The most common method used to set up the brake caliper alignment is described below:
1) Loosen the bolts holding the brake caliper to the adaptor/frame. Just loosen it sufficiently so that the brake caliper can slide from side to side.
2) Push the brake caliper flat against the adaptor/frame, and pull the brake lever. The brake caliper should self-centre on the rotor.
3) While still holding on to the brake lever, tighten the bolts on the brake caliper.
4) The brake caliper should now be centred on the rotor.
This method works most of the time, but sometimes, even after the alignment, the brake caliper will tend to be offset to one side, causing intermittent or constant brake rub on one side. The Hayes caliper alignment tool is designed to help solve this issue.
Original packaging of the Hayes Caliper Alignment Tool
Comes in a funky purple colour!
Anodised aluminium for a high quality feel
Slight wedge at the end can be used to pry apart the brake pistons if required.
The 2 thin metal feeler gauges, of about 0.3mm thickness each.
There are many uses for this tool. One of the function is to help push apart the pistons, if they have closed up. This can happen if the brake lever is pulled when the rotor is not in-between the pistons (Eg. when the wheel is off the bike).
Slide the wedged portion of the tool into the brake caliper to help push apart the pistons.
If the system has been properly bled, it should be a snug fit!
The other usage of this tool is to help set the clearance between the brake pads and the rotor. The two thin feeler gauges simulate the clearance between the brake pad and the rotor. Before using the feeler gauges, loosen the bolts fixing the brake caliper to the adaptor/frame.
With the rotor already in between the brake caliper, insert the feeler gauges along both sides of the rotor. It may be a tight fit.
Feeler gauges placed on both sides of the rotor.
The purpose of adding these two feeler gauges is to help set the clearance on both sides of the rotor. With the thickness of the feeler gauges in place, it helps to make the clearance more consistent and equal on both sides.
Once the feeler gauges have been inserted, pull the brake lever and tighten the bolts as per normal. This will center the brake caliper, taking into account the equal clearance on both sides (created by the feeler gauges).
I found that when the feeler gauge is used, the clearance between the brake pad and the rotor seems to be slightly larger. The clearance on both sides of the rotor is also more equal. This greatly reduces the chance of having brake rub issues.
Overall, I feel that this tool may be useful to have, but not really necessary. The normal way of centering the brake caliper should work for most bikes, most of the time.