Oils & Additives

RANDYS stocks top quality gear oil from Red Line and Penzoil for standard differentials and Yukon Friction Modifier (posi additive) for your limited slip differential.

Third Member Installation Kits are also available containing 3 quarts of oil, housing nuts, dropout gasket and friction modifier (in LSD applications).

Scroll down to view all available oils, additives and kit packages, or read on for a full detailed guide to gear oils and additives.

Lubrication Maintenance

Lubrication maintenance is critical to axle longevity and gear oil wears out just like any other oil. A light car living an easy life could probably survive 100,000 miles without a gear oil change while a truck that tows, a motor home, or a 4×4 that gets into water may all need more frequent changes.

For trucks in moderate to severe conditions check the gear oil every 30,000 to 50,000 miles. Vehicles forced to carry or tow extreme loads may require an axle-oil change every 10,000-15,000 miles, or less.

Gear Oil Rating

Running lube is almost always SAE 90 gear oil, or a variant. In some cases, very rare among cars and trucks under 1.5 tons capacity, SAE 140 is used. The SAE stands for Society of Automotive Engineers, the agency which sets the standards for testing.

The number in the SAE grade is the viscosity index which refers to the pouring characteristics of the oil and is measured at a standard temperature of 212 degrees Fahrenheit. A lower number means that the oil is thinner and a higher number means that the oil is thicker.

Multigrade gear oil is designed for operation in areas with large variations in temperature. Multigrade oil will have two numbers separated by a W, with the number in front of the W referring to the SAE grade in cold temperature and the number after referring to the SAE grade in hot temperatures.

The advent of multigrade gears oils made summer and winter gear oil changes unnecessary. If you live and run your vehicle in an area where winter temps drop near or below 30 degree Fahrenheit with regularity, you should be running a multigrade gear oil.

Choose the Right Gear Oil for a Yukon Dura Grip

Oil Additives

Another important gear oil quality is its “Hypoid” or “Extreme Pressure” (EP) designation. Hypoid gear sets create more friction and, as a result, they need more additives.

The additives in EP-rated oil bond to the metal and prevent the two contact surfaces (the teeth of the ring and pinion gears) from seizing or galling, even after pressure of the hypoid gears has forced out most of the oil between them.

Many axles are of the hypoid design and require an EP or hypoid-rated oil. Most quality gear oil produced these days is EP rated and there is no reason to shop for non-EP rated oil for your axle.

Synthetic Oils

Synthetics oils are a modern alternative to petroleum-based gear lubricants. Synthetics are best known for their superior pour characteristics in cold weather, resistance to damage at high temperatures, and ability to reduce axle temperatures due to better friction reduction. Synthetic oil manufacturers claim their product can reduce differential oil temperatures between 10 and 70 degrees Fahrenheit.

A hard worked axle can generate temperatures of 250 degrees, plus. These temperatures reach or exceed standard petroleum-based oils’ thermal limits. A quality synthetic gear oil may stay stable well into the 300 degree range, but will cost two to three times more than petroleum-based oil.

Gear oil grades:

The API (American Petroleum Institute) is a petroleum trade association which rates gear oil according to gear type, load, and application. There are six classifications total, though three are uncommon or obsolete.


A current classification, this is light, low pressure oil is commonly used in manual transmissions. You don’t want to put this in an axle.


This classification has fallen into disuse, but was used for worm gear axles and manual transmissions.


Another uncommonly seen classification designed for manual transmissions in moderate to severe conditions, or spiral bevel axles in mild to moderate conditions.


This is a common and current classification, frequently used for light-duty gear oil, which is designed for spiral bevel axles in moderate to severe conditions or hypoid axles under moderate conditions. It can also be used in manual transmissions.


This classification is also common and can be used in all axles, even in severe conditions. This oil provides the best overall protection, so just buying GL-5 rated oil for all axles is recommended.


An older classification for an extreme-duty oil used in high-offset hypoid axles or in severe duty classifications. GL-5 has largely replaced it. Oil industry sources indicate that the GL-6 tests aren’t used any longer as the GL-5 classification largely covers the old GL-6 situations.

18 Parts Found
sort by