How much, if at all, should pads drag on the rotor?


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bofler
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How much, if at all, should pads drag on the rotor?

Post by bofler »



I just finished redoing my brakes. MCs and calipers rebuilt. New lines and new pads. Got everything back together and have bled the brakes (might be a bit of air still, but levers are pretty firm). My issue is that all of the pads are slightly dragging on the rotor. All 3 calipers on all 3 rotors. It's not a heavy drag. With a good spin from the hand both the front and rear wheels can make it through a couple rotations.

Is it acceptable to have a the pads lightly dragging on the rotor? If not, what might my issue be? It's crazy to me that, after such an extensive rebuild, I would have all 3 calipers with this same issue.



johnny42
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Re: How much, if at all, should pads drag on the rotor?

Post by johnny42 »

I would expect a certain amount of drag with a total rebuild, that is, until you put a few miles on it.

bofler
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Re: How much, if at all, should pads drag on the rotor?

Post by bofler »

johnny42 wrote:
Thu Jul 30, 2020 3:13 pm
I would expect a certain amount of drag with a total rebuild, that is, until you put a few miles on it.
i hope so...really, really, really don't want to have to pull things off the bike again

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OldguyGlen
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Re: How much, if at all, should pads drag on the rotor?

Post by OldguyGlen »

Don't worry about it. If you feel the rebuilds went ok, the slight drag is normal. There is no spring return on the pads. When pressure is relieved, the pads are only moved back by the rotor. The rotors have a few thousandths of run out, and the wheel bearing as well. So the pads get pushed back enough to just barely have minimal "kiss contact" with the rotor. Hand spinning new pads isn't quite as effective as actual road conditions. Ride the bike... If it coasts freely all is well.

bofler
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Re: How much, if at all, should pads drag on the rotor?

Post by bofler »

Thanks for the responses. I think it's ok. On a test ride yesterday the brakes weren't hanging up at all, and just walking the bike I can't notice resistance. I think I'm just a bit paranoid because I had the front brake lock-up twice before this (and that's what prompted me to do the full rebuild).

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PAPete
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Re: How much, if at all, should pads drag on the rotor?

Post by PAPete »

When you come back from a ride, just feel the discs. If they're extremely hot, you might have to bite the bullet. Otherwise, you're probably ok. I'm no mechanic, but that's how I check them.
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bofler
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Re: How much, if at all, should pads drag on the rotor?

Post by bofler »

Well, I went out for about 60 miles today. Stopping a couple of times along the way to check the brakes. Seems like the rear rotor is getting pretty hot. Not smoking hot, but certainly hot enough that I wouldn't want to have my hand on it for much longer than a quick touch. The front right (linked to the rear on my '83, with 25mm pistons rather than the 32mm of the rear) is obviously heating up, but significantly less hot than the rear. The front left is somewhere in the middle, but pretty close in temperature to the other front brake.

Guess I'm a bit worried about the rear. Where would I start if I wanted to try to make the pads drag less and keep the rotor cooler? Or should I put some more miles on the mostly new braking system and see if it improves?

johnny42
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Re: How much, if at all, should pads drag on the rotor?

Post by johnny42 »

As long as the slider pins are lubed and things can move left and right, there's not much more you can do. The hydraulic pressure pushes the pistons onto the pads then onto the rotor. When you release the brakes, they should "slide" back. You've already determined there's no real braking action when rolling/pushing the bike, so I think you're good.

As the pads wear, the hydraulics should keep the same pressure and the fluid reservoir makes up the difference in the amount of wear. So to think that wearing the pads a bit will free them up is not really going to happen.

Although, if the rotors have pits, etc. that might affect the way the pads wear, and the pads will eventually adapt to the rotors.

bofler
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Re: How much, if at all, should pads drag on the rotor?

Post by bofler »

johnny42 wrote:
Fri Jul 31, 2020 7:53 pm
As long as the slider pins are lubed and things can move left and right, there's not much more you can do. The hydraulic pressure pushes the pistons onto the pads then onto the rotor. When you release the brakes, they should "slide" back. You've already determined there's no real braking action when rolling/pushing the bike, so I think you're good.

As the pads wear, the hydraulics should keep the same pressure and the fluid reservoir makes up the difference in the amount of wear. So to think that wearing the pads a bit will free them up is not really going to happen.

Although, if the rotors have pits, etc. that might affect the way the pads wear, and the pads will eventually adapt to the rotors.
Everything is lubed up. Got a new slider pin since the old one was horribly rusted and pitted. All the rubber parts are new. Only thing that I guess could be an issue is that I perhaps didn't get the caliper seal grooves cleaned out well enough and they're not allowing the pistons to retract as much as they should.

Think I'll put some more miles on them and see if there's any change, better or worse.

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julimike54
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Re: How much, if at all, should pads drag on the rotor?

Post by julimike54 »

Not sure if you checked but, make sure the rear brake lever is returning all the way up. The rear brake pivot point is an often missed lubed maintenance step.


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