Whats the best possible gear oil

[Two6DK]

so i have a 91 tt and i recently drained all the gear oil out of the transmission planning on doing a gear oil change. my only problem is i cant find any reccomendations on what i should put back in. all i know is that it has to have a gl4 rating and apparently redline sucks. any suggestions would be apreciated. thanks for the help in advance.

[car nut]

If you're looking for GL-4 I'm assuming you have a 5sp. Since when does Redline suck? I'd recommend MT90 to anyone, it's excellent stuff. You could also try NEO 75w90 HD from SPL. Either one will be good. You need 3qts fyi.

[es.biggs]

I hear great things about Redline MT-90 and Amsoil MTG. Just make sure you get a fully synthetic GL-4 oil, 75W-90 weight. I'm planning on trying the Amsoil fluid at some point

[Zwicked]

Redline MT-90 for the trans is fantastic. It makes it shift noticeably smoother and in a lot of cases reduces or eliminates grind due to worn synchros when shifting if yours has this issue. Royal Purple is a good one for the dif.

[Two6DK]

thanks for your help. ya i just went on a couple of different forums for all sorts of different cars and heard that redline wasnt the best, but i guess with all this input from actual z owners im going to go with redline which is great b/c i can get it at my work for cheap. thanks for the advice guys, ill post up when i put it back on the road in a couple weeks and let you know how it goes.

[mn300zx]

my '90 n/a trans made alot of noise and grinded in 4th. I used Redline 75-90 and it went away. you'll use damn near all of 3 qts. I have a friend who works at valvoline, he let me bring my car in, flushed it with valvolines synthetic and let me put the redline in. no more grinding or noise.

[Two6DK]

thanks for all the help guys. i used the mt90 and now it shifts great

[Ghut300zx]

someone explain this to me. i put gl-5 in my transmission is that bad?

GL-4 and GL-5 are standards set by the American Petroleum Institute for gear oils. GL-4 are intended for axles with spiral bevel and hypoid gears operating under moderate to severe conditions of speeds and loads. They are also suitable for sychronized manual transmissions when MT-1 gear oils are NOT recommended. GL-4 should be used in limited-slip differentials. The GL-4 generally indicates "Limited Slip" properties in the gear oil; sometimes abbreviated as LS.

GL-5 is indicated for high-speed/shock loads and low-speed/high-torque conditions. GL-5 also has multi-purpose or mild EP (extreme) properties too. GL-5 is often seen with the MT-1 designation too.

MT-1 indicates lubricants intended for NON-sychronized manual transmissions. MT-1 indicates the additional additives necessary to protect against thermal degradation, component wear and oil-seal deterioration which are not requirements by GL-4 or GL-5 approval.

GL-5 is not the latest and greatest improvement over GL-4; unlike oil classifications where higher classification numbers mean tougher standards and backward compatiblity. It is important to know what type of gears you are lubricating, their applications and follow the manufacturer's recommendations! More information can be found at http://www.api.org.