Overview
The axles in 1973-1987 GM Square Body trucks are critical drivetrain components that transfer power from the transmission and transfer case to the wheels. Understanding axle identification, maintenance, and replacement is essential for Square Body owners, as these trucks came with various axle configurations depending on model year, payload rating, and drivetrain type. This comprehensive guide covers both front and rear axles, including the solid front axles found in 4WD models and the various rear axle options ranging from light-duty 10-bolts to heavy-duty 14-bolts.
Proper axle maintenance ensures reliable power transfer, prevents costly failures, and maintains the truck's capability for work and recreation. Whether you're restoring a C10 or upgrading a K20 for heavy-duty use, understanding your axle setup is fundamental to making informed decisions about repairs, upgrades, and parts selection.
Common Issues
Rear Axle Problems
- Bearing failure - Wheel bearings wear out, causing noise, play, and potential wheel separation
- Seal leakage - Axle seals fail, allowing gear oil to leak onto brake components
- Ring and pinion wear - Improper setup or lack of maintenance causes gear noise and failure
- Limited slip clutch wear - Posi-traction units lose effectiveness over time
- Axle shaft breakage - Particularly common in 10-bolt axles under heavy loads or aggressive driving
Front Axle Problems (4WD Models)
- U-joint failure - Constant velocity and universal joints wear out, causing clicking or binding
- Hub bearing failure - Front wheel bearings require regular service and eventual replacement
- Ball joint wear - Upper and lower ball joints develop play, affecting handling and tire wear
- Steering knuckle problems - Kingpin bushings and seals require periodic service
General Issues
- Differential fluid contamination - Water intrusion or metal particles indicate internal problems
- Gear oil leaks - Pinion seals, cover gaskets, and axle seals commonly fail
- Vibration problems - Worn components cause driveline vibrations
Parts & Materials Needed
Identification Tools
- Flashlight or work light
- Wire brush for cleaning casting numbers
- Measuring tape for ring gear diameter verification
Basic Maintenance Supplies
- Gear oil - 80W-90 or 75W-90 GL-5 gear lubricant
- Limited slip additive - GM Part #1052358 or equivalent
- RTV silicone sealant - Permatex Ultra Black #82180
- Differential cover gaskets - Various part numbers by axle type
Common Replacement Parts
10-Bolt Rear Axle (7.5" and 8.5")
- Axle bearings - Timken SET401 (7.5"), SET415 (8.5")
- Axle seals - National 710733 (7.5"), National 710735 (8.5")
- Pinion seal - National 710140 (7.5"), National 710142 (8.5")
- Ring and pinion sets - Richmond Gear, Motive Gear, or OEM
12-Bolt Rear Axle
- Axle bearings - Timken SET414
- Axle seals - National 710734
- Pinion seal - National 710141
14-Bolt Full Float Rear Axle
- Wheel bearings - Timken SET410
- Axle seals - National 710736
- Spindle nuts - Various torque specifications by year
Front Axle (4WD)
- Hub bearings - Timken SET1 (inner), SET2 (outer)
- Wheel seals - National 710108
- U-joints - Spicer 5-260X (most common)
- Ball joints - Moog K6136 (upper), K6145 (lower) - varies by year
Tools Required
- Axle pullers - OTC 4579 slide hammer set
- Bearing race drivers - OTC 4520 set
- Torque wrench - 0-150 ft-lbs minimum
- Gear oil pump - For refilling differentials
- Seal drivers - Various sizes
- Ball joint press - OTC 7249 or equivalent
Step-by-Step Guide
Axle Identification
Rear Axle Identification
- Locate the axle code on the differential cover or axle tube
- Measure ring gear diameter through the fill plug hole
- Count cover bolts: 10-bolt (10 bolts), 12-bolt (12 bolts), 14-bolt (10 bolts)
- Check axle type: Semi-float vs. full-float (14-bolt only)
Front Axle Identification (4WD)
- Check casting numbers on differential housing
- Identify Dana 44 (most common) by round differential cover
- Verify gear ratio using axle code or tooth count method
Rear Axle Bearing Replacement (Semi-Float)
Removal Process
- Raise vehicle and secure with jack stands
- Remove wheel and brake drum/rotor
- Drain differential fluid
- Remove differential cover
- Remove cross pin by removing bolt and sliding out
- Push axle shaft inward and remove C-clip
- Pull axle shaft using slide hammer if necessary
- Remove old bearing using bearing puller or press
Installation Process
- Press new bearing onto axle shaft
- Install new axle seal using seal driver
- Insert axle shaft carefully to avoid damaging seal
- Install C-clip and cross pin
- Apply thread locker to cross pin bolt (10 ft-lbs torque)
- Install differential cover with new gasket
- Refill with proper gear oil (approximately 3.5 quarts for 10-bolt)
Front Hub Service (4WD)
Disassembly
- Remove wheel and brake caliper
- Remove dust cap and cotter pin
- Remove spindle nut and washer
- Pull hub assembly straight out
- Remove outer bearing from hub
- Drive out inner bearing race if replacing
Reassembly
- Pack bearings with high-temperature wheel bearing grease
- Install inner bearing and new seal
- Install hub on spindle
- Install outer bearing, washer, and nut
- Adjust bearing preload: Tighten to 12 ft-lbs while rotating hub, then back off 1/6 turn
- Install new cotter pin and dust cap
Year/Model Differences
1973-1980 Models
Rear Axles
- C10: 7.5" 10-bolt standard, 8.5" 10-bolt optional
- C20: 8.5" 10-bolt or 12-bolt corporate
- K10: 8.5" 10-bolt standard
- K20: 12-bolt corporate or 14-bolt full-float
Front Axles (4WD)
- Dana 44: Standard on all K-series trucks
- Closed knuckle design through 1977
- Open knuckle design 1978-1980
1981-1987 Models
Rear Axles
- C10: 7.5" 10-bolt standard, 8.5" 10-bolt with V8
- C20: 8.5" 10-bolt or 14-bolt full-float
- K10: 8.5" 10-bolt standard
- K20: 14-bolt full-float standard
Front Axles (4WD)
- Dana 44: Continued through 1987
- Improved ball joint design 1981+
- Different brake configurations by year
K5 Blazer and Suburban Specifics
- K5 Blazer: Typically 10-bolt rear, Dana 44 front
- Suburban: Heavier-duty axles standard, 14-bolt rear common
- Shorter wheelbases affect driveshaft lengths and U-joint angles
Tips & Best Practices
Maintenance Best Practices
- Change differential fluid every 30,000 miles or 2 years
- Inspect for leaks during regular maintenance
- Check fluid level monthly on work trucks
- Use proper gear oil viscosity for climate conditions
- Add limited slip additive only to posi-traction equipped axles
Upgrade Considerations
- 10-bolt to 12-bolt swap: Requires new driveshaft and possibly spring perches
- Gear ratio changes: Consider overall drivetrain compatibility
- Limited slip upgrades: Eaton Posi or Detroit Locker options available
- Disc brake conversions: Available for most rear axle applications
Installation Tips
- Clean all surfaces thoroughly before assembly
- Use proper torque specifications for all fasteners
- Pre-load bearings correctly - too tight causes premature failure
- Break in new gears properly - 500 miles with initial fluid change
- Check backlash and pattern when installing ring and pinion
Common Mistakes to Avoid
- Mixing gear oil types - stick to one brand and viscosity
- Over-tightening bearing adjustments - causes rapid wear
- Reusing old seals - always install new seals during bearing service
- Ignoring axle codes - ensures correct parts ordering
- Improper break-in procedures - can cause premature gear failure
Troubleshooting
Noise Diagnosis
Rear Axle Noises
- Whining on acceleration: Ring and pinion wear or improper setup
- Howling on deceleration: Ring and pinion backlash issues
- Clicking in turns: Limited slip clutches or spider gears
- Grinding or rumbling: Wheel bearing failure
- Clunking: Worn U-joints or loose yoke
Front Axle Noises (4WD)
- Clicking when turning: CV joint or U-joint wear
- Grinding when braking: Wheel bearing or brake issues
- Squealing: Ball joint lubrication needed
- Popping during lock-to-lock: Steering knuckle problems
Fluid Leak Diagnosis
- Rear of differential: Pinion seal failure
- Axle ends: Axle seals leaking
- Differential cover: Gasket or RTV sealant failure
- Vent tube: Overfilled or plugged vent
Performance Issues
- Poor traction: Limited slip unit needs service or fluid additive
- Vibration: U-joint wear, bent axle, or improper driveshaft angle
- Pulling to one side: Unequal tire pressure, brake issues, or bent axle housing
- Excessive tire wear: Alignment issues, worn suspension components, or bent axle
Diagnostic Procedures
- Road test to identify when noise occurs
- Visual inspection for obvious leaks or damage
- Fluid analysis - check for metal particles or contamination
- Measurement checks - bearing play, backlash, runout
- Component testing - individual part function verification
When to Seek Professional Help
- Ring and pinion installation - requires special tools and expertise
- Differential case machining - precision work beyond typical DIY capability
- Axle housing straightening - specialized equipment required
- Custom gear ratio calculations - for modified applications