Honda Shadow Differential

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I've been scratching my head over this for a few months. Not that I really expect anyone to know--maybe the tribologists might.

If bevel gears need GL-4, and the 750 Honda Shadow has a bevel gear final drive, then why do they ask for hypoid gear oil which requires GL-5?

Not hard at all to buy GL-5. This is really just an oil nerd question.

 

[Kira]

Sulphur compounds, which are used in one or the other (GL-4 vs, GL-5), effect brass/bronze adversely.

Ergo, I'd conclude the hypoid gear oil the manufacturer recommends comports with the materials used in their products.

Brass & bronze are used for synchros and bushings.

 

[Overfill]

The sulfur compounds, sulfurized olefins, are typically blended to a higher concentration in GL-5, and yes, they affect copper alloys adversely. It is common that a buffer/corrosion inhibitor is included to passivate/protect copper alloy components.

To put it short, GL-5 gear oil is a riskier option from a material compatibility ie. "corrosion" standpoint (even though the risks are mitigated in common blends.)
The EP capabilities of GL-5 are greater than GL-4, and that is my suspicion for why they spec it for GL-5. Basically, its free risk reduction on Honda's part that they'd be leaving on the table if they otherwise spec'd just GL-4. Meaning, there's no objective need for GL-5. If this is wrong, then why?

 

[barryh]

I don't think it's anything to do with copper alloys. Motorcycles are usually a spiral bevel drive so not hypoid. I've asked myself the same question - why GL5 if it's not a hypoid drive. My BMW is the same, it's spiral bevel but GL5 is recommended. Given GL5 has more of the same additives as GL4, I suspect GL4 wouldn't do any harm but it's not so easy to source anyway. Given GL5 seems over specified I do exercise some judgement and run something a little thinner than the original spec.

 

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