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A rubbing disc brake is a common problem,

and even the slightest rub,

which might not really be slowing you down, can still be annoying.

This is hydraulic disc brake alignment, and regardless of brand or model,

this video will help you get rid of that pesky rub.

Hey, I'm Truman with Park Tool.

Hydraulic brake alignment is a relatively simple procedure

But there are other things that can cause the pads to rub

so we're gonna start with diagnosing the problem,

and then we'll take you step by step through the alignment process.

If you have mechanical brakes, which are actuated by a cable, see this other video for alignment.

Typical tools and supplies include:

4 or 5 mm hex wrenches, or a T25,

Also a torque wrench such as a TW-5.2,

A light source to backlight the caliper,

And a repair stand, or some way to hold the bike up while spinning the wheel.

First we'll elevate the bike, spin the wheel, and sight the gaps between the rotor and pads.

Back light the caliper to make it easier to see.

This is a good time to give the pads a quick visual inspection for wear.

These pads have lots of life left

but these other pads need to be replaced.

See this other video to learn how to measure the wear, and replace the pads if needed.

Back on our spinning wheel, we see there is no rub bewteen the rotor and pads.

So in this case we would consider ourselves done with the alignment.

And in this example there is slight rotor rub, and there's barely any noise...

so you might just call this one good to go.

But even with clear rotor rub, we should at least be aware of other things that can cause or amplify this symptom.

Wheel allignment is critical to check.

Especially on open dropout bikes, fully seating the wheel can solve the problem

and it can even work on thru-axle bikes.

A bent rotor will show a lot of movement side to side,

and this makes pad alignment difficult or impossible.

Rotor replacement is a good option, but some rotor truing may be possible,

and that process is shown in this other video.

You should also check the rotor for play.

Rotors are secured using either mounting bolts, or a lockring.

See this other video for rotor installation.

Bearing play at the hub is also easy to check for. Just rock the wheel back and forth as shown.

If there's play, fix it.

Another issue is when dust and dirt collects on one or both of the pistons and causes them to stick.

In many cases, you can still achieve proper alignment with sticky pistons,

but for more information see this other video.

That's finally it for diagnosis. Let's get into the alignment procedure.

Aligment procedures are the same for front and rear brakes.

Loosen the mounting bolts until the caliper body is able to freely move side to side.

Note that on some bikes, the mounting bolts are under the stay

or on a bracket.

Now we squeeze the brake lever.

This centers the caliper body over the rotor.

While holding the lever, snug up the bolts.

Release the brake lever.

Spin the wheel to test for pad rub. If there is no rubbing, the pads are aligned.

Secure the mounting bolts to full torque — 6-8 Nm — and your work is complete.

If the pads are still rubbing, we need to do some fine tuning.

Loosen one bolt at a time, and adjust until there is a gap on either side of the rotor.

Take extra caution with your fingers and tools while working near a spinning wheel.

Once the pads are not rubbing, fully secure each mounting bolt — typically 6-8Nm — and the process is complete.

Some brakes have conical washers to assist in perpendicular alignment.

Do not add washers if none were designed to be there in the first place, as the pads will no longer align with the rotor.

Conical washers can also be found between the bolt head and the caliper.

These washers allow for proper bolt head alignment.

If after trying all these procedures, and nothing seems to work for an adequate alignment,

there maybe issues with your caliper mounting system.

It is assumed the frame mounts are correctly machined and square with the rotor.

But if mounts are not square, bike shops are able to face or machine the mounts

with the Park Tool DT-5.2 to improve alignment, as seen in this other video.

Thanks for joining us on hydraulic disc brake alignment.

If this video helped you out, please share it with your friends, and subscribe to our channel.

Sometimes all it takes is that one bit of knowledge to take your ride, your friends ride, or your customer's ride to the next level.

Thanks for watching.