Mark Williams Rear End Assemblies

Ford 9"- The Ford 9" is definitely the most popular of the rear ends in drag racing. It offers good strength characteristics and the largest variety of gear choices. The thirdmember type center section allows a racer to have multiple gear ratios available and is much easier to change than a rear loading type rear end. Work can be done on the rear while it is out of the car without major disassembly. With a full-floater style rear the brakes do not even have to be removed to remove the thirdmember. There are basically two negatives to the Ford 9". First it weighs about 10 lbs. more than a comparable 12 bolt. Second, because of the larger pinion offset the gears tend to be about 5% less efficient, although this can vary depending on gear ratio.

Mark Williams 11"- The Mark williams 11" is by far the strongest of the three types. The 11" system runs virtually maintenance free through entire race seasons. With dimensions and offsets very similar to the 9" Ford, very little modifications are necessary to change over to the 11". The downside to the 11" is that it weighs about 75 Lbs. more than a comparable 9" Ford. Gear changes can be rather difficult also. It is recommended that the 11" be run in situations where gear changes are not frequent. The cost of replacing worn gears and the dependability of the 11" make up for its downsides.

GM 12 Bolt - The lightest of the three, the 12 bolt offers a large selection of gear ratios (although not as large as the 9") and good dependability. 12 bolt modular housings are also narrower than a 9" or 11" at 14" wide instead of 16" wide. The 12 bolt is mainly run in situations where weight and efficiency are major factors, such as Comp and Comp Eliminator. The disadvantage to the 12 bolt is that gear changes can be difficult.