Steering Play in 1st Generation Cars
| 31 October 2006
I have a friend named Mike who several years ago owned a full size Bronco with real challenging steering. The truck had several new front end parts including ball joints, tie rod ends, and idler arm but the steering wheel still had a quarter turn of nothing, no connection at all with the rest of the steering mechanism. A full quarter turn of free play! Believe me that truck was a handful but Mike said it was ok because it had “all new parts.” Well, it wasn’t ok and the problem was mostly, if not all, in the steering box. Mike didn’t think there was anything wrong with the box but you could watch the pitman arm as it remained stationary while the steering wheel was turned through the quarter turn void. Mike was convinced that the truck was as good as new even though he should have remembered that when be bought it new, there was no free play. The truck had 110,000 miles on it and the steering box needed a little TLC. Which brings me to the point of this article.
Many (most?) first generation Mustangs have high mileage and many have free play in the steering. Any or all of the parts that Mike saw fit to change in his truck could contribute to the problem and they should be replaced with new parts if the steering isn’t “tight.” But in addition, the steering box should be serviced. It’s a fairly easy job. All it needs is an a pair of adjustments assuming all of the internal parts are in good condition and that it’s properly lubricated. If the parts are not in good condition or if the seals are leaking, the box needs to be rebuilt prior to adjustment. This pony trick will only discuss the adjustment part of the equation and leave the rebuild procedure for another day.
If the box is out of the car, it can be adjusted on the bench but it can also be adjusted while it’s still in the car. The procedure is the same. For the sake of this pony trick, we’ll assume the box is still in the car.
There’s some prep work that must be done before the adjustments can be made. The steering wheel needs to be removed so get out your wheel puller and take care of that step. The pitman arm also needs to be disconnected. It can be pulled off the sector shaft at the steering box or it can be separated from the center link. I prefer to separate it from the center link because with it still attached to the sector shaft, it’s easy to tell when the shaft is at the center of its arc. The steering should be pointed straight ahead when the sector shaft is centered. One of the adjustments needs to know the sector shaft position.
Ok, the two adjustments are called the worm gear preload and the sector shaft mesh load. If you’ve heard the term over-center load, that’s the same as mesh load. The worm gear preload is the first adjustment. When it’s within spec, the over-center load can be adjusted.
To begin the procedure, put the steering wheel retaining nut back on the steering shaft. Turn it down to the bottom of the threads and snug it in place. Now loosen the worm bearing adjuster lock nut. This is the large pressed steel nut on the steering box where the steering shaft sticks out of the box facing the firewall. With the lock nut loose, back off the worm bearing adjuster relieving any preload on the bearings. Finally, loosen the sector shaft adjusting screw lock nut and then loosen the adjusting screw to relieve any preload between the sector and the worm. This adjuster is located on top of the box and has a screw driver slot.
Steering box preloads are measured in inch-pounds and the values are quite low. A torque wrench calibrated for inch-pounds below 20 in-lb is needed to measure the load or you can improvise. If you choose to improvise, mount a lever of known center-to-center length at the top of the steering shaft. For example, a 2-inch lever will work. Drill it to a close tolerance fit over the shaft and then drill another hole two inches from the center of the first hole. A ¼ inch hole is good and a ¼ x 20 bolt fastened in place will complete the lever. The threaded part of the ¼ inch bolt should point up toward you when the large hole is secured over the shaft.
This improvised torque measuring device needs one more component and that would be a scale designed to weigh a load hanging from a hook attached to the scale. The scale should be accurate and be able to weigh as little as one pound, perhaps a fish-weighing scale.
Have a helper spot the pitman arm at the straight ahead position. Look up the preload torque for the worm bearings and then use the torque wrench to turn the shaft by engaging it with the steering wheel retaining nut. Have your helper slowly tighten the worm bearing adjuster as you rotate the steering shaft back and forth with the torque wrench. When the torque wrench “sees” the correct load (for example, the value might be between three and five inch-pounds), tell your helper to stop tightening the adjuster. Next, lock the adjuster in place with its lock nut and then measure the preload again because it may change when the lock nut is tightened. If it’s still in range that part of the job is finished. If it’s not in range, repeat the process until you have the correct preload after the lock nut is tightened.
If you used the improvised torque measuring device and you used a 2-inch lever, the preload or weight you are looking for on the scale is one half of the specification, 1½ to 2½ pounds using the same three to five in-lb example from above. Or say you used a 3-inch lever. Then the preload on the scale would be the value from the chart divided by three. The rest of the procedure is the same as described in the previous paragraph.
With the worm bearing preload set to specification, move on to the over-center preload. Have your helper confirm that the pitman arm is in the straight ahead position. Next have your helper tighten the sector shaft adjusting screw until light resistance is felt. Continue to slowly tighten the screw as you turn the shaft back and forth through center using your torque wrench or improvised device to measure the load. Stop the procedure when you reach the torque listed in the specification chart. The value may be something like 8 to 10 in lb and it includes the preload that you already set for the worm bearings. In other words, if you set the worm bearing preload to 4 in-lb and the over center preload specification is 8 to 10 in-lb, don’t add 4 in-lb for a total of 12 to 14. Just work to the total listed in the chart, in this example 8 to 10.
The term “over-center preload” has special significance. It’s the preload when the sector shaft is turned through the straight ahead position. Maximum torque will be read as the shaft arcs through center and it will fall off on each side of center. So turn the shaft slowly and smoothly back and forth through center and read the highest torque value. When the adjustment is correct, hold the adjusting screw in place and tighten the lock nut around it. When the nut is tight, read the over center load again. If it’s still in spec, the task is done except for putting the steering wheel back on and reattaching the pitman arm. If the reading is out of spec, loosen the lock nut and repeat the process until the correct over-center preload is read after the lock nut is tightened.
That’s it. The steering box should be as tight as new, again assuming that the all parts are in good shape. Confirm that free play has been removed from the box by having your helper turn the steering wheel back and forth through center as you watch the pitman arm. The arm should move whenever the steering wheel is turned.