Honda TRX400 Front Brake Caliper Rebuild

An ATV that won’t stop is a clear-cut sign of a failing brake caliper, but it’s not the only one. Leaking brake fluid also means the caliper may need to be repaired. 

Watch the video above and follow the steps below to learn how to rebuild the front brake caliper on a Honda TRX 400EX.

Tools and Supplies - Honda TRX400 Front Brake Caliper Rebuild

• Ratchet and 12mm socket
• 5mm, 6mm Allens
• 10mm wrench
• Screwdriver
• Pick tool

• Contact/brake cleaner
• Brake fluid
• 3/16th hose
• Brake caliper seal set

Removing a Honda TRX400EX Front Brake Caliper

Step 1. Remove the front wheel.

Step 2. Drain the brake system by attaching a 3/16” hose to the bleed valve, then opening the valve and pumping the clutch lever until all the brake fluid has left the system.

Step 3. Remove the two brake pad pin caps, then unscrew the two pad pins (5mm Allens) to the end of their screw threads without removing them.

Step 4. Remove the dust cover from the slide pin and unscrew the slide pin (6mm Allen) without removing it.

Step 5. Remove the banjo bolt and the two washers that secure the brake line to the caliper.

Step 6. Remove the two 12mm bolts that hold the caliper assembly to the wheel hub.

Step 7. Rotate the bracket and slide it out from the caliper. 

NOTE: Be careful not to lose the small conical spring washer that sits on the end of the slide pin beneath the bracket.

Rebuilding a Honda TRX400EX Front Brake Caliper

Step 1. Remove the two brake pad pins and the brake pads.

Step 2. Remove the piston by shooting compressed air into the caliper to force the piston out. Use a shop towel to protect the piston and the caliper.

Step 3. Remove the outer and inner seals from within the caliper bore.

Step 4. Thoroughly clean the caliper with contact/brake cleaner and inspect the bore for scratches, pits or wear. Replace the caliper if it’s worn, but if it’s in good condition you’ll only have to replace the seals.

Step 5. Install the new inner and outer seals into the caliper bore. 

Step 6. Thoroughly clean the piston, then inspect it for pitting or scratches and replace it if it’s worn.

Step 7. Smear the seals and the piston in brake fluid to lubricate them, then push the piston back into the caliper. 

Step 8. Clean the bracket and reinstall it. 

NOTE: If the conical spring washer came off the slide pin at any time while you were working on the caliper, make sure you reinstall the washer with its raised outer edges facing the bracket.

Step 9. Tighten the slide pin so it re-engages with the bracket and is hand-tight.

Step 10. Reinstall the brake pads, followed by the two brake pad pins, and hand-tighten them.

Reinstalling a Honda TRX400EX Front Brake Caliper

Step 1. Slide the caliper assembly back onto the brake rotor, and reinstall the two 12mm caliper mounting bolts.

Step 2. Reconnect the brake line to the caliper by reinstalling the banjo bolt and its two washers.

Step 3. Tighten the two brake pins, the slide pin, the two caliper mounting bolts and the banjo bolt.

Step 4. Reinstall the two brake pin caps and the slide pin dust cap.

Step 5. Bleed the brakes. 

NOTE: Bleed the brake on both sides of the ATV to remove the air that got into the brake lines when you first drained the system.

Step 6. Reinstall the front wheel and you’re done.