Rear Wheel Bearings
By Ron Bramlett

(From our February 2000 Newsletter)

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      In the last issue of the Mustangs Plus Newsletter, we went over front wheel bearings. In this issue, we're going to finish up with rear wheel bearings. Then, in our next issue, we're going to take a look at rear end assemblies. We'll show you how to tell an 8" from a 9", a posi from an open, and how to check gear ratios. We'll even get into rear disc brakes vs. rear drum brakes and help you decide which is better for you. Now, on to Rear Wheel Bearings.

       Rear wheel bearings are not nearly as complicated as front wheel bearings and we tend to not think much about them. But there are a few things worth going over because the rear wheel bearings do more than just allow the tire and wheel to go around and around. They also keep the rear tires and wheels on the car!

    On our classic ‘65 to ‘73 Mustangs, the front wheel bearings do not hold the tire and wheel on the car. That job is done by the nut and cotter pin on the end of the spindle. Not true on the other end of the car!

     A rear wheel bearing failure can result in much more loss than just the cost of a bearing. The rear wheel bearings and their retainers are the only things which hold the rear tires and wheels on the car. If a rear wheel bearing comes loose or if the bearing comes apart, the axle can slide right out of the rear end with the brake drum, tire and wheel attached to it!  This can be quite dangerous as well as expensive.  So we need to make sure our rear wheel bearings are always in good shape and up to the job.


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New rear wheel bearings with their respective retainers.   Our Classic Mustangs all came from the factory with the smaller diameter rear wheel bearings as shown on the left.  However, due to rear end swaps, it's possible to find them now equipped with the larger style as shown on the right


   Our Mustang's rear wheel bearings are what's called a "sealed bearing". Sealed bearings are used in many places on our Mustangs besides the rear wheel bearings. Bearings for accessories such as alternators, air conditioning pulleys, and heater motors are good examples of sealed bearings. What this means is that the bearing and the grease the bearing needs to keep it lubricated during use are all sealed together as a unit. You never have to service it. If, for some reason, it loses its lubrication, you simply replace it.
    This brings up an interesting point. Many people are under the wrong concept about how the rear wheel bearings are lubricated. They assume that the gear oil from the rear end also lubricates the rear wheel bearings.

     This is not true. The axle housing has a grease seal in each axle tube. The axle itself has a machined journal for this seal to ride on. The purpose of this seal is to keep the gear oil from getting into the area where the rear wheel bearing rides. But many people are confused because Ford uses rear axle flange gaskets for the axle retainers.

     The axle retainers are the flat plates with the four holes in them that bolt to the axle housing and hold the rear wheel bearings in place. In fact, Ford has two of these gaskets per side. One for the rear brake backing plate and another for the axle retainer. The backing plate is sandwiched between the rear axle housing and the axle retainer and has these gaskets on both sides. These gaskets are designed to keep the brake dust out of the bearing, not to keep gear oil in. But I've seen people change them, even use silicone on them, to stop gear oil from leaking onto their rear brakes. Of course what they actually need to change is the axle seal.

     If you look closely at the bearing retainer plates, you'll see that most of them provide a vent to the outside for the bearing. This means that even if you silicone all around the gaskets, if the axle seal is leaking, you will still have gear oil getting on the rear brakes! So remember. These gaskets are for keeping something out, not keeping something in. Can you reuse these gaskets if you want? You bet!

    Now, on to the rear wheel bearing itself. When you buy a new rear wheel bearing, it has two parts. The actual rear wheel bearing and a ring of metal which is called the bearing retainer. If you were to take the rear wheel bearing apart, what you would find is an inner and outer race, several ball bearings, grease, and two thin plates which are the grease retainers. The inner and outer races are grooved for the ball bearings to ride in. This allows the bearing to be loaded from side to side, such as when your car goes around a turn, and not to have the inner race pull away from the outer race.

    The rear wheel bearing and the bearing retainer are pressed onto the axle. Since this requires the use of a hydraulic press, which most people do not have access to, this job should be done by a competent shop. I say competent shop for a couple of reasons. You only get one shot at pressing on a rear wheel bearing and retainer. Once the bearing and the retainer have been "stretched" onto the axle, they're meant to stay there. If they're pressed off and then on again, they will go on easier the second time and not have the holding power that they're supposed to.


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  This photo shows a small bearing axle with the axle retainer, wheel bearing, wheel bearing retainer and the machined area that the oil seal rides on.  You can tell exactly where the seal rides by the shiny area around tthe axle.  This is the style of axle that our Classic Mustangs came from the factory with.


    I've seen people press on the bearing and retainer and forget to insert the retaining plate between the bearing and the hub end of the axle. In a case like this, the "new" bearing which has just been installed, is now junk. Since these bearings are made to press on one time and one time only, if you have to remove a new bearing and retainer from the axle, even if it has never been used, you might as well throw it in the garbage.

     So it goes without saying that you never take a rear wheel bearing off one axle and put it on another.

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