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Differential Fluid

Posted: Wed Oct 21, 2009 4:17 am
by JohnB
What type and weight fluids are being used in front and rear differentials, 435/445 transmissions, and transfer cases? The manual says, 140 weight or 90 weight. What would be the difference in performance between 140 and 90? Also in my old FFPW, I used 50 weight oil in the trans and transfer case and 90 wt in the diffs. Are the multi 85W-140W a good choice?
John

Re: Differential Fluid

Posted: Wed Oct 21, 2009 8:29 am
by Trailmaster
I always used 80W90 in the gear cases on my older stuff, never had any problems with it.

Re: Differential Fluid

Posted: Wed Oct 21, 2009 9:12 am
by MikeMc
JB, I read about oil a while back but don't remember all the details :withstupid The different weights of oils are related to the ambient temperature on start up. The lighter weight oil carbons lube in cold weather while the heavier lubes better when it warms up. This is why a 10-40 motor oil is suppose to be so much better than strait 30 wt. The 10 is lubing on fire up and the 40 is doing it's job at operating temp.

Since you live down in Florida you could run the 140 wt. but if you don't have a bunch of oil leaks the 90 wt. will be less drag and get better fuel mileage.

Re: Differential Fluid

Posted: Wed Oct 21, 2009 2:40 pm
by nfury8
Unless you really work the truck, I would stick with the 80-90 or a straight 90w if available.

Re: Differential Fluid

Posted: Fri Sep 01, 2017 8:34 am
by hmaynord
probably been in there for decades. thinking about about evacuating and replacing.
any suggestions?

Re: Differential Fluid

Posted: Fri Sep 01, 2017 3:19 pm
by JohnB
hmaynord wrote:probably been in there for decades. thinking about about evacuating and replacing.
any suggestions?
Drive it until trans, rear etc are warm; drain it and replace.

Re: Differential Fluid

Posted: Fri Sep 01, 2017 3:40 pm
by hmaynord
right. I always get my oil up to operating temp before i change it.
never thought about doing the same for diff.

Re: Differential Fluid

Posted: Sun Sep 10, 2017 10:08 am
by hmaynord
for my chrysler RA36 rear axle, 66 SM states:
delivered from factory with 90W gear oil,
can use 90W as low as -10 F, and
above 90 F, use 140W.

down here, driving it below 45 F will be rare, but there will be a lot above 80 F, some above 90 F, and rarely above 100 F.
I'm going to leave the same fluid in year round.
maybe I can find straight 90W, but most is 80W-90.

should I use 80W-90 or 140?
half and half (never done that)?
does it matter that I have had over the decades a tendency for the right rear axle seal to leak into the brake drum?

Re: Differential Fluid

Posted: Wed Sep 13, 2017 11:01 am
by hmaynord
forget it. found the answer.
as some of you probably already know, they make an 85W-140.

Re: Differential Fluid

Posted: Wed Sep 13, 2017 10:33 pm
by marklein
Do not put synthetic in the trans. Will not be able to shift it. Too slippery for those aluminum blockers. Use heavier diff oils in hot weather and thinner in cold weather.

Re: Differential Fluid

Posted: Thu Sep 14, 2017 6:44 am
by hmaynord
right. this is not synthetic. just the good old natural stuff.
as you say, manual says to change it according to expected temp.
like any other multi-viscosity oil, this 85W-140 should satisfy those requirements.