Reactive vs non-reactive Sulfur?

[LM]

I don't know if all GL-4 specifically calls for non-reactive S? and/or that reactive S is needed for the higher EP in GL-5? (Or if reactive S hasn't been used in any gear lubes for years? is now outdated?)

But the crux of my question regards changing manual gearbox oil products, and the possible caveats.

There have been anecdoctal reports wrt gearbox failure, in less than 5K miles, after changing from gear lube with - it's not clear whether it's reactive or non-reactive - S (maybe it's just the former that has compatibility probs, if they indeed exist), to what have you: Redline MTL/MT-90 (GL-4 w/non-reactive S), dino engine oil (when specified), synth engine oil, etc.

Failures have been reported not only in the soft transmission metals, but also in the bearings. Could be the transmissions were on their way out, anyway

Is there a chemical and/or metallurgical reason that might cause failure when changing from reactive or non-reactive S to something else w/contrary S or no S content? I have vague memory of "etching", but can't recall the context or if it's a misnomer

Can any flush effectively/safely remove the reactive or non-reactive S, or does an "uptake" process, similar to AW/FM behavior, occur with or into the transmission metals?

I've read recommendations (on other forums) to buffer flush, between gear lube or oil product changes, w/a non-detergent SA-rated 20W or 30W air-compressor oil??

 

[68redlines73]

The correct terms are "active sulfur" and "inactive sulfur". The level of active sulfur affects how much the yellow metal (copper, brass, bronze) is attacked during operation. Active sulfur is corrosive to yellow metal. The terms generally come up when taking about metalworking fluids. The active sulfur in a gear oil is countered with a metal deactivator.

Think of a GL-4 oil as an oil that has half the amount of EP additives as a GL-5 oil. That difference in additives and related performance describes why one should not use one in place of the other for its intended application.

API GL-4 oils are for synchonized light and heavy duty transmissions where a ZF synchromesh test is key. API GL-5 oils do terrible in this test. Thus, the two are not interchangable. I'm not sure how bad things will be if you use a GL-5 oil in a true GL-4 application but I'll bet it's beyond a simple "flush".

There's good general detail here.

 

[LM]

Thanks for the correction & info, redlines.

I found some more info here

http://sbcc.ca/tech/lube1.htm

http://www.lube-tips.com/BackIssues/2002-04-03.htm
(not auto-specific)

Apparently both active & inactive sulfur are being used in GL-4 & GL-5 formulations, with a trend towards less active sulfur.

It seems inferred that most/all current formulations that use active sulfur, have had it 'deactivated'?

So is deactivated active sulfur the same as inactive sulfur? And will either post-drain damage the bearings, soft transmission metals, etc., such as when changing from a GL-4 to engine dino (or synth) oil??

 

[LM]

"such as when changing from a GL-4 to engine dino (or synth) oil??"

I meant to say 'such as when changing from a GL-4 "or GL-5" to engine dino (or synth) oil??'

 

[TheLoneRanger]

When changing the transmission oil in my Bronco a couple years ago, I had the same questions. After talking with a Coastal Lubes rep, I went with the GL-5 oil, both in the trans and diffs.

He said that Coastal along with "most"? mfgs are using buffers to deactivate the sulfur. I assume this is what redlines73 "metal deactivator" is referring to.

quote:

---

API GL-4 oils are for synchonized light and heavy duty transmissions where a ZF synchromesh test is key. API GL-5 oils do terrible in this test. Thus, the two are not interchangable

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Redline73, does this synchromesh test mean that there are shifting differences between the GL-4 and GL-5? I was under the impression that they were very similiar oils except for the AW/EP properties.

[ April 29, 2003, 11:38 AM: Message edited by: TheLoneRanger ]

 

[68redlines73]

Sorry for the delayed reply. I lost track of this thread. Here's a quick answer. Let me know if you need more info:

• If you need a gear oil for a manual transmission, using a GL-5 oil will mess with the synchros, and thus, the shifting efficiency. If GL-4 is called for, I suggest you use it.
• If you need an EP gear oil for a differential, using a GL-4 oil will give reduced gear life relative to a GL-5 oil (which is what is typically called for in this application).

Hope this helps.

[ May 08, 2003, 01:39 PM: Message edited by: 68redlines73 ]

 

[MolaKule]

We had a similar discussion in:

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=16;t=000054#000012

My experimentation and experience has shown that Redline Gear Oils for manual transmissions, such as MTL and MT-90 contain none of the Olefin Sulphide that is reactive to copper and copper alloys such as bronze and brass. These lubricants have the a GL-5 EP rating but have an equivalent GL-4 additive package.

Gear Lubes that contain Olefin Sulphide in levels of over 2.5% by weight have the propensity of discoloring and corroding brass parts.