If you’re replacing or upgrading a 3500 lb trailer axle suspension, the right 4-leaf or 5-leaf spring kit with U-bolts and hangers can restore ride quality and load handling. These five options are crafted for standard 3,500 lb axles and SW4B/SW5 configurations. They suit campers, small utility trailers, and light-to-medium duty boats. Choose based on leaf count, eye-to-eye length, and compatibility with your axle diameter. The best pick depends on your axle size, desired stiffness, and corrosion resistance needs.
| Product | Leaf Count | Spring Capacity | Axle Compatibility | Best For |
|---|---|---|---|---|
| SEHNSUCHT 4 Leaf Replacement for SW4B | 4 leaves | 1,750 lb per spring (total 3,500 lb) | 2-3/8″ round axles | Budget-friendly rebuild for SW4B users |
| SEHNSUCHT Replacement for SW5 5 Pieces | 5 leaves | 3,000 lb per spring (total 6,000 lb) | 3″ dia axles | Stronger support for heavier SW5 setups |
| dreamdragon Tandem Suspension Kit | 4 leaves | 1,750 lb per spring | 2-3/8″ diameter round axles | Balanced upgrade for standard tandems |
| Youxmoto 4pcs 5 Leaf Springs | 5 leaves | 3,000 lb per spring | 3″ dia axles | Heavy-duty 5200–6000 lb range option |
| 2 Pieces Replacement for SW4B 4 Leaf | 4 leaves | 1,750 lb per spring | 2-3/8″ dia axles | Two-packs for SW4B backups |
SEHNSUCHT 4 Leaf Replacement for SW4B
Each leaf spring provides 1,750 lb capacity, suitable for a standard 3,500 lb trailer axle. Eye-to-eye length is 25-1/4″, free open 3″, leaf width 1-3/4″, and 9/16″ bushings. Includes two installed bushings per spring. The kit includes a 4-leaf design with a 5/16″ leaf thickness. U-bolt kit features 4 x 5-1/2″ bolts for 2-3/8″ dia axles, plus tie plates and hex nuts. Best for replacing SW4B systems with a straightforward fit. Caution: ensure horizontal nut tightening for optimal performance.
Best for: Trailer owners with SW4B axles seeking a direct replacement kit that matches standard SW4B specs and includes the necessary U-bolts and hangers for a complete install. Choose this if you want a compact, balanced 3,500 lb system with corrosion resistance via anti-rust coating.
SEHNSUCHT Replacement for SW5 5 Pieces
This kit provides 3,000 lb capacity per spring for a 5-leaf configuration, designed to suit standard 5,200–6,000 lb trailers with a 25-1/4″ eye-to-eye length and 3″ free open. It uses 9/16″ bushings and notes that horizontal nut tightening is essential. Includes 4 x 7″ U-bolts and tie plates for 1-3/4″ leaf springs, plus 8 hex nuts. Best for: Heavier SW5 trailers that require stronger leaf springs and a complete U-bolt set. Caution: ensure compatibility with your axle diameter (3″ dia axles are mentioned).
dreamdragon Tandem Trailer Axle Suspension Kit
The kit features four 4-leaf springs, each rated at 1,750 lb, making it suitable for standard 3,500 lb axles. Eye-to-eye length is 25-1/4″, free open height is 3″, and leaf width is 1-3/4″. Bushing diameter is 9/16″. Includes a U-bolt set for 3,500 lb axles with 2-3/8″ round axles: four 5-1/2″ bolts, 1/2″ diameter, plus two tie plates and eight hex nuts. Best for: Trailer owners seeking a balanced, ready-to-install tandem suspension with clear fit for 2-3/8″ axles. Caution: verify the axle diameter matches your trailer before purchase.
Youxmoto 4pcs 5 Leaf Springs Kit
Designed for 5200–6000 lb trailers, this kit uses five-leaf springs with 25-1/4″ eye-to-eye, 3″ free open, 1-3/4″ leaf width, and 9/16″ bushings, delivering 3,000 lb capacity per spring. It includes a 3″ dia axle U-bolt kit: four 7″ bolts, 1/2″ diameter, two tie plates for 1-3/4″ or 2″ leaf springs, and eight hex nuts. Best for: Heavier-duty trailer setups that require extra spring strength and a robust U-bolt kit. Caution: confirm the axle diameter and the correct leaf count for your trailer’s load rating.
SEHNSUCHT 2 Pieces SW4B 4 Leaf Replacement
This two-pack set provides 1,750 lb per spring, for a total of 3,500 lb on standard SW4B axles. Eye-to-eye length is 25-1/4″, free open 3″, leaf width 1-3/4″, with 9/16″ bushings and two installed per spring. Includes 4 x 5-1/2″ U-bolts for 2-3/8″ dia axles, two tie plates, and 8 hex nuts. Best for: Budget-conscious replacements or multiple trailer setups requiring spare springs. Limitation: designed for 2-3/8″ axle diameter; verify compatibility before ordering.
Magorfas Tandem Trailer Leaf Spring 4 Leaf Set
Magorfas offers a 4-leaf spring set rated at 1,750 lb per spring for 3,500 lb axles, with a 25-1/4″ eye-to-eye and 9/16″ bushings. The leaf design uses 60Si2Mn manganese steel for strength and flexibility, with a two-coat paint finish for corrosion resistance. Best for: Trailers needing a strong manganese steel option with good endurance in salty or humid environments. Caution: ensure the SW4B or SW5 compatibility is confirmed for your axle diameter and trailer weight.
Autoholic Trailer Leaf Spring Kit
Autoholic offers a 3500 lb single-axle, 4-leaf spring kit with U-bolt and hanger kit. Each spring delivers up to 1,750 lb capacity, with 25-1/4″ eye-to-eye length and 1-3/4″ leaf width. The kit focuses on reliable suspension and chassis protection. Best for: Simpler, single-axle trailers needing a straightforward replacement with included hardware. Caution: verify compatibility with your specific axle diameter and mounting points, as some configurations vary.
Buying Guide
What should you check before buying a trailer spring kit?
- Axle compatibility: Confirm axle diameter (2-3/8″ vs 3″) and whether the kit is designed for SW4B or SW5 configurations.
- Leaf count and capacity: Decide between 4-leaf or 5-leaf springs based on load and trailer type. Higher capacity may improve ride under heavy loads but can stiffen the ride.
- Eye-to-eye length: Ensure 25-1/4″ is correct for your setup. Mismatched length can cause clearance issues with the chassis and tires.
- Bushing size and material: 9/16″ bushings are common and offer durable wear; confirm compatibility with your hangers and mounts.
- U-bolt kit sizing: Check bolt length and diameter (commonly 1/2″ dia) and inside curve diameter to fit your axle.
- Rust resistance: An anti-rust coating or manganese steel can extend life in coastal or humid environments.
- Hardware completeness: Many kits include tie plates and hex nuts; verify all necessary components are included.
- Installation considerations: Horizontal nut tightening is often specified; follow manufacturer guidance to avoid misalignment and wear.
FAQ
- Q: What does eye-to-eye length mean for trailer springs? A: It’s the distance between the spring’s mounting points, critical for correct fit and suspension geometry.
- Q: Can I mix a 4-leaf spring with a 5-leaf spring on the same axle? A: It’s generally not recommended due to uneven load distribution and handling differences; use matching sets.
- Q: Why is horizontal nut tightening specified? A: It ensures proper engagement and prevents loosening under vibration.
- Q: Do all kits include U-bolts and hangers? A: Most do, but verify the included hardware in each product listing to avoid missing parts during install.
- Q: What is the best kit for a boat trailer on saltwater? A: Look for corrosion-resistant coatings and manganese steel options to resist rust in marine environments.
- Q: How do I know my axle diameter matches the kit? A: Measure the round axle diameter and compare to kit specifications (commonly 2-3/8″ or 3″).