Hydraulic disc brake adjustment
10-27-19, 11:30 AM
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Hydraulic disc brake adjustment
Hey guys,
I would like to ask for your help with adjusting disc brakes.
Bike: 2019 Kona Mahuna
Caliper: BR-M395
Lever: BL-M396
Problem: Rear disc rubs on pad only on the NDS.
Have done: I watched multiple videos on how to adjust disc brakes.
- Moved pistons (without pads) in with a tire lever and out by pulling the brake lever to lubricate them properly and to make sure they move evenly in the caliper. They seemed to move evenly..
- Bled system using Shimano's funnel (front of bike was raised).
- Tried to center caliper the usual way (loosen bolt, press lever, tighten bolt) many times with no success.
Could be the issue:
- too much oil in the system
- bent rotor (slight bend)
Do you guys have any idea where I could be making a mistake?
I would like to ask for your help with adjusting disc brakes.
Bike: 2019 Kona Mahuna
Caliper: BR-M395
Lever: BL-M396
Problem: Rear disc rubs on pad only on the NDS.
Have done: I watched multiple videos on how to adjust disc brakes.
- Moved pistons (without pads) in with a tire lever and out by pulling the brake lever to lubricate them properly and to make sure they move evenly in the caliper. They seemed to move evenly..
- Bled system using Shimano's funnel (front of bike was raised).
- Tried to center caliper the usual way (loosen bolt, press lever, tighten bolt) many times with no success.
Could be the issue:
- too much oil in the system
- bent rotor (slight bend)
Do you guys have any idea where I could be making a mistake?
10-27-19, 01:02 PM
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The method of holding the brake lever and tightening the caliper bolts rarely works properly for me. The tightening of one bolt, while the other is loose, causes the caliper to twist from the rotation of tightening the bolt. It can work if you lightly snug up both bolts before tightening them. I have had much better success with eyeballing the caliper to have an even space on both sides of the rotor. I just tighten the bolts to the point that there is some tension on the caliper, so I can move it but it stays where I put it. Then I tighten the bolts completely and test.
If it keeps rubbing on one side, that usually indicates a stuck piston. I just replaced one of those calipers on my bike after less than a year of use, because one of the pistons cracked.
If it keeps rubbing on one side, that usually indicates a stuck piston. I just replaced one of those calipers on my bike after less than a year of use, because one of the pistons cracked.
10-27-19, 02:48 PM
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The loosen caliper mounting bolts, squeeze lever and retighten bolts only gets one close many times. I'll slightly loosen one bolt and completely loosen the other bolt then push that end of the caliper into a better position. Slightly snug that bolt back and loosen the first bolt, push that side into place and snug the bolt down a bit. Test and repeat as needed. You're essentially "walking" the caliper one end at a time till the results are a centered pair of pads. Andy
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10-28-19, 03:20 AM
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A few additional things I suggest from experience:
1. Make sure the bolts have washers under the heads. When you tighten the bolt the washer should remain stationary so the bolt torque is less likely to 'twist' the caliper.
2. If you still get movement when tightening check that the caliper mounting faces (top of the posts) are flat. Sometimes you get a paint build up on the top of the post on some frames. The caliper will 'tilt' slightly as the bolts tighten rather than 'twist' in this is the case which causes the pads to be misaligned radially (rather than circumferentially). In this case you need to carefully scrape the paint off the top off the posts.
3. You should have a pad spacing tool (usually red plastic) to insert between the pads when the wheel is removed. This is useful for setting the pads spacing. Often you will need to open the filling port in the lever when using this tool to set the pad spacing. If you do have too much oil in the system the excess will come back out through the filling port.
1. Make sure the bolts have washers under the heads. When you tighten the bolt the washer should remain stationary so the bolt torque is less likely to 'twist' the caliper.
2. If you still get movement when tightening check that the caliper mounting faces (top of the posts) are flat. Sometimes you get a paint build up on the top of the post on some frames. The caliper will 'tilt' slightly as the bolts tighten rather than 'twist' in this is the case which causes the pads to be misaligned radially (rather than circumferentially). In this case you need to carefully scrape the paint off the top off the posts.
3. You should have a pad spacing tool (usually red plastic) to insert between the pads when the wheel is removed. This is useful for setting the pads spacing. Often you will need to open the filling port in the lever when using this tool to set the pad spacing. If you do have too much oil in the system the excess will come back out through the filling port.
10-28-19, 08:48 AM
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If you say you have a slight bend then that is your issue after doing everything you have listed.
10-28-19, 09:01 AM
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This is a pretty limited claim. It assumes there's no other issue that the OP doesn't know of (yet). We see calipers where one piston hangs up in it's movement more then the other. We see hub/frame dimensions that are out of spec. so centering requires added shims (and this use to be the norm). Andy
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