Apparently GL-4 is safe for gears with brass parts as GL-5 contains sulfur. Looking to change my LSD differential oil and want to know if any brass is in there?

Also for transfer case.

1992 Montero with LSD.

Thanks.

Use the GL-4 with LSD additive. I've used Valvoline most often.

Russ, I think you meant to type "use the Gl5" for the rear diff.

The hypoid rear gears need the EP level that's in a GL5.

GL4 and Gl5 both have sulfur / phosphorus as an EP additive, but Gl5 has more. For the LSD unit, as Russ pointed out you will get chatter without it as well as more metal from the clutches.

I have had good results using Redline GL5 with the LSD additive premixed.

Was GL-5 even available back in 1992? Back then the dealers were adding GM's LSD additive. I can't find any info on Mitsubishi's spec of 8149630EX.

Right now I've got Moble1 75w-90 in the diff. It comes with the LSD additive and is classed as a GL-5. I was still getting some minor diff chatter/shudder on some from-a-stop sharp turns. I added an oz of LSD additive but still the chatter continued. I added a little more but can't get rid of the chatter/shudder. It's been 30K since last change so want to do something different.

I've emailed Redline on their MT-90 GL-4 but I'll have to add the LSD additive. Redline is so darn expensive though.

Do these diffs/transfer cases have brass?

Gl5 was an option when I was in High School... That might have been a while ago.

Gl5 dates back to at least the early 70's.

In my experience, Mobil 1 that says "for LSD units" will chatter. My testing showed that Redline GL5 with LSD additive did not. What you need: Any high quality GL5 and enough anti chatter additive. The factory additive from Mits is expensive.

Years ago I built a custom LSD and had a chatter problem, the only lube that worked was Redline. I actually found that it was too slippery and bought the non LSD GL5 gear lube and added the Redline LSD additive separately; putting in just enough to get it to feel smooth.

If you still have the owner's guide in the glove box go out and check it, it calls out GL5 for the front rear diff for non LSD units. Same thing with the service manual: 80W-90 ( I use 75W-90 synthetic).

For LSD units the service manual calls out Mitsubishi PN 8149630 or equivalent. That is a Gl5 with LSD additive.


GL5 Redline


Redline Gear Lube Without LSD Additive

Redline LSD Additive

For most applications, a good GL5 dino base gear lube will work, its just a matter of getting enough LSD additive in it.

For a more demanding application, I went with Redline, I'm sure there are other synthetics that will work, I stopped testing when I found one that worked.

Short Story? Check the owner's manual, it says Gl5, make sure you add enough LSD additive. I have been using 75W -90

BTW, I typically pay about $15 or so a quart, 2X the cost of dino, but less expensive that some of the factory fill synthetic gear lubes.

Decent Read

Overview ASTM Standard from 1972 lists GL5

BTW, no brass in the rear diff.

Wow, thanks for that detailed explanation and link.

Here is what my FSM says:
Transfer Case - GL-4 or higher - would that mean GL-5 is OK?
Front Axle - GL-5 or higher
Rear Axle (LSD) - nothing, just a reference to the Mitsu # 8149630EX, which you say is GL-5 with additive.

Owners manual specs GL-5 in non-LSD and the same above # for LSD.

I believe you are right about Mobil1 as I seem to remember my last Diff oil was Redline. Redline was hard to get around here, but now, thanks to Amazon, is as close as UPS.

On Amazon, Redline's 75w-90 Syn gear oil GL-5 is $16.49 with free shipping on my Prime.

At one point the dealer was recommending LSD additive to the transfer case. Have you tried that?

While there is brass in the transfer case, it's a bushing that is not subject to the same film shearing issue of a synchro.

In my opinion and experience, GL5 will work in the transfer case without issue. Its not needed, but won't hurt.

I have never tried LSD additive in the transfer case, no clue if it would help at all.

If you're still watching Kevin, are the rear diff gears "hypoid" type?

At some point I wrote in my FSM "hypoid" in the oil spec sheet for rear diff.

Fortunately they are.