Packard Forum Index » Pre-War (1899-1942)

Below is a cut and past from The Filling Station website:

Additives in modern gear oils will attack the bronze bushings in early differentials & transmissions. Caution! USING MODERN GEAR OILS CAN DAMAGE YOUR TRANSMISSION OR DIFFERENTIAL. Our 600W gear oil is specially formulated to be used in 1936 & earlier transmissions, differentials, shackles & steering boxes from the 1920's & mid 1930's.

The Filling Station, however if for antique Chev and GMC.

Jay Lenno can't say enough about Red Line MTL. But when mentioning MTL Lenno has not specified what era of automobile he uses it in.

I have a PDF of the original owners manual for my car and it simply states to use "600 weight oil or Whitmores compound.

I have found 3 sources for 600 weight oil. Here they are:(not sure if this forum will allow you to use these links though)

store.fillingstation.com/shop/?year=All& ... /cwmoss.com/products/gear-oil-600-w


mikes-afordable.com/product/A600W.html


cwmoss.com/products/gear-oil-600-w

ANY HELP WILL BE APPRECIATED IN HELPING ME FIND THE BEST OIL TO USE

Thanks, Greg Martin.
Ontaro, Canada

I suspect those are all fine. When i was first researching this question for my 443, I was told “go to the Model A forums and see what they’re suggesting for their 600W gear oil” which led me to this. I’ve had no issues.

macsautoparts.com/differential-oil-600w-quart-bottle-16-16020-1.html

[edit: after posting I realize that oil is no longer sold on that site - whoops. Still I imagine an equivalent is available.]

Generally, GL-5 gear oil should not be used in applications with brass components because its extreme pressure additives can cause corrosion or damage to soft metals like brass.

GL-4 vs. GL-5:

GL-4 gear oil is designed for transmissions with brass components, while GL-5 is formulated for heavy-duty applications with steel gears and differentials, where extreme pressure protection is needed.

Why GL-5 is problematic with brass:

GL-5 gear oil contains high levels of sulfur and phosphorus additives, which form a protective layer on steel gears under extreme pressure. However, this protective layer can also react with brass, leading to corrosion or damage.

Alternative for brass components:

If your application uses brass components, you should always use GL-4 gear oil or a gear oil specifically designed for use with soft metals.

Modern GL-5 oils:

Some modern GL-5 oils have "buffered" additive packages that are designed to be less corrosive to soft metals, but it's still best practice to use GL-4 if the application specifies it.

Examples of applications:

GL-4 is commonly used in manual transmissions, while GL-5 is used in differentials and other heavy-duty applications.

GL-4 gear oil is generally considered safe for use with brass and other "yellow" metals in gearboxes and transmissions, unlike GL-5 oils which can be corrosive to these metals due to their higher sulfur content.

GL-4 vs. GL-5:

GL-4 gear oils are formulated to be compatible with brass, bronze, and other "yellow" metals commonly used in synchronizers, bushings, and thrust washers. GL-5 oils, on the other hand, often contain higher levels of sulfur and phosphorus additives that can react with and damage these softer metals.

Why GL-4 is preferred:

GL-4 oils have a lower sulfur content, which makes them less likely to cause corrosion or damage to brass or bronze components.
As long as you're careful about where you're using a modern GL-4 or GL-5 gear oil, they can be used successfully in vintage transmissions and differentials.

When to use GL-4:

If your vehicle or machinery uses brass or bronze components in its transmission or gearbox, GL-4 gear oil is generally the recommended choice.

When to use GL-5:

GL-5 oils are typically used in applications where there are no brass or bronze components, or where the manufacturer specifically recommends their use.

Examples of GL-4 uses:

GL-4 oils are often used in manual transmissions, especially in older vehicles or those with manual transmissions that use brass synchronizers.

Red Line MT-90 is a popular GL-4 gear oil that is specifically designed for use with brass synchros and other soft metals