unhappy with 80w-90 gear oil

[Abletobecain]

I just won $400 off of a re-gear at an overland rally raffle. Because they can't re-gear a T4 they gave me a case of gear oil instead. It looks like good stuff but it's 80w-140. Anyone have any ideas if I could run this in the T4...perhaps as some percentage of a mixture?

This is the stuff here: https://www.polyperformance.com/80w-140 ... gKHE_D_BwE

[The Professor]

That's a GL5 oil, so no, don't put it in your transmission. I'd call them up and see if you can swap out the GL5 with the Redline GL4 fluid I mentioned previously. I took some photos/video of my synchro dust from just a few thousand miles of GL5 use, and it ain't pretty. Need to upload those and share.

Recap: NO GL5 GEAR OIL!

[dlb]

Prof, did you previously run conventional gear oil before making your recent swap to the Redline synthetic stuff, and if so, did you track your fuel economy? I'm interested to see if you notice an improvement with synthetic gear oil. Of course, there are tons of variables that have to also be considered (I find ambient temps to have the single biggest effect on fuel economy), but any info I can glean on the topic is appreciated.

[Terbo4WD]

Up in Canada, we have this stuff that says it meets GL-4 and Gl-5 requirements. I'm inclined to think it's the perfect gear oil for the T4 since the other variations from the same brand only mention Gl-5.

[jimijuma]

Ok, after reading through this thread I have decided to go with The Professor and use the Redline MT-90.

My question is should I go 100% synthetic, or should I do a half MT-90 and half conventional GL-4 mix???? That is what I am leaning towards, however it sounds like The Professor is using 100% synthetic MT-90. Thoughts??

[The Professor]

DLB - Yes, I believe it was straight conventional gear oil, but I'd have to go look at the receipt to be certain of the brand and weight. I don't think my fuel economy is applicable, since I was having carb trouble, but I was in the mid 20's.

Terbo4wd - If that fluid is GL4/GL5 compatible then it is neither a great GL4 oil, nor a good GL5. GL5 has extreme pressure additives and friction modifiers that have traditionally not been compatible with yellow metals (brass synchronizers, as in AL25 transaxles). To be GL4 compatible, this oil probably isn't as good at protecting hypoid gearsets.

Jimijuma - I would start with a full transaxle of the MT-90 and see how that feels first. If you still want to try a mix, then drain out 2 quarts of fluid and replace with conventional/ATF. I think you'll find the MT-90 is sufficient.

[Abletobecain]

Prof, thanks for sharing your insight and experience with the MT-90 but I've read and re-read this entire thread and it seems to me there's no clear consensus on whether GL4 or GL5 is the way to go. That is, many members have high mileage transmissions and have only ever used GL5 while others swear by GL4. With the FSM saying to use either one, it's all very confusing and seemingly determined by localized driver/vehicle specific scenarios. What worries me about the MT-90 is that at the bottom of the page it says "MT-LV, MTL, MT-85 & MT-90 are not for use in differentials with hypoid gears." Our front diff has hypoid gears, correct? Perhaps a call to Redline is in my near future. As well as a call to Schaeffer's Oil as that's who manufactures the Nitro stuff I won. Unfortunately, this is the only gear oil that Nitro Gear has so I'll likely be selling it on Craigslist if it's a no-go.

[The Professor]

True, GL4 isn't rated for hypoid gears, which our transaxles absolutely do have. That said, if Toyota spec'ed GL4, they must have been aware of this. Besides, it's not like the 3A is a torque monster that will be putting loads of stress on the ring and pinion. I'd say if you have synchro problems, stay away from GL5 because it will only get worse. If you're offroading with larger tires, using low range a lot, have a high-torque engine, then GL5 may be a better choice.

I looked up the Tercel on the Redline website and this was the gear fluid they recommended, though I don't know if I had to email or if I used their application-based search...

[Abletobecain]

I would think if Toyota spec'ed GL4 OR GL5 then they have some reasoning to both. Maybe a 50/50 blend experiment is in order, lol.

Good advise on the off-roading set up...now I'm thinking of using GL5 in my 87 off-road/camping rig and GL4 in my 83 daily driver.

[Petros]

my experience using synthetic gear oil in the trans was on my worn transmission, it made the syncros act like they were suddenly worn out (they require some friction to operate properly), and it was seeping past all the seals, even the recently replaced ones.

I went to a 50/50 blend of synthetic gear oil/conventional gear oil, and the shift and leaking problems went away.

[The Professor]

Mid-summer follow up: The transmission is still shifting beautifully even in ~90* F weather. Redline MT-90 for the win!

[Abletobecain]

I've read and re-read this thread and several others. I finally decided on the Redline MT-90 as well...largely from your report, Professor. I just got mine in the mail today so it's nice to see this update.

[jimijuma]

A couple weeks ago I changed all fluids on my Terc, bumper to bumper. I used Redline MT-90 for the transmission with no issues whatsoever so far. I can't say it shifts better because it was fine before I changed the oil, but it definitely did not make it worse. I'll be using Redline MT-90 as long as I have the car. For the rear diff, I just used some synthetic GL-5 gear oil that I happened to have in the garage. From what I understand, the consensus view is GL-4 in the transmission, GL-5 is ok in the rear differential. No leaks whatsoever so far, though my Terc isn't worn.....just getting broken in.

This weekend I plan on replacing the bushing and seat for the shifter with hopes to eliminate some of the play. I also have some aftermarket boots (even one for the 4wd shifter) that I think will work fine. Be nice to get rid of the deteriorating factory ones. I don't want to take the time to sew some new ones, so we will see what happens. I am sure what I found should work reasonably well.

[The Professor]

I used Redline MT-90 for the transmission with no issues whatsoever so far. I can't say it shifts better because it was fine before I changed the oil, but it definitely did not make it worse. I'll be using Redline MT-90 as long as I have the car. For the rear diff, I just used some synthetic GL-5 gear oil that I happened to have in the garage.

Great feedback! Let us know how it holds up over time (I don't put many miles on my Tercel, so I can only really comment on the shifting).

I also used generic parts store GL-5 fluid in the rear differential.

[The Professor]

Mid-summer follow up: The transmission is still shifting beautifully even in ~90* F weather. Redline MT-90 for the win!

Mid-winter update: I drove around in some low-to-mid-30s (*F) temperatures in the Tercel over the last few weeks. The Redline MT-90 still feels great with no grinding in any gear and smooth operation despite the cooler temps.