How do manufacturers choose manual trans oil weight?

[Fabulous50s]

I think the biggest difference is that for the last 40 years needle bearings are used on the main shaft, whereas bronze bushings were previously used.

Hollow shafts with holes in gears males for an oil pump of sorts and is how all older units (Mazda still) work. I cannot speak for newer Tremec or otherwise.

 

[MolaKule]

If you want to get into more technical details:

"...The American Gear Manufacturers Association standard 9005-D94 Industrial Gear Lubrication specifies that a gear’s pitch line velocity is one of the primary criteria for selecting gear lubrication.

Pitch line velocity also determines the contact time between gear teeth, which has a significant impact on the required oil viscosity.

High pitch line velocities are usually accompanied by light loads and short contact times, making low-viscosity oils suitable. However, low pitch line velocities are associated with high loads and long contact times, which make high-viscosity or even EP-rated oils necessary..."

Pitch line velocity in gearbox sizing - Issuu

In gearbox sizing, it’s key to determine the required input speed in rpm and ensure that it doesn’t exceed the gearbox maximum-speed capability. But the linear velocity of the gear teeth known as pitch line velocity also plays a significant role in gearbox performance.

issuu.com

Another factor one has to consider in manual transmission design is the thickness of the lubricant film between the slider fork and the gear assembly that it is forcing, but mainly the force required to overcome the lubricant's viscous drag force between the gear assembly and the shaft on which it is sliding.

The force required by the moment arm of the shifter has to overcome those various oppositional forces. So we have another design tradeoff here--shifter moment arm force verses lubricant viscosity.

 

[2000Trooper]

If you want to get into more technical details:

"...The American Gear Manufacturers Association standard 9005-D94 Industrial Gear Lubrication specifies that a gear’s pitch line velocity is one of the primary criteria for selecting gear lubrication.

Pitch line velocity also determines the contact time between gear teeth, which has a significant impact on the required oil viscosity.

High pitch line velocities are usually accompanied by light loads and short contact times, making low-viscosity oils suitable. However, low pitch line velocities are associated with high loads and long contact times, which make high-viscosity or even EP-rated oils necessary..."

Pitch line velocity in gearbox sizing - Issuu

In gearbox sizing, it’s key to determine the required input speed in rpm and ensure that it doesn’t exceed the gearbox maximum-speed capability. But the linear velocity of the gear teeth known as pitch line velocity also plays a significant role in gearbox performance.

issuu.com

Another factor one has to consider in manual transmission design is the thickness of the lubricant film between the slider fork and the gear assembly that it is forcing, but mainly the force required to overcome the lubricant's viscous drag force between the gear assembly and the shaft on which it is sliding.

The force required by the moment arm of the shifter has to overcome those various oppositional forces. So we have another design tradeoff here--shifter moment arm force verses lubricant viscosity.

Beautiful! Definitely checking this out! I’m all about factual information like this, and the engineering standards that go behind it.

 

[Mackelroy]

I replaced my chevy colorado manual tranny oil at 150,000 miles, the oil came out clean, but the stifter was getting sticky. I installed Motul motlygear 75w90.

nothing obvious in the first 50 miles, but it really improved the shift quality , cause it really was deteriorating yet stock fluid came out shockingly clean. I was getting to where i could not deal, with shift quality beforehand.