Advance Service Info - Rear Axle Fluid Level May Appear To Be Lower Than Published Specification

On full-size 2500 and 3500 Series Four Wheel Drive Chevrolet and GMC Pickups equipped with the 11.5" ring gear rear axle assembly, the factory lubricant fill level may appear to be lower than the published specification. This unit can be identified by the location of the fill plug on the rear axle housing cover, instead of on the front of the axle housing.

All axle assemblies are filled by volume of fluid during production. They are not filled to reach a certain level. On the 11.5" rear axle, the fill quantity is 3.0 Liters plus or minus 0.1 Liter (3.18 Quarts plus or minus 0.1 Quart). Testing has shown fluid level readings as low as 35 mm (1.4 in) below the bottom of the fill plug opening are acceptable, even with the correct amount of fluid in the axle, compared to the currently published specification of 17-21 mm (0.6-0.8 in) below the fill plug opening, even when the correct amount of fluid was installed in the axle assembly during production.

It is NOT necessary to add axle fluid to the axle when the fluid level is at or above 35 mm (1.4 in) below the bottom of the fill plug.

When checking the fluid level on any rear axle, variations in the readings may be caused by factory fill differences between the minimum and maximum fluid volume. Also, if a vehicle has just been driven before checking the fluid level, it may appear lower than normal because fluid has travelled out along the axle tubes and has not drained back to the sump area. Therefore, a reading taken five minutes after the vehicle has been driven will appear to have a lower fluid level than a vehicle that has been stationary for an hour or two. Remember that the rear axle assembly must be supported to get a true reading.

A procedure is being developed that will update the fill levels and amounts on all axle assemblies.

This bulletin will be revised once the service fill levels and fill amounts are established.