What is gl classification for old agricultural gearboxes?

Firstly, let's answer – What does GL classification mean?

A general liability class codes are groups of numbers that insurance companies use to classify businesses of risk, to aid them in assigning the appropriate rate, coverages, and exclusions for GL insurance.

Secondly, why is it to be considered for agricultural gearboxes and old ones?

It is basically for the oil you would choose for your agricultural gearboxes or or PTO drive or agricultural PTO shaft.

A GL-4 & GL-5 are two classifications for transport and agricultural gearboxes.

Choosing the right classification is extremely important since they have different properties & the wrong usage would result in severe damage to your vehicle.

Let's try and understand all the different classifications. There are four main classifications for transmission/gear oil.

They are allocated based on the performance of the driven axles and manual gearboxes. And mainly for the transport & agriculture sectors 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 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 number 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 over 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.

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