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Stuck brake pistons?

Old 05-20-16, 05:17 PM
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uRabbit
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Stuck brake pistons?



Tektro HD-E710 brakes.

As you can see, I'm changing the pads on our brakes. Unfortunately, I'm stuck on the first set. The piston simply will not go in...

I have burped the line (no bubbles, actually), so I'm not sure what's keeping that piston extended like that... Looking at our other bike (exactly the same), the same piston is out almost as far. This is due to the design of the system, but obviously it shouldn't be out that far.
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Old 05-21-16, 03:11 AM
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Bike hydros have two pistons meant to pinch together. Looks like one side of yours didn't move which caused the other to overshoot. Depending on age, I might try pushing that as a warranty issue.
Otherwise, some gentle prying with something wide and flat to push it back in.
Or pull the piston apart.
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Old 05-21-16, 05:42 AM
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I don't know anything about hydraulic disc brakes but I do know Park Tool make a tool for pushing pistons back.
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Old 05-21-16, 08:33 AM
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Have you tried opening the bleed valve as you push the piston back? When I replaced my contaminated rear pads, the pistons didn't reset so I had to give them a little push with a wedge while I cracked the bleed and it worked fine. (This trick I knew from working on cars with overextended pistons.)
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Old 05-21-16, 11:36 AM
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Hydro disc brake should push fluid back up the line to the expansion tank in the lever , when the slave pistons are forced apart.
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Old 05-22-16, 02:43 PM
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Originally Posted by Wheever View Post
Have you tried opening the bleed valve as you push the piston back? When I replaced my contaminated rear pads, the pistons didn't reset so I had to give them a little push with a wedge while I cracked the bleed and it worked fine. (This trick I knew from working on cars with overextended pistons.)
This worked best. Opened it up, gave it a push and heard a sort of pop. Closed it back up so as to not lose too much fluid, and was able to get both pistons back to flush.
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Old 05-22-16, 06:47 PM
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Originally Posted by uRabbit View Post
This worked best. Opened it up, gave it a push and heard a sort of pop. Closed it back up so as to not lose too much fluid, and was able to get both pistons back to flush.
Excellent.

You our might want to bleed them now.
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Old 05-22-16, 09:25 PM
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Originally Posted by Wheever View Post
Excellent.

You our might want to bleed them now.
Thinking so. I ended up only replacing one set of pads because the others are fine. Now, however, that brake lever (the rear one) needs to be fully applied in order to engage the brakes. If you rapidly pump the lever, pressure will build, but not all the way back to where it was before. You can hear the oil squirting inside the lines, especially at the brake. This leads me to believe that there's not enough oil in the line. I checked the reservoir and it appears to be almost full, but I imagine even a drop adds quite a bit of pressure to such small lines.

Am I correct?
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Old 05-22-16, 10:09 PM
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Originally Posted by uRabbit View Post
Thinking so. I ended up only replacing one set of pads because the others are fine. Now, however, that brake lever (the rear one) needs to be fully applied in order to engage the brakes. If you rapidly pump the lever, pressure will build, but not all the way back to where it was before. You can hear the oil squirting inside the lines, especially at the brake. This leads me to believe that there's not enough oil in the line. I checked the reservoir and it appears to be almost full, but I imagine even a drop adds quite a bit of pressure to such small lines.

Am I correct?
No, that's air in the line. I guess I didn't do a very good job of explaining how to crack the bleeder so as not to allow air into the line. Sorry.

But bleeding isn't so difficult if you have the correct tools. (Crap, I was going to link you to this bleed kit, which I have, but I see it out of stock and may never be I stock again. There are other kits out there that are the same general idea.) there are plenty of how to videos out there.
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Old 05-23-16, 02:15 PM
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Originally Posted by Wheever View Post
No, that's air in the line. I guess I didn't do a very good job of explaining how to crack the bleeder so as not to allow air into the line. Sorry.
I tried burping the line but nothing came up. I will bleed if my kit ever gets here.
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Old 05-23-16, 02:44 PM
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Originally Posted by uRabbit View Post
I tried burping the line but nothing came up. I will bleed if my kit ever gets here.
Most likely air trapped in the caliper. When the piston popped out it probably introduced an air pocket behind the piston. I had a similar problem, and got several large air bubbles out of the caliper. It should be fine after a decent bleed operation.

When bleeding, it's best to un-bolt the caliper and that was you can easily move it around to free all the trapped air.
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Old 05-23-16, 03:48 PM
  #12  
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Originally Posted by uRabbit View Post
I tried burping the line but nothing came up. I will bleed if my kit ever gets here.
You have to bleed it. It's a whole procedure. You have to force air out of the lines with more fluid.

https://www.youtube.com/watch?v=LhKKe6av-0U
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Old 05-23-16, 04:46 PM
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Originally Posted by Wheever View Post
You have to bleed it. It's a whole procedure. You have to force air out of the lines with more fluid.

https://www.youtube.com/watch?v=LhKKe6av-0U
I can't find a bleed bolt on my HD-e710's...



Obviously, if I loosen that bolt with the hose going to it, brake fluid will come out of there. But I certainly cannot refill it there, or perform a bleed in the manner being described.
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Old 05-23-16, 05:50 PM
  #14  
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Looking at this pdf http://www.tektro.com/_english/03_su...1327026621.pdf it looks like you're missing the bleed nipple, or I can't see it in the picture. . It should be on that same hump of metal where the banjo nut is. I can kind of see what looks like the edge of a hex or torx bolt over there, so maybe someone plugged it at some point?

If that's not it, it's there somewhere. But maybe you should take it to a bike mechanic, at this point?

I just wanted to add that I am only familiar with shimano hydraulics...and cars, of course.
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Old 05-23-16, 08:52 PM
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Originally Posted by Wheever View Post
Looking at this pdf http://www.tektro.com/_english/03_su...1327026621.pdf it looks like you're missing the bleed nipple, or I can't see it in the picture. . It should be on that same hump of metal where the banjo nut is. I can kind of see what looks like the edge of a hex or torx bolt over there, so maybe someone plugged it at some point?

If that's not it, it's there somewhere. But maybe you should take it to a bike mechanic, at this point?

I just wanted to add that I am only familiar with shimano hydraulics...and cars, of course.
Yep, been using that, but as you can see the diagrams are horrible. I finally found it when someone from my bike's manufacturer got back to me. So I did a full bleed and that didn't work. I did a full step-by-step process of burping the brakes that someone from the manufacturer (Juiced Bikes in Portland) gave me, which is as follows:

- Get some of the Tektro Mineral oil or use the Shimano Mineral Oil.
- Pull the caliper off so it is clear of the Rotor (nothing between the pads)
- Change the pads if your pads are low.
- Use a 4mm Hex tool to move the brake lever to the horizontal position.
- Turn the lever reach adjustment screw to the closest position using the 2mm Hex tool.
- Use the T15 torx tool to remove the bleed valve on the handle bar lever.
- Add as many oil drops to the bleed valve, just till its almost spilling out.
- lightly squeeze the lever and let it flick back, you will see the air bubbles come out of the bleed valve, keep adding oil as it gets lower, so its always remains topped up as the oil is replacing the air bubbles.
- Now squeeze the lever harder and the pads will touch, its ok, keep pumping and releasing the lever to get the air out.
- Screw in the bleed valve stopper to the top of the lever, clean any oil that has spilled.
- Now use the flat head screw driver to carefully push apart the pads just so they can clear the rotor.
- Install back on the caliper and center it.
- Now pump the lever and the pads will automatically reset and retract to the right position.
- Use the 2mm hex tool to put the lever reach back into the desired position.

That. Did. Not. Work.

At this point, I'm wondering why I even went car-free if I cannot simply change the pads without completely disabling the brakes afterwards and scratching my head for days on end. So I'm done f-ing with it, and I'll have to fork over cash I didn't budget for someone else to f with it.
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Old 05-23-16, 09:56 PM
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Originally Posted by uRabbit View Post
Yep, been using that, but as you can see the diagrams are horrible. I finally found it when someone from my bike's manufacturer got back to me. So I did a full bleed and that didn't work. I did a full step-by-step process of burping the brakes that someone from the manufacturer (Juiced Bikes in Portland) gave me, which is as follows:

- Get some of the Tektro Mineral oil or use the Shimano Mineral Oil.
- Pull the caliper off so it is clear of the Rotor (nothing between the pads)
- Change the pads if your pads are low.
- Use a 4mm Hex tool to move the brake lever to the horizontal position.
- Turn the lever reach adjustment screw to the closest position using the 2mm Hex tool.
- Use the T15 torx tool to remove the bleed valve on the handle bar lever.
- Add as many oil drops to the bleed valve, just till its almost spilling out.
- lightly squeeze the lever and let it flick back, you will see the air bubbles come out of the bleed valve, keep adding oil as it gets lower, so its always remains topped up as the oil is replacing the air bubbles.
- Now squeeze the lever harder and the pads will touch, its ok, keep pumping and releasing the lever to get the air out.
- Screw in the bleed valve stopper to the top of the lever, clean any oil that has spilled.
- Now use the flat head screw driver to carefully push apart the pads just so they can clear the rotor.
- Install back on the caliper and center it.
- Now pump the lever and the pads will automatically reset and retract to the right position.
- Use the 2mm hex tool to put the lever reach back into the desired position.

That. Did. Not. Work.

At this point, I'm wondering why I even went car-free if I cannot simply change the pads without completely disabling the brakes afterwards and scratching my head for days on end. So I'm done f-ing with it, and I'll have to fork over cash I didn't budget for someone else to f with it.

Well, okay, but you didn't bleed the slave cylinder at the caliper itself! That procedure you describe actually makes no sense to me, because it does nothing for the air at the slave! That can only be gotten out by pushing the bubbles out with fluid from the caliper bleeder.

The problem began because you cracked the bleeder before you pushed the caliper back. And I should have explained that you should have applied pressure to the caliper as you were pushing the caliper back, and only *then* cracked the bleeder. I'm sorry I didn't verify beforehand that you understood this.

Taking it it to a bike shop to be bled shouldn't cost much, I wouldn't think. But After that I think you would do well to study up on hydraulic brakes so you have a better grasp of their operation and maintenance.
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Old 05-23-16, 11:17 PM
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Originally Posted by uRabbit View Post
That. Did. Not. Work.
The bleed nipple on the caliper seems to have broken off, without that you can't bleed the brakes. See Step 5 & 6 in the instructions. Without being able to open the valve, there's no real way for the fluid to move. Hopefully the bike shop will be able to source a new one.

If not I recommend just buying a set of Shimano brakes.
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Old 05-24-16, 05:20 PM
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Originally Posted by Wheever View Post
Well, okay, but you didn't bleed the slave cylinder at the caliper itself! That procedure you describe actually makes no sense to me, because it does nothing for the air at the slave! That can only be gotten out by pushing the bubbles out with fluid from the caliper bleeder.

The problem began because you cracked the bleeder before you pushed the caliper back. And I should have explained that you should have applied pressure to the caliper as you were pushing the caliper back, and only *then* cracked the bleeder. I'm sorry I didn't verify beforehand that you understood this.

Taking it it to a bike shop to be bled shouldn't cost much, I wouldn't think. But After that I think you would do well to study up on hydraulic brakes so you have a better grasp of their operation and maintenance.
That list of instructions is what was given to me by the folks at Juiced. That's not all I did. I also did a full bleed, with a hose and bag at the top (bleed valve on lever assembly) and a syringe and hose at the bottom (caliper). I pumped a few times, and pushed air out until all that would come out was air-free mineral oil. I then screwed the valves back in and gave it a go. Lever was still spongy and gave no response. So that's when I followed the instructions from Juiced.

Hmm. So push the caliper back, then open both bleeder valves and proceed with a bleed? Kind of confused here. Also, the bleed valve on the caliper is just like the one on the lever assembly. You must screw on a fitting that allows you to attach a hose. This, to me, sounds like an insanely obvious design flaw. The nipple idea makes more sense – place the wrench over/around the nipple with it still fully tightened, placing the hose and syringe in place, then loosening the nipple slightly with the wrench. This minimizes contact with air. Unfortunately, this system is not like that at all.

edit: I truly appreciate your time and patience.

Originally Posted by gsa103 View Post
The bleed nipple on the caliper seems to have broken off, without that you can't bleed the brakes. See Step 5 & 6 in the instructions. Without being able to open the valve, there's no real way for the fluid to move. Hopefully the bike shop will be able to source a new one.

If not I recommend just buying a set of Shimano brakes.
I actually found the bleed valve on the caliper. It is on "top" of the caliper.
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Old 05-26-16, 02:25 AM
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Isnt it the same as bleeding a motorcycle caliper?

e.g. whilst its on the wheel, pump the brake a few times, hold the brake in, open the bleed nipple letting out the air and some fluid, tighten it back up, release the brake lever and repeat?

Remember to flex the hose a bit whilst bleeding, to work any pockets out, I don't know if the master cylinders are the same for pedal bikes but I keep the cap and diaphragm off when bleeding.

I have a bleed kit that basically lets you pump from the bleed nipple, another one that I can draw from the nipple too. They're very useful.
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