pitman arm

[katy]

So, what is the length of the stock pitman arm? And, how short is the shorter version?

Asking because I'm new to fixing Model As. Owned and drove a few of them years ago but didn't do much fixing, just drove them and replaced parts from an auto wreckers when parts were needed.
Right now I'm working on a "refurbished" '31 CCPU that I need to get ready for the safety inspection before I can insure and license it.

[J Witt]

Just installed the shortened arm from Snyders. I like the steering feel a great deal over the stock one. The wheels still turn the same angle left and right as before, just requires a bit more steering wheel rotation, as the mechanics dictate. Just a matter of taste and muscle, I guess. 34 psi in the tires.

I could not get the repro arm to tighten up on the sector shaft. Torqued it to about 100 ft-lbs and the bolt snapped, still never was completely tight. Solved this issue by coating the sector shaft with stud lock grade loctite and giving it 24 hours to set up (with a new retaining bolt, of course).

I overhauled the drag link with new steel ends. Steering wheel centering not a noticeable issue for me. Overall, I like it, but some revision to material, process or tolerances needs to happen to allow the arm to clamp down properly.

John

[MikeK]

Originally Posted by katy

So, what is the length of the stock pitman arm? And, how short is the shorter version? . .

The original arm is 7.5" from ball center to sector shaft center. The shorter arms are 6.0".

Simple math, whatever steering wheel force you need to grind the tires into a turn while not rolling (parking) you will need 20% less force (torque) on the steering wheel with the 6.0" arm. You will also need to move the steering wheel more to make the same change in direction while driving. To me a shorter arm feels like you are driving a bus. Major wheel movements to make minor directional adjustments. I got rid of mine, went back to stock. Also, whatever total free play you have in the wheel with the stock arm will increase proportionally with a shortened arm.

Some 7-tooth steering boxes may not have sufficient angular range to run the steering linkage lock to lock with the shorter arm. All the 2-tooth boxes can accommodate the greater angular range required but you may notice an increase in the slight slight off-center 30-31 steering wheel while driving straight ahead. To fix that requires an adjustable (or slightly shortened) drag link.

Before the new forged shorter arms were available it was common practice to cut and weld arms to varying shorter lengths. An stock arm shortened 1" (to 6.5") will go lock to lock on a 7-tooth car and require 13.3% less force.