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Centering hydraulic disc brake pads

Old 06-18-18, 02:45 PM
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taz777
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Centering hydraulic disc brake pads

Iím after a consensus here.

Iíve always centred pads in my calipers by loosening the calipers bolts and then squeezing the brake lever hard, and then tightening the caliper bolts up to the correct torque.

However, one video I watched recently from a bike shop did this differently: they spun the wheel and then squeezed the brake lever very slightly so it only just rubbed on the rotor, and then they tightened up the bolts slightly and repeated the process until the bolts were fully tightened.

Which is the correct method?
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Old 06-18-18, 02:50 PM
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Consensus , complete agreement , on this forum ?
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Old 06-18-18, 03:03 PM
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Originally Posted by taz777 View Post
Iím after a consensus here.

Iíve always centred pads in my calipers by loosening the calipers bolts and then squeezing the brake lever hard, and then tightening the caliper bolts up to the correct torque.

However, one video I watched recently from a bike shop did this differently: they spun the wheel and then squeezed the brake lever very slightly so it only just rubbed on the rotor, and then they tightened up the bolts slightly and repeated the process until the bolts were fully tightened.

Which is the correct method?
Well there are at leas two desired things:
No rub on the rotors while freespin
Same force either side without pushing the rotor axially (it can warp and twist rotors and all sorts of nasty stuff) while braking

So everything should check fine to align it correctly. That means go with a true rotor and the caliper should extend evenly left and right (hard to check)
But anyway, squeezing the brake moderately hard (like braking in normal use) will give the exact tendency to rest under that type of braking. So I'd go by this reasoning. So not the tightest squeeze but moderately like you would brake normally while riding. At this position the caliper will be ensured to press evenly and not force the rotor axially.
If the caliper is good it will maintain equal distance when freespin and apply equal amount of force each side on center at any braking force applied.. but with a less than perfect balanced caliper at least you get true equal force at that particular type of lever squeeze you set it to.
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Old 06-18-18, 03:13 PM
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I grab a brake lever, fairly firmly, then tighten bolts. Sometimes calipers like to settle in off center, so I have to put a feeler guage in between rotor and one pad before tightening.
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Old 06-18-18, 03:14 PM
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I usually try the "squeeze lever while tightening" method but in some cases when it still rubs slightly then I nudge the caliper one bolt at a time slightly while the wheel is spinning until there is no rub.
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Old 06-19-18, 09:50 AM
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Yeah I have tried and tried the "loosen; squeeze hard; tighten" method and it never seems to work for me. I get a little better success if I retighten the bolts with glacial slowness, attempting to avoid moving the caliper by sudden bolt movements, but still I sometimes get rub and have to apply an ad hoc nudge like scycotic. A shim like Lester might work too. I'll also give a try to your alternate method. Can you give the link for that video?
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Old 06-19-18, 11:46 AM
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Originally Posted by RubeRad View Post
Yeah I have tried and tried the "loosen; squeeze hard; tighten" method and it never seems to work for me. I get a little better success if I retighten the bolts with glacial slowness, attempting to avoid moving the caliper by sudden bolt movements, but still I sometimes get rub and have to apply an ad hoc nudge like scycotic. A shim like Lester might work too. I'll also give a try to your alternate method. Can you give the link for that video?
I'll try to locate the video again - I've watched so many over the last 48 hours and I'm not sure if I watched it on my iPad or Mac. It was definitely a YouTube video.
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Old 06-19-18, 12:24 PM
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I don't have a lot of experience with disc brakes, and own just one bike with them (hydraulic). I loosened both calipers to re-center them, just to gain experience with it, but I didn't find a lot of success with the Squeeze The Lever method. In my case, I just spun the wheel and played with the caliper alignment by hand and slowly cinched down the bolts until they were tight enough that the caliper didn't move on its own with further tightening, then I torqued them down. After ensuring the wheel was installed correctly in the dropouts, that is.
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Old 06-19-18, 02:00 PM
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I've never had great results with the lever squeeze method. The pads always end up rubbing at least a little (and sometimes so much that the wheel won't spin freely), and even when they don't rub, they are off-center enough to flex the rotor while braking. For mechanicals, it's good for at least getting the pads parallel to the rotor, but then you use the pad adjusters to dial in the centering. For hydros, frankly it's kind of useless in many instances. Even with shims, facing the mounts, and various other tricks, you often end up just eyeballing it and hoping you got somewhat parallel alignment.

I will have to check out that YouTube video as I'm not familiar with that technique. It sounds similar to one I read about where you sort of "walk" the caliper into alignment by tightening one bolt a little, then use that as sort of a pivot to swing the other side to center, then tighten that side and loosen the first side, and repeat, but I've never gotten it to work. At the end of the day the final torquing of the fixing bolts always disturbs any careful alignment you've done.
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Old 06-19-18, 03:06 PM
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I think I found the video that I was referring to earlier. Check out the brake pad adjustment method that starts at the 5 minute mark in this video:

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Old 06-19-18, 03:30 PM
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Thx. Interesting. So loosen the caliper bolts, make sure caliper moves freely, squeeze brakes only lightly, tighten partway, let go, spin, tighten again, finish tightening? I'm not sure what that accomplishes separate from the simpler loosen/squeeze/tighten method. But it can't hurt to try.

Maybe a hard squeeze applies some kind of sideways-torquing force to the caliper?
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Old 06-19-18, 03:36 PM
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I’m changing pads on my hybrid next weekend so will try this method out.
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Old 06-19-18, 03:40 PM
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Originally Posted by RubeRad View Post
Thx. Interesting. So loosen the caliper bolts, make sure caliper moves freely, squeeze brakes only lightly, tighten partway, let go, spin, tighten again, finish tightening? I'm not sure what that accomplishes separate from the simpler loosen/squeeze/tighten method. But it can't hurt to try.

Maybe a hard squeeze applies some kind of sideways-torquing force to the caliper?
I thought he loosened them up again before the second spin? Not sure what this accomplishes either. Maybe if the rotor is a little warped it lets the caliper float around a little and find the best average center or something. Doing it a few times maybe just helps work out any dirt and stickiness that would impede the process? He did a similar thing with the pistons earlier in the video.
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Old 06-19-18, 03:45 PM
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I didn't see him do that, but that does seem to be what the camera man was asking about, although 'loosen' might just mean let go of the brake lever
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Old 06-19-18, 04:26 PM
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internal fluid balancing between the 2 pistons, should make pad pressure be = ..
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Old 06-19-18, 04:42 PM
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Originally Posted by fietsbob View Post
internal fluid balancing between the 2 pistons, should make pad pressure be = ..
The pistons inevitably end up with different levels of drag so its not how it works in reality.
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Old 06-19-18, 04:51 PM
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Cite your references in the footnotes.. they're on both sides of the same disc, joined by a fluid.


my Magura Rim brakes have a balance tube,
1 pad may lead inward, but no real pressure is exerted between them , until both are in contact.
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Old 06-19-18, 11:43 PM
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Originally Posted by fietsbob View Post
Cite your references in the footnotes.. they're on both sides of the same disc, joined by a fluid.


my Magura Rim brakes have a balance tube,
1 pad may lead inward, but no real pressure is exerted between them , until both are in contact.
but if they don't advance at the same rate then the rotor ends up deflecting to one side before the pads equalize the pressure that leads to squeaking. Happens all the time with dirty pistons and why they need to be periodically cleaned
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Old 06-20-18, 12:16 AM
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^ Cleaning pistons is an interesting discussion too. I’ve heard that you shouldn’t use strong brake cleaning sprays as they may damage the piston seals. One source recommended using IPA. That then may cause the issue of the pistons seizing if they’re not lubricated after being cleaned. Then the choice of lubricant becomes important as silicone grease is recommended due to the high temperatures that could be generated.

Is there an easier way to clean the pistons? All of the above seems overkill to me.
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Old 06-20-18, 02:16 AM
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Originally Posted by taz777 View Post
Iím after a consensus here.

Iíve always centred pads in my calipers by loosening the calipers bolts and then squeezing the brake lever hard, and then tightening the caliper bolts up to the correct torque.

However, one video I watched recently from a bike shop did this differently: they spun the wheel and then squeezed the brake lever very slightly so it only just rubbed on the rotor, and then they tightened up the bolts slightly and repeated the process until the bolts were fully tightened.

Which is the correct method?
neither is the correct method. Both are easy fixes made for people who can't really do much bike maintenance and they are for some reason still in official manuals made by avid/sram etc. I mean yeah they work if you have completely even piston movement on both sides, but so far I have never come across as brake that does this.

The method outlined in this video takes longer, but afterwards you don't have to touch the caliper until you need to take it off for some reason.
There's also a nifty way of getting the pistons to bite evenly which is necessary with brakes which don't have equal piston movement.

With the method you outlined you'd need to make the caliper adjustment every time you change brake pads for example.
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Old 06-20-18, 08:39 AM
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Originally Posted by taz777 View Post
^ Cleaning pistons is an interesting discussion too. Iíve heard that you shouldnít use strong brake cleaning sprays as they may damage the piston seals. One source recommended using IPA.
Could I use a regular Pale Ale, or does it have to be full India? Does a DIPA work better? Could I get away with lager in a pinch?
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Old 06-20-18, 08:47 AM
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Originally Posted by elcruxio View Post
neither is the correct method. Both are easy fixes made for people who can't really do much bike maintenance and they are for some reason still in official manuals made by avid/sram etc. I mean yeah they work if you have completely even piston movement on both sides, but so far I have never come across as brake that does this.

The method outlined in this video takes longer, but afterwards you don't have to touch the caliper until you need to take it off for some reason.
So basically, eyeball it?
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Old 06-20-18, 08:52 AM
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The next video Youtube showed (also by Hope) is a bit better done, and gives the same information (as well as cleaning the pistons)


Love those broad Northern accents! Brings back memories of living in England for 2 years and learning to understand all the regional English accents by watching BBC shows
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Old 06-20-18, 09:00 AM
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Originally Posted by RubeRad View Post
So basically, eyeball it?
Essentially yes. you just have to eyeball it really accurately to get the best results. But the time you use fiddling with it once will pay back multiple times over when you don't need to touch the mounting bolts again if you don't take the caliper off for some reason
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Old 06-20-18, 10:05 AM
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Originally Posted by taz777 View Post
^ Cleaning pistons is an interesting discussion too. I’ve heard that you shouldn’t use strong brake cleaning sprays as they may damage the piston seals. One source recommended using IPA. That then may cause the issue of the pistons seizing if they’re not lubricated after being cleaned. Then the choice of lubricant becomes important as silicone grease is recommended due to the high temperatures that could be generated.

Is there an easier way to clean the pistons? All of the above seems overkill to me.
A lot of the YouTube vids I’ve seen do use isopropyl alchohol for cleaning in and around the caliper. It’s a fairly mild solvent that doesn’t appear to damage seals (or paint). For piston lube, my understanding is that you usually just use the same brake fluid that is in the lines, so that you won’t damage the seals or contaminate the lines with something incompatible. I’m pretty sure I’ve seen one or two vids that also use brake fluid as the cleaning solvent (typically on a cotton bud or rag). Again you don’t need anything aggressive, as the abrasion of the cotton bud itself should dislodge most of the gunk, which then sticks to the cotton with the help of the fluid.
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