Diagnosing And Fixing Power Steering Gearbox Leaks On Medium-Duty Trucks

[MikePhua]

Understanding The Power Steering Gearbox And Pitman Arm
On many medium-duty trucks like the International 1900 series, the steering system uses a recirculating ball steering gearbox rather than a rack-and-pinion setup. Inside the box, a worm gear and ball nut move a sector shaft, and that sector shaft is splined to the pitman arm. When you turn the steering wheel, the pitman arm swings left or right and moves the steering linkage.
Because the pitman arm is clamped tightly onto the splined sector shaft and sees huge loads, this joint is a common place for the sector shaft seal to start leaking. When you see power steering fluid dripping from the steering gear area, especially around the pitman arm, the usual suspects are:

• Sector shaft (pitman shaft) oil seal
  
• Top cover gasket
  
• Hose fittings or cracked lines
  
• Corrosion or pitting on the shaft itself
  

Ignoring those leaks can be expensive. A typical rebuilt steering gear for a medium truck can run from several hundred to over a thousand dollars plus labor. Losing power assist on a loaded truck is also a real safety risk.
Below is a structured way to diagnose and repair those leaks, with special focus on safely removing a stubborn pitman arm.
Step 1 – Confirm The Source Of The Leak
Before you grab the puller, you need to be sure the leak is actually coming from the steering gearbox:

• Clean the whole area with solvent or brake cleaner and let it dry.
  
• Have an assistant turn the wheel from lock to lock while the engine runs, then shut it off.
  
• Check:
  • Top and side of the steering gear housing for wetness
    
  • Hose fittings and crimped ends
    
  • The bottom of the sector shaft where the pitman arm exits the box
    

If fresh oil appears right at the sector shaft where it enters the box, the pitman-shaft seal is the prime suspect. If the top of the box is wet, the input or cover seals might be leaking instead.
Step 2 – Safety Precautions Before Working On Steering Components
Steering components are safety-critical and heavily loaded. Before removing the pitman arm:

• Park on flat, solid ground.
  
• Chock rear wheels front and back.
  
• If you’re working under the front, support the frame with heavy-duty jack stands, not just a floor jack.
  
• Center the steering wheel and note the position of the pitman arm relative to the frame or crossmember. Take photos or scratch alignment marks so you can re-install it in the same orientation.
  
• Disconnect the battery if you’ll be working near the starter or wiring.
  

Step 3 – Tools And Setup For Pitman Arm Removal
Pitman arms on medium-duty trucks are pressed on extremely tight. Many techs are surprised how stubborn they are the first time. Typical tools you’ll need:

• Heavy-duty pitman arm puller or two/three-jaw puller rated for truck use
  
• Long breaker bar or impact wrench
  
• Penetrating oil
  
• Wire brush to clean splines
  
• Oxy-acetylene torch (or at least a good heat source) for controlled local heating
  
• Paint marker or scribe for orientation marks
  
• Big hammer (for tapping the puller, not beating on the shaft)
  

Don’t try to pry the arm off with bars or beat on the end of the sector shaft with a hammer – you can damage the bearings and worm gear inside the box.
Step 4 – Removing The Pitman Arm Without Damaging The Gearbox
A proven approach that many experienced mechanics use goes roughly like this:

1. • Clean the exposed sector shaft and pitman hub with a wire brush.
     
   • Soak the joint with penetrating oil and let it work in.
     
2. • Remove the pitman arm retaining nut and lock washer.
     
   • Inspect the threads; if they’re damaged, stop and repair before continuing.
     
3. • Install a heavy-duty puller squarely on the pitman arm.
     
   • Make sure the puller jaws are fully engaged and not slipping off the taper/hub.
     
4. • Tighten the puller as much as you safely can with a breaker bar or impact.
     
   • Do not exceed the puller’s rating; a cheap puller can explode under load.
     
5. • Once the puller is under significant tension, apply light, localized heat to one area of the pitman arm hub (not all the way around, and not to the sector shaft or seal area).
     
   • The idea is to expand the arm bore slightly. Heating in two opposite areas can actually “pinch” the bore instead of opening it, so focus on one spot.
     
6. • While it’s hot, give the puller screw head a sharp rap with a hammer.
     
   • That shock, combined with the thermal expansion, often makes the arm “pop” loose very suddenly.
     

Key points:

• You only want a dull warmth on the arm – no cherry-red metal. Overheating can damage the temper, seals, and gearbox internals.
  
• Keep a wet rag or heat sink near the seal area if the seal is still in place to protect it from heat transfer.
  
• When the pitman arm breaks free, it often lets go with a loud bang; make sure your hands, face, and body are out of the line of fire.
  

Step 5 – Replacing The Sector Shaft Seal And Inspecting The Gear
Once the pitman arm is off:

• Drain or catch any fluid remaining in the steering box.
  
• Clean around the sector shaft seal area thoroughly.
  
• Remove the dust shield (if present) and then pry or press out the old seal using a suitable hook or seal puller. Take care not to scratch the shaft or bore.
  
• Inspect the splines and sealing surface of the shaft:
  • If there’s a groove worn into the shaft where the seal rides, consider a shaft repair sleeve or replacing the box.
    
  • Light corrosion can be removed with very fine emery cloth.
    

When installing the new seal:

• Lubricate the seal lip with clean power steering fluid.
  
• Use a seal driver or a socket that matches the outer diameter to press the seal in evenly.
  
• Make sure it sits squarely at the correct depth and is not cocked in the bore.
  

If the steering box is heavily corroded, stiff, or has excessive play, it may be more cost-effective and safer to install a quality remanufactured unit rather than just replacing seals.
Step 6 – Reinstalling The Pitman Arm Correctly
Incorrect pitman arm installation can cause off-center steering and limited turning radius. To avoid that:

• Align the earlier marks on the shaft and arm, or line up the factory index marks or master spline if present.
  
• Slide the pitman arm fully onto the splines by hand first; do not use the nut to “pull” a misaligned arm onto the shaft.
  
• Install the lock washer and nut, then torque the nut to the manufacturer’s specification (often well over 200 ft-lb on medium trucks – check a proper manual for your specific model).
  
• After torquing, re-check that the steering wheel is centered when the wheels are straight ahead.
  

Step 7 – Bleeding And Final Checks
After any steering gear or hose work:

• Top off the power steering reservoir with the correct fluid.
  
• With the front wheels off the ground, engine off, slowly turn the steering wheel from lock to lock 10–15 times to push air out of the box and lines.
  
• Start the engine and repeat several slow sweeps from lock to lock, watching for foaming fluid.
  
• Recheck the fluid level and inspect again for leaks at:
  • Pitman shaft seal
    
  • Hose connections
    
  • Top cover and input shaft seals
    

On a road test, pay attention to:

• Steering effort – should be smooth and consistent
  
• On-center feel – no dead spot or excessive play
  
• Unusual noises (whine, groan, knocking) when turning
  

When To Repair And When To Replace The Gearbox
A simple seal leak with otherwise good steering feel is a good candidate for in-chassis seal replacement. But replacement is usually the better choice if you notice:

• Excessive free play in the steering wheel
  
• Notchy or tight spots when turning
  
• Metal shavings in the drained fluid
  
• Heavy corrosion or damaged splines on the sector shaft
  

In commercial use, uptime and safety often justify paying more for a quality reman steering box with a warranty rather than experimenting with a marginal unit.
Practical Tips From The Field

• Use the right-size puller – light-duty automotive pullers often bend before a heavy truck pitman arm moves.
  
• Pre-soaking the joint with penetrating oil the day before can make a big difference.
  
• Never weld or heat the sector shaft itself; any change in hardness or straightness can be catastrophic.
  
• If you’re not comfortable working on steering components, it’s one of the few jobs that really is worth paying a specialist for. A mistake here can literally cost a life.
  

By methodically confirming the leak, safely removing the pitman arm, and properly servicing the sector shaft seal or gearbox, you can extend the life of the steering system on an older International 1900-class truck and keep it steering safely for years to come.