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Disc brake "lock out(?)" on easy descent

Old 01-20-22, 09:31 AM
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mdoleman
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Disc brake "lock out(?)" on easy descent

Bear with me, I am new to disc brakes. I searched for similar issues and couldn't find anything that specifically matched my experience, so I hope this thread might be useful.

For frame-of-reference, I've been riding for many, many years, and have built-up/maintained dozens of bikes. I recently had a new custom frame built for all-roads style sport touring -- a bit of a do-everything bike. I outfitted it with fairly top-end components, including Yokozuna Ultimo, flat-mounted disc brake calipers. These are a cable-actuated hydraulic brake, four piston, and use Shimano Deore XT (Saint/Zee) style pads. I set them up, initially, to be about as "tight" as I could get them, without rubbing. Meaning I adjusted them such that the calipers would start grabbing at almost any degree of lever pull.

I took a couple initial rides to get the pads bedded-in, more or less as suggested in the instructions. But I honestly didn't do anything really specific, other than pedal up to speed and brake to a stop, medium-hard, a couple dozen times. After that, everything seemed fine to me. The brakes worked great, seemed like no problem. TBH I am slightly mystified by the whole bedding-in process, as I didn't feel much (if any) before/after difference.

On my first "real" ride, I descended a stretch of muddy dirt road that dropped about 500 feet in a little under a mile -- certainly nothing epic, but consistent 10 to 12 percent, and a little technical. Brakes seemed to be doing fine. Toward the end of the descent, however, I noted that the brakes were really grabbing immediately, upon the slightest activation of the lever. At the bottom of the descent, after stopping, I noticed that the rear wheel was basically locked-up. The rotor had the slight discoloration indicating overheating. I had to loosen the caliper to proceed -- which was no big deal, and the remainder of the ride went on without a hitch.

I already know that at least part of problem (and maybe the whole problem) is: 1) my perhaps too-tight initial set-up, and 2) my very lazy technique of dragging the rear brake down the descent. Yet -- as I've said -- this wasn't exactly an epic, taxing descent -- three/four minutes and it was over. I have to believe the something else is perhaps up. This is the type of terrain and riding that I will be tackling all the time on this bike, so I want to get it right. Do I just set the calipers a little looser? Do I work on my braking technique? Different rotors? Different pads?

On that last point, I know it will be asked, and I have to honestly say that I do not know exactly what kind of pads came with the brakes. If I had to guess, I'd assume they are a semi-metallic. So far they have made absolutely zero noise at all, if that's a clue. They seem to modulate quite well.

Thanks for any information.
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Old 01-20-22, 10:13 AM
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My guess is that this is 100% attributable to riding the brake for an extended period. If the pads are almost but not quite engaged (which is how they're supposed to be), then nothing is happening. There's nothing in that to warp the rotor. But if you ride the brake for a long time, and the rotor doesn't have a chance to cool off, that could warp it. I don't think loosening the calipers would have any effect, although it could be useful as a diagnostic measure to see if the rotor is pinging intermittently on the pad, or continuously. If it's continuous, you need to recenter the caliper (easily done). If it's intermittent, the rotor is warped, and needs to be trued or replaced. I don't think different pads will make a difference—you still need to dissipate the same amount of energy. A different kind rotor might, but I'm not aware of any high-heat rotors. You could also probably put the caliper on a different adapter plate (or flip the one you've got, not sure) and get a bigger rotor, which would allow that heat to radiate away over a larger surface area. Road and gravel bikes are often set up with 160-mm rotors front, 140 rear, but you should be able to put a 160-mm rotor in the rear.

Also, I would call a mile at 10% a long, steep descent. I alternate front/back every few seconds in situations like that.
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Old 01-20-22, 10:40 AM
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Don't drag the brakes. Use them when you need them, then let them cool. The front brake provides the majority of the stopping/slowing power, the rear brake does very little.
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Old 01-20-22, 10:58 AM
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Thank-you, Adam. That's a good reality-check for me to hear, and it makes a lot of sense. I am thinking that it is not much more than a matter of me getting used to disc brakes and improving my braking habits.

I live in Portland, and ride all over Oregon, southern Washington, and northern California. So, needless to say, much of my riding includes long, steep, occasionally technical descents (and I am by no means a fast descender -- I make use of my brakes). I had never really thought of a mile at 10-ish percent as long, but I can see how realistically it -- indeed -- is, and requires a bit of technique if I'm going to be taking it slow and easy.

Do you think I might benefit from something like the Shimano "ICE" technology? The rotors that came with the Yokozuna brakes seem okay, but they are just a basic, one-piece, stainless steel rotor.
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Old 01-20-22, 11:10 AM
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Originally Posted by mdoleman View Post
Do you think I might benefit from something like the Shimano "ICE" technology? The rotors that came with the Yokozuna brakes seem okay, but they are just a basic, one-piece, stainless steel rotor.
Apparently Shimano claims a 40 heat reduction compared to other discs, which sounds significant. I don't know what they're comparing to or how realistic their test conditions are. And of course, I don't know how hot you were getting your brakes, so I don't know whether it would have made a difference.

If you want to go crazy, there are apparently ceramic rotors out there, which should be immune to warping.
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Old 01-20-22, 11:13 AM
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I think my tendency and habit of dragging the rear brake stems from me putting a premium on control, since I'm not great on technical descents.

To be clear, too, this little "issue" I'm describing seems to hardly have been an issue at all. Just something that surprised me as a total disc brake n00b. Sounds like the answer is simply `get better at riding bikes.' :-)
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Old 01-20-22, 11:35 AM
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You don't need to get better at riding brakes.

You don't ride them at all, you brake at a good rate and slow to below the speed you want to be at and then release them and allow the brakes to cool as you speed up, when you get too fast for your ability, then brake to slow again, rinse and repeat.

What you need to get better at is riding your bike.
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Old 01-20-22, 11:42 AM
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Originally Posted by mdoleman View Post
TBH I am slightly mystified by the whole bedding-in process, as I didn't feel much (if any) before/after difference.
Bedding-in your rotors and pads helps eliminate squeal and vibration and maximizes their stopping power, but it doesn't necessarily affect the way the brakes "feel" in any noticeable way.
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Old 01-20-22, 11:51 AM
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Originally Posted by Iride01 View Post
What you need to get better at is riding your bike.
That is literally what I said.
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Old 01-20-22, 11:59 AM
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Originally Posted by mdoleman View Post
That is literally what I said.
Good, then we agree!
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Old 01-20-22, 12:10 PM
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If you drag both brakes equally or alternate, the brake energy is distributed between the two. Meaning way less chance of overheating. I don't believe in "not dragging the brakes". They are there to control speed to you desire and safety. If they cant, without overheating, get a bigger and beefier brake rotor or bite the bullet and stop to cool down.
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Old 01-20-22, 05:19 PM
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Originally Posted by jp911 View Post
Without enough room/play, the thermal expansion of the rotor could result in lockup. The travel in the hydraulic disc brake levers (especially road levers) can be unsettling at first, but the piston travel is there to allow the pads enough room to retract from a hot brake rotor.
Doesn't happen.
Originally Posted by Racing Dan View Post
If you drag both brakes equally or alternate, the brake energy is distributed between the two. Meaning way less chance of overheating. I don't believe in "not dragging the brakes". They are there to control speed to you desire and safety. If they cant, without overheating, get a bigger and beefier brake rotor or bite the bullet and stop to cool down.
Dragging any brake is wrong. Use them, slow down, then don't use them. Use the front brake when you need to slow down, use the rear or both when you need a little more control. If you can't do your current descents w/o dragging the brakes the whole way down you're in over your head and need to find a mellower way down.
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Old 01-20-22, 05:44 PM
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I have a similar brakes, Juin Tech R1, equivalent of Yokozuna Motoko. The only problem I had was the loss of brake power when Shimano organic pads overheated.

Can it be that your brakes have some air in the system (both Motoko and Ultimo are closed system) in addition to oil? Does the problem go away when the caliper and the rotor cool down?

Did you check if the rotor is true? I am not sure about the Juin Tech/Yokozuna rotors, but Shimano makes cheaper rotors for use with organic pads and stronger ones for metallic pads. Maybe using those will help?

I think if the rotor is slightly warped it should not result in locking the wheel since you have a hydraulic system -- the pads will recenter on the rotor. There will be constant rubbing, no doubt, but it should not lock the wheel. I think air in the brakes or a similar problem is a more likely culprit.
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Old 01-20-22, 07:02 PM
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We had a thread with a similar problem a few days ago and I postulated that heat from the braking heated and expanded the brake fluid. In a closed system that pushed the pistons out further and bound the rotor. You said you have the brakes set so the pads "bite": as soon as the brake lever moves so that leaves little or no room for fluid expansion.
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Old 01-20-22, 07:31 PM
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Originally Posted by mdoleman View Post
Do you think I might benefit from something like the Shimano "ICE" technology?
Yes. Also increasing rotor size will help (if that's possible with flat mounts). And I think resin pads conduct less heat into the calipers than metallic pads.
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