Trailer Parts Maintenance & Upgrade Guide – Brakes, Hubs, Suspension, and Lights

Keeping your trailer in peak condition isn’t just about safety—it’s about preventing breakdowns, saving money, and maximizing towing performance. This guide gives you specific steps, tools, and OEM part references to maintain, repair, and upgrade your trailer.

1. Trailer Brakes – Smooth & Reliable Stopping Power

Common Types:

• Electric brakes (10"x2-1/4" for 3.5K axles, 12"x2" for 6–7K axles)
• Hydraulic surge brakes (common in boat trailers)
• Electric-over-hydraulic systems (heavy-duty applications)

Inspection & Adjustment:

• Every 3,000 miles: Check brake shoe thickness (replace if under 1/16"), inspect magnets for uneven wear, and verify return springs are intact.
• For electric brakes: Adjust the star wheel until shoes drag slightly, then back off 8 clicks.
• For hydraulic brakes: Bleed system with DOT 3/4 fluid until no air bubbles.

Upgrades Worth Doing:

• Swap to self-adjusting electric brakes (e.g., Dexter K23-468-00 LH / K23-469-00 RH for 3.5K axles).
• Install disc brake conversion kit for 20–30% shorter stopping distance on boat trailers.
• Add a proportional brake controller like Tekonsha Prodigy P3 for smoother braking.

2. Trailer Hubs & Bearings – Prevent Failures on the Road

Service Interval:

• Repack bearings every 12 months or 12,000 miles.
• Replace seals at every service (prevents water & dirt ingress).

Standard #84 Spindle (3.5K Axle) Bearing Set:

• Inner: L68149 (1.378" ID) + Race L68111
• Outer: L44649 (1.063" ID) + Race L44610
• Seal: 1.719" ID × 2.565" OD

Heavy-Duty #42 Spindle (6–7K Axle) Bearing Set:

• Inner: 25580 + Race 25520
• Outer: 14125A + Race 14276
• Seal: 2.125" ID × 3.376" OD

Pro Tips:

• Use a bearing packer to fully coat rollers in high-temp marine grease (if boat trailer).
• Upgrade to oil-bath hubs for heavy equipment trailers—easier inspection and longer service life.

3. Suspension – Leaf Springs, Shackles, & Hangers

Signs of Wear:

• Flat or cracked leaf springs, elongated shackle bolt holes, uneven tire wear.

Quick Measurement:

• Double Eye Leaf Springs (3,500 lb axle): 25-1/4" eye-to-eye, 1-3/4" wide.
• Double Eye Leaf Springs (6K axle): 25-1/4" × 1.75", 3,000 lb per spring.

Replacement Example:

• SW4B – 3,500 lb, 4-leaf
• SW5 – 6,000 lb, 5-leaf
• Pair with Grade 5 U-Bolt Kit (APUBR-1 for 2-3/8" axle, APUBR-9 for 3" axle)

Upgrade Tip:

• If replacing springs, also replace shackles, bolts, and equalizers—cheap insurance against uneven load distribution.

4. Trailer Lighting & Wiring – Stay Legal & Visible

Maintenance Checklist:

• Test brake lights, turn signals, and running lights before every trip.
• Use dielectric grease on plug pins to prevent corrosion.
• Replace incandescent bulbs with sealed LED assemblies for vibration resistance and 50,000+ hour life.

Common LED Upgrade Sizes:

• Oval stop/turn/tail: 6.5" × 2.25"
• Round marker/clearance: 2.5" diameter

Wiring Tip:

• Run a dedicated ground wire to every light instead of relying on frame ground—eliminates flickering issues.

Quick Reference – Common OEM Replacements