Tailgate Repair and Replacement - GM Square Body Trucks (1973-1987)

Overview

The tailgate is one of the most frequently used and abused components on GM Square Body trucks (C10, C20, K10, K20, K5 Blazer, and Suburban). This comprehensive guide covers everything needed to repair, restore, or replace tailgates on 1973-1987 GM Square Body vehicles. Whether dealing with rust damage, broken hinges, faulty latches, or complete replacement needs, this article provides the technical knowledge and procedures necessary for successful tailgate restoration.

Proper tailgate function is critical for both utility and safety. A properly functioning tailgate ensures secure cargo transport, maintains the truck's structural integrity, and preserves the vehicle's value. Given the age of these vehicles, tailgate issues are extremely common and often require immediate attention.

Common Issues

Rust and Corrosion

Lower tailgate edge: Most common failure point due to water accumulation and road salt
Hinge mounting areas: Corrosion around hinge bolt holes causes structural weakness
Inner reinforcement panels: Hidden rust that compromises tailgate strength
Handle and latch mounting points: Rust causes loose or failed hardware

Hardware Failures

Hinge pin wear: Causes tailgate to sag or bind during operation
Latch mechanism failure: Prevents proper closing or causes accidental opening
Handle spring breakage: Results in loose or non-functioning tailgate handle
Cable and chain wear: Safety chains stretch or break; support cables fray

Structural Damage

Dented outer skin: Impact damage from loading/unloading
Bent hinge brackets: Usually from overloading or improper use
Cracked welds: Stress fractures at mounting points and reinforcement areas

Alignment Issues

Uneven gaps: Poor fit with truck bed sides
Binding operation: Difficulty opening/closing due to worn components
Water leaks: Compromised weatherstripping or misalignment

Parts & Materials Needed

OEM and Reproduction Parts

Complete Tailgates

1973-1987 C/K Series Pickup:
- LMC Truck: 40-1436 (Complete tailgate assembly)
- Classic Industries: T1436 (OE-style replacement)
- Brothers Trucks: BT-1436-TG (Premium reproduction)

1973-1991 Suburban/K5 Blazer:
- LMC Truck: 40-1437 (Suburban tailgate)
- Classic Industries: T1437 (K5 Blazer tailgate)

Hardware Components

Hinge Sets:
- ACDelco: 15995398 (Driver side hinge)
- ACDelco: 15995399 (Passenger side hinge)
- LMC Truck: 40-1438 (Hinge pair with pins)

Latch Mechanisms:
- Dorman: 38457 (Tailgate latch assembly)
- LMC Truck: 40-1440 (Complete latch kit)

Handle Assembly:
- Dorman: 77110 (Outside handle)
- LMC Truck: 40-1442 (Handle with springs)

Tools Required

Basic Tools

Socket set: 7mm, 8mm, 10mm, 13mm, 15mm
Wrenches: Combination set 7mm-15mm
Screwdrivers: Phillips and flathead assortment
Pliers: Needle-nose and standard
Center punch and drill bits: For hinge pin removal
Wire brush: For cleaning threads and surfaces

Specialized Tools

Hinge pin removal tool: OTC 4530 or equivalent
Panel beating tools: For minor dent repair
Welding equipment: MIG welder for structural repairs
Cutting tools: Plasma cutter or angle grinder for rust removal

Materials and Supplies

Restoration Materials

POR-15 rust preventive paint: For treating surface rust
SEM metal prep: 39722 for surface preparation
3M weatherstrip adhesive: 08008 for seal installation
Anti-seize compound: For hinge pins and hardware

Fasteners

Hinge Bolts: 1/2"-13 x 1.5" Grade 8 hex bolts
Hinge Nuts: 1/2"-13 hex nuts with lock washers
Latch Screws: #10-24 x 1" Phillips head screws
Handle Rivets: 1/8" aluminum pop rivets (if applicable)

Step-by-Step Guide

Tailgate Removal

Preparation

Open tailgate fully and engage safety chains to prevent accidental closure
Disconnect any electrical connections (if equipped with rear window defroster on Suburban/Blazer)
Remove tailgate cables by disconnecting at bed-side mounting points
Have assistant support tailgate weight during removal process

Hinge Pin Removal

Clean hinge pin ends with wire brush to remove rust and debris
Apply penetrating oil (PB Blaster or equivalent) to both hinge pins
Center punch hinge pin on the side with the removable end (typically driver side)
Drive out hinge pin using 3/16" punch and hammer, working from bottom to top
Repeat process for passenger side hinge pin

Safety Warning: Always support tailgate weight when removing second hinge pin to prevent dropping.

Tailgate Installation

Hinge Alignment

Position new/repaired tailgate with assistant supporting weight
Align hinge brackets ensuring proper spacing and level orientation
Insert hinge pins from top down, ensuring smooth operation
Apply anti-seize compound to hinge pins before final installation

Hardware Installation

Install latch mechanism using factory torque specifications:
- Latch bolts: 15 ft-lbs
- Handle screws: 8 ft-lbs
Connect support cables ensuring proper length and secure mounting
Adjust latch engagement for proper closing force and alignment

Rust Repair Procedures

Assessment and Preparation

Remove all loose rust using wire brushes and sandpaper
Cut out severely damaged sections using plasma cutter or angle grinder
Clean bare metal with SEM metal prep solution
Prime immediately with POR-15 or equivalent rust-preventive primer

Patch Panel Installation

Create templates for replacement panels using cardboard
Cut replacement metal from 18-gauge steel sheet
Weld patch panels using proper MIG welding techniques:
- Wire size: 0.023" solid wire
- Gas mixture: 75% Argon/25% CO2
- Amperage: 90-110 amps for 18-gauge steel
Grind welds smooth and apply rust preventive treatment

Year/Model Differences

1973-1980 vs 1981-1987 Differences

Structural Changes

1973-1980: Heavier gauge steel construction, more robust hinge design
1981-1987: Lighter construction with revised hinge geometry for improved operation

Hardware Variations

1973-1980 Handle Design:
- Part Number: GM 14045715
- Mounting: Three-bolt pattern
- Spring mechanism: Dual coil springs

1981-1987 Handle Design:
- Part Number: GM 14088641
- Mounting: Two-bolt pattern with clips
- Spring mechanism: Single torsion spring

Model-Specific Considerations

C10/C20 Standard Bed

Tailgate width: 62.5 inches
Hinge spacing: 54 inches center-to-center
Standard features: Basic latch, manual operation

K10/K20 4WD Models

Identical dimensions to 2WD counterparts
Additional considerations: Ground clearance affects loading angle
Hardware compatibility: Same parts as C-series trucks

K5 Blazer Tailgate

Unique specifications:
- Width: 62.5 inches (same as pickup)
- Height: Reduced compared to pickup
- Window integration: 1973-1975 models
- Spare tire mounting: Optional equipment

Suburban Tailgate

Distinctive features:
- Split design: Upper window, lower tailgate
- Electric window operation: Available 1979+
- Heavier construction: Additional reinforcement
- Unique hardware: Window regulators and motors

Convertible Top Models (K5 Blazer)

Soft top considerations: Tailgate must seal properly with convertible top
Hardware differences: Modified latch mechanisms for top integration
Weatherstripping: Special profiles for soft top sealing

Tips & Best Practices

Restoration Best Practices

Rust Prevention

Apply undercoating to inner tailgate surfaces during restoration
Use stainless steel hardware where possible to prevent future corrosion
Seal all welded joints with seam sealer to prevent water intrusion
Install drain holes at low points to prevent water accumulation

Hardware Maintenance

Lubricate hinge pins annually with white lithium grease
Adjust latch mechanisms seasonally as metal expands/contracts
Replace weatherstripping every 5-7 years for optimal sealing
Inspect safety chains regularly for wear and proper attachment

Professional vs. DIY Considerations

DIY-Friendly Tasks

Hardware replacement: Latches, handles, and basic components
Minor rust repair: Surface rust treatment and small patch work
Adjustment procedures: Latch and hinge alignment
Weatherstripping replacement: Straightforward with proper adhesives

Professional Recommended

Major structural welding: Requires proper equipment and expertise
Frame straightening: Bent hinge mounting points need professional repair
Paint matching: Color matching for visible repairs
Electrical integration: Suburban rear window systems

Budget vs. Premium Approaches

Budget Restoration

Estimated costs:
- Used OEM tailgate: $200-400
- Basic hardware kit: $75-125
- DIY rust repair materials: $50-100
- Total budget approach: $325-625

Premium Restoration

Estimated costs:
- New reproduction tailgate: $600-900
- Complete hardware upgrade: $200-300
- Professional bodywork: $400-800
- Total premium approach: $1,200-2,000

Troubleshooting

Diagnostic Procedures

Tailgate Won't Stay Closed

Possible Causes:
1. Worn latch mechanism: Replace latch assembly
2. Misaligned strike plate: Adjust bed-side mounting
3. Stretched safety chains: Replace with proper length chains
4. Bent tailgate frame: Professional straightening required

Testing Procedure:
1. Check latch engagement with tailgate in closed position
2. Measure gap consistency around tailgate perimeter
3. Inspect strike plate wear for unusual patterns
4. Test spring tension in latch mechanism

Tailgate Binds During Operation

Possible Causes:
1. Worn hinge pins: Replace pins and bushings
2. Misaligned hinges: Adjust mounting bolt positions
3. Bent tailgate frame: Straighten or replace tailgate
4. Debris in hinges: Clean and lubricate thoroughly

Resolution Steps:
1. Remove hinge pins and inspect for wear
2. Check hinge bracket alignment using straight edge
3. Measure tailgate for squareness using diagonal measurements
4. Lubricate all pivot points with appropriate grease

Tailgate Rattles or Makes Noise

Possible Causes:
1. Loose hinge pins: Tighten or replace worn components
2. Worn weatherstripping: Replace perimeter seals
3. Loose hardware: Tighten all mounting bolts to specification
4. Missing bump stops: Install rubber cushions at contact points

Diagnostic Steps:
1. Road test to isolate noise source
2. Visual inspection of all mounting points
3. Hand operation test to identify binding or loose components
4. Torque verification of all accessible fasteners

Common Repair Mistakes

Installation Errors

Incorrect hinge pin orientation: Pins must be installed from top down
Over-tightening hardware: Can cause binding and premature wear
Misaligned strike plates: Results in poor latching and wear
Inadequate lubrication: Leads to premature component failure

Material Selection Issues

Wrong gauge steel: Too thin for structural repairs
Incompatible primers: Can cause paint adhesion problems
Incorrect fastener grades: Low-grade bolts fail under load
Poor quality weatherstripping: Premature deterioration and leaks

Preventive Maintenance Schedule

Monthly Inspections

Visual check for rust development
Operation test for smooth opening/closing
Hardware tightness verification
Safety chain condition assessment

Annual Maintenance

Lubricate hinge pins with white lithium grease
Adjust latch mechanisms for proper engagement
Inspect weatherstripping for wear and damage
Touch up paint any chips or scratches immediately

Long-term Care (3-5 Years)

Complete hardware inspection with replacement as needed
Weatherstripping replacement for optimal sealing
Comprehensive rust treatment of any developing problems
Professional alignment check if operation issues develop

This comprehensive approach to tailgate repair and replacement ensures Square Body truck owners have the knowledge and procedures necessary for successful restoration and long-term reliability.

Tailgate Repair and Replacement - Square Body Trucks