Transmission and differential fluid

Kappste

Gear Grinder
Apr 3, 2021
5
Grove, Oklahoma
First Name
Steve
Willys Model
  1. CJ
Willys Year:
  1. 1948
I’d like to thank the people that responded to my question about transmission and differential fluids. From what I have read the SAE 90 W mineral gear oil (API GL1) from NAPA seems to be the best choice.

But can this same fluid be used for each - transmission and differential. I think it can, but I’m not for sure.
 

Blue Duck

Sharpest Tool
Mar 16, 2020
281
Western Texas
First Name
Stan
Willys Model
  1. Pickup
Willys Year:
  1. 1955
Yes it can, the transmission and transfer case are open between the two. The fluid moves between the two as they turn. If you fill the transmission It will flow over to the transfer case. You need to drain both the transmission and the transfer case to be sure you get the case bottoms where any residue collects. I usually put the driver side front tire up on a ramp, easier to get under and ensures better flow as you fill. Fill until fluid runs back out the filler hole.
 

Bitzf4

Bigger Hammer
Oct 13, 2020
161
Hastings mn
First Name
Jim
Willys Model
  1. CJ
Willys Year:
  1. 1948
Yes it can, the transmission and transfer case are open between the two. The fluid moves between the two as they turn. If you fill the transmission It will flow over to the transfer case. You need to drain both the transmission and the transfer case to be sure you get the case bottoms where any residue collects. I usually put the driver side front tire up on a ramp, easier to get under and ensures better flow as you fill. Fill until fluid runs back out the filler hole.
So you leave the wheel on the ramp during fill? Haven’t done this yet so just don’t want to be under filled when level
 

Bigbill

Bigger Hammer
Mar 19, 2021
44
Ct
First Name
William
Willys Model
  1. Other
  2. CJ
Willys Year:
  1. 1955
I use a moly additive in gear oil and engine oil. There’s moly gear oil too.

Moly.
Eliminates all wear, it wears against itself.
Reduces friction.
Prevents Galling.
Fights Corrosion.
 

Blue Duck

Sharpest Tool
Mar 16, 2020
281
Western Texas
First Name
Stan
Willys Model
  1. Pickup
Willys Year:
  1. 1955
Yes, I put The drivers side front wheel up on a ramp or jack the front end up a little, drain both sides then fill thru the transmission fill hole until oil comes out the transfer case fill. One note, the plugs are all tapered threads, don’t over tighten them. Teflon tape helps seal the threads. Warming the oil up good before you start will make it pump a lot easier.
 
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