i need to do an oil change in my 6 speed trans and transfer case.. should i use ATF or 70-90w gear oil?

i know that ford says to use ATF...but why not gear oil? i would think that it would be alot better for the units, unless i am missing something...

 

Tolerences are too close I guess. They shift like crap with gear oil in them. Nearly impossible to shift when it's cold.

A good synthetic ATF makes a world of difference in how it shifts.

 

I fully agree with what Cookie 88 says.
For a time I used Redline synthetic MTL gear oil. I noticed no difficulty in shifting, even when cold.
But I recently lost my overdrive gear bearing and I have to wonder if that wasn't a factor.
Since then I've put back ATF in there.
I put in Redline D-4 ATF. Shifts and drives like a dream. It's what is going back into my new transmission when it arrives next week.

 

Hey Dan
Will that D-4 ATF also go into the transfer case?

 

Yes, the x-fer case takes ATF.

 

Royal purple synchromax here. Its specifically made to be run in manual tranny's that require ATF. That alone sold me on it. No other manufacture had a listing of a syn. ATF thats formulated for manual's that require it. IMO : Shifts on my cold tranny, in 45 deg. or lower temps, are not an issue for me anymore. With the motorcraft ATF it was hesitant about going into anotherr gear with cold fluid. . I like it.

IMO: Gear oil in any way shape or form (syn. or not) ,is just to thick! I may get schooled here , but im very hesitant about running anything other than ATF in these ZF's. Being that it cools the oil by using a pump to circulate it to the radiator. To me by putting a thicker oil in would strain the pump. Not only that but it probably doesnt get into those tight spaces in the gears/bearings as well. Air pockets would occur of areas on gears/bearings that need lube.

Same thing that would happen to a rear diff if you added to heay of an oil.
My buddy was h*ll bent on that amsoil crap and swithced every oil out on his truck for it. He ended up ordering and adding to heavy of an oil for his axles and it destroyed his diff's from the lack of lubrication from the airpockets that were formed at highway speeds.Im wondering with these 6th gear/OD's going out may be related from the use of a thicker oil other than ATF. Any thoughts?

 

Yes. ............

 

Pullinair that's an interesting thought about the oil.
I was running with Redline MTL last time I was out. It's rated 75-90, but being a synthetic oil it's only a bit thicker than the ATF. I figured it would be a good substitute for the ATF and gain some added protection as well.
Since I lost my OD bearing, I cannot discount the notion that it gave up because of that oil in the trans and have been thinking along those lines for quite some time now.
So everything is going by the book this next go around and we'll see what happens.
And the Redline ATF is rated for gearboxes as well, like the RP oil is. It can be substituted for a GL4 gear oil if desired.
Either oil is just as good. I use the Redline because is so much easier for me to order and have it delivered.