Differential gear oil/ GL 5 pits yellow metals?

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Jun 4, 2002
I recently read that what ever is used in the new GL5 rated gear oils may pit or corrode the yellow metals in the gear box and differentials of older cars. Any truth to this? If so,would it be a moly doing it? I have been living in a cave! I recently saw a new GF6 spec gear oil?
I had the same question a while back, and called the gear oil mfgr that I use (which was "Coastal") They told me that it was true the GL5 USED to have the problem with the EP compounds, but in the last few years the formula had been changed to use less reactive compounds. So now the GL5 can be used in all the gear boxes. The gear oil I have says it meets the GL5/4 specs, so I am using it in all my gear boxes now. Just to clarify, I am using this GL5 in Manual transmission,Transfer case, Front and Rear diffs. [ July 21, 2002, 10:16 AM: Message edited by: ZR2RANDO ]
Its not necessarily older cars. I am not aware of any problems with the differentials. Not sure about the transfer cases. The problem is with the synchros of the transmission. Bottom line is that if the manufacturer doesn't recommend GL-5, don't use it. BTW Mobil 1 Gear Lube is GL-5. I put it in my son's Cavalier and a day later drained it out and replaced it with 2 qts (@$10 each) of GM SynchroLube, which is very good stuff BTW.
The older formulations were much harder on bonze and soft metals than the newer sulfur/phospourus formulations. I believe most US blenders are using newer formulations, but I know that many of the foreign blenders of the same brands are NOT. There is a lot of confusion on the GL ratings. Some cars say GL-4 because it is the minimum proteccion required. Many can easily take GL-5 or GL-6. But there are transmissions that cannot take the higher additive treatments. When an oil says GL-4/GL-5, it can be used in most GL-4 applications, but not all. I've seen Z-F transmissions dissasembled that have overheated and blackened the syncronizers from the Sulfur/Phosphorous not being able to let go and syncronize. Many people will tell you that GL-6 is obsolete. Technically that is correct, but that is because the equipment to test it on is not manufactured anymore. It was a differential with highly offset gears. Lubrizol.com has more on the different clasifications. A product can meet GL-5 standards with 40 lbs Timken. A GL-6 product will pass the timken test with at least 60 lbs. This can be done with Sulfur/Phosphorous or other extreme pressure additives. Read the spec sheets to see how much protection is offered if you do any towing, off-road, racing, or other abuse. Personally, I no longer use (although I sell for those who won't pay $1.00 more per gallon) Sulfur/Phosphorous products. I use only Group II products with Borate extreme pressure additives. Delo Gear Lube provides 75 lbs on the Timken test, does not discolor yellow metals, and can be used in GL-4 applications as well as LSD applications. I don't know what other brands have this additive. If you don't mind navigating in Spanish, I have some pictures and charts on this on my site under "Aplicaciones".
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