Chassis Building Part 3

A lot of work went into the design of the IRS. The suspension was setup not only for maximum suspension travel, but also with some thought given to instant center, roll center, anti-dive, and all of those other cool terms for racecar handing traits. Here's a look at the mounting points for the upper A-arms:

Note that jamb nuts for the rod ends are not in place nor are the rod ends adjusted properly. Dont start sending hate mail about it, okay?

With the rear arms mocked up, we took the stock Expedition half shafts to the bandsaw and cut a four inch section out of each shaft. We then sleeved the shaft with chromoly tubing so that it could telescope as we cycled the suspension. This allowed us to verify our plunge figures, resulting in final measurements we'd use to have new shafts made from super-strong 300M material.

Here's a look at one of the upper A-arms. That piece of tubing on the right will eventually get cut off flush and capped.

how much travel do we get out of the IRS? Well, ride height is set with the arms level to the chassis and the chassis is 7-inches off the ground. With the axles in place, the suspension has 7-inches of up travel and 7-inches of down travel for a total of 14-inches. Nice!


Once we had the IRS mounted and the control arms built, we made a pair of sheetmetal mounts for a fuel cell. The aluminum fuel cell came from Brother's Truck Parts in Corona, California and is built for '67-'72 Chevy trucks.

At some point when I get brave, I'm gonna have to modify the fuel cell because it holds less than 12 gallons and I won't get out of the state with my lead foot controlling the throttle.