M-body steering boxes are hydraulic power assisted units that are used to control steering. The boxes convert motion from the steering wheel to circular motion at the sector shaft which exits at the bottom of the steering box. The sector shaft connects to the steering gear arm (called the pitman arm), which converts the circular motion of the sector shaft into linear motion (back and forth) needed to turn the front wheels. The pitman arm connects to and supports a center link (called the drag link), which is supported on the passenger side by the idler arm. The drag link connects to a tie rod on either side of the car. Each tie rod connects to the arm of a steering knuckle on either side of the car. The steering knuckles have spindles which the hub/brake rotor assemblies are attached to with a large center bolt and a cotter pin. Each wheel bolts to a hub with five lug nuts. When the steering wheel is turned, the pitman arm moves the drag link. The drag link moves the tie rods. The tie rods move the knuckles/spindles which turn the wheels. Below are diagrams showing the steering linkage and the steering knuckle.
Quick Ratio or "Firm Feel" Power Steering Boxes
All M-body power steering boxes (cop cars and civilian) use the same steering ratio, which is around 15.7:1 to 16:1. This was the fastest power assisted ratio available from the factory. There were no "quick ratio" cop car power steering boxes. The "firm feel" power steering setup offered on cop cars was achieved by building extra turning resistance into the box to provide more "road feel". Firm feel, Steer & Gear and other steering box retailers sell rebuilt power steering boxes with various stages of steering resistance. If you need a replacement steering box, it is highly recommended that you deal with one of these firms instead of buying a rebuilt unit from a parts store. The rebuild quality of parts store boxes is very spotty, and some of them can be downright dangerous to install or drive with. Dbdartman, a member on another board, lost half a finger dealing with one of the parts store boxes, so beware.
As far as it is known, there were no differences in pitman arms during the M-body production run. However, a fast ratio pitman arm is available from FirmFeel.com and probably from other suppliers. Manual Steering Boxes
Manual steering boxes for older Mopars (except vans and C-bodies) can be adapted to M-bodies if weight savings is a goal. There is a weight savings of 40 to 50 pounds, and a slight horsepower savings by going to manual steering, but the swap is probably not worthwhile unless you are planning an all out drag race car. Steering columns set up for power steering are shorter than those for manual steering, so an adapter must be used to convert them. Firm feel, Steer & Gear and other steering box retailers sell the adapters. However, you can also look in junkyards for old 1970s to early 1980s utility company vans with manual steering. The Dodge bean counters got smart and standardized the length of the steering columns to the shorter power steering length, so that only a simple adapter was needed if a van was ordered with manual steering. Back then, utility companies were usually too cheap to order any frills, so their vehicles were mostly ordered as stripper versions without power steering.
Firm Feel and Steer & Gear have manual boxes in various ratios that can be adapted to M-bodies:
- 16:1 is 3.5 turns lock to lock - about the same as a stock power assisted box
- 20:1 is 4.5 turns lock to lock - this ratio was never offered by the factory
- 24:1 is 5.5 turns lock to lock
Flaming River also sells a brand new 16:1 manual box with a steel housing .
The 16:1 manual box will be a total beast when trying to either park with it, or turn corners at slow speeds. Andy Finkbeiner, Mopar enthusiast, freelance car magazine article writer and owner of AR Engineering
commented; "The 16:1 box is pretty brutal. Many have tried it, few have kept it!" Many Mopar enthusiasts have settled on the 20:1 ratio box as being the most drivable. The 24:1 manual box offers far less response time and control, and is thus more dangerous. Several people who have tried this ratio described it as being "like trying to turn the wheel of a school bus or steering a ship". Photos:
Courtesy of the Chrysler Factory Service ManualSources: