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Old 02-14-2021, 11:14 PM   #1
Furno68C20
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GL-4 or GL-5 80w90?

Got a sm420 that needs an oil change. I heard that gl-5 80w90 has additives that don’t mesh well with older brass internals of the gears. Is this true?

Any recommendations on the correct oil.
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Old 02-14-2021, 11:33 PM   #2
truckster
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Re: GL-4 or GL-5 80w90?

From the website of a lubricant manufacturer:

The main difference between GL-4 and GL-5 gear oils is the amount of EP additives. Sulphur/Phosphorus containing products are used as EP-additive. This additive has the purpose to prevent the occurrence of micro-welds on the gear flanks at the local high temperatures which prevail in EP circumstances (temperatures well in excess of 800℃!) GL-5 has roughly twice the amount of EP additives compared to GL-4, which is why it is often used in high-pressure circumstances such as in a front axle and rear axle differential.

Sulphur/Phosphorus additives however have an unfavourable property: they can react aggressively towards bronze and copper. This can be disastrous for the synchromesh rings of a gearbox. Therefore it is not recommended to use GL-5 in a gearbox unless the manufacturer allows this.
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Old 02-15-2021, 01:09 AM   #3
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Re: GL-4 or GL-5 80w90?

The guy who did my 4 speed recommended "Driven" brand GL4 which you can buy at Summit.
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Old 02-15-2021, 11:20 AM   #4
Furno68C20
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Re: GL-4 or GL-5 80w90?

Quote:
Originally Posted by truckster View Post
From the website of a lubricant manufacturer:

The main difference between GL-4 and GL-5 gear oils is the amount of EP additives. Sulphur/Phosphorus containing products are used as EP-additive. This additive has the purpose to prevent the occurrence of micro-welds on the gear flanks at the local high temperatures which prevail in EP circumstances (temperatures well in excess of 800℃!) GL-5 has roughly twice the amount of EP additives compared to GL-4, which is why it is often used in high-pressure circumstances such as in a front axle and rear axle differential.

Sulphur/Phosphorus additives however have an unfavourable property: they can react aggressively towards bronze and copper. This can be disastrous for the synchromesh rings of a gearbox. Therefore it is not recommended to use GL-5 in a gearbox unless the manufacturer allows this.
Thank you. looks like gl-4 is the stuff
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