Taymar

I know the subject of the correct or the best oil has been done to death, bear with me on this. I've read many threads and have a good idea of the most popular fluids to be using.

With that said, I'm interested in the reasons behind conflicting information in the Porsche documentation.

The owner's manual for my car (1989 turbo) says "Hypoid oil SAE 80 labeled "For Service API/GL 4 or MiL-2105"

The factory workshop manual, transmission section (printed 1991) says "Hypoid transmission oil SAE 75W 90 to API Class GL or MIL-L 2105 B, or SAE 80 to API Class GL 4 or MIL-L 2015" note that they omitted the GL number, either intentionally or by accident.

The factory workshop manual, turbo supplement (printed 1991) says Hypoid transmission oil SAE 75W 90 to API Class GL 5 or MIL-L-2105 B or SAE 80 to API Class GL 4 or MIL-L-2105"

Curiously there is no mention of limited slip additives or compatible fluids (total guess on my part but I wonder if 25 years ago fluids weren't marketed as such?). I also assume that as time went on and oil chemistry changed, the recommendations may have changed with it.

I know there are a lot of knowledgeable people here who have been around these cars a long time. If anyone can shed some light on any of this I'd be interested to learn.

odonnell

Our mechanical LSDs don't need special additives... the viscous LSDs do. Someone correct me if I'm wrong.

GL-5 used to be a problem for setups with yellow metals (i.e. we have brass synchros in there) but modern GL-5 compliant oils are perfectly fine. I know that doesn't really answer much, but hopefully it helps someone.

mel_t_vin

I wouldn't issue such a general statement. I think it depends on the manufacturer, the oil's base stock, and the particular additive package, if any.

Can't confirm or deny the fact that all GL-5 oils work [well] in our gearbox. Aren't some GL-5 oils silicone based?

In the 911 world, conventional Swepco 201 has been the gold standard lubricant in 915 and 930 gearboxes for decades. Things changed when Porsche moved to the Getrag-derived G50 gearbox utilizing Borg Warner double-cone syncros, as those G50.XX variants [87+ 911/964, 89+ 930/965], especially the ones with an LSD, performed much better with synthetic gear oil.

Even synthetics, without friction modifiers, have posed problems for G50.XX owners. Excessive noise, mechanical chatter, and wheel hop while turning, have all been symptoms of using a gear oil without adequate "slip" properties.

Isn't the 944 box a Getrag-derived G16 variant? And the 968 a G64 variant? As such, I suspect most here with an LSD-equipped gearbox are running a synthetic fluid with some sort of LS package.

I'm running Mobil 1 LS in my LSD. What are others running in their open/LS differentials? Has anyone had problems [noise, chatter, wheel hop] with any particular fluid?

V2Rocket

I use off-the-shelf Lucas heavy-duty diff oil, something like 85W90, has worked great for many years now.

Am considering a fluid change, any suggestions on stuff to quiet the trans down? Trans is 86 turbo, open diff, with cooler.

Taymar

Do you mind if I break this down a bit for the benefit of my own understanding?

This would explain quite a bit. When these cars were new, assuming they had a non-LSD fluid specced even for LSD cars, I wonder if there were reports of LSD chatter/issues?


Please could you explain this conclusion to me? Not refuting it in the slightest - I'm not familiar with the different transmission model numbers. I'm not 100% clear on whether what applies to the G50 in terms of fluid performance/safety also applies to the 944/968 boxes.

This is a GL-5 fluid, correct?

Van

I really don't know much about tranny fluids... but if your tranny is loud, are you sure the Lucas fluid has been "working great for many years"?

V2Rocket

its not loud, but it could be quieter...

Voith

This.

V2Rocket

think there's any aviation-spec oil that would work? i can get my hands on just about anything of that variety.

Voith

Liqui moly is in a league of its own. Try it.

mel_t_vin

Regarding the G64 moniker, I believe I was incorrect there...the 968 box is actually a G44 variant.

Regardless, based on my limited knowledge of the G50.XX variants, and speaking with folks [more experienced than I] that operate those Getrag-derived boxes in high-stress, high-performance, and high-endurance environments, all fingers pointed to a synthetic gear oil [with an LS additive] for the Getrag-derived, M220-equipped, box in my 944. As this "formula" worked well for the G50.XX boxes utilizing BW syncros, that is what I [eventually] went with. My understanding is/has been that the BW syncros work/perform better with a synthetic gear oil.

Sidebar: I have no idea what was in my gearbox, or how long it was there, when I adopted Heidi in 1999. I started developing shifting problems over the course of 2 or 3 years [primarily 1-2, 3-2, and 2-1], the box starting making more clatter/racket, and I began noticing driveline vibrations [all probably due to dirty fluid]. I tried Redline synthetic [non-LS] on a recommendation but it did not significantly improve clatter or vibration. In Redline's defense, I never tried their LS-formulated gear oil. After running the Redline for a year, I tried Swepco, again based on a recommendation, which resulted in some notchy up/down-shifting [especially when cold] but less clatter and less vibration [all possibly due to more viscous conventional oil?]. After running the Swepco a couple years, I went with Mobil 1 LS and feel, to date, it has provided the best shifting experience with moderate gear clatter and little, to no, driveline vibration.

Environment: All of these fluids were tested in a stock, refreshed, box [pinion bearing, mainshaft bearing, carrier bearings, syncro rings] with a re-shimmed LSD and external cooler.

YMMV...

Yes, I believe Mobil 1 LS meets/exceeds specifications for GL-5.

Taymar

Thank you, this helps fill in some gaps in my understanding nicely.

mel_t_vin

One thing to remember is that not all synthetics are created equal.

Take for example Mobil 1, they have a synthetic LS formulation [with an additive package] specifically designed for LSD applications. The additive package allows the differential to work as intended and "slip" when the outside wheel has to travel further than the inside wheel while negotiating a corner.

Mobil 1 also has a synthetic non-LS formulation, Delvac, which has not performed well in LSD applications, as would be expected. Folks that have put this gear oil in LSD-equipped G50/XX variants developed excessive chatter from the LSD, to the point of locking up in turns/corners, resulting in unusual/unwanted driveline vibrations.

Whereas this combination [non-LS in LSD] is bad, I suspect putting an LS-formulated oil in a non-LSD gearbox would cause little, to no, discernable side effects. If anyone has had other experiences, please feel free to share.

Van

This is anecdotal, but I've been running the Mobil 1 Delvac for many years in 4 cars. 2 with LSD and 2 without; 3 of them track cars. I have not had an LSD problem... On my street car (996 with open diff) the Delvac greatly improved the shifting, especially while cold.

Delvac was recommended to me as the best "compromise" fluid (since our transaxles are both transmissions and differentials, which, ideally, require different fluids with different properties) by Lufteknic Porsche.

However, lots of people are running other high-quality fluids with good success, too.

V2Rocket

Is there a particular blend/weight you use, or is it just one product?