classic car

Do You Own a Classic Car?

Choosing both the right and best gear oil for your classic car is critical to protect the drivetrain and your investment. Classic cars are a source of enjoyment for millions of consumers. Maintaining them requires paying close attention to the required engine and drivetrain lubricants. Modern lubricants contain additives that could damage the softer bronze, brass, or copper metals inside your classic car drivetrain. As a result, choosing the proper oil is extremely important.

When it comes to gear oils, the American Petroleum Institute (API) classifies them via a range from API GL-1 to API GL-5. For example, the higher the number, the more modern the oil and, consequently, the number of additives that are in that oil. Therefore, you must know which rating you need when selecting the best gear oil for your application.

Then and Now

Over the years, gear oil anti-wear additives have evolved, going from lead to phosphorus, and then to active sulfur. However, it was discovered that the active sulfur caused corrosion of soft metals, such as brass, that are used in differentials and transmissions. They replaced active sulfur with a deactivated or buffered sulfur that was not corrosive to brass, copper, etc. Although this solved one issue, a different one emerged. They found that as the sacrificial coating became stronger on one or more surfaces of brass or other soft metals, rather than just peeling off, it took a few microns of brass with it.

A traditional GL-4 gear oil, regardless of viscosity, has about half the level of sulfur/phosphorus additive that you’ll find in GL-5 gear oil. As a result, the bond layer is not as strong. It peels off without taking a layer of brass with it. It should be noted that the use of a GL-5 product in a transmission requiring GL-4 will cause the synchronizers to wear. Eventually, they’ll no longer contact the other half of the cone. Consequently, they’ll end up bottoming out before stopping the opposing gear.

Difference Between GL5 and GL4 Gear Oil?

Another key point is that while GL-5 oils claim they meet API GL-4 requirements for gear oils, which is true, it doesn’t mean that GL-5 oils are satisfactory for synchromesh or synchronized transmissions. Why? While they do meet the gear oil specifications, they don’t meet the transmission oil specifications. Moreover, API GL-4 and GL-5 categories do not have anything to do with transmission synchronizers. Therefore, problems arise when you try to use the same product in the transmission that you use in the differential (regardless of what the oil company Tech Support reps tell you).

If a manufacturer tells you that their GL-5 product covers GL-4, they are correct as far as EP protection. However, that’s only part of the answer. Furthermore, a manufacturer that claims their sulfur/phosphorus additive will not corrode the yellow metals is technically correct. But if there is enough sulfur/phosphorous additive to meet GL-5 protection, it will slowly eat away your brass synchronizers.

So, what is the best gear oil for your classic car? Make sure you buy a GL-4 oil designed for the soft metal components found inside your classic car drivetrain. This includes both your gears and your brass synchronizer rings.

The Best Gear Oil for Your Classic Car

The experts at VP Racing Fuels have formulated the best GL-4 Classic Gear Oil line for classic cars. VP designs it for use with yellow metals. This includes synchronizers, thrust washers, and bushings. These and other components are typically found in classic manual transmissions and transaxles. Our Classic Gear Oil is great for use in traditional manual transmissions such as Rockwell, Muncie, Borg-Warner, Ford, and Saginaw. We also design it for use with import manual transmissions/transaxles that call for an API GL-4 gear oil.

Your classic car is an investment. You want to use only the best gear oil for it –  one that’s formulated for the soft metal components found in a classic car drivetrain. When in doubt, ask the experts at VP Racing Fuels.

If you have an application that calls for GL5, VP has a Hi-Performance line of premium GL5 gear oil

VP Classic Non-Synthetic Racing Oils

VP also develops a line of Classic Non-Synthetic Racing Motor Oils, which includes SAE 10W-30, 20W-50 oil, and SAE 30. They use only high-quality conventional base stocks. In fact, many engine builders prefer conventional oil because they feel it provides better film strength and wear protection compared to synthetic oils.  VP formulates its Classic Racing Oil with high levels of ZDDP (zinc/phosphorous) and multiple anti-wear chemistries. This not only provides extended engine durability but also protects highly sensitive flat tappet cams and roller cams.

VP uses a significant amount of a unique base oil cut, which clings to engine parts. This affords additional protection to the valve train area and other engine parts. Moreover, the unique base oil cut provides wettability to engine parts even when the engine is idle for long periods, which eliminates dry starts.


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