GL-4 vs GL-5 gear oils

[MoSinister]

So I've read a few posts about manual transmission fluid and more than once I saw people state that you'll "blow up" your Nissan transmission using GL-5 rated gear oil. Well, I haven't really found any scientific explanations as to what the difference is between the two nor why that would happen.

I'd like a little discussion to edify future searchers like myself. The reason I bring this up is because I couldn't even find any gear oil rated for GL-4 only. They all essentially said "Meets or exceeds specifications for both GL-4 and GL-5 applications." I found Mobil 1, Royal Purple, Castrol, and one other (name escapes me) that all say that. Do the manufacterers even sell a non-combined product anymore? Is the GL-4 vs GL-5 debate a non-issue these days?

Regards.

[98s14inaz]

Your search should have turned up something...

I will tell you that most 90's nissan manual trans use brass syncros that need gl-4 gear oil. I didn't know when I got my first manual 240 and put the gl-5 stuff in and the shifting went to hell. I drained and put the gl-4 in and it shifted like butter. Do what you want, it's your car.

[240 Trainee]

I really don't think it's a debate

Your Nissan transmission requires gear oil that meets GL-4 standards

get some that meets GL-4 regs, your good to go.

Redline MT-90 is the ****.

[churro]

The diff takes GL-5.

[MoSinister]

I'm not using just GL-5 in my transmission. The point I was trying to make is that these two specifications serve (at least they used to) two different purposes. Now it looks like manufacturers are combining the formulas as evidenced by the fact that they say that they meet BOTH requirements. Some of the info I read made it sound like anything having to do with GL-5 in the transmission was a seriously bad thing. Other info states use GL-4 ONLY. With combined formulas, this might lead to some first-time DIYer confusion.

So I guess the real question is, are the combined-formula versions as good as a GL-4 ONLY product?

[seejaytoo]

im pretty sure GL-5 has some anti wear additives that will eat our syncros (i think its cuz theyre brass) ive always heard use GL-4 ONLY no combination. Redline, AMS OIL, and i think Pennsoil Syncromesh is ok too, at least one of my friends runs it no prob