Porsche Enthusiasts Club Forum

After reading the guide "TRANS-06 - Manual Transaxle Fluid Change" on Clark's Garage, I've decided to do the gearbox oil change myself. As the car hardly gets used in the winter, I can do it when I have some spare time.

In there guide, it states "The factory shop manual calls for hypoid transmission oil SAE 75 W 90 to API Class GL5", so I placed an order with Opie Oils for 3 bottles of Red Line Synthetic 75W90 High Performance Gear Oil, as that meets the spec, showing "SAE 75W90 API GL5+ Hypoid Gear Oil" on the bottle. However, even though the website recommends it for manual gearboxes (which mine is), the back of the bottle states "This product is not designed for use in most manual transmissions."

I've sent a PM to oilman, who has promptly replied and said "The Redline should be ideal for your gearbox is it is recommended API GL5. A lot of Japanese gearboxes prefer API GL4 and for these applications it can be a bit slippy."

I'm sure he's correct, but I'd like to throw it open to the forum for opinions.

Cheers,
Bryan

Isn't. ... 'a bit slippy' a good thing?

I've had problems with using additived (?) Oil in my bikes gearbox - wet clutch - but in a transmission surely less friction is better?


G

I think he means that GL5 is a bit slippy for applications designed to use GL4.

I'm just keen to know if what I've bought (GL5) is right for my S2.

Cheers,
Bryan

I have redline MT90 in mine which is GL4.

Traditionally, GL-5 oils had a higher level of additive for protection in high pressure applications such as differentials, the downside being that they can accelerate wear of the yellow metal components used in the synchros of a manual transmission. GL-4 reduces this wear, but offers less protection for a differential. Obviously, in a transaxle there has to be a compromise. Whether the latest GL-5 oils are suitable, only the manufacturers can tell you.

Well, oilman has said it's ok, it conforms to the spec on the workshop manual and nobody has said "DON'T DO IT", so I'll go ahead with what I've bought.

Hoping to get rid of the occasional stickiness when changing gear, plus there's nothing in the service book or receipts to say it's ever been done.

Cheers,
Bryan