Rear Wheel (Axle) Bearings
| 01 February 2006
Front wheel bearings for first generation Mustangs were covered in the October 2005 issue of Pony Express. In this issue, we’ll look at the rear wheel bearings or should I say we’ll listen to them. A rear wheel bearing that’s quiet is probably ok but if you hear the typical rhythmic . . . brum . . . brum . . . brum . . .brum . . . of a failed bearing coming from the rear of the car, it could be a rear axle bearing. It could also be a differential bearing so spend some time trying to locate the exact location of the noise. If the axle bearing is noisy or if there’s any rear gear lube leaking down the rear-brake backing plate(s), it’s time to pull the axles and replace the bearings and the seals.
Rear wheel bearings aren’t very complicated but they do more than support the outboard ends of the axle shafts and allow the wheels to go around. They also keep the rear wheels from falling off the car. And because of the way they’re assembled to the axle, a hydraulic press is one of the tools needed to work on them. Even so, the driveway mechanic can do the R and R work when it comes time to replace them.
As a point of interest, I’ve heard it over and over for many years and maybe you have too: “Rear wheel bearings should rarely fail because they receive constant lubrication from the rear gear lube.” That’s not true. The bearings are lubricated for life and sealed. They reside outside the rear axle seal. Gear lube should never reach them.
Ok, let’s look at the way these things are built and for the sake of this column, we’ll assume you have rear drum brakes, not an upgrade such as a 9” Granada axle assembly with disk brakes. To get at the axles, remove the rear wheels, the brake drums, and the brake shoes. Remove the four nuts behind the axle flange. These are the nuts that hold the axle retainer plate and the brake backing plate to the axle housing. They’re accessible through the hole in the axle flange. Use a slide hammer attached to the wheel lugs to loosen the axle so you can remove it from the axle housing. With the axle out of the housing install one nut to secure the brake backing plate to the axle housing.
When you look at the axle assembly, you’ll see that it has a retainer plate behind the flange followed by a gasket, then the bearing, and a ring called the bearing retainer ring. The seal is in the end of the axle tube inside of the pocket where the bearing rides.
You’ve come this far so you’re probably going to replace the bearing and the seal. But if you’re curious about the condition of the bearing, stand the axle on the wheel lugs, and rotate the bearing by hand. If it was noisy when you were driving the car, you’ll probably feel some roughness as you turn it. It shouldn’t wobble but you may find that it does. Spin it to see if it quickly slows down when you let go of it; it should. If it doesn’t and it spins freely for a turn or more, it has used up the grease inside the sealed unit. Roughness, wobble, and free-wheeling are all signs of excessive wear.
Ok, here’s where the machine shop comes into the picture. The bearing and the retainer ring are not removable by hand. And new ones need to be pressed into place. The bearing and the retainer ring come as a kit. Make sure the machine shop will not try to reuse the old ring because it won’t fit tightly enough. The new one must be used to ensure the new bearing stays in place. Otherwise the axle could come right out of the car while you’re driving down the road. The machine shop will leave the bearing retainer plate between the axle flange and the outside wall of the new bearing.
You can replace the axle seal yourself. Pry the old one out or use a seal puller. Install a new seal and lubricate the sealing lip with a very light coating of oil. Also lightly lubricate the shiny area of the axle next to the bearing retainer. That’s where the seal rides after the axle is installed.
Put a new gasket over the axle so it will mount between the bearing retainer plate and the brake backing plate. Or if the original gasket isn’t torn, use it again. There’s a second gasket the same shape and size between the axle tube and the brake backing plate. There’s no need to replace it if it isn’t damaged. Don’t use any sealer on the gaskets. They’re there to keep dirt and brake dust out of the bearing, not to seal a liquid.
To put the axle back into the axle tube, you’ll have to balance it so that it doesn’t contact the seal while it’s being pushed into place. Contact with the seal can cut or abrade the lip of the seal where it rides on the axle. In turn, there could be a resulting immediate leak or a compromised seal that fails prematurely. The slide hammer that was used to remove the axle can be used as a counterbalance tool to make it easier to install the axle without touching the seal. Or a wooden balance lever can be fabricated. To fabricate the wooden tool, you’ll need a 24” length of 1”x6” or 1”x8” pine board. At center length, lay it against the wheel lugs, tap it with a hammer opposite each log, and then drill a 1/2” hole where the lugs marked the board. Put the board over the lugs and tap it with a hammer to mark the location of the hub. Use a scroll saw or hole saw to cut a circle that will fit over the hub. Push the wooden tool over the lugs and down to the surface of the axle flange. Fasten it in place with lug nuts turned upside down so that the flat surface contacts the board. Pick up the board with the axle attached to it, hold the board in a vertical position, and slowly slide the axle into the housing. If the axle won’t seat completely, turn it until the splined end slides into position inside the differential. Make sure the gasket and the retainer plate line up so they will seat correctly against the brake backing plate. Finally, install the retainer plate nuts and tighten them, install the brake shoes and drum, and then the wheel.
The new bearings and the new seals will last a long time and unless you drive a lot of miles or need to work on the differential, the axles may never need to be removed again.