Short Arm=Long Radius

Brobrian

Brobrian

Senior Member
After hearing good things here about shorter pitman arms, I put one one my coupe. I do perceive less effort in turning the wheel. However, there are a couple of other changes I'm not sure I prefer. First, the turning radius of my car is wider. I nearly took out the mail box yesterday because I expected to be able to make at u-turn in the street as before. Also, the steering ratio is a little different and I'm not yet used it yet. I have, and regularly drive, two A's. Now, the pickup has a different steering ration than the coupe.
Since changing the pitman arm is so simple, I'm actually thinking about putting the stock one back on and driving it for a while again to see which one I really do prefer.
 
Being a Ford Model A owner for almost a year the 1.5" of play in my steering was at first a tad scary --esp. that I drive in city traffic. I guess I've learned to steer it and likewise double clutch up/down shift it reasonable well. I guess like yourself, I might one day try a shorter arm to know for sure... with the shorter arm how much play does one typically need up with?
 
A shorter pitman arm will add to the steering wheel freeplay. If the arm is half the length, then the steering wheel freeplay will double.
 
mshmodela said:
Being a Ford Model A owner for almost a year the 1.5" of play in my steering was at first a tad scary --esp. that I drive in city traffic. I guess I've learned to steer it and likewise double clutch up/down shift it reasonable well. I guess like yourself, I might one day try a shorter arm to know for sure... with the shorter arm how much play does one typically need up with?
Click to expand...

I put the shorter arm on after tightening up the whole steering mechanism from king pins and spindle bearings to the steering box. So I took a fair amount of the play out. However, there is still some. As all these pro's will no doubt tell you, the play in your steering comes from a number of sources not related to the length of the pitman arm. The shorter arm is meant to make it easier to turn the steering wheel.
 
This has been said before many times but I will repeat it one more time.
A short pitman arm WILL NOT change the turning radius of the car if nothing else is changed. As long as the spindles contact the stops at full turn nothing will change except the effort required to turn the steering wheel and the amount of turns.
You will have to turn the steering wheel FASTER to achieve the same turn radius you did with the stock arm.

Ever wonder why dirt race cars only have a half turn of the steering wheel for lock to lock??
 
If the steering box is a 7 TOOTH you WILL lose turning radius to the left if you install a shortened pitman arm, the reason is the sector shaft will now contact the inside of the steering box housing and not allow the spindle to reach the stop on the left side.
As the drag link is raised higher than the spindle arm to connect to the short arm it moves away slightly so you will need to either turn the steering wheel or the road wheels to make the connection thus moving the steering off center.
I now have a complete rebuilt front suspension and steering installed in my Double A, which is the first thing to do if you want easier steering, however you need all the help you can get with these trucks, I installed the short arm and the Teflon pads in the rod ends, I have a adjustable drag link (work in progress) I am making.
Here is a simplified drawing which may explains why this happens.
 
Attempting to attach drawing to above post regarding short pitman arm.
 

Attachments

  • PITMAN ARM.JPG
    PITMAN ARM.JPG
    118.7 KB · Views: 91
I'll let you guys determine why or whether. I'll just practice my 3-point turns in my '28 with a 7-tooth steering box.

Just checked and the steering will turn to full lock right, but not left. Odd because it's 1 1/4 turn of the steering wheel from center in either direction.
 
Last edited:
Brobrian said:
I'll let you guys determine why or whether. I'll just practice my 3-point turns in my '28 with a 7-tooth steering box.

Just checked and the steering will turn to full lock right, but not left. Odd because it's 1 1/4 turn of the steering wheel from center in either direction.
Click to expand...


This indicates your wheels are not centered with the box center. The drag link length may be the culprit, or more likely bent ball-arms on the axles. When all is OK a two tooth box with a shorter pitmann will reach both axle stops.
 
Perhaps, Mike, but I have a 7-tooth steering box. I just put the original pitman arm back on and get full lock in both directions. The steering is tougher but it was easier than moving the mailbox. :)
 
Tom Wesenberg said:
A shorter pitman arm will add to the steering wheel freeplay. If the arm is half the length, then the steering wheel freeplay will double.
Click to expand...

Technically if all the freeplay is in the steering box (which is common) then the freeplay at the wheel will remain the same. If however, the the car tends to wander when going straight and is moving the steering arm in doing so (utilizing that freeplay) then the range of motion for wandering will DECREASE.

When there is freeplay in the steering box that allows the steering wheel to rotate 2" back and forth, that means the wheel is moving while the steering arm is stationary. A stationary steering arm is still stationary regardless of it's length.
 
There are two stops connected with steering. One is the stop built into the axle which doubles as the pin used to hold the kingpin in place.

The second is the capability of your steering box, either 7 tooth or 2 tooth.

Ford sort of matched these two. Knowing the fragility of a cast box I dare say that Ford probably engineered the system so the axle stops are predominant.

Putting a shorter pitman arm brings the capability of the steering box to be predominant. If you bring a short pitman arm to full turn - and hit something hard enough to do damage - likely you'll have damaged the steering box and not the axle.

Heh. Back in the day the replacement kingpins came with a wedge that did not have a full size stop/nut in the kit. I used the regular hex nut given - and threw the larger well rusted acorn away.

Gosh, could I get that car to swing a tight turn! I could enter my father's garage on the left hand door, turn a full 180 degrees INSIDE the garage, and come out the right hand door - all without going below 20 mph.

Well, kidding about the speed. It's also the reason I tore up the tire edge hitting the tires against the fender brackets.

Now I know better.

Joe K
 
Ahh, so that's the reason for those long nuts on the spindle bolts. Cool.
Not sure which is stopping the wheels from turning further, sorta looks like the spindle bumps up against the axle, but I didn't look that closely at the nuts. In any case the tire tread rubs against my brake rod on both sides if I turn too sharp. Scares the crap outa me every time.

BTW: You know what's cool about monkeying with your A? All the test drives you have to take to check out how things turned out. :)
 
Here's a pix of the Kingpin retaining pin (some call it a taper pin - but the pin is straight except for the key part where it touches the groove in the kinpin.)

A312224-7155-xl.jpg


The large nut is the stop for the front spindles. Early 1928 pins have a stop on BOTH front and back of the axle.

In my circa 1978 kingpin kit, there was no heavy nut - only a standard nut and lockwasher.

Joe K
 
My '28 has the same thing. I replaced the taper pin but kept the nut. In the set of pins and nuts I got from Snyders the nut seemed longer than the ones I reused. Since my tire rubs against my brake rod, I'm thinking I'll put the longer ones on there. Maybe I'll stop startling myself.
 
"Putting a shorter pitman arm brings the capability of the steering box to be predominant. If you bring a short pitman arm to full turn - and hit something hard enough to do damage - likely you'll have damaged the steering box and not the axle."

Joe, I don't follow this statement. A shorter pitman arm with lessen the torque leverage on the steering box from the front wheels hitting a bump.

Marco is right about the steering box freeplay. I was only thinking about the freeplay ahead of the pitman arm, such as worn bushings and steering balls that might be loose. However, as Marco said, I do believe much or most of the steering slop is likely to be in the steering box. Another added benefit of the shorter pitman arm is less torque on the gas tank bracket while turning the wheels.
 
Think of it this way Tom. Shorten the pitman arm shortens the travel front-back of the pitman arm ball - thus the box bottoms out before the arm drives the front steering arm to limit.

I haven't followed Marco's description of freeplay except to say he is right in that there are two sources of freeplay: that in the front axle and that in the box. He separated the effect of the shortened arm against the two freeplays. He makes sense.

Joe K
 
You must log in or register to reply here.
Back
Top