Peterbilt Air Trac torque arms

The lengths have changed over the years so I can’t be much help. I have a ‘73 with AirLeaf and a ‘74 with Air Trac. Also Sometimes there was a difference between Rockwell and Eaton axle housing's, but they usually used shims on the mounts to make up difference in lengths.
If all else fails and you have access to a spring shop locally they should be able to press out the old bushings and press new ones in the old original rods.

 

How could you even install the wrong length? 3" is a big difference. You have to be pushing or pulling the axles way out of line to even get them bolted up. Things would be way out of wack.

 

The pinion angles would be so f'd too. Should be very obvious.

 

The arms he’s talking about shouldn’t change pinion angle. They are the arms that control the side to side movement. With the wrong length you will have one axle on a tandem kicked out farther to the side then the other.
Measure between frame and inside tire on each axle. Put tape measure from outside of frame rail to side wall of tire. See how much different the gap is. That will tell you how far over each axle is kicked out. Should not be more than 1” difference from side to side on the older AirTracs. That is were proper length and shims between frame and frame mount for bar come in.

 

You can also get an idea how far out the axles are kicked out when hooked to a 96” wide trailer. If perfectly straight look at each side and you will see that most of the time the sidewalls of tires on axles on one side will be just past the edge of a trailer and the other side my be flush or just inside the edge. Small detail I know but it is there. But having said that I have seen many trailers with kingpins installed off center, so if that is questionable that measurement needs to be confirmed as well.