Bike Repair – Bleeding Formula Hydraulic Brakes

Bicycle hydraulic brake

If your levers feel squishy or braking has become inconsistent, it’s likely air has got into the system. Here’s how to get them back to full power.

1. Wedge the pad

Clamp your bike in a workstand. Remove the front wheel if you want to bleed the front brake, and vice versa. Check that the brake pads still have a good amount of material left but leave/refit them in the calliper. Then carefully wedge the Formula pad spacer that should have been supplied with your brakes or bike in between the pads, pushing the pistons back into their bores.

2. Position lever

You now need to position the brake lever so that the bleed port is pointing upwards. The bleed port is located at the base of the lever body, between the hose entry point and the bar clamp, so you’ll need to remove the lever from the bar using a 3 or 4mm Allen key and then use a ziptie to reattach it to the bar with the bleed port pointing skyward.

3. Fill syringes

Now it’s time to start the bleed. First, put your latex gloves on – DOT brake fluid isn’t good for your skin (or your bike’s paintwork, for that matter). Next, make sure the syringes from the bleed kit are correctly assembled, with the tubes and brass bleed fittings in place. Fill one syringe with 20ml of DOT 4 brake fluid and the other with 5ml.

4. Remove port screw

Use a T10 Torx key to remove the bleed port screw from the brake calliper, turning it anticlockwise. Be careful to leave the bleed port O-ring in position inside the bleed port.

5. Drain system

Place your waste brake fluid tray underneath the calliper. Then squeeze the brake lever repeatedly to drain the system of fluid. Be careful not to get brake fluid on your skin, clothes or on the brake pads in the calliper if you plan to re-use them.

6. Attach syringe

Attach the syringe filled with 20ml of fluid to the calliper, screwing the brass fitting on the end of the syringe into the calliper’s bleed port. Turn it clockwise until finger-tight. Be careful not to lose or damage the bleed port O-ring in the process.

7. Let the fluid flow

Use the T10 Torx key to remove the bleed port screw from the brake lever body, turning it anticlockwise. Be careful not to lose the bleed port O-ring. Attach the remaining syringe filled with 5ml of fluid to the lever’s bleed port, turning the brass fitting clockwise until it’s finger-tight.

8. Keep lever closed

Hold the calliper syringe vertical and push around two-thirds of the fluid through the system. The lever syringe should fill with a mixture of air bubbles and fluid.

9. Force out air

Now hold the lever syringe vertical. If there are air bubbles visible in the fluid, give the syringe a light tap – this should encourage the bubbles to rise. Keep tapping until the bubbles have reached the top of the fluid. Now force around two-thirds of the fluid back through the system, watching for air bubbles entering the calliper syringe.

10. Pump the fluid

Holding the calliper syringe in the same vertical position as before, push the same amount of fluid back though the system again, this time while pumping the brake lever repeatedly. More bubbles of air will work their way into the lever syringe.

11. Remove lower syringe

Hold the lever syringe in the vertical position. Then pull on the calliper syringe’s plunger, creating a vacuum in the calliper syringe. This will pull fluid back through the system, so keep an eye on the lever syringe’s fluid level and make sure it doesn’t drop below 5ml. The fluid entering the syringe should now be free of air bubbles.

12. Remove lever syringe

Remove the calliper syringe from the calliper, turning the brass bleed fitting anticlockwise and being careful not to lose the bleed port O-ring. Put the syringe to one side, then refit the bleed port screw with a torque wrench, turning it clockwise until you reach 2Nm.

13. Clean-up fluid

Remove the lever syringe, turning the brass fitting anticlockwise. Put the syringe to one side and refit the bleed port screw using the Torx key, making sure the bleed port is brimming with fluid and the O-ring is still sat in place inside. Tighten the bleed port screw to 2Nm.

14. Test the system

Use brake cleaner and a clean rag to clean any surface that brake fluid has come into contact with during the bleed. Pay particular attention to the calliper, as well as to the lever body. Remove the Formula pad spacer and check the pads haven’t come into contact with any brake fluid.

15. Back on the bike

If you’ve spilled any fluid on your brake pads, you’ll need to replace them. Use a 2.5mm Allen key to remove the pad-retaining pin, then remove the pads. Give the calliper a thorough clean with brake cleaner before fitting new pads and replacing the pad retaining pin.

16. Finishing touches

Re-adjust your brake lever so it’s back in its original position. Refit your wheel, then test the brake to make sure the bleed has been successful. If you’ve fitted new pads, be sure to bed them in before you go smashing any big descents!

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