der Mond

What if someone wanted to try a little Mobil1 75W-140 in the trans to tweak synchro performance? Have you heard of GL-5 lubricants having extreme pressure additives that attack brass, bronze and copper? Is it an issue?

Peter Zimmermann

Dennis: I don't think that's a legit thing to try, and I'm told that the additives can harm the mentioned metals (although I'm certainly not qualified to know why). Synthetic 75W/140 is a product that truckers use in their differentials, but not the transmissions. For truck trans oil a synthetic 50W is the typical choice (again this is info from a trusted source). I know that Porsche has never recommended anything other than 75W/90 GL-5. I don't think that it's a good idea to use the 140, I know that some manufacturers say it's OK, but Porsche does not. I wish that I could remember clearly the conversations that I've had with P-car reps and oil suppliers, but I do remember that no one that I've talked with about 75W/140 has thought it to be something good in a P-car. Cheers!

der Mond

Pete: I did some searching on the Mobil1 site and found this: http://www.mobiloil.com/USA-English/...hronizers.aspx. So, the word from Mobil is that any GL-5 lube, which includes 75W-90 as well as 75W-140, can damage synchronizers. That seems to indicate that what I have heard many owners recommend here and on Pelican, which is the use of Mobil1 75W-90, is actually bad advice. I think I will ask Redline about this as well. I wonder how long it takes for the sulphur additives to cause noticeable harm to a G50? Years ago I had a Suburu that had a gear-grinding problem, and using 75W-140 Mobil1 in that tranny made it shift 'just right" for 100K miles, when I traded it in. That's why I was asking. By the way, that web page has an archive list on the left side that covers just about any question you could ever think of regarding lubricants.

dvkk

GL-5 attacking brass transmission parts is a myth. All GL-5 gear oils you can find today, also have a MT-1 rating. This makes it harmless to brass parts.

Nobody has ever seen any damage due to GL-5 gear oil.

der Mond

dvkk,
I'm just trying to learn, so plaese enlighten me about the MT-1 rating and what it means; I'm not stupid, just naive...how and why does that fly in the face of what Mobil says? I'm glad to hear it, and it fits with my prior experience...I want to make the most intelligent choice I can.
Dennis

Steve Weiner-Rennsport Systems

Hi,

For the life of me, I have no idea where these things start but after 33+ years at this, I've never seen ANY GL-5 lubricant affect any brass part in a Porsche transmission or even some VW FWD ones.

This includes several top-notch synthetics as well as dino oils and Mobil 1 is included on that list,....

JMHO so YMMV.

Peter Zimmermann

I agree. After I read Dennis' original post I called an oil distributor in Long Beach, CA. I spoke with a guy there who I've known for close to 30 years, and he told me about a concern, in the trucking industry (as I posted above), about using 75W/140 in transmissions, because of additive wear. My first post was based partially on that info. Regarding GL-5 75W/90, I've never seen any damage of any kind to internal trans parts, no matter what kind of metal a part was made from. Personally, I've never used/recommended 75W/140 oil in P-cars, I've always preferred to stick with Porsche's recommendations, so without personal experience regarding unusual wear I can't offer any first-hand info. I like Kendall Super Three-Star synthetic 75W/90 in G 50s, and Kendall Three-Star dino 80W/90 in 901/911/915 applications. Stick to what the factory wants in there, sometimes the wheel doesn't need to be re-invented.

dvkk

This whole fear of GL-5 is a big fat myth. Why would the oil companies create a product that would eat your trans? I posed this question to the Amsoil tech guy a few years ago, and here's his response:

"A GL-4 or, to a greater extent GL-5, lubricants can, if not properly formulated, become corrosive to yellow metals if the lubricant temperature exceeds 250 degrees F. The API recently came out with a new specification to address this possibility. It's called MT-1. You'll find that AMSOIL gear lubes all meet this new spec. therefore do not attack yellow metals. Two things work in your favor if AMSOIL Synthetic gear lube is used. 1. AMSOIL will run cooler, reducing the possible high temperature situation. 2. AMSOIL gear lubes meet MT-1, therefore will not attack yellow metal even if the temperature does climb to this extremely high 250 degree mark."

This myth is rampant in the VW world, partly I think, because the manuals written 35 years ago specified GL-4 when GL-5 didn't exist.

der Mond

I sure want to go with Steve, but as I've said before, it's heck to be an OCD half-German. I seached the API site for MT-1 and the only thing that came up was their "Lubricant Service Designations for
Automotive Manual Transmissions, Manual Transaxles, and Axles", Seventh Edition, 1995. I quote:
3.4 API MT-1
The designation API MT-1 denotes lubricants intended for
nonsynchronized manual transmissions used in buses and
heavy-duty trucks. Lubricants meeting the requirements of
API MT-1 service provide protection against the combination
of thermal degradation, component wear, and oil-seal
deterioration, which is not provided by lubricants in current
use meeting only the requirements of API GL-1, 4, or 5.
API MT-1 does not address the performance requirements
of synchronized transmissions and transaxles in passenger
cars and heavy-duty applications.
API MT-1 lubricants should not be mixed with engine oils
in the same transmission unit.
Transmission manufacturersÕ specific lubricant quality
recommendations should be followed.

dvkk, do you have something newer from API?

der Mond

Further from API 1995:

3.2 API GL-4
The designation API GL-4 denotes lubricants intended for
axles with spiral bevel gears operating under moderate to severe
conditions of speed and load or axles with hypoid (see
note) gears operating under moderate speeds and loads.
These oils may be used in selected manual transmission and
transaxle applications where MT-1 lubricants are unsuitable.
The manufacturerÕs specific lubricant quality recommendations
should be followed.
Although this service designation is still used commercially
to describe lubricants, some test equipment used for
performance verification is no longer available. Procedures
to define this performance are currently being reviewed for
adoption by ASTM.
Note: Frictional requirements for axles equipped with limited-slip differentials
are normally defined by the axle manufacturer.

3.3 API GL-5
The designation API GL-5 denotes lubricants intended for
gears, particularly hypoid (see note) gears, in axles operating
under various combinations of high-speed/shock load and
low-speed/high-torque conditions. Lubricants qualified under
U.S. Military Specification MIL-L-2105D (formerly
MIL-L-2105C) satisfy the requirements of the API GL-5 service
designation, although the API designation does not require
military approval. Performance test details are in
ASTM Publication STP-512A.
Note: Frictional requirements for axles equipped with limited-slip differentials
are normally defined by the axle manufacturer.

dshepp806

No 75W-140 in my G50r!!! Anybody here run this in their G50? Betcha' there's not many (if any)....
I, too, will stick with Porsche's recc's on this...

dvkk

The contact pressures are greater with hypoid gears, so GL-5 has a better extreme pressure rating than GL-4. Given the severe wear that occurs within the gearbox, I'll use GL-5 every time.