No Bum Steer Here
Make sure that when you turn the wheel, your tractor goes where you tell it to.
When it comes to steering, you need to be 100 percent free of doubt when you drive. If you turn your wheel, the tractor must respond as you expect it to, whether you’re inching into a tight dock or dodging a wreck about to happen in front of you.
But like a lot of other equipment, steering is too often left untested and unchecked.
It’s not hard to do, and one day it might save you, or your load. Let’s start with the steering wheel itself.
If your steering wheel has play in it, the first thing to do is determine how much freeplay is allowable. You may be able to find the permissible freeplay listed in the owner’s manual. It will be listed in factory repair manuals, if you have them.
You can also look up allowable freeplay in the Commercial Vehicle Safety Alliance inspection criteria (see sidebar).
Finding out just how much freeplay you have is important because it’s a safety concern. If you have too much, it’s vital to find out why.
Mark Stathopoulos, the service manager at Bergey’s Truck Center, a Volvo, Mack, GMC and Isuzu outlet in Conshohocken, Pa., showed us the nine steps to finding, and fixing, steering trouble.
- Measure the freeplay
Shut the engine off and open the hood. Turn the wheel back and forth until you feel pressure or resistance on either side, and try to estimate the freeplay. If it seems to be near the allowable limit, you will need to measure it more precisely.
First mark the rim of the wheel. Then run a cloth or flexible metal tape measure around the wheel and hold it in place while someone else turns the wheel back and forth. You should be measuring the circular motion with the tape following the curve of the rim.
If there is a significant mechanical problem, the freeplay will be well above the allowable limit, and you should proceed with the steps below.
- Watch it as it works
A quick way to find trouble is to operate the steering while watching the steering mechanism as it works. To do this, first make sure the truck is in neutral and the parking brake applied. Block the drive wheels so it won’t roll. Then start the engine.
Safely lean out of the cab and turn the wheel while watching the front suspension. If necessary, get a helper to operate the steering wheel so you can watch. Turn the wheel slowly from lock to lock, watching everything that is going on. Especially when you change the direction you’re rotating the wheel in, you may see parts moving in relation to one another that should be tied tightly together. For example, both ends of a U-joint should move right together. Or, you may see something flexing that should not be moving at all – like the steering box moving around on the frame.
If you see one of these problems, you need to replace the U-joint or bearing that is allowing relative motion, or tighten or replace a component’s mounting bolts that are allowing it to shift around.
If this fails to end the problem, shut down the engine and proceed to the next step.
- Inspect the U-joints
Get out of the cab and check the U-joints at both top and bottom of the steering shaft. This runs from the wheel down to the steering box. On some trucks, like the midrange International we inspected, the joints will be visible below the steering wheel. On others, such as the Volvo VN, you may need to remove a plastic steering column cover to see the U-joint.
The best way to check the joint is to have someone rotate the wheel gently back and forth as you watch. If the upper part of the joint (nearer the wheel) starts rotating noticeably before the lower part, it is worn.
If you are alone, grab the shaft tightly in your hand and try to rattle it back and forth. If it moves, that’s a sure indication that the joint has play in it. Make this check for the joint right below the steering wheel as well as the one where the lower end of the shaft connects with the steering box.
- Check the input and output shafts
Look at the input shaft on top of the steering box. The bottom of the U-joint is splined to the input shaft and held tight by a pinch bolt. Make sure the splines fit tightly (are not worn) and that the pinch bolt is tight.
The output shaft of the steering box emerges from the bottom or side of the box and drives the pitman arm. The pitman arm carries the motion from the output shaft to the drag link, which, in turn, carries it to the steering knuckle.
Check to see if the pitman arm is tightly mounted to the sector shaft and that the splines are tight (not worn). There should be no relative motion between the pitman arm and the shaft when the output shaft turns. If necessary, have someone slowly rotate the steering wheel back and forth with the engine running to check.
- Service the steering box
Inspect the steering box mounting bolts – are they all tight? Put a wrench on them and check if the box feels at all loose.
This would also be a good time to check the steering box itself. With power steering, this check must be made with the engine running. Start the engine and making sure the wheels are still securely blocked. For either type of box, have someone very slowly rotate the wheel back and forth as you watch to make the check. They will have to measure how far the wheel turns as they rotate it back and forth, and keep the rotation centered between the two points where resistance is felt.
If rotating the steering wheel back and forth beyond the allowable arc clearly turns the steering box input shaft with no response from the sector (output) shaft, and there is no looseness in the system between the wheel and the box, the problem is in the box itself. It should be removed and rebuilt, or at least adjusted for proper internal clearances, or the power steering valves should be serviced. This should be done by a steering specialist.
If the pitman arm moves before the wheel reaches the freeplay limit, then have your helper continue to rock the steering wheel back and forth as you inspect the rest of the system parts. If parts are tight, the motion will be carried directly from one component to the next without any relative motion between the two. Wear will reveal a telltale movement of the part closer to the steering box before the part it drives begins to move. Check the motion of the pitman arm and drag link where they rotate the spindle (the rotating part the wheel is mounted onto) on the side of the truck where the steering box is. Follow the motion through the tie rod, which is the part linking the spindles on either side. Make sure that when one spindle turns, the other turns right along with it.
- Take a look under the truck
If all these parts are tight, shut the engine off and get onto a creeper. Roll under the truck and look at the springs where they mount to the axle. Is there any evidence, such as rust worn away, or clearance between the parts, that the spring mount is moving on the axle?
Jack the truck up on either side and inspect each side with the wheel off the floor. Inspect the shock and spring mounts – are they tight in relation to the axle? Replace or tighten loose or damaged U-bolts or shock absorber mounting bolts, as necessary. Check the spring hangers for looseness and replace parts as necessary. Sometimes, the spring pin bushing is worn and needs to be replaced to cure relative motion here.
- Evaluate kingpin wear
Get a prybar and use it to pry the wheel so that it will rock up and down. This serves as a check on kingpin wear. If the wheel rocks up and down noticeably, the kingpin and bushings should be replaced. If there is only a tiny bit of motion, you may want to check the specification to make sure the kingpin and bushings are not worn beyond limits.
Then hold the wheel front and back and try to rock it. If it’s loose in this direction, the wheel bearings need to be serviced or replaced.
- Check the alignment
If the steering system is OK and the truck still wanders, Stathopoulos says the problem could be alignment of the drive axles or even a dry fifth wheel. Proper fifth wheel lubrication keeps the trailer from forcing the tractor to take the same arc through a turn the trailer takes.
- Protect your truck
You also need to know how to prevent trouble in the future. The best advice is to grease all the suspension and steering fittings as frequently as you can – at least as often as you change your oil, even if you change at conservative intervals. Use high quality grease that meets the truckmaker’s specifications as to NGLI grade.
While greasing, inspect the seals and make sure they are intact. Replace any that have failed before they begin allowing water and road dirt to get in and grease to drain out – a common cause of worn steering components.
How much freeplay am I allowed?
The amount of freeplay the Commercial Vehicle Safety Alliance allows depends upon the steering wheel diameter.
Current criteria allow, for trucks with power steering, the following freeplay arc dimensions:
22-inch wheel – 85/8 inches
21-inch wheel – 81/4 inches
20-inch wheel – 77/8 inches
19-inch wheel – 71/2 inches
18-inch wheel – 71/8 inches
For manual steering, the dimensions are:
22-inch wheel – 53/4 inches
21-inch wheel – 51/2 inches
20-inch wheel – 51/4 inches
19-inch wheel – 5 inches
18-inch wheel – 43/4 inches
For further information, please contact the following:
Bergey’s Truck Center
Mack Trucks, Inc.
Volvo Trucks North America