The wheel hub on a vehicle is the central rotating part that holds the wheel in place. Wheel hubs can be attached to wheel bearings on some vehicles that have CV shafts or stub axles. On other vehicles, the wheel hub is mounted directly to the end of the axle. The wheel hub contains bearings on front-wheel-drive vehicles, and has electrical connections for wheel speed sensors and anti-lock brake sensors on some vehicles. The wheel hub also contains the studs or stems that are threaded to allow the installation of the wheel lug nuts.
Lift the front or rear of the vehicle on one side, depending on which hub you wish to measure. Use a 2-ton or greater capacity jack to lift the vehicle. Set a jack stand beneath the lower control arm or the axle housing, just behind the wheel you have lifted. Remove the wheel from the vehicle completely, using a wheel lug wrench or tire iron.
Remove the caliper mounting bolts from the disc brake assembly, using a three-eighths-inch drive ratchet and socket. The caliper bolts are on the rear or inner side of the caliper. Slide the caliper slightly off of the caliper mounting bracket by placing a pry bar between the top of the rotor and the caliper.
Insert a pry bar into the caliper housing in the hole provided. Slide the pry bar between the rotor and the caliper piston, and push the handle of the pry bar outward to compress the caliper a small portion. You do not need to compress the caliper completely inward. Remove the caliper, and set it on the lower control arm, or hang it on top of the axle housing, behind the brake assembly.
Remove the caliper bracket from the vehicle, using a three-eighths-inch driver ratchet and socket to remove the mounting bolts. Slide the rotor off of the vehicle once you have removed the caliper bracket in order to expose the wheel hub.
Measure the wheel hub diameter by placing a tape measure across the entire face of the hub. Make sure your tape measure intersects the centre of the hub. The wheel hub is a flat, round piece of metal with the wheel lug studs sticking out of it. The wheel hub is connected to the steering knuckle or knuckle assembly, depending on if you are measuring the front or the rear of the vehicle. Write your measurement down.
Lift the front or rear of the vehicle on one side, depending on which hub you wish to measure. Use a 2-ton or greater capacity jack to lift the vehicle. Set a jack stand beneath the lower control arm or the axle housing just behind the wheel you have lifted. Remove the wheel from the vehicle completely, using a wheel lug wrench or tire iron.
Remove the brake drum from the brake assembly by hand. If the brake drum resists being taken off, apply a pry bar between the back side of the brake drum and the backing plate. Shimmy the pry bar to loosen the brake drum from the wheel. Repeat this step until you have completely removed the drum.
Place a tape measure across the face of the exposed wheel hub, which it protrudes out from the centre of the drum brake assembly. Take the measurement across the front of the hub, which is the diameter of the hub. Make sure your tape measure intersects the centre of the hub. Write your measurement down.
Never lift a vehicle on a slope or uneven ground. Lifting a vehicle on uneven ground can cause jacks or jack stands to collapse. Failure to adhere to this warning could cause personal injury, property damage, or even death if you are beneath the vehicle when it collapses.