View Full Version : Rear Diff Fluid

02-19-2011, 06:26 PM
Hey guys, what brands do you like for rear differential fluid? Both my gt4's are due, time to change.

Also, out of curiosity, how often does everyone change the fluid on your 4's?

Interestingly my Acura RDX recommends replacement at 24,000km's. Just did it last weekend with the preferred Honda/Acura ATF.

02-19-2011, 07:35 PM
I used mobil1 75w90

02-19-2011, 09:53 PM
I use whatever's in the shop, it's not really going to make much of a difference [unless you're racing].

Toyota recommends rplc all gear oils every 15k miles [for our cars].
Interestly enough there's no replacement interval for gear oil on newer cars, it's just inspect [like the fuel filter].
The exception is if you're towing, then they rec rplc every 60k miles.
For trucks if you tow it's every 15k, if you don't tow there's no rec, just inspect.

However, IMO while I replacing that often won't hurt anything, you can run much longer. Honestly I'd be comfortable going over 100k without changing it, though I haven't made it that far yet on any of my Alltracs [truck has though]. :P

02-20-2011, 12:05 AM
I've got 75W90 Mobil 1 in mine. I've probably got 40K on mine.

02-21-2011, 01:52 AM
I'm a HUGE fan of Amsoil. Thats what I would use if it were available to you. Redline and Mobile 1 would be a 2nd choice. Chris, look up the spec sheets on Amsoil and you will find out there is nothing out there that compares.

02-21-2011, 02:04 AM
Myself - and I am no expert by any means - but for gear lube I would think a 50k mile cycle would be fine unless you live in a climate that the temperature changes drastically such that you might expect condensation.

I am always confused here - when some talk about using ATF in a gearbox while others use the (normal?) gear oil in the same gearbox?

02-21-2011, 05:47 AM
I don't think it really matters as long as it is a 75W90 gear oil. Usually comes down to personal preference, but I prefer Redline MT90.


The manual states you should use a GL-5 gear oil, however GL-5 oils have reactive sulphurs that attack brass, bronze, and coppers (which is your syncros). I find that the GL-4 Redline MT90 is a good compromise as it wont attack the syncros and will be much easier on them by giving extra lubrication.

02-21-2011, 06:00 AM
You WANT a GL5 fluid for the rear differential. Thats what theyre made for.

In an alltrac, your front transfer case uses hypoid gears, so GL5 is what Toyota calls for on those as well.

Chris, you know youre just stirring up shit asking for this. It really seems like opinions of this nature are like assholes and everyone has em. Id run whatever Jeremy recommends in this regard. If he says it doesnt matter much, it prolly doesnt LOL.

02-21-2011, 06:17 AM
^ Yes that is right. Sorry my brain isn't working tonight. For the Rear Differential I would use a GL-5 gear oil that is a 75W90. For the transmission I would use a GL-4 product to protect the syncros.

02-21-2011, 06:27 AM
I wouldn't run straight gl-4 in your tranny. I run half gl-5 and half gl-4. Gl-4 is basically a syncro mesh style gear lube although it is rough on the gears compared to Gl-5.

I remember a thread years back about quite a few mr-2 guys exploding their tranny's running straight GL-4.

02-21-2011, 06:37 AM
LOL, really? Ive been an MR2 guy for over 10 years and Ive never seen an MR2 tranny explode cause it was running GL4. In fact one of the MR2 guys proved Toyota was full of shit when they recommended GL5 fluid for it. It SHOULD be running GL4. But the alltrac differential, and transfer case are different animals than the MR2 tranny so you cant compare fluid types between the two.

All of Toyotas new manual trannies call for GL4. Most guys with E153s run GL4. Youre not going to aslpode your tranny cause youre running a GL4 fluid.

02-21-2011, 08:21 PM
LOL, I guess I'm a shit disturber then. :D I just noticed we hadn't really had a chat on this much before, so thought I'd bring it up. And it was fresh in mind since I just did the RDX, which uses ATF as I mentioned.

To all the tranny q's - I don't really want to debate that, there is a lot of back and forth about harm to synchros which no one ever agrees on. More or less just looking to discuss rear diff fluid options. I've used Redline in the past and liked it, but may try Amsoil. In the end I suspect that it will make little difference. I have some spare Redline MT90 still that I might make use of too.

02-22-2011, 07:13 PM
You are best off to use a GL5 in the alltrac transmission because of the hypoid gears. Newer GL5 oils are not harmful to the synchros like they used to be.

Redline makes a 75W90NS product that does not have the slip modifier, that is ideal for use in the transaxle - GL5 for the hypoid gears, no slip modifier for better shifting, and it is specifically designed for transaxles. You can use 75W90NS or just the regular 75W90 in the rear end.

02-23-2011, 01:35 AM
- GL5 for the hypoid gears, no slip modifier for better shifting, and it is specifically designed for transaxles. You can use 75W90NS or just the regular 75W90 in the rear end.

FunkyCheese - by "no slip modifier" do you mean "friction modifier" like would be bought to use regular gear lube in a 60's style liimted slip differential with the clutch plate type LSD mechanism?

02-23-2011, 01:55 AM
Yep. The NS desginates "no friction modifier"

Redline 75w90ns is like the MT90 of GL5s. So MT90 is a 75w90 GL4 without friction modifier. 75w90ns is GL5.

02-23-2011, 03:22 AM
i put redline heavy shockproof on my gt4. but personally , as long as u change the fluid. any gear oil will do (gl5 gear oil).

03-11-2011, 05:20 AM
I am running Castrol Hypoid GL-5 75W90 in my rear diff, no issues to report.
I will be changing fluid soon and I picked up some Toyota Factory GL-5 gear oil 75W90.
The same discussion went on at www.alltrac.net, LOL