Weatherstripping and Seals - GM Square Body Trucks (1973-1987)

Overview

Weatherstripping and seals are critical components that protect the interior of 1973-1987 GM Square Body trucks from water, dust, wind, and road noise while maintaining proper door, window, and tailgate operation. This comprehensive system includes door seals, window weatherstripping, tailgate seals, vent window seals, and various body panel seals throughout the vehicle.

Over time, the original rubber and foam weatherstripping deteriorates due to UV exposure, temperature cycling, and normal wear. Proper weatherstrip maintenance and replacement is essential for:

• Interior protection from water intrusion and dust
• Noise reduction from wind and road noise
• Climate control efficiency by sealing heated/cooled air
• Door and window operation with proper fit and alignment
• Rust prevention by keeping moisture out of critical areas
• Overall comfort during driving

Square Body trucks used various weatherstrip materials including EPDM rubber, foam-backed rubber, and felt-lined channels. Understanding the specific applications and replacement procedures ensures proper sealing and authentic restoration.

Common Issues

Door Weatherstripping Problems

• Hardened primary door seals causing wind noise and water leaks
• Compressed or missing foam backing on door frame weatherstrip
• Torn or separated corner joints at door frame intersections
• Improper door adjustment causing weatherstrip binding or poor sealing
• Missing or damaged door sill plates and threshold seals

Window Weatherstripping Issues

• Deteriorated window run channels causing binding or water intrusion
• Hardened vent window seals on 1973-1982 models
• Missing or damaged windshield and rear window seals
• Cracked quarter window weatherstrip on Blazer and Suburban models
• Failed sliding rear window seals on applicable models

Tailgate and Body Seals

• Missing tailgate weatherstrip causing dust and water intrusion
• Deteriorated cab-to-bed seals on pickup models
• Failed cowl seals allowing water into HVAC system
• Missing hood-to-cowl weatherstrip causing engine bay debris intrusion

Age-Related Deterioration

• UV damage causing cracking and hardening
• Ozone deterioration making rubber brittle
• Adhesive failure causing weatherstrip separation
• Compression set where foam backing permanently compresses

Parts & Materials Needed

Essential Tools

• Weatherstrip adhesive - 3M Super Weatherstrip Adhesive (08008) or equivalent
• Plastic trim removal tools - Prevent damage to painted surfaces
• Heat gun or hair dryer - For adhesive removal and installation
• Adhesive remover - 3M General Purpose Adhesive Cleaner (08984)
• Clean rags and tack cloth
• Utility knife with fresh blades
• Measuring tape
• Door adjustment tools (if needed)

Door Weatherstripping Parts

Primary Door Seals (Attaches to Door)

1973-1980 C/K Pickup:
- Front doors: GM 20298049 (LH), 20298050 (RH)
- LMC Truck: 33-1436 (pair)

1981-1987 C/K Pickup:
- Front doors: GM 15571753 (LH), 15571754 (RH)
- LMC Truck: 33-1437 (pair)

1973-1991 Blazer/Suburban:
- Front doors: GM 20298049 (LH), 20298050 (RH)
- Rear doors: GM 20370513 (LH), 20370514 (RH)

Door Frame Weatherstrip (Attaches to Body)

1973-1987 All Models:
- Complete kit: LMC Truck 33-1434
- Front door frames: Steele Rubber 70-1307-80
- Individual pieces available by location

Window Weatherstripping

Window Run Channels

1973-1987 C/K Pickup:
- Front door: LMC Truck 33-1449 (inner), 33-1450 (outer)
- Felt-lined channels: Steele Rubber 70-1315-80

1973-1991 Blazer/Suburban:
- Front doors: Same as pickup
- Rear doors: LMC Truck 33-1451 (inner), 33-1452 (outer)

Vent Window Seals (1973-1982)

Complete vent window weatherstrip kit:
- LMC Truck: 33-1445
- Individual seals: Steele Rubber 70-1320 series

Windshield and Fixed Glass

Windshield seal (non-adhesive glass):
- 1973-1987: LMC Truck 33-1460
- Rear window seal: LMC Truck 33-1461
- Quarter window seals (Blazer/Suburban): 33-1463

Tailgate and Body Seals

Tailgate weatherstrip:
- 1973-1987 Pickup: LMC Truck 33-1470
- Blazer/Suburban rear door: 33-1471

Cab-to-bed seal:
- 1973-1987 Pickup: LMC Truck 33-1480

Hood seals:
- Hood-to-cowl: 33-1490
- Hood perimeter: 33-1491

Adhesives and Sealants

• 3M Super Weatherstrip Adhesive (08008) - Primary adhesive
• 3M Weatherstrip Adhesive (08001) - Alternative option
• Permatex Form-A-Gasket - For custom applications
• Butyl tape - For windshield and fixed glass sealing

Step-by-Step Guide

Door Weatherstrip Replacement

Primary Door Seal Replacement

1. Remove old weatherstrip
   - Open door fully and support properly
   - Carefully pull weatherstrip from door perimeter
   - Use heat gun to soften stubborn adhesive
   - Clean all adhesive residue with adhesive remover

2. Prepare door surface
   - Sand lightly if necessary to remove adhesive buildup
   - Clean with tack cloth and adhesive cleaner
   - Ensure surface is completely dry

3. Install new weatherstrip
   - Start at bottom center of door
   - Apply thin, even coat of weatherstrip adhesive to door flange
   - Press weatherstrip firmly, working around door perimeter
   - Pay special attention to corner areas for proper sealing
   - Trim excess material with sharp utility knife

4. Final adjustment
   - Close door gently to check fit
   - Adjust door alignment if necessary before adhesive fully cures
   - Allow 24 hours cure time before normal use

Door Frame Weatherstrip Replacement

1. Remove interior trim panels
   - Remove door sill plates
   - Carefully remove A-pillar and B-pillar trim
   - Access varies by year and model

2. Remove old weatherstrip
   - Pull weatherstrip from body channels
   - Clean channels thoroughly
   - Inspect for rust or damage, repair as needed

3. Install new weatherstrip
   - Start at door sill area
   - Work weatherstrip into body channels
   - Ensure proper seating in corners and joints
   - Some sections may require adhesive, others press-fit

4. Reinstall trim panels
   - Replace all removed trim pieces
   - Ensure proper alignment and fit

Window Run Channel Replacement

Front Door Window Channels

1. Remove door panel and window
   - Follow door panel removal procedures
   - Lower window to access upper channel mounting
   - Remove window regulator if necessary for access

2. Remove old channels
   - Inner channel: Remove screws at top and bottom
   - Outer channel: Usually held by clips and adhesive
   - Note orientation and positioning for installation

3. Install new channels
   - Test fit before applying adhesive
   - Apply weatherstrip adhesive to mounting surfaces
   - Install inner channel first, then outer
   - Ensure smooth operation throughout window travel

4. Reassemble and test
   - Reinstall window and regulator
   - Test window operation before installing door panel
   - Adjust as necessary for smooth operation

Vent Window Seal Replacement (1973-1982)

1. Remove vent window assembly
   - Remove interior door panel
   - Disconnect vent window linkage
   - Remove vent window frame bolts
   - Carefully remove complete assembly

2. Disassemble vent window
   - Remove glass from frame (note orientation)
   - Remove old weatherstrip and clean frame
   - Inspect frame for damage or corrosion

3. Install new seals
   - Apply new weatherstrip to frame channels
   - Use appropriate adhesive for permanent installation
   - Ensure proper glass fit and sealing

4. Reassemble and install
   - Install glass in frame with new weatherstrip
   - Test operation before final installation
   - Reinstall complete assembly in door

Tailgate Weatherstrip Installation

1. Prepare tailgate
   - Clean tailgate perimeter thoroughly
   - Remove any old adhesive or weatherstrip remnants
   - Ensure proper tailgate alignment and operation

2. Install weatherstrip
   - Start at bottom center of tailgate
   - Apply adhesive to tailgate flange
   - Press weatherstrip firmly around perimeter
   - Pay special attention to corner areas

3. Test fit and adjust
   - Close tailgate to check sealing
   - Adjust tailgate alignment if necessary
   - Trim excess material as needed

Year/Model Differences

Early vs. Late Square Body Changes

1973-1980 Models

• Vent windows standard on all models until 1982
• Non-adhesive windshields with rubber weatherstrip seals
• Different door handle configurations affecting weatherstrip routing
• Unique Blazer removable top seals on convertible models

1981-1987 Models

• Revised door weatherstrip design with improved corner sealing
• Elimination of vent windows starting 1983 (varies by model)
• Adhesive-mounted windshields on some late models
• Improved HVAC sealing with revised cowl weatherstrip

Model-Specific Differences

C10/C20 vs. K10/K20 Trucks

• Identical weatherstrip applications for most components
• Same door and window seals across 2WD and 4WD models
• Cab-to-bed seals identical regardless of drivetrain

K5 Blazer Specific Items

• Removable hardtop seals (1973-1975)
• Quarter window weatherstrip different from pickup trucks
• Rear door seals (4-door models)
• Tailgate vs. rear door weatherstrip applications

Suburban Differences

• Extended body seals for longer wheelbase
• Rear door weatherstrip (all Suburbans)
• Rear quarter window seals unique to Suburban
• Tailgate weatherstrip similar to pickup but longer

Heavy Duty Truck Variations (C20/K20)

• Same weatherstrip applications as light duty trucks
• Heavier duty door hinges may affect door alignment
• Identical part numbers for most weatherstrip components

Special Applications

Crew Cab Models (1973-1987)

• Rear door weatherstrip required
• Extended cab sealing considerations
• Additional door frame weatherstrip

Diesel Engine Models (1982-1987)

• Standard weatherstrip applications
• No specific diesel-related weatherstrip changes

Tips & Best Practices

Installation Best Practices

Surface Preparation

• Always clean thoroughly - Remove all old adhesive and dirt
• Use proper solvents - 3M adhesive cleaner or equivalent
• Allow complete drying - Moisture prevents proper adhesion
• Light sanding may help - Improves adhesion on painted surfaces

Adhesive Application

• Thin, even coats - Too much adhesive causes mess and poor bonding
• Follow temperature guidelines - Install between 65-85°F when possible
• Work in sections - Don't apply adhesive faster than you can install
• Allow proper cure time - 24 hours before normal use

Weatherstrip Handling

• Store flat when possible - Prevents permanent kinks
• Warm before installation - Makes rubber more pliable
• Don't stretch excessively - Can cause premature failure
• Test fit before adhesive - Ensure proper length and routing

Professional Techniques

Door Alignment Priority

1. Fix door alignment first - Weatherstrip won't compensate for misaligned doors
2. Check hinge wear - Replace worn hinges before weatherstrip
3. Verify door gaps - Should be consistent around perimeter
4. Test operation - Doors should close easily without slamming

Corner Treatment

• Miter corners properly - Prevents bunching and improves sealing
• Use extra adhesive - Corners see the most stress
• Form carefully - Don't stretch around tight corners
• Consider pre-formed corners - Available for some applications

Window Channel Installation

• Check window alignment - Before installing new channels
• Lubricate lightly - Silicone spray on felt-lined channels
• Test throughout travel - Window should operate smoothly
• Adjust door glass - May be necessary with new channels

Common Mistakes to Avoid

Installation Errors

• Installing over dirty surfaces - Causes premature failure
• Using wrong adhesive - Not all adhesives work with all materials
• Stretching weatherstrip - Causes gaps when material relaxes
• Ignoring door alignment - Poor alignment ruins weatherstrip quickly

Material Selection

• Using cheap aftermarket parts - Often poor fit and short life
• Wrong material type - EPDM vs. neoprene vs. foam applications
• Incorrect dimensions - Measure twice, order once
• Missing backing materials - Some weatherstrip requires separate adhesive

Timing Issues

• Installing in wrong weather - Avoid extreme temperatures
• Not allowing cure time - Premature use causes failure
• Working too fast - Take time for proper installation
• Ignoring seasonal effects - Materials expand and contract

Cost-Effective Approaches

Budget Options

• Prioritize critical seals - Doors and windows first
• Shop multiple suppliers - Prices vary significantly
• Consider universal materials - For non-critical applications
• DIY installation - Save labor costs with proper preparation

Premium Approaches

• OEM or OEM-equivalent parts - Best fit and longevity
• Professional installation - For complex applications
• Complete system replacement - All seals at once for consistency
• Upgrade materials - Modern compounds may outlast original

Troubleshooting

Water Leak Diagnosis

Door Area Leaks

Symptoms: Water dripping from door panels, wet floor mats, musty odors

Diagnosis Steps:
1. Spray test with garden hose - Start low, work up
2. Check door alignment - Gaps should be consistent
3. Inspect primary door seal - Look for gaps, hardening, or damage
4. Check door frame weatherstrip - Ensure proper seating
5. Verify door sill seals - Often overlooked leak source

Common Causes:
- Hardened or damaged primary door seal
- Misaligned doors causing weatherstrip compression
- Missing or damaged door sill weatherstrip
- Clogged door drain holes allowing water backup

Window Area Leaks

Symptoms: Water on door panels, wet window sills, fogged glass

Diagnosis Steps:
1. Check window run channels - Look for gaps or damage
2. Inspect vent window seals (1973-1982) - Common failure point
3. Test window alignment - Should seal evenly when closed
4. Check windshield seal - Look for separation or cracking

Solutions:
- Replace damaged window run channels
- Reseal vent window assemblies
- Adjust window alignment in door
- Professional windshield seal replacement if needed

Wind Noise Issues

Door-Related Wind Noise

Symptoms: Whistling or rushing air noise, especially at highway speeds

Diagnosis:
1. Drive with windows slightly open - Isolate noise source
2. Check door closure - Should close firmly without slamming
3. Inspect weatherstrip compression - Should compress evenly
4. Look for gaps or damage - Use flashlight to check sealing

Solutions:
- Replace hardened or damaged weatherstrip
- Adjust door alignment for proper sealing
- Add weatherstrip thickness if gaps exist
- Check for missing weatherstrip sections

Window and Vent Noise

Common Sources:
- Worn vent window seals (1973-1982 models)
- Misaligned door glass
- Damaged window run channels
- Missing quarter window seals (Blazer/Suburban)

Difficult Door Operation

Doors Hard to Close

Possible Causes:
- Weatherstrip too thick or improperly installed
- Door misalignment
- Worn hinges or striker plates
- Binding in window channels

Solutions:
1. Check weatherstrip thickness - May need thinner material
2. Adjust door alignment - Hinges, striker plates
3. Lubricate moving parts - Hinges, latches, window mechanisms
4. Verify proper installation - Weatherstrip shouldn't bind

Windows Binding or Sticking

Diagnosis Steps:
1. Test window operation - Note where binding occurs
2. Inspect window channels - Look for debris or damage
3. Check door alignment - Affects window travel
4. Verify channel installation - Proper positioning critical

Solutions:
- Clean and lubricate window channels
- Adjust door alignment if necessary
- Replace damaged or improperly installed channels
- Check for interference from door panel or trim

Premature Weatherstrip Failure

Common Failure Modes

• Adhesive failure - Weatherstrip separates from mounting surface
• Material deterioration - Cracking, hardening, or tearing
• Compression set - Permanent deformation, loss of sealing
• UV damage - Surface cracking and brittleness

Prevention Strategies

1. Use quality materials - OEM or equivalent weatherstrip
2. Proper surface preparation - Clean, dry mounting surfaces
3. Correct installation techniques - Follow manufacturer procedures
4. Regular maintenance - Clean and protect weatherstrip
5. Address door alignment - Prevents premature wear

Extending Service Life

• Clean regularly with mild soap and water
• Protect from UV - Use rubber protectant products
• Avoid petroleum products - Can damage rubber compounds
• Check and adjust doors - Maintain proper alignment
• Replace in complete sets - Ensures consistent sealing and appearance

Troubleshooting Tools and Techniques

Leak Detection Methods

• Garden hose spray test - Systematic water application
• Smoke testing - Professional technique for air leaks
• Fluorescent dye - Added to water for precise leak location
• Ultrasonic detectors - Professional equipment for wind noise

Measurement and Alignment Tools

• Door gap gauges - Ensure consistent spacing
• Alignment bars - Check door and window positioning
• Compression gauges - Verify weatherstrip sealing pressure
• Feeler gauges - Measure gaps and clearances

This comprehensive guide covers the essential aspects of weatherstripping and seals for 1973-1987 GM Square Body trucks. Proper installation and maintenance of these components is crucial for vehicle comfort, protection, and longevity.