Suspension Systems - Square Body Trucks

Overview

The suspension system on 1973-1987 GM Square Body trucks is a critical component that affects ride quality, handling, load capacity, and overall vehicle safety. These trucks utilized different suspension configurations depending on the model and intended use, with 2WD models (C10/C20) featuring a different front setup than their 4WD counterparts (K10/K20). Understanding your Square Body's suspension system is essential for proper maintenance, upgrades, and restoration.

Front Suspension:
- 2WD (C-Series): Independent front suspension with upper and lower A-arms, coil springs, and tube shocks
- 4WD (K-Series): Independent torsion bar front suspension with upper and lower A-arms and tube shocks

Rear Suspension:
- All Models: Solid axle with semi-elliptical leaf springs and tube shocks
- Load Capacity Variations: Different spring rates and configurations based on model (1/2-ton vs 3/4-ton)

Common Issues

Front Suspension Problems

• Worn ball joints - Upper and lower ball joints wear over time, causing steering play and tire wear
• Sagging coil springs (2WD) - Loss of ride height and poor handling
• Torsion bar adjustment issues (4WD) - Improper ride height or worn torsion bar bushings
• Shock absorber failure - Leaking fluid, poor damping, or complete failure
• Control arm bushings - Deteriorated rubber bushings cause noise and handling issues
• Steering knuckle wear - Particularly common on 4WD models

Rear Suspension Problems

• Leaf spring sag - Especially common on work trucks and high-mileage vehicles
• Broken leaf springs - Individual leaves crack or break completely
• Worn spring bushings - Rubber bushings deteriorate, causing noise and poor ride quality
• U-bolt stretch - Can cause axle wrap and poor handling
• Shock mount failure - Upper shock mounts can tear out of the frame

Parts & Materials Needed

Front Suspension Components (2WD)

Upper Control Arms:

GM Part Numbers:
- 1973-1980: 14044677 (RH), 14044678 (LH)
- 1981-1987: 15570579 (RH), 15570580 (LH)

Lower Control Arms:

GM Part Numbers:
- 1973-1980: 14044679 (RH), 14044680 (LH)
- 1981-1987: 15570581 (RH), 15570582 (LH)

Ball Joints:
- Upper: Moog K6136 or AC Delco 46D0002A
- Lower: Moog K6024 or AC Delco 46D0003A

Coil Springs (2WD):
- Standard: Moog 5374 (front)
- Heavy Duty: Moog 5375 (front)

Front Suspension Components (4WD)

Torsion Bars:

GM Part Numbers:
- K10: 14044685 (RH), 14044686 (LH)
- K20: 14044687 (RH), 14044688 (LH)

Torsion Bar Keys:
- GM 15570585 or Moog K6291

Rear Suspension Components

Leaf Springs:
- C10: 5-leaf standard, 6-leaf heavy duty
- C20: 8-leaf standard configuration
- K10/K20: Model-specific multi-leaf configurations

Spring Hardware:
- Center Bolts: GM 11515490
- U-Bolts: Vary by axle diameter and spring width
- Spring Bushings: Energy Suspension 3.2106 (polyurethane upgrade)

Shock Absorbers

Front Shocks:
- Standard: Monroe 34671 or Gabriel 82671
- Heavy Duty: Bilstein 24-011294 or KYB 344137

Rear Shocks:
- Standard: Monroe 34672 or Gabriel 82672
- Heavy Duty: Bilstein 24-011295 or KYB 344138

Tools Required

• Floor jack and jack stands
• Torque wrench (1/2" drive)
• Ball joint separator or pickle fork
• Spring compressor (for coil springs)
• Torsion bar tool (4WD models)
• Basic hand tools (wrenches, sockets, ratchets)
• Penetrating oil (PB Blaster, Liquid Wrench)

Step-by-Step Guide

Front Ball Joint Replacement (2WD)

Safety Warning: Always use proper jack stands and never work under a vehicle supported only by a jack.

1. Preparation
   - Raise vehicle and secure on jack stands
   - Remove wheel and tire
   - Support lower control arm with floor jack

2. Upper Ball Joint Removal
   - Remove cotter pin and castle nut from upper ball joint
   - Use ball joint separator to disconnect joint from steering knuckle
   - Remove rivets or bolts securing ball joint to upper control arm
   - Install new ball joint with provided bolts and nuts

3. Lower Ball Joint Removal
   - Remove cotter pin and castle nut from lower ball joint
   - Disconnect ball joint from steering knuckle
   - Use ball joint press or C-clamp tool to remove pressed-in joint
   - Press in new ball joint ensuring proper seating

4. Reassembly
   - Reconnect ball joints to steering knuckle
   - Torque upper ball joint nut to 65 ft-lbs
   - Torque lower ball joint nut to 90 ft-lbs
   - Install new cotter pins
   - Perform wheel alignment

Torsion Bar Adjustment (4WD)

1. Measurement
   - Measure ride height from ground to bottom of frame at specified points
   - Standard height: approximately 8.5-9.0 inches for K10

2. Adjustment
   - Locate torsion bar adjustment bolt at rear of torsion bar
   - Turn clockwise to raise, counterclockwise to lower
   - Make small adjustments (1/4 turn) and re-measure
   - Ensure both sides are equal

3. Final Check
   - Road test vehicle and re-check measurements
   - Verify proper headlight aim after adjustment

Leaf Spring Replacement

1. Rear Axle Support
   - Raise vehicle and support frame on jack stands
   - Support rear axle with floor jack
   - Remove wheels and tires

2. Spring Removal
   - Remove shock absorbers (lower mounting bolts)
   - Remove U-bolts securing axle to springs
   - Remove front spring eye bolt
   - Remove rear shackle bolts
   - Remove spring assembly

3. Installation
   - Install new spring with front eye bolt (do not fully tighten)
   - Install rear shackles (do not fully tighten)
   - Position axle on spring and install U-bolts
   - Torque U-bolts to 120 ft-lbs in cross pattern
   - Lower vehicle to load springs, then torque eye bolts to 175 ft-lbs

Year/Model Differences

1973-1980 vs 1981-1987 Changes

Front Suspension Updates (1981+):
- Revised control arm geometry for improved handling
- Different ball joint specifications
- Updated shock mounting configurations
- Modified coil spring rates on some models

Model-Specific Variations:

C10 vs C20:
- C20 models feature heavier-duty springs and components
- Different shock absorber valving
- Upgraded steering components on 3/4-ton models

K10 vs K20:
- K20 models use larger diameter torsion bars
- Heavy-duty ball joints on 3/4-ton 4WD models
- Different ride height specifications

K5 Blazer/Suburban Specifics:
- Shorter wheelbase affects rear spring rates
- Different shock absorber mounting on some Suburban models
- Tailgate weight considerations for Suburban rear suspension

Frame Differences

• 1973-1980: Fully boxed frame sections
• 1981-1987: Some C-channel sections for weight reduction
• Different shock mounting configurations between generations

Tips & Best Practices

Maintenance Best Practices

• Lubricate grease fittings every 3,000 miles or per manufacturer recommendations
• Inspect ball joint boots regularly for tears or damage
• Check torsion bar adjustments annually on 4WD models
• Monitor shock absorber condition - replace in pairs

Upgrade Recommendations

Performance Improvements:
- Polyurethane bushings - Energy Suspension complete kits available
- Upgraded shocks - Bilstein or KYB for improved handling
- Heavy-duty springs - Increase load capacity and reduce sag

Common Upgrade Paths:
1. Budget Refresh: OEM-equivalent parts with polyurethane bushings
2. Performance Build: Premium shocks, upgraded springs, tubular control arms
3. Off-Road Setup: Heavy-duty components, increased ground clearance

Installation Tips

• Always replace components in pairs (left and right sides)
• Use anti-seize compound on threaded fasteners
• Pre-load torsion bars before final tightening on 4WD models
• Perform alignment after any front suspension work

Cost-Saving Strategies

• Rebuild vs Replace: Many components can be rebuilt with bushing kits
• Shop Multiple Vendors: Compare prices between LMC Truck, Classic Industries, and local parts stores
• Group Purchases: Buy complete suspension kits for better pricing

Troubleshooting

Diagnostic Procedures

Front End Noise:
1. Clunking over bumps - Check ball joints, control arm bushings
2. Squeaking when turning - Inspect ball joint boots and lubrication
3. Grinding noise - Worn ball joints or steering knuckle bushings

Handling Issues:
1. Vehicle pulls to one side - Check tire pressure, alignment, worn suspension components
2. Excessive body roll - Worn shock absorbers or anti-sway bar components
3. Steering wheel vibration - Ball joints, tire balance, alignment issues

Ride Height Problems:
1. Front end sag (2WD) - Worn coil springs, check for proper spring identification
2. Front end sag (4WD) - Torsion bar adjustment, worn torsion bar bushings
3. Rear end sag - Leaf spring fatigue, overloading, worn spring bushings

Testing Procedures

Ball Joint Inspection:
1. Raise vehicle with tire off ground
2. Grasp tire at 12 and 6 o'clock positions
3. Rock tire vertically - excessive movement indicates worn ball joints
4. Maximum allowable play: 0.050" axial, 0.125" radial

Shock Absorber Testing:
1. Visual inspection for fluid leakage
2. Bounce test - vehicle should settle within 2-3 oscillations
3. Road test for excessive bouncing or poor control

Spring Condition Assessment:
1. Measure ride height at specified points
2. Visual inspection for cracked or broken leaves
3. Check for proper spring arch and alignment

Common Diagnostic Mistakes

• Assuming alignment issues are suspension problems - Always check tire condition first
• Replacing shocks without addressing worn bushings - Address root causes
• Ignoring frame condition - Inspect mounting points for cracks or damage
• Mixing component generations - Ensure compatibility between year ranges