In my 1978 5-speed 280Z I recently changed the oil in my transmission to Mobil 1 75W-90 synthetic GL-5 gear oil. No sooner did I do this than I started reading that GL-5 rated oils will attack the copper/brass metal parts inside the transmission and that you must use "safe" GL-4 rated oils if your transmission contains "yellow" metals. This did not make me happy at all and drove me into an intense research mode. There is much, MUCH conflicting information on the internet concerning this topic. After hours of research I came across this engineering white paper, which is the most logical, scientific and rational information I could find. I wanted to share it with you.

The engineering study is all interesting, but if you want the facts on the corrosive natures of different oils on "yellow" metals scroll down to page 16. Bottom line is I will be keeping my GL-5 Mobil 1. 

http://www.oilteksolutions.com/GearLubeWhitePaper.pdf

 

 

Edited January 10, 20169 yr by Consigli

That's a good find and an interesting paper.  Unfortunately, and I hate bring out my inner cynic, it's somewhat typical of what a consulting firm will produce for a customer.  It seems to address an issue but doesn't really get there.  Lots of pages, but questions still unanswered.  Seems to support the products of the company that paid for the report.

Page 17 is the page we'd all look at for the "yellow metal" issue in manual transmissions, the synchros.  But they use a copper corrosion test.  Yellow metals would be alloys of copper, not pure copper.  Alloys have different properties than their components so the copper test doesn't really mean too much.  Also, a synchro undergoes high speed friction in use, so a simple chemical attack test would not be the best indicator of potential problems.

Still, worth reading.  Just add a grain of salt.

Here's an old paper, attached. I found that actually calls out the "yellow metal" problem.  Same issue though, it's written by the company selling the product.

Here's another interesting thing - the Royal Purple product that failed the copper test, Royal Purple Max-Gear 75W-90, is called out specifically in their ad copy as okay for GL-4 manual transmissions.  Hard to imagine that they would do that since it opens them up to all kinds of liability.  So, in the end, we're all still wondering.

http://www.royalpurpleconsumer.com/products/max-gear/

SWEPCO GL4 and 5 TG_199508.pdf

I added my SWEPCO file to the Downloads area.  You should add your OilTek file.  More info is always good.

I don't want to pile on.  But, Mobil seems to be avoiding the whole yellow metal issue entirely.  They've written their documentation in a vague way, that leaves the question unaddressed, directly.

Just saying, you're probably fine.  But Mobil is not going to say, one way or another.  Corporate baffle-speak.

http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil1_Syn_Gear_Lube_LS_75W-90.aspx

That White paper ( By Amsoil )  is a test of Gear Oils for Differentials. Not Transmissions. It's stated throughout the whole article. All Hypoid gear differentials require extreme pressures additives and that is GL-5 spec. It is those higher concentrations of additives ( mainly Sulfur and Phosphor ) that attack yellow metals. Specifically Brass and Bronze.

GL-4 is the recommended fluid for most manual Transmissions because you do not require the extra high pressure additives that Hypoid gears require. The Datsun FSM recommends GL-4 Fluid for the manual Transmission for a very good reason. Just as it recommends GL-5 for the differential.

The OP seems to be confusing the standard ASTM-130 Corrosive test of Copper strips as " proof " that GL-5 is safe for " Yellow Metals " in Transmissions.   That is a flawed conclusion and not what the test is designed to illustrate. ZH also mentioned this. Copper is not Brass or Bronze. Differentials rarely have any components made out of Brass, Bronze or even Copper. And certainly not the same alloys as Synchro rings.

GL-4 corrosion tests allow far LESS percentage of the " Yellow Metal " corrosive High Pressure additives and the Test standards are entirely different than GL-5.

Amsoil themselves recommend GL-4 Transmission Oil for our cars.

http://www.amsoil.com/mygarage/vehiclelookuppage.aspx?url2=1980+NISSAN/DATSUN+280ZX+K

http://www.amsoil.com/shop/by-product/transmission-fluid/manual/manual-transmission-and-transaxle-gear-lube-75w-90/?code=MTGQT-EA

Mobile 1 doesn't even make a GL-4 compatible transmission oil.

 

 

 

 

 

 

 

 

Edited January 11, 20169 yr by Chickenman

Direct from Mobile 1 Product Data. No mention of this being recommended as a manual transmission fluid. It is recommended as a Rear end differential oil only. No mention of it being " Yellow Metal " compatible.... and that is the important part.

 

Quote

Mobil 1™ Syn Gear Lube LS 75W-90

Supreme Performance Synthetic Multi-Purpose Automotive Gear Lubricant

Product Description

Mobil 1™ Syn Gear Lube LS is a supreme performance, synthetic, multi-purpose, SAE 75W-90 automotive gear lubricant designed to help meet the highest level performance requirements of modern passenger vehicles in all types of operating conditions including limited slip applications, as well as, deliver outstanding power transfer performance. Compared to conventional hypoid gear lubricants, Mobil 1 Syn Gear Lube LS 75W-90 performs exceptionally over a wide range of temperatures. Mobil 1 Syn Gear Lube LS 75W-90 achieves this through a unique proprietary formulation, that deliver optimized viscosity-temperature properties together with the highest level of inherent formulation stability and helps to protect against thermal and oxidative degradation, wear and corrosion, viscosity loss associated with premature shearing. It also can be used in extended service and for aiding in fuel economy performance.

 

Features and Potential Benefits

Mobil 1 Syn Gear Lube LS 75W-90 combines wax-free synthesized hydrocarbon base oils and a specially designed extreme-pressure, limited-slip, sulfur-phosphorous additive system to help provide a significantly higher level of performance in rear axles and differentials versus conventional fluids. Great film strength at higher operating temperatures, reduced fluid friction and low-temperature application down to -50ºC helps to provide significant advantages versus conventional mineral oil formulations. It helps to reduce wear and spalling under the high speed, high torque and high horsepower conditions in competitive racing and high performance automobiles. This unique, high technology final drive gear lubricant has demonstrated outstanding performance including fuel economy, extended drain, long-term friction retention, low-temperature capability and improved differential/axle durability and cleanliness. Key features and potential benefits include:

 

Edited January 11, 20169 yr by Chickenman

Further research from BobIsTheOilGuy.com. Answer from Mobile about using Mobil 1 Syn Gear Lube LS 75w-90 in manual transmissions with Yellow metals. Specifically Brass and Bronze synchros:

Quote

Question: Clarify Comments on Use of GL-5 vs. GL-4 Gear Oil Concerning the GL-5 gear oil, on your website you state the following: "Mobil 1 Synthetic Gear Lubricant LS 75W-90 can also be used in rear axles where API Service GL-4 lubricant is recommended." However, you also say in this "Ask Mobil" section that: "Mobil 1 Synthetic Gear Oil is recommended for all applications where a GL-5 lubricant is specified. GL-5 type lubricants, which have a higher level of additive chemistry, can be corrosive to yellow metals such as copper, brass, etc., and in these applications a GL-4 product is usually specified." Can you clarify this disconnect here? Thank you. -- John Goetz, Newport News, VA Answer: There are transmission applications that recommend API GL-4 type products where we would not recommend using an API GL-5 fluid because transmissions typically have components made from “yellow” metals. However real axles where GL-4 fluids are recommended do not have “yellow” metal components. As a result, the application of an API GL-5 fluid is acceptable.

Top

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=3062144

It is important to understand that GL-4 and GL-5 are pressure standards for gear oils. GL-5 is formulated to handle much higher pressures than GL-4. It is the high pressure additive packages ( Sulphor and Phosphates ) added to conventional ( Dino oil )  GL-5 oils and "most " Synthetic oils that damage " Yellow Metals " susch as Brass synchro rings.

You can make a gear oil that is both GL-4 and GL-5 compatible. The Swepco that ZH mentioned is one brand. Motul 300 75w-90 is another. It is also $29.95 a liter. These combination oils are typically used in Trans-axles that require both Yellow Metal compatibility and the High pressure shear strength for Hypoid differential gears. They can do this with using extremely high quality Ester Synthetic oils. Ester Synthetics are superior to normal synthetics, but they are not cheap. The important thing to note is that is a GL-5 oil that is made to be used in Manual Transmissions or Trans-axles with " Yellow Metal " components will categorically state that it is safe for " Yellow Metals". And they will be expensive.

http://motul.speclube.com/products/all-products/gear-300-75w90-1l/

Mobile 1 Syn Gear 75w-90 LS is a Hydrocarbon base oil... not Ester based. And it does NOT state that it is safe for " Yellow Metal" components. Seems pretty clear.

Edit:  Sorry for the Novel. Insomnia again... so i get " wordy "

Edited January 11, 20169 yr by Chickenman

Well.....Hells Bells! And just when I thought I had discovered clarity! I guess I'll be changing out the Mobil 1. Would this be good for the Z transmission?

http://www.redlineoil.com/product.aspx?pid=46&pcid=7

 

^ That's the stuff that I and a lot of others here use.

I used it until I picked up a very worn ZX 5 speed, then I went to a mysterious controversial blend (SWEPCO 201 w/ATF).  

MT-90 works great in good condition transmissions.  It even fixed a 3rd gear high RPM grinding problem in a 1978 5 speed, over plain old Valvoline 75W-90 gear oil.  I used my leftover MT-90 in my Pathfinder 5 speed.  Works great there too.

This has been covered before, but GM Synchromesh Friction Modified Transmission Fluid also works very well in Nissan transmissions with Brass synchros. There's a thread on here somewhere and lots of info on the Internet. Really great stuff from personal experience.

Both my Audi A4 and 1976 280Z with a 83 ZX 5 speed had crunchy second gear synchros. I'd tried various fluids in the Audi, including Redline MTL and Amsoil Synthetic Manual Transmission fluid. Nothing seemed to cure it. Then I heard about the GM Friction Modified fluid. Gave that a try in the Audi and with in a day it was shifting like butter. Same thing on the ZX 5 speed. Went from crunchy and hard to shift ( particularly when cold ) to literally a 1 finger shift.

Seems to work well with any brass synchro ring transmission and is certified as being Yellow Metal safe.