How to regain firm brake levers.

This document details the procedure for checking and adjusting brake piston travel for an UBCO 2x2 model 2021-2023 equipped with SR manufactured brakes. Some brake calipers have been sitting still for a long time or have negative pressure and need ex

UBCO 2x2 - How to regain firm brake levers by resetting brake caliper pistons.

Introduction

This document details the procedure for checking and adjusting brake piston travel for an UBCO 2x2 model 2021-2023 equipped with SR manufactured brakes. Some brake calipers have been sitting still for a long time or have negative pressure and need exercise for them to work more effectively.

Tools and Consumables

2.5mm Allen wrench
4mm Allen wrench
5mm Allen wrench
Torque wrench for 12nm
5mm Allen to fit driver on torque wrench
Brake pad wedge or non-sharp flat blade screwdriver

Brake bleed kit contains:
20cc Syringe with clear hose and adapter fitting to fit threads on brake reservoir. Shimano Mineral Oil Brake Fluid or equivalent mineral oil brake fluid

Additionally, you will need
Isopropyl alcohol (preferably in spray bottle)
A clean (lint free) absorbent towel or paper towel Loctite 243 or equivalent medium strength thread lock

Check the hydraulic system for any air.

You should always start by making sure the system is fully filled and without any air. CAUTION: Cleanliness is a very important part of any hydraulic disk brake system maintenance. If the pads or rotor become contaminated with mineral oil or if the hydraulics become contaminated with impurities, braking performance will be greatly impaired. Use only mineral oil brake fluid with the system as other fluids may not be compatible and may damage the system. Be sure to clean any fluid spills with isopropyl alcohol immediately.

Instructions:

1) Check how far the brake pistons travel before pads contact rotor.
2) Ifthereisatotalgapofabout1mm(ormore)airgapfromrotortobrakepads,

then the piston seals may cause pistons to retract into caliper, resulting in long

brake leaver travel. See image 1
3) Before installing syringe:
1. With4mmAllenloosentheleaverassemblyandrotatesoreservoirscrew is at the highest point.
2. Useaclothorpapertoweltocaptureexcessmineraloil(brakefluid)spill while removing fill cap with 2.5mm Allen wrench. NOTE 2.5mm Allen may be very tight from factory, be sure Allen wrench is not worn out and engagement feels good before attempting to loosen. See image 2
3. Pre-bleed syringe and line with fresh mineral oil brake fluid then install syringe. See image 3
4) With reservoir or syringe installed “burp” any air out by pumping the leaver – hold it compressed and look for air bubbles traveling out of leaver reservoir into syringe. Move handlebars left to right while pumping brake leaver -removing any trapped air in line. Gentilly/ slowly pulling syringe to vacuum air can be beneficial as well, just be sure to add fluid back into reservoir and activate brake leaver a few times before detaching syringe.
5) Repeatsteps1-2andifstill>1mmpistontravelcontinuenextstep. a. Testtoseeifleaverismorefirm/solidfeel.
6) Withoutremovingsyringeordisconnectingbrakeline,removecaliperfrombike with brake pads in place.
7) Place a disk brake pad wedge or thin flat bladed screwdriver as a wedge between pads so there is free room for piston/pads to move. See image 4
8) Press brake leaver gently and pay attention to the pistons not extending too far. a. Makesureallpistonshavemovedin/outbeforeendingprocess(moving

wedge side to side ensuring all pistons had a chance to move).
9) Use wedge to set pistons evenly and as close as you can to rotor without

excessive contact.