How to Rebuild Motorbike Brake Calipers
Rebuilding your motorbike’s brake calipers is a critical maintenance task that ensures your brakes are functioning optimally. At Apex, we provide high-quality caliper seal kits to help you perform this task efficiently. Follow these steps to rebuild your brake calipers and keep your bike’s braking system in top shape.
Preparing the Calipers
Before Removing the Calipers from the Bike:
Extend the Pistons: With the brake pads removed, use the brake lever to pump the pistons out towards the brake disc. Protect the disc with cardboard if necessary.
Stuck Pistons: If any pistons are stuck, apply penetrating oil and let it sit for 30 minutes. If the pistons remain stuck, warm the caliper with a hot air gun. Special tools may be required for stubborn pistons.
Loosen Joint Bolts: For jointed calipers, loosen the joint bolts while the calipers are still mounted on the bike.
Removing the Pistons
Piston Removal:
Special Tools: If you lack specialist piston removal tools, be very careful not to damage the pistons. Various grips or a vice can be used, but line the jaws with rubber, lead, or aluminium sheets to protect the pistons.
Damaged Pistons: If the pistons get damaged, we offer replacements – contact us!
Cleaning and Corrosion Removal
Corrosion Removal:
Clean Thoroughly: Ensure all dirt and corrosion are removed from the seal grooves using a blunt scraper and/or a brass Dremel brush. This is crucial—using brake cleaner and a tissue is not effective on aluminium oxide.
Consequences of Poor Cleaning: Improper cleaning can lead to the seals binding on the brake pistons, leaking seals, and potential damage during piston fitting.
Piston Cleaning:
Light Corrosion: Minor corrosion on the pistons can often be cleaned with a Scotch-Brite pad or similar.
Severe Damage: If there is any pitting or damage where the seals contact, replace the pistons. We offer stainless steel pistons – Contact us!
Preparation:
The meticulous preparation of the caliper is the most time-consuming part of the rebuild. Once all corrosion is cleared from the seal grooves and debris is cleaned out, and the pistons are either cleaned or replaced, you can proceed with the rebuild.
Reassembling the Calipers
Fitting Seals:
Seal Orientation: Apex seals are square section and can be fitted either way up. Seals might seem loose over the pistons when not in the caliper, but this is normal. Once constrained in the seal groove within the caliper bore, they will fit perfectly.
Dust Boots: New external dust boots and slide rod boots may appear small compared to old parts, which can swell with age and exposure to chemicals.
Lubrication:
Lubricate Seals: Use a thin smear of rubber grease or brake fluid to lubricate the seals.
Lubricate Pistons: Apply the same lubricant to the pistons. Carefully align the pistons in the bore and use only thumb pressure to ease them past the seals. Do not force the pistons in—if they are stiff, recheck that the seal grooves are completely clear of corrosion.
Final Steps
Bleed Screws:
Torque Settings: Avoid over-tightening bleed screws. For 7mm bleed screws, 4 Nm is usually sufficient—just enough to seal.
Bleeding the Brakes:
Gravity Feed: Open the bleeds and allow gravity to feed fluid until it shows at each bleed.
Lever Pumping: Quick lever pumping with the bleed open on one side at a time will purge most air.
Dislodge Air Bubbles: Tap down the brake lines to dislodge any trapped air bubbles.
Final Bleeding: Use the slow ‘open bleed/squeeze/close bleed/release’ method to remove the last air bubbles. Keep the reservoir full. If necessary, leave the system overnight to settle and perform a final bleed the following day.
By following these steps, you can rebuild your motorbike brake calipers with confidence. Remember, Apex is here to support you with top-quality caliper seal kits and replacement parts. Happy riding!