Valvoline High Performance 80W90 in manual trans?

[ascdesigns]

Hi -

I couldn't see anything specific to this by searching so I thought I'd ask.

I'm about due for a manual trans fluid change, I'd just not like to break the bank doing so. I'm not a hardcore 'wheeler nor a 0-60 racer. Valvoline lists their High Performance 80W90 as both GL-4 and GL-5 specific. It's possible with the friction modifiers associated with GL-5 that the shifting may be a little "notchier" since blocker rings may not engage as quickly but my question is whether anyone's been running this in their manual trans for a significant time without issues, i.e. your direct experiences.

I do know our transmission's call for GL-4 but according to Valvoline their composition includes "buffered" EP additives so it shouldn't be corrosive to the yellow metals in our trans. I'm sure I'll get the "just buy XYZ brand, it's the best" but please understand that's not my question.

Thanks!

[Towncivilian]

No, use GL-4 only. GL-5 gear oils contain additives that can be harmful to yellow metals (brass synchros). When a fluid states that it is GL-4 and GL-5 suitable, it is likely referring to use in a differential, not in a manual transmission. While GL-4 fluids can sometimes be difficult to obtain, I would not chance significant transmission damage, especially when the lubricant in question is changed out at relatively lengthy intervals, in order to save a few dollars by using an easily-obtained GL-5 rated lubricant. Redline MT-90 and Amsoil MTG are excellent options suitable for use in our manual transmissions.