1978 Jeep CJ7 Model. 20 Rear End Housing For Sale Used: Your Comprehensive Buyer’s Guide

1978 Jeep CJ7 Model. 20 Rear End Housing For Sale Used: Your Comprehensive Buyer’s Guide jeeps.truckstrend.com

The 1978 Jeep CJ7 stands as an icon of off-road capability and classic American ruggedness. For enthusiasts and restorers alike, maintaining these venerable vehicles often means sourcing original or period-correct parts. Among the most critical components of any drivetrain is the rear axle, and for the 1978 CJ7, the standard was the AMC Model 20 rear axle. While often mistakenly referred to as a "Dana 20 rear end" (the Dana 20 is actually a transfer case, a completely different component), the AMC Model 20 Rear End Housing is the core subject when discussing the rear axle of this vintage CJ.

This comprehensive guide is dedicated to understanding, sourcing, and evaluating a used 1978 Jeep CJ7 AMC Model 20 Rear End Housing. Whether you’re replacing a damaged axle, undertaking a full restoration, or planning an upgrade, knowing what to look for is paramount. Acquiring a used housing can be a cost-effective and authentic solution, but it requires careful consideration to ensure you’re getting a reliable component.

1978 Jeep CJ7 Model. 20 Rear End Housing For Sale Used: Your Comprehensive Buyer’s Guide

The AMC 20 Rear Axle in the 1978 Jeep CJ7: A Closer Look

The AMC Model 20 rear axle was a staple in Jeep CJ models from 1976 through 1986, including the 1978 CJ7. Designed by American Motors Corporation (AMC), it was intended to be a robust axle for light trucks and SUVs. While generally adequate for stock applications, it gained a reputation among serious off-roaders for certain weaknesses, primarily its two-piece axle shafts and relatively thin axle tubes, especially compared to its more robust cousin, the Dana 44, which was an option on some CJ models.

Key Characteristics of the 1978 CJ7 AMC 20 Rear Axle:

• Semi-Float Design: The axle shafts support the weight of the vehicle and are bolted to the wheel hub.
• Two-Piece Axle Shafts: The notorious original design featured a flanged outer shaft bolted to the inner shaft. This joint was a common point of failure under stress, especially with larger tires and aggressive off-roading.
• Differential: Typically equipped with an open differential, though Limited Slip Differentials (LSDs) were available as an option.
• Gear Ratios: Common factory ratios included 2.73, 3.54, and 4.10, depending on the engine and transmission configuration.



• Bolt Pattern: 5 on 5.5 inches (the standard Jeep CJ pattern).
• Axle Tubes: Relatively thin-walled, making them susceptible to bending under extreme conditions without reinforcement.

Despite its perceived weaknesses, the AMC 20 is a very common and readily available axle. Its large ring gear (8.875 inches) and widespread availability make it a popular candidate for upgrades, especially the conversion to one-piece axle shafts.

Why Seek a Used AMC 20 Rear End Housing?

The decision to purchase a used AMC 20 rear end housing is often driven by several practical factors:

1. Cost-Effectiveness: New, bare axle housings for vintage vehicles are scarce and, if available, significantly more expensive than used counterparts. A used housing can save hundreds of dollars, allowing budget for other parts or upgrades.
2. Authenticity for Restoration: For purists aiming for a period-correct restoration, a used original housing maintains the authenticity of the vehicle.
3. Availability: The AMC 20 was widely produced, meaning there’s a larger supply of used housings compared to more obscure or specialized axles.



4. Donor for Upgrades: Many enthusiasts purchase used AMC 20 housings specifically as a foundation for performance upgrades, such as installing one-piece axle shafts, a locker, or trussing the tubes.
5. Replacement for Damage: If your current housing is bent, cracked, or severely rusted, a used housing provides a direct replacement option.

Critical Factors When Purchasing a Used AMC 20 Housing

Buying a used axle housing isn’t like buying a new part off the shelf. Careful inspection and due diligence are crucial to avoid costly mistakes.

1. Condition of the Housing:

   • Rust: Surface rust is common and generally not an issue, but severe, pitting rust can compromise the structural integrity. Pay close attention to welds and mounting points.
   • Dents/Damage: Inspect for any significant dents, especially on the axle tubes. Large dents can weaken the tube or indicate a previous impact.
   • Cracks: Look for cracks, particularly around the differential housing, spring perches, and shock mounts. These can be signs of extreme stress or impacts.
   • Straightness: This is perhaps the most critical factor. A bent axle housing will cause premature bearing wear, alignment issues, and can be impossible to correct without specialized equipment.

2. Completeness:

   • Are you buying just the bare housing? Or does it include axle shafts, differential, ring and pinion gears, and brake components? A bare housing is cheaper but requires more parts sourcing. A complete axle might be more expensive but offers convenience.
   • If it includes components, are they in usable condition? Axle shafts should be checked for straightness and spline wear. Gears should be inspected for pitting or chipped teeth.

3. Gear Ratio: If you’re buying a complete axle, ensure the gear ratio matches your existing front axle (if you have 4WD) or your intended use. Mixing ratios will cause severe drivetrain damage in 4WD.

4. Axle Shafts (if included): If the housing comes with shafts, confirm if they are the original two-piece design or if they have been upgraded to one-piece shafts. One-piece shafts are a significant upgrade in terms of strength and reliability.

5. Bearing Surfaces: Inspect the ends of the axle tubes where the wheel bearings sit. Any significant wear, pitting, or damage here can lead to premature bearing failure.

6. Seller Reputation and Documentation: Purchase from a reputable seller. Ask for detailed photos from multiple angles, and inquire about the vehicle the axle came from (e.g., mileage, accident history).

Inspection Checklist for Potential Buyers

Before committing to a purchase, use this checklist to thoroughly inspect the AMC 20 housing:

• Visual Scan: Walk around the entire housing. Look for obvious signs of impact, bending, or severe rust.
• Tube Straightness (Visual & String Method):
  • Visual: From a distance, sight down the axle tubes from one end to the other. They should appear perfectly straight.
  • String Method: While not perfectly precise, you can run a taut string or fishing line from one end of the axle tube to the other, ensuring it doesn’t touch in the middle. Do this on both sides. This can reveal major bends. For ultimate certainty, a professional shop with a jig is recommended.
• Differential Housing: Check for cracks, especially around the welds where the tubes meet the pumpkin. Look for signs of impact on the bottom or front.
• Spring Perches & Shock Mounts: These are common areas for stress cracks, especially if the vehicle was heavily off-roaded. Ensure they are intact and not bent.
• Brake Backing Plate Mounts: Check for damage or stripped bolt holes.
• Drain and Fill Plugs: Ensure they are not seized or stripped.
• Axle Flanges (if present): If shafts are included, check the flanges for bends or cracks.
• General Cleanliness: A clean axle doesn’t guarantee quality, but it suggests the seller took care of it. Excessive grime can hide issues.

Preparing and Installing Your Used Housing

Once you’ve acquired your used AMC 20 housing, there are several steps to prepare it for installation:

1. Thorough Cleaning: Degrease and pressure wash the housing to remove all dirt, oil, and grime.
2. Surface Prep & Painting: Once clean and dry, use a wire brush or sander to remove loose rust. Apply a rust-inhibiting primer, followed by a durable topcoat (e.g., chassis paint, epoxy paint) for protection.
3. Internal Inspection (if bare): If you purchased a bare housing, thoroughly clean the inside of the tubes and differential housing.
4. New Components: Plan to install new wheel bearings, seals, and differential bearings. If installing new gears, ensure proper setup with shims and backlash adjustment. This often requires specialized tools and expertise. Unless you are an experienced mechanic, consider having a professional shop set up your gears.
5. Upgrades (Optional): This is the ideal time to perform any desired upgrades, such as installing one-piece axle shafts, a locker, or welding on a truss kit for added strength.

Upgrading the AMC 20: Enhancing Durability and Performance

While the stock AMC 20 has its limitations, it’s highly modifiable, making it a viable option for many Jeepers.

• One-Piece Axle Shaft Conversion: This is the most crucial and recommended upgrade. Kits are widely available and replace the weak two-piece design with robust, single-piece chromoly shafts. This eliminates the primary failure point.
• Full-Float Conversion: Less common but highly effective, a full-float conversion moves the vehicle’s weight off the axle shafts and onto the axle housing and hub assembly, similar to heavy-duty truck axles.
• Axle Tube Trussing/Reinforcement: Welding a steel truss along the top or bottom of the axle tubes significantly increases their resistance to bending, especially for vehicles running larger tires or subjected to aggressive off-roading.
• Differential Upgrades: Installing a locker (e.g., Detroit Locker, ARB Air Locker) or a limited-slip differential will greatly enhance traction off-road.
• Heavy-Duty Differential Cover: A thicker differential cover can add rigidity to the housing and provide better protection for the gears.

Table: Estimated Pricing for Used 1978 Jeep CJ7 AMC 20 Rear End Housings

Please note: Prices for used auto parts can vary wildly based on condition, location, seller, market demand, and completeness. These are general estimates. Shipping costs can be substantial for an axle housing.

| Component Description | Estimated Price Range (USD) | Notes