Gear Oil question

[I Leak Oil]

Right, but again, I don't know anyone who can say with any certainty or prove that their sychro went bad, sooner than it would have because of the oil they used.
Again, I'm not advocating one way or another but seems like the religious use of GL4 might be more of a feel good measure than a practical one. If it's readily available then by all means go for it. Dumping a quart of GL5 in isn't going to turn your truck into a pile of parts overnight though.

[TeriAnn]

Right, but again, I don't know anyone who can say with any certainty or prove that their sychro went bad, sooner than it would have because of the oil they used.
Again, I'm not advocating one way or another but seems like the religious use of GL4 might be more of a feel good measure than a practical one. If it's readily available then by all means go for it. Dumping a quart of GL5 in isn't going to turn your truck into a pile of parts overnight though.

Nope. nothing happens quickly. And we don't have any scientific evidence on Land Rovers that I am aware of, but a lot of research has been done on the reactive sulfurs found in most GL-5 oils that causes damage to brass parts. Which is why everyone recommends against using GL-5 in older gearboxes.

If ya want to put GL-5 in your gearbox go right ahead. It is your vehicle.

[I Leak Oil]

ASTM D130 is one test a manufacturer can (and assume most do) put their product through to test the corrosiveness of it on brass based (yellow metals) parts.

Not everyone recommends against using GL5. Many modern oils used additives to eliminate or minimize any ill affects of sulfers. Some more modern gear boxes use yellow metals in conjunction with GL5 spec oils. In fact, not all GL5's are recommended for gear boxes. The GL rating is only one factor in making your choice.

You're safer going with an oil that is listed as GL4/GL5 rather than an older, straight GL5 product.

Lot's of debate about it on other car forums. At work, we have 50 year old stamping presses that have very large bronze bearings. When these were built it called for GL4 (I suspect this is why many older cars called for it specifically), primarily because that's what they had back then. Now, we use GL4/GL5 with no ill affects. I guarantee you replacing one of these bearings is far more expensive and complicated than doing the synchros in a series gear box.

[jac04]

... but a lot of research has been done on the reactive sulfurs found in most GL-5 oils ...

As far as I know, almost all major gear lube manufacturers are using non-active sulfur now. As I stated previously, the issue is typically not the EP additives attacking the yellow metal, it is the Limited Slip additives that don't work well with the syncros. And, again, even if active sulfur is being used, yellow metal attack does not take place at normal operating temperatures (yellow metal attack would happen at around 240F and above).

I work on worm drive industrial gearboxes that use bronze worm gears and specify the use of EP gear oil, so I'm quite familiar with the issue of EP additives and yellow metal attack.

[I Leak Oil]

That's a good point about the temperature activation component Jeff. I suspect if your gear oil is running at that temp for long periods of time you might have more to worry about than just the synchros!