Overseas Brake Drum Problems Background
In 1969, Chrysler changed the design of its steel wheels. The new design consisted of two raised concentric mounting rings on the mounting surface of the wheel - one inside of the bolt circle around the center hole, and one outside of the bolt circle. The new "ring mount" feature was introduced to help prevent rotor warpage after front disc brakes became commonplace. The design provided a better clamping effect by ensuring a more positive contact between the wheel and the mounting hub.Aftermarket Brake Drum Compatibility Problems
Recently, there has been an upsurge of aftermarket parts made by offshore suppliers. While some of the products are satisfactory, others can cause problems. Below is information excerpted from a Mopar Action Magazine tech article on aftermarket brake drums by Richard Ehrenberg, S.A.E.
Many parts chains such as AutoZone, sell replacement rear brake drums that have a raised ramp around the center hub hole. This design is probably not a problem if the drum is used with early 1968-down wheels. However, using this design with 1969-up wheels can cause clamping problems, as the center "ramp" can prevent the wheel from making contact across the full surface ot the wheel-to-drum contact flange. Using this type of drum with 1969-up wheels will cause the wheel to deform as it is torqued to specifications. With the proper brake drum, the "ring mount" 1969-up wheels should rest flat across the mounting surface of the drum with the lug nuts just hand tight. With brake parts, as well as with anything else that your life depends on
, you will always fare better if you ask for parts made by a brand name supplier such as Bendix. Many overseas parts use substandard metal which can have hard spots, causing uneven or premature wear, and even complete failure.
Below are photos showing examples of the incorrect design and the correct design for aftermarket rear brake drums. Sources:Photos:
- Top: Incorrect brake drum design showing raised rim around center hole. (Not an actual Chrysler brake drum - courtesy of www.orchestralibrary.com)
- Bottom: Correct brake drum design showing flat surface around center hole. (Not an actual Chrysler brake drum - courtesy of www.brakeperformance.com)
- Correct 11" X 2.5" brake drum for Chrysler products - Courtesy of www.partsamerica.com
- Mounting surface of a cop car wheel showing the concentric mounting rings (Courtesy of Reggie)