Transfer case and Differential gear oil

[twocommas]

I am looking to replace the gear oil in my transfer case and differential in a 1998 Montero. The car was bought with about ~150k miles and no records, so it seems like a good idea

I called the Mitsubishi dealer and they told me that oil for the differential depends on whether I have a "regular" or a posi differential. They can't tell me over the phone, but if I pay a billion dollars for their service, they will put in the right gear oil. :Wow1: I saw some photos of how to change this out, and it looks pretty easy, so I wanted to do it myself.

This is a bit outside of my wheelhouse, and my research online didn't get me an answer. I am wondering if you can tell me which ones I will need. And are the transfer case and differential oils different?

 

[Inyo_man]

Not sure if your '98 calls for the same lube as my '02, but my FSM specs GL-4 for the transfer case and GL-5 for the differentials.
I'm running Amsoil gear lube in my rig and couldn't be happier.
Don't worry, it's an easy job- drain, check the plug magnet (and clean), reinstall plug to spec. torque, and fill.

 

[limp_noodle]

Inyo_man is correct.

GL-4 for the transfer case
GL-5 for the diffs

It's a simple drain and fill for all 3.

- make sure the vehicle is level
- remove the drain and fill bolts
- drain fluid
- replace drain plug
- fill with fluid until fluid is level with fill hole

 

[jeep-N-montero]

If I can't find an answer online I always find it funny that the local Napa has better specs on fluids and specs than the dealer....

 

[off-roader]

If you have a limited slip, the rear diff gear oil needs a limited slip friction modifier additive. To determine if you have an LSD, lift the rear end and while its on jack stands or a floor jack, front wheels chocked, go ahead and turn the rear wheel on one side and if the other side turns in the same direction, you have an LSD. Opposite directions open diff.

If this was a factory installed option there should also be a plate on the diff housing noting it having an LSD and requiring LSD additive as well as a sticker in the cab saying the same thing.

 

[jlocster]

Axle, Front API Class GL-5 (1.3 qt)
>-10 deg F SAE 90, 85W-90, 80W-90
-30 deg F to -10 deg F SAE 80W, 80W-90
<-30 deg F SAE 75W

Axle, Rear API Class GL-5 (3.3 qt)
>-10 deg F SAE 90, 85W-90, 80W-90
-30 deg F to -10 deg F SAE 80W, 80W-90
<-30 deg F SAE 75W

Transer Case API Class GL-4 (2.6 qt)
SAE 75W-90 or 75W-85W

Make sure the fill plug opens before you drain...

 

[mapper]

Make sure the fill plug opens before you drain...

If you have changed diff oil before this is a key step in the process on any older vehicle...especially in the rust belt.

 

[twocommas]

Thanks for all the replies!

Autozone guy recommended "Coastal" brand, and Mitsubishi obviously wants me to buy their stuff. If price isn't an issue, is this one of those things where Mitsubishi oil is a better choice?

 

[off-roader]

No... Not for diff's or xcases. I'd be the last to recommend only Mitsu stuff in this situation.

Auto Transmissions? That's a different story.

 

[GFO]

If it helps, here's what I recently used:


-Red Line MT-90 for the transfer case. It's GL-4(don't use a GL-5, it can eat away at the yellow metals in the t-case) and synthetic. Shifter slides right into 4WD with little or no resistance at all.



-Lucas Oil 75-90 gear oil for the Frt/RR Diffs. It's GL-5; I used the synthetic version. I've not had a problem with it that I know of, but I do wish I had used a Red Line brand instead.



-Red Line D4 ATF for the transmission. It's synthetic and the tranny loves this stuff, shifted smoother immediately after.

 

[Inyo_man]

If I can't find an answer online I always find it funny that the local Napa has better specs on fluids and specs than the dealer....

The FSM has all the specs.

 

[Inyo_man]

If you have a limited slip, the rear diff gear oil needs a limited slip friction modifier additive. To determine if you have an LSD, lift the rear end and while its on jack stands or a floor jack, front wheels chocked, go ahead and turn the rear wheel on one side and if the other side turns in the same direction, you have an LSD. Opposite directions open diff.

If this was a factory installed option there should also be a plate on the diff housing noting it having an LSD and requiring LSD additive as well as a sticker in the cab saying the same thing.

Not sure about the '98 LSD, but the Gen. III LSD does not require an additive.

 

[nckwltn]

I assume using oil with the slip additive doesn't hurt, right?

 

[jeep-N-montero]

I assume using oil with the slip additive doesn't hurt, right?

For an air locked rear axle like you are swapping in I would use straight gear oil with no additive or synthetics, google "arb air locker gear oil" if you have any doubts.

 

[nckwltn]

For an air locked rear axle like you are swapping in I would use straight gear oil with no additive or synthetics, google "arb air locker gear oil" if you have any doubts.

Bingo that's the ticket, thanks!