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Yellow BReeZe · 02-18-2020, 12:36 AM

When it comes down to it, we all will have different opinions as to which oils to use in our cars.

I've been going over posts and articles about transmission fluids for the past few weeks and am trying to get to a fact based solution to our 2nd-gear-crunch in cold weather issue. As of yet, and I am surprised that there hasn't been something done gear wise, there hasn't been a mechanical "FIX" to the 2nd gear crunch, like in the 2002-03 WRX "glass transmission." And not having the mechanical expertise to follow a gear swap myself, fluids are the priority, especially since the problem diminishes once the fluids heat up in the transmission.

Starting with some factual information:

The findings in the Rymax Lubricants website, which are reflected in many of the articles pertaining to GL-4 and GL-5:

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.

The Subaru BRZ transmission contains both copper and bronze synchronizer rings. So it is completely up to you to use a gear oil (GL-5 rated) that can damage these rings over time (leading to costly repairs). Which could also be part of the reason we have this issue to begin with (My local Subaru dealership put GL-5 in my transmission last week and made my issues worse).

If you are using a GL-5 product in your transmission and are having great results in eliminating the 2nd gear "crunch" in colder weather (seems anything sub 50°F), Awesome! Please let us know and do not spare the details.

But the fact that all your lubricant manufacturers warn that GL-5 oils should not be used in transmissions like ours, should weigh on your decision on what should be put in your transmission.

Sadly, doing a search of the 2nd gear "crunch" shows that this problem has been around since the 1st gen BRZ/FRS. So this tells me that there isn't a real solution to the 2nd gear "crunch" and we are just looking for a fluid solution that most alleviates this issue.

Again, I am no mechanic, so I don't know if there is a mechanical solution worth pursuing, like the gear swap on the 2002-03 WRX 5 speed manual "glass" transmission. The only reason I know about this, I had 2 '02 WRXs and was close to taking the 2nd one up to a place in Northern Virginia that would swap out the "bad gears with some German gears.

I guess when I get up tomorrow and find out if the recent transmission oil change has helped or not, will lead to me searching out the gear swap route. Or perhaps wait and see what's coming in a 2021 BRZ.

Thank you to everyone who has added pertinent info to this topic!

02-18-2020, 12:36 AM	#34
Yellow BReeZe Member Join Date: Feb 2020 Drives: '17 Charlesite Yellow BRZ Location: Virginia Posts: 16 Thanks: 6 Thanked 4 Times in 3 Posts Mentioned: 0 Post(s)	GL-4 vs GL-5 Rated Fluids When it comes down to it, we all will have different opinions as to which oils to use in our cars. I've been going over posts and articles about transmission fluids for the past few weeks and am trying to get to a fact based solution to our 2nd-gear-crunch in cold weather issue. As of yet, and I am surprised that there hasn't been something done gear wise, there hasn't been a mechanical "FIX" to the 2nd gear crunch, like in the 2002-03 WRX "glass transmission." And not having the mechanical expertise to follow a gear swap myself, fluids are the priority, especially since the problem diminishes once the fluids heat up in the transmission. Starting with some factual information: The findings in the Rymax Lubricants website, which are reflected in many of the articles pertaining to GL-4 and GL-5: 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. The Subaru BRZ transmission contains both copper and bronze synchronizer rings. So it is completely up to you to use a gear oil (GL-5 rated) that can damage these rings over time (leading to costly repairs). Which could also be part of the reason we have this issue to begin with (My local Subaru dealership put GL-5 in my transmission last week and made my issues worse). If you are using a GL-5 product in your transmission and are having great results in eliminating the 2nd gear "crunch" in colder weather (seems anything sub 50°F), Awesome! Please let us know and do not spare the details. But the fact that all your lubricant manufacturers warn that GL-5 oils should not be used in transmissions like ours, should weigh on your decision on what should be put in your transmission. Sadly, doing a search of the 2nd gear "crunch" shows that this problem has been around since the 1st gen BRZ/FRS. So this tells me that there isn't a real solution to the 2nd gear "crunch" and we are just looking for a fluid solution that most alleviates this issue. Again, I am no mechanic, so I don't know if there is a mechanical solution worth pursuing, like the gear swap on the 2002-03 WRX 5 speed manual "glass" transmission. The only reason I know about this, I had 2 '02 WRXs and was close to taking the 2nd one up to a place in Northern Virginia that would swap out the "bad gears with some German gears. I guess when I get up tomorrow and find out if the recent transmission oil change has helped or not, will lead to me searching out the gear swap route. Or perhaps wait and see what's coming in a 2021 BRZ. Thank you to everyone who has added pertinent info to this topic!