I put my new striking rod seal and boot in today and had to get some more manual tranny oil to put in. I know it's supposed to be GL-4 but nobody carries just GL-4. They all have GL-3, GL-4, GL-5 all in one. So here's what I can't seem to figure out. If GL-5 ruins synchros in our trannies, how is it that they can sell that fluid? My understanding is that like Dexron III, which which is backward compliant for Dexron and Dexron II, GL-5 is backward compliant for GL-3 and GL-4. Then I've also seen oil that just says GL-5 on it, doesn't say anywhere that it's Gl-3 and Gl-4 compliant. I've had 3,4,5 oil in my tranny for 2 years now, so the damage is done by now if that oil is corrosive to the synchros. I just don't understand how that can be though. If the differences between gl-4 trannies and gl-5 trannies is enough that the gl-5 fluid will damage a gl-4 tranny, then I can't see why you'd be able to buy a bottle of oil that says it's compatible with both. Everyone I've talked to confirms that gl-5 is backward compliant, and on the net, the only place I can find that says otherwise, is posts on Nissan related forums.

Use Redline or Royal Purple oils, you should be able to find them at any local speed shop or use websites to get it. Its the best and it works fine for our trannys

Right, but I shouldn't have to buy higher priced, performance market gear oil to get the right thing, or to know for sure that I'm getting the right thing. I wrote Red Line an e-mail asking about it, we'll see what they have to say.

Rob-
a. Thanx for the bars coming. Glad you're out there making a few pennies and saving us a few.
b. Buy the Redline oil. Pay the few bucks. Cutting corners doesn't pay on our tender gearbox. When somebody builds a Getrag or Hewland for us, then we can appreciate paying BIG bucks.
Jer

You can go to nissan and buy gear oil. But at that point, I'm sure it will be just as much to get redline.

Well this tranny only needs to last until the next step, which is a swap next spring hopefully, or if work and weather permit, this winter. Either way a newer tranny will be used. So it's not cost I'm avoiding, I just want a straight answer to my question.

GL-5 is not backwards compliant with GL-4. GL-5 has more EP additives that may eat at the synchros (sulfer based additives do this). However if the lubricant is both GL-4 and GL-5 compatible, they either use a EP that does not corrode yellow metals (Inorganic Borate for Chevron) or might be splitting the difference in the EP levels.

At least get a Lube that is GL-4 certified, and NOT ONLY GL-5 certified and you should be ok.

--Eric

Just to clarify, GL-4 and GL-5 are performance specifications, and not formulation specifications.

So, a gear lube could comply with both specifications, but a GL-5 only lube is more likely to have higher levels of EP sulpher compounds that will form acids that will destroy our transmissions. If it says GL-4 on it and is from a well known oil manufacturer, it is OK to use.

--Eric

i use the royal purple.. its real nice, ive decided to just buy the more expensive oil so i dont get stranded anywhere with broken gears lol

I think Eric is the winner. Here's the reply that Redline sent me:

Rob,

In your Sentra manual transaxle I would recommend the MT-90, this is a GL-4 gear lube. A GL-5 gear lube could be used in some applications calling for a GL-4 or GL-3 gear lube though isn't backwardly compatible. Most GL-5 gear lubes contain sufficient EP reactive additives to be corrosive to brass, bronze and copper, though our GL-5 lubes don't. GL-5 gear lubes are so popular due the the number of applications, hypoid rear wheel drive differentials calling for that type fluid. Most GL-5 gear lubes also contain a friction modifier and are consequently too slippery for the synchros in a transmission/transaxle application.

Regards, Dave
Red Line Oil

So I think I'm okay with the Coastal cheapo stuff I bought from Advance.

Redline MT-90 worked extremely well for me. Comes very highly recommended by me. :biggthump

I was also told by a mechanic that for the Nissan cars, if you didn't go with the Redline gear oil, then to make sure to pick up a GL-4 compliant gear oil and not a GL-5. He didn't go into as much detail, but I did trust his word based on past experience. Now I know why.