Manual Transmission & Transfer Case Fluid: GL-4 vs GL5?

[nobb]

So I did a bunch of reading and searching, still haven't come up with a clear conclusion on this. For our 3rd gen 4Runners with the manual transmission, the owners manual says that for the transmission and transfer case you can use a 75W90 rated GL-4 OR GL-5. This is kind of strange because usually manufacturers recommend only GL-4 for a transmission application due to the presence of yellow metals in the syncros, of which GL-5 sulfur EP additives can cause corrosion.

Has anyone ever taken apart/rebuilt a manual transmission & transfer case and can confirm if there exists any yellow metals in there?

I'm trying to figure out what is the best fluid to use in the transmission + transfer case. I buy 75W90 GL-5 in bulk that I use for the differentials and it would be nice to be able to use this in the transfer case + transmission as well. Or is it better to stick with a GL-4 in the transmission + transfer case? In my other vehicle I use Redline MT-90 which is a GL-4 rated fluid but it's super expensive. I'm also assuming it's a good idea to stick with the same fluid in the transmission & transfer case because the only thing separating the two is a seal which could leak and mix the two.

 

[Riceye]

There are yellow metals in your synchronizers that live in your transmission. Classic GL-5 lube has sulfur compounds that can damage these parts, particularly when the lube is heated up through use. The high sulfur content is apparent when you smell the lube, as it smells like a pile of buffalo poo near a hot spring in Yellowstone.

Newer synthetic GL-5 lubes have a much lower sulfur content, and do not smell nearly as bad. You can look up the corrosive nature of a lube simply by reading its spec sheet. The ASTM D130-10 copper strip tarnish test ranks corrosiveness from 1A (least corrosive) to 4C (most corrosive).

Red Line and Amsoil are superior products, but more common and economical products such as Mobil1 are equally good. Go with a quality synthetic that has a low tarnish test number and you can't really go wrong.

 

[nobb]

....

Thanks, so what about the transfer case? Is a GL-4 necessary here too?

 

[Riceye]

Thanks, so what about the transfer case? Is a GL-4 necessary here too?

GL-5 has superior lubricating qualities compared to GL-4. The primary need for this is for hypoid (differential ring and pinion, for example) gear sets. That said, there is no reason not to run the very same GL-5 with a low corrosiveness index in your transmission and transfer case. And your A.D.D. front differential, as well. The Owner's Manual calls for a heavier lube for the rear differential, though. Like an 80W-90, or SAE 90. In all reality, the high quality synthetic 75W-90 would probably suffice if you're trying to unify your products.

 

[DaMonkey]

for the manual trans, there seems to be consensus for Redline MT90. Several instances of guys doing it twice... first without Redline and then noticeable dissatisfaction until they change to Redlline which is when they post about what a nice difference.

interesting point about using same lube in transfer, but i'm not sure i have read any reports about them mixing from a bum seal. or maybe just not aware it happened?

after doing my own clicking around and reading factory specs, i'm about to the same fluids and opted for Redline in trans and the specified GL5 in transfer and diffs.

 

[JZiggy]

Like others have said it’s not really a corrosion concern any more. But GL5 is too slippery for synchros to engage well. GL4 gives much better results.

The GL package is “extreme pressure” additives for sliding wear. Only your diffs really need this. The helical gears, ball, and roller bearing in your trans and xfer don’t care. They just want a nice lubricating oil with the right viscosity.

Use GL5 or GL5 in both without worry. GL4 preferred for transmission for shifting performance only. Redline MT-90 is the best you can get.

 

[nissanh]

Use redline trans fluid. I spend a good amount of time deciding what goes into my 5 speed corolla and I found only Redline synthetic offers GL4.

 

[TheDurk]

I use MT-90 in my trans and any good synthetic GL-5 in TC and both diffs. I'm not worried about mixing. I can't believe a failed seal would allow enough mixing to cause a problem--IF it happened. The MT-90 just works really well in the trans, but GL-5 should be better for the the others. I've been doing it this way for years.

 

[Chuckles89]

Don't use GL5 in the trans! Ruined my synchronizers. I only use Redline MT-90 now and I wish I didn't cheap out in the start, because now I have to rebuild my transmission because it grinds going into gear sometimes. Going to replace the synchros and bearings in about a month.