Help! Transfer Case and Axle Fluid Recommendations

[cparks101]

Gentlemen, I have a dumb question. I don't have an owners manual for my '77. Anyone know what fluids I should use in the front axle differential, rear axle differential and transfer case?

 

[Broncobowsher]

Oh boy, another internet oil thread!!!

Axles, gear oil. Something around 90wt. 75W90, 80W90,
Transfer case, factory recommendation is 50wt motor oil, which happens to be about the same as 90wt gear oil. Gear and motor oil weights have different scales, like temperature can be had in Celsius or Fahrenheit but both are in degrees. Some go hunting down the 50wt racing oil thinking it is the only thing that can go in there. Others just fill it with gear oil. To this day no one has ever had an issue that was related to using gear oil over motor oil. In fact gear oil is the recommended fill in all non-bronco Dana 20 transfer cases. For some odd reason Ford had this thing about using motor oil in manual transmissions up through the 70s.

These gears and boxes are fairly crude by todays standards. They will live with just about anything in them. The hypoid gear sets do need gear oil. And there are reports of people who didn't know better filling the transfer case with AFT and not having issues.

 

[DirtDonk]

And just in case you had the oddball manual 3speed trans, you can use that same 75w/90-whatever gear oil in your trans too.
Of course, you didn't say that, and most '77's had automatics, but figured I'd mention it just in case.

Paul

 

[cparks101]

Yep. Mine is an automatic. Thank you, guys. I really appreciate the help.

 

[Builtnotbought0]

So I just used royal purple 75-90 gear oil/ with friction modifier in it...will I still need to add the little 4oz Spicer friction modifier or is the royal purple with modifier good
Thanks

 

[DirtDonk]

You will have to drive it to find out.
First, every limited-slip can be different. Is yours new or used?
Second, I've personally never had to add modifier to a synthetic in the past. Maybe here the oils are not all the same either, but before adding anything I would always drive it to see what happens.
If you're using standard dino-oils, I automatically add the first can of modifier (I needed 2 on my Motorsport Tracklock) but with synthetic I don't add any. Then if needed you can add it after.

Of course, that means that maybe it's best to leave the fill level a little low to begin with, but that does not cause any harm in the short term.

Paul

 

[Builtnotbought0]

You will have to drive it to find out.
First, every limited-slip can be different. Is yours new or used?
Second, I've personally never had to add modifier to a synthetic in the past. Maybe here the oils are not all the same either, but before adding anything I would always drive it to see what happens.
If you're using standard dino-oils, I automatically add the first can of modifier (I needed 2 on my Motorsport Tracklock) but with synthetic I don't add any. Then if needed you can add it after.

Of course, that means that maybe it's best to leave the fill level a little low to begin with, but that does not cause any harm in the short term.

Paul

Sounds good.thanks

 

[sykanr0ng]

The reason gear oil was not recommended was that the additives in GL5 oil would destroy soft metals, aka brass and bronze, which are used in the Bronco Dana 20

The additive formulas may have changed, but ideas and attitudes linger on.