In the Northeast and Midwest, a flat tire and an alloy wheel seizing on the hub (two parts jammed or stuck) is a common occurrence caused by corrosion. Corrosion and rust are nasty problems that make repairing a vehicle difficult. Corrosion is the product of an electrochemical reaction, in a vehicle’s case, between two dissimilar metals and an electrolyte — so, an alloy wheel, a steel bearing hub and saltwater, for example.
Know that there is a difference between corrosion and oxidation. Oxidation is an element combining with oxygen. The process is accelerated by the presence of water and heat. Iron oxidizes to form rust (iron oxide); aluminum oxidizes to form a white powder (aluminum oxide).
The best example of readily visible corrosion is the white or bluish green stuff that appears around battery connections. The end result is this stuff fills the gap and either seizes parts into one immovable object or destroys them altogether.
A wheel that has seized on a bearing or axle hub can slow down a brake job.
Shop solution: Loosen the lug nuts and spray a penetrating agent on the hub. Try rocking the vehicle from side to side.
Last resort: Drive the vehicle slowly 50 to 100 feet and rock the steering wheel from side to side. Heat is not your friend. The gas wrench can lead to some not-so-good results.
Composite and Cast Drum
The first brake drums used on passenger cars and light trucks were full cast drums. The additional stiffness of these drums allow tighter machining tolerances, as well as better static balance.
The type of drum you have to remove can make a difference in the removal technique.
The composite drum was developed out of a need to reduce the weight of passenger cars and light trucks. The composite drum is produced by stamping a steel flange and placing it into a mold. Molten iron is poured into the mold, and the flange fuses with the molten iron to form the drum. Tabs cut during the stamping process also help form a mechanical bond.
Composite drums can be difficult to remove and often a stuck drum can be distorted if a great deal of force is used. Cast drums can take a lot of abuse, but always check for cracks after a brutal removal.
How do you get a seized drum off without destroying it and/or ruining the hub or drum flange? The options are penetrating agents, pullers, hammers and the gas wrench.
A penetrating agent can’t hurt. Pullers can distort a drum flange. Heat must be used with great caution. Lubricants and seals burn. Hammers break things — but there is a twist when using a hammer. It starts with a 2-inch and a 2.5-inch galvanized pipe cap (you may have to try a plumbing supplier to find a 2.5-inch). These will cover most of the axle and bearing hubs.
Next, cut the tapered tip off a punch chisel. Place the pipe cap over the hub and, using an air hammer and the modified tool, apply pressure to the center of the cap. The impact will vibrate the drum flange and break up the corrosion around the hub so that the drum can be removed.
You should wear a respirator when you use the tool because it will raise dust.
Rotor Seized on the Hub
A rotor welding itself to a flange is no fun. Before pulling out the sledge hammer, grab a can of penetrating oil and a wire brush and look for retaining screws.
Heat is a good option. The heat is not meant to cut or melt. Heat breaks down corrosion and destroys the bonds between the rotor and flange. Heating the entire rotor until it is cherry red will only destroy the wheel bearing seals.
Rotors can be full cast or composite with a stamped steel center hat section mated to a cast iron rotor friction surface that is either solid or vented. You can use the same process used on the drum to remove this type of rotor.
The composite rotor is lighter than a conventional one-piece cast iron rotor, but it can become distorted in the hat area and prove difficult to machine runout. On most older composite rotor applications like the old Jeep Cherokee XJ and turn of the century Chevy Malibu, it normally was replaced with a full cast rotor. So, if you are replacing a composite rotor, replace both of the rotors to ensure proper braking. On some applications the wheel studs will need to replaced with longer studs.
Preventing corrosion is near impossible. If you apply any friction modifying substance, like oil or anti-seize, to the wheel stud threads, it is going to change the measured torque values. With less friction on the threads, the torque values increase. So, when you tighten a wheel to 85 ft.-lbs, it may actually be torqued at 95 ft.-lbs (this includes torque wrenches and sticks). The increase in force will mean that the studs will stretch under the increased torque. This stretching can lead to metal fatigue, changes in thread geometry and possible failure.
Many vehicles use the hub to center the wheel. These “hub-centric” designs can benefit from a very light coating. A high-temperature lubricant can be used where the hub goes through the center of the wheel. On some conical lug nuts, you can put a light coating on the seating surfaces of the cone, while avoiding any contamination with the threads.