Overview
The suspension system on 1973-1987 GM Square Body trucks was designed for utility and durability, but after 35+ years, most original components are worn beyond acceptable limits. Whether you're dealing with a sagging rear end, wandering steering, or simply want to improve ride quality and handling, a comprehensive suspension upgrade can transform your Square Body's performance.
This guide covers front and rear suspension upgrades for all Square Body variants including C10/C20 (2WD), K10/K20 (4WD), K5 Blazer, and Suburban models. Modern aftermarket options provide significant improvements in ride quality, handling, and adjustability while maintaining the truck's classic character.
Why upgrade your suspension:
- Restore proper ride height and load capacity
- Improve handling and steering response
- Reduce body roll and nose dive during braking
- Allow for custom stance and wheel/tire combinations
- Replace worn bushings and components with modern materials
Common Issues
Square Body owners typically encounter these suspension-related problems:
Front Suspension Problems
- Sagging torsion bars - Loss of ride height, especially on driver's side
- Worn ball joints - Play in steering, uneven tire wear, clunking noises
- Deteriorated bushings - Control arm, sway bar, and shock bushings crack and fail
- Shock absorber failure - Leaking fluid, poor damping, bottoming out
- Steering box wear - Excessive play, wandering, hard steering
Rear Suspension Problems
- Leaf spring sag - Rear end sits low, especially when loaded
- Spring eye bushing failure - Squeaking, harsh ride, axle wrap
- U-bolt stretch - Allows axle movement, affects pinion angle
- Shock mounting failure - Upper shock mounts tear out of frame
Parts & Materials Needed
Front Suspension Components
Torsion Bar Systems (All Square Bodies):
Stock torsion bar diameter: 1.18" (C10), 1.25" (C20/K10), 1.37" (K20)
Upgraded bars available up to 1.50" diameter
Essential Front End Parts:
- Ball joints - Upper and lower, greaseable preferred
- Moog K6136 (upper), K6145 (lower) for C10
- AC Delco 46D0013A/46D0012A alternative
- Control arm bushings - Polyurethane or rubber
- Energy Suspension 3.3113 (complete front bushing set)
- Tie rod ends - Inner and outer
- Moog ES3482T (outer), ES3481T (inner)
- Idler arm - Heavy-duty version recommended
- Moog K6654HD
- Pitman arm - Match to steering box ratio
- Sway bar - 1.25" diameter upgrade from stock 1" bar
- Hellwig 7714 front sway bar kit
Shock Absorbers:
- Budget option: Monroe 34671 (front), 34672 (rear)
- Performance: Bilstein B6 4600 series
- Adjustable: QA1 18-Way adjustable shocks
Rear Suspension Components
Leaf Springs:
- Stock replacement: Eaton Detroit Spring 25-1441
- HD upgrade: General Spring 4" drop or 2" lift options
- Multi-leaf vs. mono-leaf considerations for ride quality
Spring Hardware:
U-bolt specifications:
- C10: 3" diameter, 2.5" wide
- C20/K20: 3.5" diameter, 3" wide
Torque specification: 85-110 ft-lbs
Additional Rear Components:
- Spring eye bushings - Energy Suspension 3.2107
- Shackles - Adjustable for fine-tuning ride height
- Rear sway bar kit - Hellwig 7720 for improved handling
Tools Required
- Floor jack and jack stands rated for truck weight
- Torsion bar adjustment tool
- Ball joint separator or pickle fork
- Torque wrench (up to 200 ft-lbs capacity)
- Spring compressor (if servicing coil springs on some 4WD models)
- Basic hand tools (wrenches, sockets, pry bars)
Step-by-Step Guide
Front Suspension Upgrade
Phase 1: Torsion Bar Adjustment/Replacement
- Mark current position of torsion bar adjuster bolts
- Support vehicle on frame rails with jack stands
- Relieve torsion bar tension by backing out adjuster bolts
- Remove lower control arm after disconnecting ball joint and shock
- Slide torsion bar forward and remove from lower control arm
- Install new torsion bars (if upgrading) with proper orientation
- Reassemble in reverse order and adjust ride height
Ride Height Specifications:
Measured from ground to bottom of frame rail behind front wheel:
- C10: 6.5-7.0 inches
- C20/K10: 7.0-7.5 inches
- K20: 7.5-8.0 inches
Phase 2: Ball Joint and Bushing Replacement
- Remove wheel and brake components for access
- Separate upper and lower ball joints using proper tools
- Press out old ball joints and bushings
- Install new components with proper orientation
- Torque specifications:
- Upper ball joint nut: 65 ft-lbs
- Lower ball joint nut: 95 ft-lbs
- Control arm bolts: 140 ft-lbs
Rear Suspension Upgrade
Leaf Spring Replacement
- Support rear axle with floor jack
- Remove shock absorbers at both ends
- Remove U-bolts and spring plates
- Disconnect spring shackles and front eye bolts
- Install new springs with proper arch orientation
- Reassemble with new hardware and proper torque values
Critical Measurements:
- Pinion angle: 2-3 degrees down from driveshaft angle
- Axle centerline to frame: Maintain factory specifications
- Spring arch: Verify proper orientation (arch up)
Year/Model Differences
1973-1980 vs 1981-1987 Changes
Front Suspension:
- 1973-1980: Used forged steel upper control arms
- 1981-1987: Switched to stamped steel arms (lighter but less durable)
- Ball joint design: Early trucks used screw-in ball joints, later models use press-in
Rear Suspension:
- Leaf spring mounting: 1981+ trucks have revised rear shackle mounting
- Spring rates: Later trucks generally have softer springs for improved ride
Model-Specific Considerations
C10 (1/2-ton 2WD):
- Lightest suspension components
- Most aftermarket support
- Easiest to lower or modify stance
C20 (3/4-ton 2WD):
- Heavier-duty torsion bars and springs
- Different ball joint part numbers
- 8-lug wheel pattern affects brake/suspension integration
K10/K20 (4WD Models):
- Front differential affects lower control arm design
- CV joint considerations with suspension modifications
- Transfer case affects driveline angles
K5 Blazer:
- Shorter wheelbase affects spring rates
- Removable top requires consideration of body flex
- Same basic suspension as K10 but different tuning
Suburban:
- Longest wheelbase requires specific spring rates
- Heavier vehicle weight affects component selection
- Rear suspension similar to pickup but with different load ratings
Tips & Best Practices
Planning Your Upgrade
Budget Approach:
- Replace worn components with OEM equivalents first
- Upgrade to polyurethane bushings for longevity
- Add sway bars for improved handling without major expense
Performance Approach:
- Upgrade torsion bars and springs simultaneously
- Install adjustable shocks for tuning capability
- Consider complete geometry correction kits
Show Truck Approach:
- Air bag suspension for ultimate adjustability
- Tubular control arms for weight reduction and clearance
- Custom shock and spring combinations for specific stance
Installation Best Practices
- Always replace components in pairs (left and right sides)
- Use anti-seize compound on all threaded connections
- Pre-load bushings at proper ride height before final tightening
- Check alignment after any front suspension work
- Break in new components gradually over first 500 miles
Common Mistakes to Avoid
- Over-tightening ball joint nuts - Can damage threads or create binding
- Incorrect torsion bar indexing - Bars are side-specific and directional
- Ignoring pinion angle - Causes driveline vibration and U-joint wear
- Mixing old and new components - Can create handling imbalances
- Skipping the alignment - New suspension geometry requires professional alignment
Troubleshooting
Front Suspension Issues
Problem: Truck pulls to one side
- Cause: Unequal torsion bar adjustment, worn ball joints, alignment issues
- Solution: Check ride height side-to-side, inspect ball joints for wear, professional alignment
Problem: Harsh ride quality
- Cause: Over-stiff torsion bars, worn shocks, binding bushings
- Solution: Verify correct spring rates for vehicle weight, replace shocks, lubricate bushings
Problem: Excessive body roll
- Cause: No front sway bar, worn bushings, soft springs
- Solution: Install or upgrade sway bar, replace bushings, consider stiffer torsion bars
Rear Suspension Issues
Problem: Rear end sags under load
- Cause: Weak leaf springs, worn bushings
- Solution: Install heavy-duty springs, add helper springs or air bags
Problem: Axle wrap during acceleration
- Cause: Worn spring eye bushings, incorrect pinion angle
- Solution: Replace bushings, install traction bars, correct pinion angle
Problem: Harsh ride over bumps
- Cause: Over-stiff springs, worn shocks, binding shackles
- Solution: Verify correct spring rate, replace shocks, lubricate shackles
Diagnostic Procedures
Ball Joint Wear Test:
1. Jack up front of truck with wheels hanging
2. Grasp tire at 12 and 6 o'clock positions
3. Rock tire vertically - excessive movement indicates worn ball joints
4. Repeat at 3 and 9 o'clock for tie rod end wear
Shock Absorber Test:
1. Push down firmly on each corner of truck
2. Release quickly and count bounces
3. More than 1.5 bounces indicates worn shocks
Spring Rate Verification:
- Measure ride height at multiple points
- Compare to factory specifications
- Check for sagging or uneven stance
Professional Service Recommendations
While many suspension components can be replaced by experienced DIYers, certain procedures require professional service:
- Wheel alignment - Essential after any front suspension work
- Ball joint pressing - Requires specialized tools and experience
- Spring arch correction - Professional re-arching services available
- Custom fabrication - Shock mounts, brackets, or geometry correction
Recommended Service Intervals:
- Ball joints: Grease every 3,000 miles if equipped with fittings
- Shock absorbers: Replace every 50,000 miles or as needed
- Bushings: Inspect annually, replace every 7-10 years
- Alignment: Check annually or after suspension work
This comprehensive approach to Square Body suspension upgrades will result in improved ride quality, handling, and reliability while maintaining the classic truck's character and utility.