Setting Differential Bearing Preload on a Case 580C Backhoe

[MikePhua]

The Case 580C and Its Transaxle Design
The Case 580C was introduced in the late 1970s as part of Case’s long-running 580 series of backhoe loaders. Known for its mechanical simplicity and rugged drivetrain, the 580C featured a cast iron transaxle housing with an integrated differential, bull gears, and inboard brakes. The differential assembly uses tapered roller bearings on each side of the carrier, with preload and backlash controlled by shim packs behind the bearing carriers.
This design allows for precise adjustment of ring and pinion engagement, but over time, wear in the bearings, thrust washers, and seals can lead to excessive end play, oil leaks, and brake contamination.
Symptoms of Lost Preload and Brake Contamination
A common issue with aging 580C units is oil-soaked brake pads caused by failed side gear seals. In one case, a right-hand seal was replaced, but the leak returned within hours of operation. Inspection revealed excessive movement—over 0.085"—on the right side gear shaft, even with the bearing plate bolted down. This level of play overwhelms the seal’s ability to contain gear oil, leading to brake failure and reduced stopping power.
Terminology clarification:
- Preload: The axial force applied to tapered roller bearings to eliminate end play and ensure proper contact
- Backlash: The clearance between ring gear teeth and pinion gear teeth, critical for gear longevity
- Rolling Torque: The resistance felt when rotating the differential carrier, used to measure bearing preload
- Carrier Shims: Thin metal spacers used to adjust bearing preload and gear backlash
Shim Adjustment Strategy and Measurement Techniques
To restore preload, technicians typically remove equal amounts of shim thickness from both sides of the carrier. This maintains ring gear position relative to the pinion, preserving backlash. However, this method assumes the original backlash was correct—something that should be verified with a dial indicator before any shim changes.
Recommended procedure:

• Remove transaxle top cover and brake assemblies
  
• Mount a magnetic dial indicator on the ring gear tooth face
  
• Measure backlash by rocking the ring gear without rotating the pinion
  
• Adjust shims to achieve 0.005"–0.009" backlash on used gear sets
  
• Check rolling torque by rotating the differential carrier with a torque wrench (target: 5–8 ft-lbs)
  

One technician reported removing 0.015" from the left and 0.020" from the right, resulting in a final backlash of 0.006" and restored preload. After resealing and reassembling, the machine ran for hours without a single drop of oil on the shop floor.
Seal Installation and Common Pitfalls
Installing side gear seals requires care to avoid rolling or cutting the seal lip. The splined shaft can damage the seal during installation if not protected. Solutions include:

• Using a seal installation sleeve or cone
  
• Wrapping splines with electrical tape, starting from the seal surface outward
  
• Lubricating the seal with gear oil before installation
  
• Inspecting the small internal seal on the differential lock shaft, which often causes right-side leaks
  

One operator found that even with a new seal and O-ring, the excessive shaft movement rendered the repair ineffective until preload was corrected.
Understanding Preload Loss Over Time
Preload loss can result from:

• Bearing wear and race deformation
  
• Thrust washer erosion between side gears and differential cage
  
• Shim compression or rust damage
  
• Improper prior repairs or missing shims
  

If preload is lost, it affects both sides of the differential. The tapered bearings push against each other, and any slack on one side transfers across the assembly. Replacing seals without addressing preload is a temporary fix at best.
Can You Replace Seals Without Resetting Preload
In theory, yes—if there’s no measurable end play and the bearings are tight. But in practice, many older machines have enough wear that preload must be rechecked. If the carrier plates are removed, shims should be reinstalled in their original positions unless a full setup is being performed.
Experienced mechanics often assess rolling torque by hand, feeling for resistance when turning both side gears simultaneously. While not precise, this method can confirm whether preload is present.
Conclusion
Restoring differential bearing preload on a Case 580C is essential for sealing integrity, gear longevity, and brake performance. By carefully measuring backlash, adjusting shims, and verifying rolling torque, operators can eliminate leaks and extend the life of their transaxle.
The 580C may be over four decades old, but with proper attention to preload and seal installation, it can still deliver reliable service. And for those who’ve spent years wrenching on these machines, the satisfaction of a dry brake housing and smooth gear engagement is worth every shim change.