Whos changed their disc brake pads? It's so hard!

The duke

Active Member
I've got about 600 very hilly miles on my 4 month old BH EMTB. My rear shimano brake just started sounding like I was killing a moose. I removed the back tire and found the left side rear brake pad worn completely down to the metal and the right side with about 33% of the pad left.

I went on YouTube and followed instructions on replacement. I ran into problems at "press the pistons back in to make room for the new brake pads"

The right piston quickly went all the way, or almost all the way back in. The left piston would barely move. I got a flathead screwdriver and used some leverage and applied a LOT of force on the piston, to the point I was worried about breaking it, and got it 3/4 of the way in. I put the new pads in and the space in between them is just slightly too small....they always touch up against the rear disc brake.

When i spin the wheel, there's slight drag, but I don't notice it when I'm pedaling. Do I leave it alone? Will the pad wear down to create space for the disc? Is there another adjustment I can do? The brake fade in the lever is gone and it stops really well now.
 

JayVee

Well-Known Member
It sounds like you did it right. Just ride the bike for about 20-40 miles. It should rub out. If it doesn’t you’ll have to align the entire caliper, which can involve a little guesswork.

I've changed pads about 15 times now. It's one of the easiest things to do once you get used to it.
 

E-Wheels

Well-Known Member
I've got about 600 very hilly miles on my 4 month old BH EMTB. My rear shimano brake just started sounding like I was killing a moose. I removed the back tire and found the left side rear brake pad worn completely down to the metal and the right side with about 33% of the pad left.

I went on YouTube and followed instructions on replacement. I ran into problems at "press the pistons back in to make room for the new brake pads"

The right piston quickly went all the way, or almost all the way back in. The left piston would barely move. I got a flathead screwdriver and used some leverage and applied a LOT of force on the piston, to the point I was worried about breaking it, and got it 3/4 of the way in. I put the new pads in and the space in between them is just slightly too small....they always touch up against the rear disc brake.

When i spin the wheel, there's slight drag, but I don't notice it when I'm pedaling. Do I leave it alone? Will the pad wear down to create space for the disc? Is there another adjustment I can do? The brake fade in the lever is gone and it stops really well now.
Suggested remedy
Loosen the two bolts that secure the brake caliper to the frame
Apply the brake, which will pull the brake pads tight against the disc rotor
While keeping the brake pressure applied, retighten the two caliper bolts
Release the brake pressure which retracts the brake pads
Both brake pads should now have even gaps on both sides of the disc rotor
Good luck
 
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Ebiker01

Well-Known Member
I've got about 600 very hilly miles on my 4 month old BH EMTB. My rear shimano brake just started sounding like I was killing a moose. I removed the back tire and found the left side rear brake pad worn completely down to the metal and the right side with about 33% of the pad left.

I went on YouTube and followed instructions on replacement. I ran into problems at "press the pistons back in to make room for the new brake pads"

The right piston quickly went all the way, or almost all the way back in. The left piston would barely move. I got a flathead screwdriver and used some leverage and applied a LOT of force on the piston, to the point I was worried about breaking it, and got it 3/4 of the way in. I put the new pads in and the space in between them is just slightly too small....they always touch up against the rear disc brake.

When i spin the wheel, there's slight drag, but I don't notice it when I'm pedaling. Do I leave it alone? Will the pad wear down to create space for the disc? Is there another adjustment I can do? The brake fade in the lever is gone and it stops really well now.

They have a tool for pushing those pistons back in.

Also carefully can put with a nozzle a bit of oil on the edges of the pistons, they will go back in easier.
 

rich c

Well-Known Member
I too find replacing the pads as one of the easiest maintenance items on a bike. Especially if you do it before it goes metal to metal. When you went metal to metal with the pad and rotor, you probably galled the metal on the rotor and it should have been replaced. By not replacing it, you've shortened the life of the new pads. That extra heat of going metal to metal likely didn't do much good to the piston and seal. You should also watch a video on sticky pistons.
 
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rich c

Well-Known Member
They have a tool for pushing those pistons back in.

Also carefully can put with a nozzle a bit of oil on the edges of the pistons, they will go back in easier.
CAREFUL WITH USING "OIL" Just any kind of oil may ruin the seal on the piston. Use the recommended brake fluid and be certain to clean it well. Just a drop of oil on a pad is horrible.
 

MikeDD

Well-Known Member
Did you break the pads in per the manufacturer's instructions? This helped even out the pads and calipers on my emtb. I also replaced my pads before 600 miles.
 

The duke

Active Member
I too find replacing the pads as one of the easiest maintenance items on a bike. Especially if you do it before it goes metal to metal. When you went metal to metal with the pad and rotor, you probably galled the metal on the rotor and it should have been replaced. By not replacing it, you've shortened the life of the new pads. That extra heat of going metal to metal likely didn't do much good to the piston and seal. You should also watch a video on sticky pistons.
Thanks
I too find replacing the pads as one of the easiest maintenance items on a bike. Especially if you do it before it goes metal to metal. When you went metal to metal with the pad and rotor, you probably galled the metal on the rotor and it should have been replaced. By not replacing it, you've shortened the life of the new pads. That extra heat of going metal to metal likely didn't do much good to the piston and seal. You should also watch a video on sticky pistons.
This is great, thanks! Video didn't say what type of brake fluid. Im hoping automotive will work?
 

The duke

Active Member
Did you break the pads in per the manufacturer's instructions? This helped even out the pads and calipers on my emtb. I also replaced my pads before 600 miles.
How do you break in brakes? Sounds like you did it and got about the same life as me. 🙁
 

Horseshoe

New Member
Absolutely don’t use automotive. I think bicycles brake fluid is a mineral oil base.

This will depend on the brand of brakes. Shimano and Tektro are mineral oil, SRAM is DOT brake fluid. However I suspect that very few ebikes use SRAM unless they are mt bikes.
 

dAz63

Member
Park tools have videos on YouTube on servicing and cleaning seals on hydraulic disc brakes.

After I have cleaned the pistons and caliper with brake fluid (Shimano mineral oil) and alcohol, I use the old pads to push the pistons back in with a large screwdriver.
 

The duke

Active Member
Park tools have videos on YouTube on servicing and cleaning seals on hydraulic disc brakes.

After I have cleaned the pistons and caliper with brake fluid (Shimano mineral oil) and alcohol, I use the old pads to push the pistons back in with a large screwdriver.
I'm trying the screwdriver thing now. One side went in easily. The other side, I'm applying about enough pressure to bend metal and it's gone in about 3/4 of the way....but the disc touches 100% of the time. Scared to push any harder on that piston.
 

sl_duck

Member
I'm trying the screwdriver thing now. One side went in easily. The other side, I'm applying about enough pressure to bend metal and it's gone in about 3/4 of the way....but the disc touches 100% of the time. Scared to push any harder on that piston.
If your new pads are a tiny bit thicker than the previous ones when they were new, you might not have anymore room in the reservoir for the fluid to back into. Try loosening the reservoir bleed screw while you push the piston back. A little fluid will leak out, so have a rag handy to wipe it up. Also try to tighten the bleed screw before releasing the pressure on the piston so air doesn't get drawn in.
 

Robie

Active Member
Speaking of bleed screws. I just completed removing air on my rear brakes on my emtb since new. Hardest part of job was breaking loose bleed screw on rear caliper. Maybe KTM used loctite, but I had to use Knocker Loose penetrating spray, and a heat gun (carefully) to slowly get that brake caliper to expand and release that screw. Unreal snapping sound when that screw finally popped loose. Never seen anything like that. Job was a success no more air in line. For the job , I ordered Shimano brake bleeding kit and extra Mineral brake fluid from Amazon. Maguras brake servicing on my Stromer 2015 St2 will be next .
 
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The duke

Active Member
If your new pads are a tiny bit thicker than the previous ones when they were new, you might not have anymore room in the reservoir for the fluid to back into. Try loosening the reservoir bleed screw while you push the piston back. A little fluid will leak out, so have a rag handy to wipe it up. Also try to tighten the bleed screw before releasing the pressure on the piston so air doesn't get drawn in.
Now that's another thing to consider....the pistons may never have been able to retract that far....I could be uselessly applying torquing and damaging pressure to them to get them to fully retract. I don't know what a reservoir bleed screw is and am afraid to start draining my brake fluid. Now I'm thinking of riding the bike for awhile with the brakes touching to see if the problem resolves itself. 🙄🤔😳
 

jim6b

Active Member
Sixty years ago (had to throw that in) I was taught in physics that the virtue of hydraulics was that pressure applied to a reservoir would be applied equally to all outlets. On a bike, pressure on the brake level is transmitted to a reservoir and applied equally to BOTH sides of the brake rotor.

It seems to me if the OP has brakes which do not spread apart equally then they are probably not hydraulic and are probably mechanical and probably not going to easily worked on using methods appropriate for hydraulic brakes.
 

indianajo

Well-Known Member
My tektro mechanical disks have a screw to back out the pad opposite the hinged one. Also to tighten the pads when they wear down and leave the caliper excursion the same. Mechanical disks are MUCH easier to work on than the kluges detailed in previous posts. Took longer to turn the bike upside down and take off the panniers than to change the pads.
Since hydraulics were invented to balance braking force to all 4 wheels, and bikes need more braking on the front than the rear, I really don't see the point of hydraulic disks. Except for bragging to the guys in the club.
 

sl_duck

Member
Sixty years ago (had to throw that in) I was taught in physics that the virtue of hydraulics was that pressure applied to a reservoir would be applied equally to all outlets. On a bike, pressure on the brake level is transmitted to a reservoir and applied equally to BOTH sides of the brake rotor.

It seems to me if the OP has brakes which do not spread apart equally then they are probably not hydraulic and are probably mechanical and probably not going to easily worked on using methods appropriate for hydraulic brakes.
But he’s levering one piston against the other, so both are getting the same force and fluid won’t go from one side to the other.
Just put the pad that was 30% in the right side and a new one in the left. That should give enough room. Check again in six months.