1978 Jeep CJ7 Model 20 Rear End Housing For Sale Used: A Comprehensive Guide

1978 Jeep CJ7 Model 20 Rear End Housing For Sale Used: A Comprehensive Guide jeeps.truckstrend.com

The 1978 Jeep CJ7 stands as an enduring icon of American off-roading, cherished by enthusiasts for its rugged simplicity and unmistakable character. At the heart of its drivetrain, particularly for the rear axle, lies a component often sought after by restorers, repairers, and customizers: the Model 20 Rear End Housing. While the term "Model 20" can sometimes refer to the Dana 20 transfer case, in the context of a rear axle for a 1978 CJ7, it almost universally refers to the AMC 20 rear axle. This comprehensive guide will delve into everything you need to know about finding, evaluating, and utilizing a used 1978 Jeep CJ7 Model 20 (AMC 20) Rear End Housing.

Introduction: The Enduring Legacy of the AMC 20 Rear Axle

1978 Jeep CJ7 Model 20 Rear End Housing For Sale Used: A Comprehensive Guide

For many vintage Jeep CJ owners, the phrase "rear end housing" conjures images of rust, worn gears, or bent tubes. The 1978 Jeep CJ7, like many CJs from the mid-70s to early 80s, primarily utilized the AMC 20 rear axle. This axle, manufactured by American Motors Corporation, served as the workhorse rear differential for countless CJs, providing the power transfer necessary for both on-road cruising and challenging off-road adventures.

Finding a used 1978 Jeep CJ7 Model 20 Rear End Housing is often a necessity for a variety of reasons: the original unit might be severely rusted, bent from off-road abuse, damaged in an accident, or simply worn beyond repair. For those embarking on a restoration project, seeking period-correct authenticity, or needing a cost-effective replacement, a used housing presents a viable and often preferred solution over expensive new aftermarket alternatives. Understanding its nuances, strengths, and weaknesses is crucial for making an informed purchase and ensuring your classic CJ remains trail-ready.

Understanding the AMC 20 Rear End in the 1978 CJ7

The AMC 20 rear axle, which is the "Model 20 Rear End Housing" in question for a 1978 CJ7, is a semi-floating axle with a relatively strong 8.875-inch ring gear. It was a common fitment for CJs during its production run.

Key Characteristics and Specifications:

• Housing Type: Solid beam axle housing.
• Differential Type: Typically open, but limited-slip (Trac-Lok) options were available.



• Ring Gear Diameter: 8.875 inches.
• Axle Shafts: Early AMC 20s (pre-1982) often came with a two-piece axle shaft design, which is notorious for spline failure, especially under stress from larger tires or aggressive driving. Later models (1982-1986) used a stronger one-piece design. A 1978 model would typically have the two-piece design unless it was already upgraded.
• Axle Tube Diameter: Approximately 2.5 inches. While the ring gear is robust, the axle tubes themselves are relatively thin-walled, making them susceptible to bending under severe off-road abuse or heavy loads.
• Bolt Pattern: 5 on 5.5 inches, common to many vintage Jeeps.
• Width: The width of the CJ7 AMC 20 varied slightly over the years, but for a 1978 CJ7, it’s generally considered the "narrow track" version, with a width of approximately 51 inches (wheel mounting surface to wheel mounting surface).



• Spring Perches: Designed for leaf springs, positioned to match the CJ7’s frame.
• Brake System: Typically drum brakes, though disc brake conversion kits are popular aftermarket upgrades.

Reputation and Considerations:

While the AMC 20’s ring and pinion are quite strong, its primary weaknesses are the thin axle tubes and, for pre-1982 models, the two-piece axle shafts. These issues are why many serious off-roaders eventually upgrade to a Dana 44 or Dana 60 axle. However, for stock or mildly modified CJs, or for authentic restorations, a well-maintained or upgraded AMC 20 can perform admirably.

Why Seek a Used 1978 CJ7 Model 20 Rear End Housing?

There are several compelling reasons why a used AMC 20 rear end housing might be precisely what a Jeep owner needs:

• Replacement for Damage: The most common reason. Original housings can rust through, bend from impacts, or develop cracks, rendering them unsafe or unusable.
• Restoration Projects: For enthusiasts aiming for a period-correct restoration, finding an original housing is paramount. Aftermarket options, while strong, may not offer the same authentic appearance or fitment without modification.
• Cost-Effectiveness: Purchasing a used housing is typically significantly cheaper than buying a new aftermarket housing, allowing budget-conscious builders to allocate funds to other critical components.
• Component Transfer: Often, only the housing itself is damaged, while the internal components (ring and pinion, differential, axle shafts) are still good. A used bare housing allows for the transfer of these existing, functional parts.
• Availability: While not as abundant as they once were, used AMC 20 housings are still available through various channels, unlike some rarer vintage components.

What to Look For When Buying a Used Model 20 Housing

Purchasing a used axle housing requires careful inspection. A damaged or compromised housing can lead to serious safety issues and costly repairs down the line.

• 1. Structural Integrity:
  • Rust: Surface rust is common and acceptable, but deep, pitting rust that compromises the metal’s thickness, especially around welds, spring perches, or the differential cover flange, is a red flag.
  • Bends: Use a straightedge or string line to check the axle tubes for straightness. Even a slight bend can cause premature bearing wear, alignment issues, and make axle shaft installation difficult.
  • Cracks: Inspect all welds, especially where the axle tubes meet the differential housing and around spring perches and shock mounts, for any signs of cracks.
  • Previous Repairs: Look for amateurish welding or signs of significant damage that has been poorly repaired. Professional trussing or re-tubing might be acceptable if done correctly.
• 2. Completeness and Condition of Mounts:
  • Spring Perches: Ensure they are present, straight, and not rusted through or bent.
  • Shock Mounts: Check for straightness and integrity.
  • Brake Line Tabs/Brackets: Confirm they are present and undamaged.
  • Differential Cover Flange: This surface must be flat and free of deep pitting or gouges to ensure a proper seal with the differential cover.
• 3. Originality and Modifications:
  • CJ7 Specific: Confirm it’s from a CJ7 and ideally a 1976-1986 model for correct width and spring perch spacing. While the basic AMC 20 housing is similar, widths can vary slightly.
  • Upgrades: Has it been "trussed" (reinforced with additional steel bracing)? This is often a desirable modification as it strengthens the axle tubes. Has it been re-tubed with thicker material?
  • Perch Location: If it’s been modified for a custom suspension, the spring perches might have been relocated. Ensure they match your needs.
• 4. Seller and Source:
  • Reputable Salvage Yards: Often strip components, so you might find bare housings.
  • Online Forums/Marketplaces: Jeep-specific forums (e.g., JeepForum, Pirate4x4) and local marketplaces (Craigslist, Facebook Marketplace) are good sources. Always ask for clear, high-resolution photos and detailed descriptions.
  • Specialized Used Parts Dealers: Some businesses specialize in parting out Jeeps and might have a higher quality inventory, though often at a higher price.
  • Ask Questions: Inquire about the vehicle it came from, its mileage (if known), and any known issues.

Installation Considerations

Once you’ve acquired a suitable used housing, installation requires careful attention.

• Preparation: Thoroughly clean the housing. Sandblast or wire-wheel off rust and apply a protective coating (paint or powder coat). Inspect all surfaces one last time before assembly.
• Component Transfer: If you’re transferring components from your old axle, ensure they are in good condition. This includes the differential carrier, ring and pinion gears, axle shafts (consider upgrading to one-piece shafts if not already present), wheel bearings, seals, and brake components.
• Professional vs. DIY: Installing an axle housing and setting up gears requires specialized knowledge and tools (e.g., dial indicator, bearing pullers, torque wrench). If you’re not experienced with differential work, it’s highly recommended to have a qualified mechanic or off-road shop handle the gear setup and final assembly. Incorrect setup can lead to premature wear and failure.
• New Parts: Plan to replace all seals, gaskets, and probably the wheel bearings and brake components (shoes/pads, drums/rotors, hardware) as a matter of course.
• Safety: Always use jack stands, proper lifting equipment, and follow safety procedures. An axle housing is heavy and awkward to maneuver.

Potential Challenges and Solutions

• Finding a Good Unit: Good, unmolested AMC 20 housings are becoming scarcer. Solution: Be patient, expand your search radius, and be prepared to pay a bit more for a truly solid piece. Consider units that have already been upgraded with one-piece shafts or mild trussing.
• Shipping: Axle housings are large, heavy, and difficult to ship. Solution: Look for local sellers to avoid shipping costs and hassle. If shipping is necessary, obtain multiple freight quotes and ensure the seller can properly package the item (e.g., on a pallet).
• Hidden Damage: Rust or damage might be obscured in photos or not immediately apparent. Solution: If possible, inspect in person. If buying remotely, ask for a video walk-around, specific close-up photos, and a clear return policy in case of misrepresented condition.
• Component Compatibility: Ensuring your existing internal components fit the "new" used housing. Solution: The AMC 20 housing itself is fairly standardized, but always confirm the year range compatibility if you’re mixing and matching.

Practical Advice and Actionable Insights

1. Educate Yourself: Understand the strengths and weaknesses of the AMC 20 before you buy.
2. Inspect, Inspect, Inspect: Never buy sight unseen without extremely detailed photos/videos and a clear return policy.
3. Budget Beyond the Housing: Remember to factor in the cost of new seals, bearings, brake components, fluids, and potentially professional labor for gear setup.
4. Consider Your Use Case: If you plan extreme off-roading, a bare AMC 20 housing, even a good one, might be a temporary solution before a stronger axle upgrade. For mild trails or restoration, it’s perfectly adequate.
5. Don’t Rush: A well-chosen used housing will save you headaches and money in the long run.

Table: Estimated Price Range for Used 1978 Jeep CJ7 Model 20 Rear End Housing

Please note that these prices are estimates and can vary significantly based on location, condition, seller, and completeness of the unit. "Condition" refers to the presence of rust, bends, or damage.

Item Description	Condition (Rust/Damage)	Estimated Price Range (USD)	Notes
Bare Housing (No internals, no shafts)	Good (minimal rust, straight)	$150 – $350	Ideal for transferring existing good internals. Check for straightness and mount integrity.
Bare Housing (No internals, no shafts)	Fair (surface rust, minor dents)	$75 – $150	May require more extensive cleaning, rust removal, and minor repairs. Good for budget builds if structurally sound.
Housing with Axle Shafts (No differential/gears)	Good (straight shafts, minimal rust)	$250 – $450	Be aware of the two-piece axle shaft design common in 1978 models; consider immediate upgrade to one-piece shafts.
Complete Housing (With shafts, differential, gears)	Good (operational, minimal rust)	$400 – $800	Best value if gearing is suitable for your needs. Always inspect differential fluid for metal shavings and check backlash/pattern if possible. Verify gear ratio.
Complete Housing (With shafts, differential, gears)	Fair (some wear, needs service)	$200 – $400	Likely requires new bearings, seals, and potentially a gear setup or differential rebuild. Factor in additional costs.
Trussed/Reinforced Housing	Good (professionally done)	$500 – $900+	Stronger than stock, often a desirable upgrade. Verify the quality of welding and reinforcement.
Salvage/Parts Only Housing	Poor (bent, heavy rust, damaged)	$50 – $100	For small sections, spring perches, or donor material only. Not suitable for direct use as a complete housing.

Frequently Asked Questions (FAQ)

Q1: Is the AMC 20 rear end strong enough for my Jeep CJ7?
A1: For stock or mildly modified CJ7s (up to 33-inch tires, light to moderate off-roading), a well-maintained AMC 20 is generally sufficient. For aggressive off-roading, larger tires (35+ inches), or V8 engine swaps, the thin axle tubes and two-piece axle shafts (common in 1978) become weak points. Upgrades like one-piece axle shafts and trussing significantly improve its strength.

Q2: How can I tell if a used AMC 20 housing is bent?
A2: The best way is to place it on a flat, level surface and use a long straightedge or a taut string line along the length of the axle tubes. Look for gaps or inconsistencies. A slight sag in the middle might be present, but severe bows or twists indicate a bent housing. You can also mount a wheel and spin it to check for wobble, or visually inspect the flange where the axle shaft goes in.

Q3: What’s the difference between a "Model 20" rear end and a "Dana 44" rear end?
A3: For a CJ7, the "Model 20 rear end" refers to the AMC 20 axle, which was standard in many CJs. The Dana 44 is another popular, stronger axle often swapped into CJs. The Dana 44 typically has a larger axle tube diameter, a reputation for greater strength, and usually came with one-piece axle shafts from the factory. While the AMC 20 has a larger ring gear, its thinner tubes and two-piece shafts are its main drawbacks compared to a Dana 44.

Q4: Can I upgrade a 1978 AMC 20 rear end housing?
A4: Absolutely. Common upgrades include:

• One-piece axle shafts: Replaces the problematic two-piece design. This is often considered the most crucial upgrade.
• Trussing: Welding steel reinforcement along the top or bottom of the axle tubes to prevent bending.
• Heavy-duty differential cover: Stronger than stock and provides better protection.
• Disc brake conversion: Replaces the stock drum brakes for improved stopping power.

Q5: What years of AMC 20 rear end housings are compatible with a 1978 CJ7?
A5: AMC 20 rear ends from 1976-1986 CJ7s are generally compatible in terms of width and spring perch spacing. However, remember that the two-piece axle shafts were standard until 1982, when AMC switched to one-piece shafts. If you find a post-1982 AMC 20 housing, it will likely come with the stronger one-piece shafts.

Q6: How much does it cost to ship a used axle housing?
A6: Shipping costs can vary widely depending on distance, weight, and freight carrier. Expect costs ranging from $150 to $500 or more for cross-country shipments. Local pickup is almost always the most cost-effective option.

Conclusion

The 1978 Jeep CJ7 Model 20 Rear End Housing, or more accurately, the AMC 20 rear axle housing, remains a vital component for maintaining, restoring, or mildly modifying these classic Jeeps. While it has its known weaknesses, a well-chosen used housing can provide a cost-effective and authentic solution for many projects. By understanding its characteristics, knowing what to look for during inspection, and planning for potential upgrades and installation complexities, you can successfully acquire and utilize this essential piece of Jeep history, ensuring your CJ7 continues its adventures for years to come. The journey of keeping these vintage vehicles on the road is as rewarding as the trails they conquer, and a sound rear end housing is fundamental to that enduring legacy.