Front Wheel Bearings
| 01 October 2005
How often do you think about the front wheel bearings in your first generation Mustang? Probably not very often. They’re just not that exciting, right? But they’re important. If they’re worn or misadjusted, wheel bearings can affect safety, steering, alignment, and braking . They need to be mechanically sound, properly lubricated, and adjusted correctly. The procedures to satisfy those criteria are relatively simple. They’re well within the reach of driveway mechanics.
Let’s do a little detective work, first of all, to see if the bearings are mechanically sound; i.e., in good serviceable condition. When you’re driving along, do you hear an unusual noise coming from the general area of one or both front wheels? The typical sound from a bearing that’s failing is a rhythmic . . . brum . . . brum . . . brum . . .brum . . . .If you hear that sound, there’s a good chance a bearing is going bad somewhere in the wheels or driveline. For the sake of this pony trick, we’ll assume you hear the sound and it seems to be coming from a front wheel.
Jack the front tires off the ground and turn them by hand. You may hear the brake dragging so you have to ignore that sound and then decide if you can feel a roughness in the rotation of the wheel. Does either wheel feel like or sound like it’s grinding? If it does, remove the grease cap, the cotter pin, the nut lock, the adjusting nut, and the washer. Now wiggle the wheel from side to side to push the outer bearing away from the race so you can grasp it and remove it from the spindle. Throw the cotter pin away and lay all the other parts on a clean surface to keep them from getting contaminated with dirt. Do one wheel at a time or if you disassemble both at the same time be sure that you keep the parts separate. Don’t intermix parts from one hub with parts from the other hub.
Pull the wheel off the spindle and pry the inner-bearing grease seal out of the hub. You’ll destroy the seal when you pry on it so make sure you have a new one on hand. Remove the inner bearing and place it on a clean surface. Using a solvent, clean all of the grease from the bearings, the bearing races, the washer, the retaining nut, and the nut lock. When everything is clean, inspect the bearing rollers and the bearing races for brown or blue discoloration. The bearing has been running hot and needs to be replaced if you find either color. The darker the color, the hotter it’s been running. A bearing that was running extremely hot may cause discoloration of the hub and/or the spindle and it may weld itself to the spindle. If you encounter a discolored spindle or a bearing welded to it, it needs to be replaced because its metallurgical properties have changed and it’s no longer safe to use. A discolored hub needs to be replaced for the same reason.
If there’s no discoloration or weld damage, over heating hasn’t been an issue. So now check for mechanical damage. Look VERY closely at the surface of the races and the individual surface of each roller in the bearing cage. All surfaces must be completely free of pitting. If you find any pitting at all, no matter how slight, the bearing is no good and has to be replaced. The pits were the source of the sound and the roughness that started this job in the first place.
It’s NOT necessary to replace both bearings in a hub if only one of them is bad so proceed accordingly. But bear in mind that since the hub has already been taken apart, it might be reasonable to replace both just to minimize the risk of having to do the job again. Buy new bearings for the ones you’re going to replace and be sure to buy seals if you don’t already have them. Always replace the bearing race when you replace the bearing. New bearings come as a kit including the caged assembly and the race.
Knock the race(s) to be replaced out of the hub. Wipe the hub clean including the surface that the back of the race will seat against. With a brass drift or a special tool designed for the job install the new race in the hub being sure to seat it completely. Be careful not to damage the bearing surface of the race.
Pack the bearings completely with a proper wheel bearing grease and smear some of the same grease on the bearing races. Remember to keep everything totally free of dirt.
Clean the spindle if you haven’t already done so. When it’s clean, smear a light coating of bearing grease on it and a VERY light coating on the surface at the back of the spindle where the grease seal rides. Install the inner bearing in its race in the hub and then carefully install the seal using a broad-face brass drift or a special tool designed for the job. The seal will resist installation so exercise patience and don’t distort the metal frame that the seal is attached to.
Slide the hub over the spindle and fully seat it being careful to not damage the seal. Install the outer bearing, the washer, and the adjusting nut. Screw the adjusting nut down finger tight for now. Get a new ⅛”x2” cotter pin to have available; it will be permanently installed after adjusting the bearing. And, as you may have guessed, adjusting bearing clearance is our next step.
As a point of reference, ball bearings like a positive preload but roller bearings do not. The front wheels use roller bearings, so adjustment is critical. Shop manuals provide the following guidance to achieve minimum bearing clearance at theoretical zero preload:
1. Torque the adjusting nut to 25 ft.-lbs. Do this while simultaneously rotating the wheel. This should seat everything firmly in place and it will squeeze any excess grease from the contact surfaces between the bearing rollers and the bearing race.
2. Install the nut lock over the adjusting nut so that the cotter pin slot in the nut lock aligns with the cotter pin hole in the spindle. Test it by slipping the new cotter pin in and out of the hole.
3. The nut lock has several offset positions so if the slot doesn’t immediately line up with the hole, try other positions until alignment is correct. If you can’t find a position that lines up, pick the closest one that would line up if you slightly backed off the adjusting nut and then back it off accordingly. (CAUTION: Don’t pick a position that’s very close but would require you to further tighten the adjusting nut.)
4. Now that the slots and the hole are lined up, remove the cotter pin if it’s still in the hole. Keeping the nut lock in place over the adjusting nut, back the nut lock and the adjusting nut off together until the next slot in the nut lock lines up with the hole in the spindle. Insert the cotter pin but don’t bend it.
5. Rotate the wheel. It should rotate freely except for possible brake drag.
6. If the wheel doesn’t rotate freely, repeat the procedure beginning with a lighter torque load but no less than 17 ft.-lbs. When adjustment is correct, the wheel will rotate freely and the cotter pin can be bent to keep it in place.
7. Don’t bend the cotter pin over the face of the spindle. Bend it around the circumference of the nut lock. Bend half of the cotter pin in one direction and bend the other half in the opposite direction.
8. Install the grease cap.
If your car has drum brakes, you’re done at this point. If it has disc brakes, be sure to pump the brakes several times after you finish installation of the caliper assembly but before you drive the car.
We did this job because you heard a noise from the front of the car and it turned out to be a faulty wheel bearing. But what if there was no noise? Should the bearings be checked periodically? Yes, they should. Do it when you do a brake job or maybe you just bought the car and don’t know the condition of the bearings. If that’s the case, it would be a good idea to check them now and then plan to check them again when brakes are needed or at 25,000 mile intervals, whichever period is shorter. Do the entire job meaning disassembly, cleaning, inspection, lubrication, reassembly, and adjusting.
Bearings that are properly lubricated and properly adjusted will last a long time. Bearings that are damaged will eventually destroy themselves completely. Bearings that are too tight will overheat eventually destroying themselves and possibly destroying the spindle and the hub.
Bearings that are too loose let the wheel wobble which in turn causes front end alignment to change as wheel loading changes. Loose bearings make steering less precise because the front wheels can “track” road imperfections. Finally, loose bearings in a car with front disc brakes can cause the car to have a low brake pedal or in severe cases, a pedal that goes to the floor until the brakes are pumped.
The brake pads in a disc brake arrangement ride only a few thousandths of an inch from the brake disc. When you take your foot off the brake pedal after applying the brakes, the pads are pushed away from the rotor by the rotor itself. If the bearings are loose, the rotor wobbles and pushes the pads away several thousandths of an inch further than normal. In order to make the brakes work again, the pads have to be pushed back up to the rotor. That’s what you’re doing when you pump the brakes. Obviously, this is an unsafe condition that requires immediate correction.
So if there’s a moral to this pony trick, it’s this: a little preventative maintenance now can save a big, frustrating, not to mention expensive, job in the future. And it can improve the safety of your favorite pony while providing a more enjoyable driving experience.