Shaft drive oil, API GL 4 and 5 - differences

[Redd]

I was looking into the oil types and specifications before changing the shaft drive oil in my GTR which calls for a GL-5 specification.

The information below has been taken from the following website...

www.rymax-lubricants.com/blog/the-differences-between-gl-4-and-gl-5/

When you are choosing a transmission or gear oil you might be wondering what GL-4 and GL-5 mean and what the differences are between these two classifications. Choosing the right classification is extremely important since they both have different properties and wrongful use could lead to serious damage to your vehicle.

There are four different classifications for transmission/gear oil. These different classifications define a certain level of performance in driven axles and manual gearboxes. They are mainly important for the transport sector in North America, Africa and Asia. The active classifications are:
• GL-1
• GL-4
• GL-5
• MT-1

The higher the Extreme Pressure (EP), the higher the GL category is. It is important to know that the SAE Motor Oil Viscosity Chart (J300) is different from the SAE Gear Oil Chart (J306). The viscosity has no relation with the API Gear Oil Classification and should be chosen based on the recommendations from the manufacturer based on the temperatures where you will drive.

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.

To conclude:
• GL-4 is suitable for hypoid gear service when they are under severe service but are without shock loading.
• GL-5 is suitable for hypoid gear service under severe service and shock loads and not for use in a gearbox.

[Redd]

I went for Castrol which is CL-5 rated, even though the Kawasaki manual states 80W90, 75W90 should provide better cold weather protection.

160ml per change so the litre bottle should last a while.

[Redd]

I guess copper drain plug washers should definitely not be used with CL-5

[virginiajim]

I used the Mobil 1 Synthetic Gear Lube LS product for 10 years without any issues.  Changed it at every oil change.

https://bestsyntheticoilguide.com/synthetic/best-gear-lubricant/

[Redd]

Regular oil changes are the key for sure. Interesting that the review stated that the Mobil product is not good for extreme pressure situations, which is exactly what you need in bevel gears of a motorcycle shaft drive, so do not believe everything you read.     

I am sure all major brand oil at the quoted specifications will be fine.

Quote on the mobil product...

Not for the most extreme-pressure applications