Transfer Case Oil

[LOTO_DLG]

Is this the fill plug? If yes is there a recommended oil?

 

[68rustbucket]

Yes it’s the fill plug. The type of fluid used is a hot topic.

 

[ugly74]

The OE spec oil is 50w. That’s i what use

 

[Spaggyroe]

My operators manual says:
- Above 10 degrees F - Engine Oil SAE 50
- Below 10 degrees F - Engine Oil SAE 30
Non detergent would probably be the way to go here.


My Atlas t-case shipped with Redline 75W-90 API GL-4 synthetic, which they recommend because it's safe for synchros. I personally wouldn't think it'd be necessary for a D20.

I have ran 80-85 wt gear oil in my dana 20's in the past with no issues...

 

[Broncobowsher]

Yes, that square head is the fill plug. Standard 1/2 NPT plug.

Factory spec is 50wt motor oil. Non-detergent is correct as there is no filter in the transfer case. The detergent oils are designed to keep dirt in suspension so it can be filtered out in an oil filter. Non-detergent lets it settle at the bottom of the pan. Almost impossible to find non-detergent 50wt.

The good news is normal ~90wt gear oil is the same viscosity. Motor oil and gear oil are on different scales, like Celsius and Fahrenheit. Other manufacturers that used the Dana 20 just call out for 90wt gear oil. So while 90wt isn't a match for the published spec that is 50+ years old, it is still a good oil choice. Lot s of people have been running 90wt for decades and don't even know it. When the corner service station did the full lube and changed it, not knowing any different, just filled it with gear oil and sent it on the road. There are even people who have filled it with ATF (like modern transfer cases) and not done any damage. The D20 is a very simple design that does not require specialty lubes. It will run with just about anything that is oily. I've even followed one for a day that ran no oil after punching a hole in the bottle on a rock. Finish the day, go home and put the spare one on.

 

[LOTO_DLG]

Thank you guys for your help. I should have asking this in my original post, what's the capacity?

 

[Broncobowsher]

Fill until it just dribbles out the threads at the bottom of the fill hole.

 

[blubuckaroo]

I've never seen a a Ford recommendation for non-detergent oil in the transfer case.
Ours has way over 300k miles on it with only Valvoline SAE 50 racing oil.

 

[LOTO_DLG]

I was gone to change the oil -- just wondering how much to buy. ??

 

[jec-3]

Specs say ~2.75 pints

 

[SHX669]

Oh and don't be tempted to overfill it - everytime I do it just creates a leak - lol - same with the rear differential.

 

[tirewater]

Does the 50w oil have less chance of weeping than the 90w gear oil?

 

[Broncobowsher]

Does the 50w oil have less chance of weeping than the 90w gear oil?

No. The actual viscosity of both oils is the same. Motor oil is on a different scale and has different additive packages for things like carbon particulate and anti-acid formation. Gear oil has the extreme pressure additives (that sulfer stink).

 

[LOTO_DLG]

Thanks for all the help, guys.