Power at Work: How to check the settings on your steering box

Friday, February 29, 2008

Many vehicles on the road and in the field are being operated with unnecessarily sloppy free-play inside the steering box. Some simple tests to help you avoid this problem

by KEITH BERGLIND

There is an art to properly setting or adjusting any steering box. Sadly, because the majority of vehicles now have power steering, most regular mechanics and home mechanics have lost this art.

So let's start this lesson with a quick look under the hood of any vehicle around that doesn't have rack and pinion steering. We are only talking now about the old style steering box, as common on old tractors. These are still used in light and heavy duty trucks.

The steering shaft connects the steering wheel to the input shaft of the steering box. The steering box output shaft (in the centre of the box) is 90-degrees to this, pointing down. There will be a short Pitman arm at the bottom, held on by a large nut. This arm connects to the steering linkage.

For beginners, let's only think about an older, manual box with no power steering. Later, you will see the same settings in a power-steering box.

And we have already determined that the tie rods ends are tight.

The three settings for all steering boxes are:

• Main shaft bearings pre-load;
• Centre point mesh pre-load;
• Centre point.

Note that the pre-load tests are most accurate if done with the Pitman arm or steering linkages disconnected. This job should be done with the vehicle on stands, with the wheels free to turn, full right to full left.

The main shaft bearings should be properly set to a slight pre-load. Look at the top end of the steering box, where the steering shaft enters the box. Look for a large lock-nut, about three inches in diameter, usually with notched up-turned ears that can be tightened or loosened with a large hammer and punch. Loosen this counter-clockwise, about half a turn. Do not let the inner nut/hub turn with the locknut. Pre-soak with penetrating oil.

Now turn the wheel fully to one side, then back about half a turn. The steering wheel will feel free. Just wiggle the wheel back and forth about one or two inches.

The first adjustment is to turn in the centre hub until the mainshaft bearings are first tight (no slack), then a bit more, to preload these bearings. Repeat this until the steering wheel shows signs of slight pre-load. About one-pound drag is nice. Now reset the lock-ring. On really old vehicles and many farm machines, this setting may be done with shims. There is a pack of thin shims, and you take them out one at a time, until there is bearing pre-load.

Next is the centre-mesh load or "high point" pressure setting. Look for the small bolt head, with lock-nut, on the top end of the output shaft (sector shaft). There will be an allen-wrench or screwdriver slot in this bolt. Hold this solid while loosening the lock-nut about back one full turn.

Now, turn the steering wheel lock to lock. As the wheel turns through the centre or half way point, you need to feel additional tightening. The load on the steering wheel should increase to about three pounds. Turn the centre bolt down in quarter-turns until you feel this centre point tight high spot. Hold the centre bolt and tighten the lock nut.

Finally, the centre of this high load spot is also the straight-ahead position. This will never be wrong unless the vehicle was poorly repaired after an accident.

Testing the settings. I test the bearing pre-load and centre-play of every vehicle I intend to drive. With the vehicle aimed forward, if I detect excessively loose settings, I may elect not to drive this vehicle.

Few operators ever have these settings checked as the years go by, so there are a lot of vehicles on the road and in the field which are being operated with unnecessarily sloppy free-play inside the steering box.

Power steering boxes. Power steering boxes have a small, spring-loaded hydraulic valve in the input section of the steering box. The bearing pre-loads still are needed, but it takes a bit of care to separate the play of the valve from the movement of the steering box gears. BF

Keith Berglind is a licensed heavy-duty mechanic.