JET951

Red Line ( the oil company ) states in their literature , quite clearly } do not use MT - 90 if the transmission has a hypoid differential ( BIG NO NO for manual Porsche transmissions from last century that has a hypoid diff )and well thats all Porsches sold to the public as road cars last century & this one as well for that matter

Red Line ( the oil company ) states in their literature , quite clearly } not for use in most ( if not all ) rear wheel drive cars , I think thats because most cars sold to the public from the 1970's onwards that were rear wheel drive were of a standard Hypoid design in nature , so again a BIG NO NO

So it just goes to show how the internet is fantastic for the exchange of ideas , but ALSO the dumb *** factor in spreading dumb *** ideas , because of a basic lack of very SIMPLE research

We do not mind , because we make a living out of humans making poor choices with their last century Porsche's , in engine oils alone the destruction of last century Porsche engines on this century low viscosity "so called " synthetic engine oils is simply fantastic for us( like 5w-40 engine oils in our climate ambient temp range ) , I simply can not get over it , humans just amaze me

And because I am doing this for free , I am not going to go down the road of saying what brand to use , because this always turns to s**t on internet forums & besides each continent/ country has its own take ( formula ) on what constitutes their version of an oil ( be it engine or trans ) from the same company / corporation in the same / similar viscosity , so the only similarity what Porsche recommends , in the old days ( decades ago ) it was ( 944 only ) }

80W gear oil that was a MIL - L 2105 = Moderate Severity Hypoid Gears ( 944 , 4 & 5 speed with Borg Warner / patent synchro's )

Later ( actually Mid 1980's ) } 75W-90 GL5 gear oil = High Severity , Hypoid Gears

968 6 speed manual trans ( Borg Warner style / patent synchro's ) 75W-90 GL5

911 915 trans & G50 ( G50 same style of Borg Warner / patent synchro's ) 75W-90 GL5 & retro to all earlier ones

930 4 speed transmission ( 1975 - 1986 ) 75W - 90 GL5

930 5 speed trans G50 1987 - 1989 ( Borg Warner style / patent synchro's )75W-90 GL5

964 / 993( 911) with manual trans ( Borg Warner style / patent synchro's ) 75W-90 GL5

928S / GT/GTS 1985 - 1995 ( same style of Borg Warner/ patent synchro's ) 75w - 90 GL5 & retro to all earlier ones

Boxter / 996 Manual trans with ( same style of Borg Warner / Patent synchro's ) 75W-90 GL5

Note } all the above transmissions are transaxle

arthropraxis

http://www.redlineoil.com/product.aspx?pid=47&pcid=7 read the product details and it supports everything Jet951 stated in his posts. I ran several different gear oils in my transaxle trying to get my car to shift better, turned out do be a dragging clutch. The transaxle felt the best with Redline 75w-90 NS and I have a LSD transaxle.
I had my transaxle rebuilt by Kevin Gross, highly recommend his services, he said to use Mobil 1 75w-90. I have been running that for one and half years and seems to do well. The Redline product made the transaxle shifting easier.

944crazy

Thanks, yeah I had a read up on different oils and I think 'll go for the 75w-90 NS next time. It should be great for my gears, and will help the lsd lock up nicely too. Some people have complained that they get a bit of chatter with it, but that's no issue for me.

I regret not properly researching the gearbox oils before I put MT-90 in my last one. That'll teach me to just go by forum posts alone. It definitely always pays to double check recommendations by properly reading through manufacturer specs. I guess the other thing that confused me at the time was that my owner's manual calls for GL4...I did not know that modern GL5's are a better replacement for the old GL4's from when my 951 was built.

KevinGross

Porsche issued Technical Bulletin 8813 on 14 October 1988 stating "Transmission oil labeled API service classification GL 5 or MIL-L 2105 B must be used on all Porsche models. Oil classifications such as GL 6 and GL 7 may cause synchronizer failure and are not recommended."

Thank you Sean and Bruce for your caution on MT-90. I've made the same point, but it's hard not to get drowned out by all the Internet experts who haven't bothered to read the maker's application guidance (LPT: it's on their web site). The hypoid pinion design that allows offset of the pinion and ring gear axes put tremendous sliding stress on the pinion teeth, and appropriate lubrication is critical to longevity of the parts (put plainly: so **** don't break).

Dimi 944

Kevin is correct. I have the Porsche Service Information Technik books for all 944 family models since '88 and all state that the transmission oil service classification is changed to GL 5.

odonnell

I remember posting the same link as above, Re: MT-90 isn't spec'd for hypoid diffs, and someone posted that Redline themselves had come back and said that MT-90 was actually fine for our transaxles (something to do with the hypoind angle not being as severe). I don't have the link, it's been a year or two, but is that legit? I'm also skeptical of MT-90 purely because of the hypoid diff issue. For the record I run Mobil Delvac 75W-90 with no issues, it has no friction modifiers and is compatible with both the synchros and the diff.

JET951

Thanks for posting the Technical Bulletin 8813 ( Oct 1988 ) Kevin , clears up the memory of what I thought I read decades ago

Regards
Bruce Buchanan
Buchanan Automotive

GlenL

Go to the store and get two quarts of Mobil1 75w90 gear lube. Three quart if you've got an oil cooler. You'll be done changing the oil long before people agree on what's "best."

KevinGross

Good one, Glen! Cheers.