1965 Dana 20 Transfer Case / Oil Swap

[CopperBronco]

I've been reading the threads on how to swap the gear oil on my Dana 20, it's a very early one, the casting says mfg date of 11-8-65. The fill bolt is only about halfway up the transfer case. When I loosened it oil started to pour out so I tightened back up. My concern is how full should the transfer case be with oil? Above the fill hole? So does that mean you have to pump it in somehow and then quickly throw the threaded bolt in there to tighten up before it all pours out?

Just want to make sure I get the case as full as it should be. I'm redoing my exhaust right now and it's easy to access the drain plug so I thought I'd get this done while I'm doing the exhaust. Many thanks in advance. I already read some of the other threads on this and bought some 75/90 synthetic gear oil to throw in there.

Many thanks in advance!

 

[EPB72]

the fill plug is the level ,fill till the fluid is just at bottom of hole...prefer using Dino oil non synthetic..50Wt racing motor oil... but others have used what you have with no ill effects

 

[Broncobowsher]

Check the oil in the transmission, it may be low. As in it leaked past the shaft seal from the transmission into the transfer case.

Did the Bronco have a tow bar on it? One of the flat towing tricks was to overfill the transfer case so the output bearings stay in the oil bath.

Pull the drain plug, does it start with water before going to oil? remember that oil floats on water. But if run they will mix into something that looks like chocolate pudding (light colored).

You are correct, the normal fill level is to the bottom of the fill plug.


Many decades ago I had a BroncoII that had a bad seal and the transfer case was way overfilled. Transmission was low. Kept topping off the transmission until it was stable. Well over 60k driving that way without issues. Finally the rest of the truck died. Not that it was right, it was what I could afford.

 

[CopperBronco]

Check the oil in the transmission, it may be low. As in it leaked past the shaft seal from the transmission into the transfer case.

Did the Bronco have a tow bar on it? One of the flat towing tricks was to overfill the transfer case so the output bearings stay in the oil bath.

Pull the drain plug, does it start with water before going to oil? remember that oil floats on water. But if run they will mix into something that looks like chocolate pudding (light colored).

You are correct, the normal fill level is to the bottom of the fill plug.


Many decades ago I had a BroncoII that had a bad seal and the transfer case was way overfilled. Transmission was low. Kept topping off the transmission until it was stable. Well over 60k driving that way without issues. Finally the rest of the truck died. Not that it was right, it was what I could afford.

Thanks, I’ll double check, I checked C4 trans fluid not long ago, it was fine. So don’t think that’s the issue. I’ll just drain transfer case and refill and watch it, and check C4 trans fluid again once I have Bronco back together.

 

[CopperBronco]

Check the oil in the transmission, it may be low. As in it leaked past the shaft seal from the transmission into the transfer case.

Did the Bronco have a tow bar on it? One of the flat towing tricks was to overfill the transfer case so the output bearings stay in the oil bath.

Pull the drain plug, does it start with water before going to oil? remember that oil floats on water. But if run they will mix into something that looks like chocolate pudding (light colored).

You are correct, the normal fill level is to the bottom of the fill plug.


Many decades ago I had a BroncoII that had a bad seal and the transfer case was way overfilled. Transmission was low. Kept topping off the transmission until it was stable. Well over 60k driving that way without issues. Finally the rest of the truck died. Not that it was right, it was what I could afford.

So I drained it tonight, no idea when/if ever drained, had this Bronco for 6 months now, but fluid came out of drain plug dark brown, but not black… not a light brown as you described, but chocolate pudding could be one way to describe it. I’ll just refill and check it again sometime from the fill hole and see if it’s overflowing again. Any idea how quickly that would happen? Did yours make fill up and leak between transmission and transfer case quickly?

 

[73azbronco]

also depends what slope you are on if it runs out by itself.

 

[Rustytruck]

I have been running synthetic gear oil in the original transfer case for over 30 years trying to help the Jshift work better. the viscosity is the same as 50 weight motor oil. it did help with the shifting.

 

[Broncobowsher]

The Dana 20 is a very simple and crude gear box. It is not fussy at all about what oil you put in it. Full and clean is all it needs for oil and it will last forever. Any of the it has to be motor oil, it has to be synthetic, it has to be an exact weight, just doesn't matter. Oil is not the limitation of this gear box.

 

[CopperBronco]

also depends what slope you are on if it runs out by itself.

Yeah, I was on flat ground, but good gut check!