Trans fluid in 79 Rear diff?

[willywoo28]

As the title states I discovered that the P.O. put straight atf in the rear diff. I just pulled the plug on the side of the diff case and found that the fluid is very thin, clear (red), and smells like roses compared to gear oil and additives that i have used on other trucks.....

Couple questions:

1) Is this okay to keep running since it is clear and no Rear end noise?
2) How Long? (my guess is that it has 65k miles from the P.O.'s engine swap).


There are no metal shavings, nor any discoloration of the fluid. It is my daily driver, so I am just curious.

Any input is always appreciated.

Thanks!

[ol'blazer]

if the fluids as clean i would fill back up with gear oil. but i wouldnt run it long before giving it another oil change, just to flush out all that trans fluid.
thats my opinion.

[bilfman]

There's a reason it aint done from the factory, nuff said. Put the recommended gear oil back in.

[y5mgisi]

How much is a rear end worth to you? If you felt frisky, you could leave it in there and see how long it lasts. Otherwise, i would switch it back over to 80-90.

[meatwagon83]

put gear oil back in it before it burns up!

[INSIDIOUS '86]

Trans fluid is partly hydraulic so it resists shock loading partly but it's thin and not good for the temp of a rear diff plus it's heavy in detergents. So it's prob nice an clean inside by now. Change the fluid and then change it again.
Posted via Mobile Device

[shipma3]

use 80 90 gear oil you probably will burn the rear axle to all glory, the damage may already be done anyway , i got my k10 home and found the seal had been leaking fixed it then a year after that returning from the auto parts my axle broke a tooth of the ring gear . does it make any grinding at all?

[piecesparts]

When I worked at the County Highway Department, we had numerous pieces of equipment that had dexron in the rear ends and the gear boxes that I would have guessed would be a heavy weight gear lube. It so happens that the ATF carries heat away faster and easier than gear lube and will stand up to just about any abuse. Cold weather does not affect auto tranny fluids like it does a heavy lube and the lubrication stays right in the gears and not channeled out like a gear lube would.