Big Rig Basics

| January 01, 2011

Synthetic Service

Changing transmission and axle lubes at recommended intervals will guarantee long life and extend your warranty

By John Baxter


Transmission and axle lubricants don’t get dirty as fast as engine oil, but they are subject to heat and mechanical stress and have additives that eventually need to be replenished. They also gradually accumulate contaminants in the form of wear metals.

“We service our rear differentials and transmissions at 250,000-mile intervals and always use synthetic fluid, usually the same brand and grade that came new in the truck,” says small fleet owner Tom Meunier. “We do not service them ourselves but usually have them serviced at our dealer.”

We visited Ransome International in Swedesboro, N.J., to witness a transmission and axle lubricant change. We thank Brian Walsh, parts and service manager, and Paul Davis, technician first class, as well as Dan Arcy of Shell Lubricants for their assistance.


1. Park the vehicle on a hard, level surface and chock the wheels to make sure it will not roll. Place a container with a capacity of at least 30 quarts under the rearward rear axle.


2.  Put a wrench into the square hole in the drain plug and turn it counter-clockwise to loosen the plug. Once loose, the plug may be removed by hand.


3.  Carefully look at the drain plug, which is magnetic, to see what kinds of metal filings may have stuck to it. A thin, grainy film is okay, but large pieces of metal are a potential sign of trouble.



4.  Wipe the plug and the threads inside the drain hole with a clean rag. Carefully screw in the plug straight, being careful not to crossthread it. It may help to turn the plug backward first till the threads catch, then gently turn it clockwise until it seats. Install the wrench and turn until just snug.

5.  Wipe off the area around the filler plug, then remove it with a wrench. Feel around the hole with your fingers for any metal that may have accumulated, a great way to check for signs of internal trouble.



6.  Fill the differential with the recommended lube, in this case a fully synthetic 75W-90 EP (for “Extreme Pressure”) lubricant. With the serial number of the vehicle, your dealer can provide information about the correct lube and how much lube will be needed, 50-64 pints in this case. Check with your finger to make sure the liquid level is right at the bottom of the hole even when liquid is dripping out. Then reinstall and torque the filler plug. Inspect the drain plug for leaks now that the unit is full.

7.  Once the rear drive axle has been changed, repeat the entire process on the forward drive axle. This is identical except that it may hold a little more fluid because the inter-axle differential is mounted on top.

8.  Empty your drain pan and place it under the transmission, which is bolted to the rear of the engine. Find the drain plug on the transmission and remove it, ensuring you pull the plug at the lowest point so all the fluid will drain out.

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