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Originally Posted by JackG
Redline MT-90 is a GL-4 rated 75W90 synthetic gear lube.
Royal Purple also has a Max-Gear synthetic that is GL-4/5 rated.
Both are claimed to not be corrosive to soft metals. Maybe these are possibilities?
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Hi,
They certainly could be. I have heard nothing but good things about the Royal Purple Line of products, and I use RedLine MT-90 in my Lotus Esprit.
The Lotus uses a Citroen SM Gearbox (modified), and it's really at the extreme of it's HP Rating in the Esprit. It uses Brass Synchros and so a GL-4 is called for. The Tranny shifts smoother and it is a must for any power-modded Esprit. In fact, Lotus introduced the Esprit SE because the Citroen Gearbox was no longer available and so they switched to a Renault Box which could take more HP, so Lotus redesigned the Head and aded a Chargecooler to up the HP to match the new Box.
If the Boxster uses hard metal synchros, there's no problem at all, but I've never been inside one and so cannot say for sure. But, GL-5 has been reported repeatedly to have attacked soft metal parts. GL-4 does not.
One other thing about the Synthetics is that they invariably make the Tranny noisier. This is because of their lower viscosity, and for some people, this may be a consideration.
I love synthetics, but not necessarily in every application. If the benefits cannot be utilized, it seems silly (to me at least) to pay a premium for the stuff. So long as the Oil level is kept at spec, a gearbox rarely fails because of the Oil it's using, except when Hypoid Lubes are used. Otherwise, most Lubes out there are really adequate. Gearboxes fail mostly because of consistent Operator Error...
Happy Motoring!... Jim'99
Happy Motoring!... Jim'99