
Mudderoy said:
I used Royal Purple 90w front 140w(?) in the back.
why would you put different weights in the front and rear? is it because the rear is under load more often (unless you have a trailer queen)
 
Gravesdiggerxj said:
maybe it "evaporates" out onto your driveway... if it's got a leaky seal:moon: :roflmao:

ATF is spec for the 231

using synthetic will definitely quiet down that chain:peace:


What happens to an auto tranny when the fluid gets too hot?

Does it foam? Where does the fluid go when it expands?

My 231 has leaky seals. ATF is factory specification.

Gravesdiggerxj = Helpfull post Winner!!
 
Here's my two cents. As far as brands go it's personal. I am an Amsoil dealer and really like their products; but, Redline is fantastic too. Application wise, an open diff is ok with 75W90 but a limited slip or locked diff needs a heavier viscosity such as 75W140. I have used ATF in the transfer case in my last truck and it was fine. I've heard from a couple mechanics that certain synthetic motor oils work well too, such as 10W-30.
 
remember to use the LSD additive in the rear if you have trac lok. BTW i am doing mine soon how much fluid is needed. My manual is long gone from the dumbass PO
 
It's usually about a quart, definitely less than 2. Get a big gallon bottle and it will do both with ease.

Edit:
dana 30 front is 2.5 pints (1.25 quarts), dana 35 rear is 2.5 pints (1.25 quarts), 8.25 rear is 4.8 pints (2.4 quarts).
 
Last edited:
DanMan2k06 said:
It's usually about a quart, definitely less than 2. Get a big gallon bottle and it will do both with ease.

Edit:
dana 30 front is 2.5 pints (1.25 quarts), dana 35 rear is 2.5 pints (1.25 quarts), 8.25 rear is 4.8 pints (2.4 quarts).

Thanks man. Thats on the list before winter for sure. Along with sliders i hope
 
Now i have never done this before but i am guessing its straight forward? Crack the diff covers, Check for damage, Clean with brake fluid or similar product, Install diff covers with RTV, Fill er up and be done. Is that about correct?
 
Ehh I wouldn't go spraying brake cleaner all over your gears. Just clean out the cover and remove all the old RTV. Slap some new stuff on and tighten it down like you would lug nuts (star pattern).
 
Ok i wasn't sure. I have heard of people doing it before. Thats why i asked
 
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