It's late at night, my bike is sleeping soundly in its shed, and for the first time, I understand what really retracts the brake pistons - and the brake pads. Thanks for sharing!
i actually 100% wanted to know about how the pads reset themselves. I just installed new brake pads last week and was wondering about that and thinking it couldn't be the little tension spring thingy that comes with the pads. I seriously appreciate you guys explaining this because I had no idea.
Thanks. I knew that the answer to "how do I spread my brake pads" is just "Stick something thin between them and lever them apart" but the part about how the brakes actually work taught me a lot.
@@erikdg "Brute" force or not; that's just semantics. A measuring tool should only be used for measuring. Applying any force to it that it wasn't designed for can make it lose its accuracy. Chain wear is measured in fractions of a percentage point, so I wouldn't risk it.
dunno I've been using the spacers that came with my brakes... worked fine; and I guess any tool that has an edge and blade that is not gonna bend / break would work as well to separate the pistons enough to fit through the rotor again
Spot on as always! Also important: Bleed your breaks only with bleed blocks. 'cause otherwise you might run into a problem once you change your rotor or pads. And when you then start to push back the calipers you might kill the membrane in your brake lever by accident. Reason: Without bleed block there is a chance you put to much hydraulic fluid into the system.
Nice video. You may need a bit more zooming but the schematics worked very well. Maybe I never asked myself the question, but I did not know the seal was responsible for pushing the piston back. Isn’t some suction from the fluid also responsible for that?
Hello. Thanks for your video but I still cannot fully insert both pistons into caliper. I have new brake pads but after installing them there is too little space for brake rotor to fit. I tried to push back pistons using screwdriver and old pads but it didnt work. Then I cleaned the pistons and tried to push pistons back separately but pushing one caused the other to come back out. How do I reset their position? Do I need to unseal system and then set them to position?
when you bleed your brakes, use a bleed block to ensure the brakes are bled with the pistons fully retracted. Post bleed; when you set the pistons/pads to touch the rotors after you've closed the system, the fluid level will fall. This fall in fluid will mean you do not need to open the bleed port when adjusting, since there's enough "vacuum" volume for you to fiddle with piston travel.
@@MTMXBLIsn't it going to slowly suck air from the atmosphere? I always bleed with the pistons in adjusted position so I leave no room for air to get into the system.
It *shouldn't* be necessary, for the reason MTMXBL explained in his reply. However, if the system is overfull of fluid, usually from doing shortcut "lever bleeds" with the pads in place instead of a bleed block, and therefore the pistons advanced a little during the process, the fluid pressure from pushing them back can potentially damage the diaphragms in the lever body causing leaks.
Both great tools. PS-1 does get between pads that are compressed together easier. The PP-1.2 does better pushing directly on the pistons. The PS-1 is able to simulate the brake feel at the lever without installing the wheel. Both are great for similar but different reasons.
I learned the hard/expen$ive way NOT to use the Park Tool PP-1.2 Hydraulic Brake Piston Press without the brake pads installed... cracked the ceramic cup/piston in the Shimano Ultegra R8020 disc brake caliper - love the new PS-1 Pad Spreader - and do not even think about using a tire lever
There are brands that offer rebuild kits and have service intervals. There are other brands that offer no serviceability when it comes to these seals. For those they recommend replacing the caliper.
You could say they have the lever and caliper all in one unit. You pull the lever and subsequently the cable which at the caliper pulls on an another lever that pushes a pushrod and so on. The piston and seal are exactly the same as in full hydraulics.
@@8BitZ0mbieI think they're talking setups like TRP HYRD's which are hydraulic at the caliper instead of full cable actuated. Both pistons move, not just one like Avid BB7's. In the case of HYRD's, treat them just like any other hydraulic pistons.
@@adamwolfram6675 Truman is describing fully hydraulic systems where there is fluid in the brake lines. My TRP brakes only have fluid in the cartridge.
What about if the pads won’t move to grip the rotor and brake? I adjusted the cable and it still won’t grip the rotor. It happened after I loosened the outside screw on the side
Very timely video I am in currently replacing my brake pads on my bicycle. I would be interested in seeing a video of how to clean that O-ring when dirt gets in there.
Not an O-ring, it's a square ring. There was a Tech tuesday a few months ago that detailed how to clean the piston and to fix a lazy piston. Since that cleans the piston-seal interface partly, that's the only thing that's reasonable for a home mechanic to do. Otherwise it's disassembly which is not advisable. In short, iirc: remove the wheel and pads. carefully squeeze the lever to reveal more piston, but not so much it pops out. Clean the outer edge, where it interfaces with the seal, with a q-tip dipped in your correct braking fluid. Push the pistons back in. Repeat until pistons both move freely and equal.
@@RenAigu one thing YOU MUST DO after you're done with the "brake fluid cleaning" treatment, you MUST clean your pistons and callipers with isopropyl before you insert the pads back in. And be very thorough about it. Otherwise you will wreak havoc on the pads and discs.
One of the pistons will typically advance quicker than the other/ others. Its not important to have them advance at the exact same time. Once one of the pads meets the rotor it stops advancing and the other piston/'s start advancing more.
The PS-1 is fine and dandy if you are at home or in a shop, however, what do you do if you accidentally actuate a brake in the field while changing a flat, or cannot justify buying a tool you hope you never need?
You use the flathead screwdriver on the multi tool that everyone should be carrying. Just don't dig the point of the screwdriver into the soft-ish parts of the piston and it'll be fine.
So the pads aren’t permanently fused together? 😂 I need to stop listening to people who don’t know what tf they’re talking about. Thank you for the simple, clear video.
If there was any danger of them fusing together, they'd have to be much more careful about how they ship the pads. Shimano just ship the pads rattling around in a cardboard box, with the spring in a paper envelope.
One thing I do wish was that disc breaks had a slightly larger gap,because it can be very annoying fine tuning the very small gap between the pads and rotor
Some brakes have a "pad contact adjust" which allows you to adjust when that happens in your lever pull. Most brakes do not have that and there is no adjustment for it.
I didnt get it. What do you mean “unless the lever is pulled”? In both cases (wheel on/ wheel off) the lever is pulled but the seal in one case adjusts the pads back but in the other doest. According to video when the wheel is in the seal adjusts the pads back in to position but when the wheel is off the seal doesnt adjust the pads back in to position. Why so?
The adjustment works like this. The seal is like a spring that can slip. If you only move the pads a little way, the seal doesn't slip, and it moves the pads all the way back. If you move the pads too far, the seal slips, so it only moves the pads part of the way back. During normal braking, the pads can only move a short distance before they bump into the rotor. Because the pads only move a short distance, the seal doesn't slip and it's as if it's just a spring. However, as the pads wear, they need to be pushed out farther to reach the wheel so, eventually, the seal slips a little bit. That's how the self-adjustment works. The adjustment means that, as the pads wear, the pistons move farther and farther out to keep the gap between the pads and rotor constant. Now, suppose you pull the brakes while the wheel's out. There's no rotor to stop the pads, so they keep moving until they bump into each other. That means they've moved a long way, so the seal has slipped and they only retract a little way. It then becomes hard to separate them, because they're so close together.
What do you do when you push 1 piston back, and the other one just comes out because of it? Tried to use 2 tyre levers to hold 1 inside, and push the other inside as well but I failed. Im going crazy here Edit: apparently it had too much oil for fresh pads
I'm surprised you didn't talk about resetting pistons during a pad replacement, and opening up the system at the lever to give the fluid somewhere to go. I also like to teach people to use the right tool to spread pistons during brake service. Cracked ceramic pistons on Shimano brakes make for a very bad day at the shop.
Yeah man. I open up the system each time I put in new pads to push back the pistons. One time I didn’t open up the system and pushed back the pistons, I blew my bladder.
No need to open the system when you always use a bleed block when bleeding. If you bleeded without a bleed block you might habe to much oil in your system. And yes, then you have to either open it or see what breaks first (usually the membrane in the brake lever).
with a flat brake disk the pads can float quite close to the disk, ready to make contact w/ little travel at the lever... a little trick to reposition the pads as close to the disk as possible on a regular basis: use rubber bands to keep the brake lever pulled in overnight. you need just enough pressure for the pads to touch the disk and w/ time the caliper piston will slightly slide thru the square seal closing the gap between the pads and the disk. in the morning the brakes will feel firm -given there's no air in the system.
Not only pointless, I read somewhere it's even detrimental. You want a bit of friction between the square seal and piston whereas with lubrication, the advancing piston doesn't flex the seal. It just slides out and does not retract.
The tool itself is a clue that you can also use an old rotor. While I don't have this one, many of the times I have purchased Park Tool tools they were chosen over cheaper options to support the production of high quality repair help videos that have been of great help to me.
Good information but except for the diagrams the explanation with the cut away parts was completely wasted because you couldn’t actually see anything except for his fingers sometimes. If you’re going to use something like the cut away parts for gods sake please position the camera above where we can actually see what you’re doing!
I struggled to get past the first two minutes of this, never use dot fluid in mineral brakes, it will destroy them. Mineral oil also has a higher boiling point than dot fluid And don't do the bleed nipple or sealing screw tight. They will shear or strip the thread.
Very good! ..I love understanding these things fully. One of the best brake caliper vids ever. Much appreciated !
It's late at night, my bike is sleeping soundly in its shed, and for the first time, I understand what really retracts the brake pistons - and the brake pads. Thanks for sharing!
Can't believe the mechanism is so simple and smart. Great video. Great topic.
i actually 100% wanted to know about how the pads reset themselves. I just installed new brake pads last week and was wondering about that and thinking it couldn't be the little tension spring thingy that comes with the pads. I seriously appreciate you guys explaining this because I had no idea.
Thanks. I knew that the answer to "how do I spread my brake pads" is just "Stick something thin between them and lever them apart" but the part about how the brakes actually work taught me a lot.
I love my PS-1. Thank you, Park Tool.
Really enjoy these, please continue making them
Allways imagined it would be more complicated but never thought I'd know. Appreciate the explanation 👍 thanks
Excellent explanation 👍
I understand this for the first time in my long cyclist life. Mistery solved :). Thanks for your clear explanation!
If you don't have that tool on hand. A chain wear measuring tool will do the job too. At least the one I have does.
I wouldn't use a measuring tool for any brute force task. A plastic tire lever would be a better, cheaper choice.
@@mattgies it's not exactly brute force. Just a little pressure is enough. If I had to use brute force on the pistons something would be very wrong.
@@erikdg "Brute" force or not; that's just semantics. A measuring tool should only be used for measuring. Applying any force to it that it wasn't designed for can make it lose its accuracy. Chain wear is measured in fractions of a percentage point, so I wouldn't risk it.
dunno I've been using the spacers that came with my brakes... worked fine; and I guess any tool that has an edge and blade that is not gonna bend / break would work as well to separate the pistons enough to fit through the rotor again
A large flat screwdriver works perfectly well
Spot on as always!
Also important: Bleed your breaks only with bleed blocks. 'cause otherwise you might run into a problem once you change your rotor or pads. And when you then start to push back the calipers you might kill the membrane in your brake lever by accident. Reason: Without bleed block there is a chance you put to much hydraulic fluid into the system.
Right?! The bleed block also needs to be the correct thickness for the system, to set that fluid volume as well.
I love knowing more than I wanted to.
This is good to know on any hydraulic disc brake, as the same pressure happens no matter the size.
Great vid, very informative. thanks for the upload.
Wolf Tooth's 8-bit Tire Levers are perfect for this job.
Nice video. You may need a bit more zooming but the schematics worked very well. Maybe I never asked myself the question, but I did not know the seal was responsible for pushing the piston back. Isn’t some suction from the fluid also responsible for that?
When do you use the PS-1 as opposed to the PP-1.2? They seem to do similar things but are shaped differently.
Hello. Thanks for your video but I still cannot fully insert both pistons into caliper. I have new brake pads but after installing them there is too little space for brake rotor to fit. I tried to push back pistons using screwdriver and old pads but it didnt work. Then I cleaned the pistons and tried to push pistons back separately but pushing one caused the other to come back out. How do I reset their position? Do I need to unseal system and then set them to position?
enjoyed your video 📹 very informative 👍
Great video! Question is it necessary to open the bleed port on the lever when resetting the pistons?
i never did that, so i dont think it is needed
Hi everyone , Thank you Merci ❤😊
when you bleed your brakes, use a bleed block to ensure the brakes are bled with the pistons fully retracted. Post bleed; when you set the pistons/pads to touch the rotors after you've closed the system, the fluid level will fall. This fall in fluid will mean you do not need to open the bleed port when adjusting, since there's enough "vacuum" volume for you to fiddle with piston travel.
@@MTMXBLIsn't it going to slowly suck air from the atmosphere? I always bleed with the pistons in adjusted position so I leave no room for air to get into the system.
It *shouldn't* be necessary, for the reason MTMXBL explained in his reply. However, if the system is overfull of fluid, usually from doing shortcut "lever bleeds" with the pads in place instead of a bleed block, and therefore the pistons advanced a little during the process, the fluid pressure from pushing them back can potentially damage the diaphragms in the lever body causing leaks.
What are those handlebars? I love them..
Whiskey Milhouse bars.
Great explanation. I kind of prefer the PP1.2 rather than the PS-1. Any particular reason to choose one over the other?
Both great tools. PS-1 does get between pads that are compressed together easier. The PP-1.2 does better pushing directly on the pistons. The PS-1 is able to simulate the brake feel at the lever without installing the wheel. Both are great for similar but different reasons.
@@parktool thanks
I learned the hard/expen$ive way NOT to use the Park Tool PP-1.2 Hydraulic Brake Piston Press without the brake pads installed... cracked the ceramic cup/piston in the Shimano Ultegra R8020 disc brake caliper - love the new PS-1 Pad Spreader - and do not even think about using a tire lever
Learned this the hard way. No longer, thanks to the PS-1 pad spreader!
Are these seals considered a maintenance item that should be replaced at recommended intervals?
There are brands that offer rebuild kits and have service intervals. There are other brands that offer no serviceability when it comes to these seals. For those they recommend replacing the caliper.
What about cable actuated hydraulic brakes? How do they work?
Usually only one pad moves with cable. And there is a spring that returns it when you let go of the brake
You could say they have the lever and caliper all in one unit. You pull the lever and subsequently the cable which at the caliper pulls on an another lever that pushes a pushrod and so on. The piston and seal are exactly the same as in full hydraulics.
@@8BitZ0mbieI think they're talking setups like TRP HYRD's which are hydraulic at the caliper instead of full cable actuated. Both pistons move, not just one like Avid BB7's.
In the case of HYRD's, treat them just like any other hydraulic pistons.
That's what he is explaining
@@adamwolfram6675 Truman is describing fully hydraulic systems where there is fluid in the brake lines. My TRP brakes only have fluid in the cartridge.
What about if the pads won’t move to grip the rotor and brake? I adjusted the cable and it still won’t grip the rotor. It happened after I loosened the outside screw on the side
Dominion brakes r good!!👍
Very timely video I am in currently replacing my brake pads on my bicycle. I would be interested in seeing a video of how to clean that O-ring when dirt gets in there.
Not an O-ring, it's a square ring. There was a Tech tuesday a few months ago that detailed how to clean the piston and to fix a lazy piston. Since that cleans the piston-seal interface partly, that's the only thing that's reasonable for a home mechanic to do. Otherwise it's disassembly which is not advisable. In short, iirc: remove the wheel and pads. carefully squeeze the lever to reveal more piston, but not so much it pops out. Clean the outer edge, where it interfaces with the seal, with a q-tip dipped in your correct braking fluid. Push the pistons back in. Repeat until pistons both move freely and equal.
th-cam.com/video/vQXFFgRButo/w-d-xo.html
@@RenAigu one thing YOU MUST DO after you're done with the "brake fluid cleaning" treatment, you MUST clean your pistons and callipers with isopropyl before you insert the pads back in. And be very thorough about it. Otherwise you will wreak havoc on the pads and discs.
@@parktool thank you for the link. I just watched it and that’s what I’m gonna do.
@@channul4887 thank you for your comment and that’s what I’m gonna do use a little alcohol
What do you do when one or more pistons advance further than the others.
One of the pistons will typically advance quicker than the other/ others. Its not important to have them advance at the exact same time. Once one of the pads meets the rotor it stops advancing and the other piston/'s start advancing more.
@@parktooldang, this is an important sub comment!❤thanks for clarifying that they balance themselves out
what handle bar is that!?
That is the Whiskey Milhouse bar.
@@parktool thanks, looks really nice
Is that I was looking for 😊
he said square seal but what i saw was a circle shaped one, or anything i misunderstood?
The cross section of the seal is square. It needs to be round to go around the piston of course.
@parktool ok, thanks for clarifying
The PS-1 is fine and dandy if you are at home or in a shop, however, what do you do if you accidentally actuate a brake in the field while changing a flat, or cannot justify buying a tool you hope you never need?
You use the flathead screwdriver on the multi tool that everyone should be carrying. Just don't dig the point of the screwdriver into the soft-ish parts of the piston and it'll be fine.
put plastic piston plugs
Great video!
So the pads aren’t permanently fused together? 😂
I need to stop listening to people who don’t know what tf they’re talking about.
Thank you for the simple, clear video.
If there was any danger of them fusing together, they'd have to be much more careful about how they ship the pads. Shimano just ship the pads rattling around in a cardboard box, with the spring in a paper envelope.
I am wondering if my brake lines really make that shwoosh sound when I pull the lever.
Just make sure whatever tool you use to spread the pads apart is clean.
One thing I do wish was that disc breaks had a slightly larger gap,because it can be very annoying fine tuning the very small gap between the pads and rotor
How to cut or reduce lever travel, i like the least travel posible but mine only 'starts' breaking middle lever...thnks
Some brakes have a "pad contact adjust" which allows you to adjust when that happens in your lever pull. Most brakes do not have that and there is no adjustment for it.
You can overfill the system, don't use a bleed block or use a thinner bleed block. This will only last a while until the pad wears away though.
There is a plastic spacer to put inside your brake caliper when tire os off.
I got these with my, very cheap, bike. I had no idea what they were at first.
So why doesnt the seal adjust the calipers when the wheel is off?
They will not adjust unless the lever is pulled. The reason you need to separate the pads after you pull the brake is because it adjusted to nothing.
I didnt get it. What do you mean “unless the lever is pulled”? In both cases (wheel on/ wheel off) the lever is pulled but the seal in one case adjusts the pads back but in the other doest. According to video when the wheel is in the seal adjusts the pads back in to position but when the wheel is off the seal doesnt adjust the pads back in to position. Why so?
@@andriskadaga 2:58 overexcursion, seal is in new position relative to the plane of the brake, piston is now at rest at seal's maximum range
The adjustment works like this. The seal is like a spring that can slip. If you only move the pads a little way, the seal doesn't slip, and it moves the pads all the way back. If you move the pads too far, the seal slips, so it only moves the pads part of the way back.
During normal braking, the pads can only move a short distance before they bump into the rotor. Because the pads only move a short distance, the seal doesn't slip and it's as if it's just a spring. However, as the pads wear, they need to be pushed out farther to reach the wheel so, eventually, the seal slips a little bit. That's how the self-adjustment works. The adjustment means that, as the pads wear, the pistons move farther and farther out to keep the gap between the pads and rotor constant.
Now, suppose you pull the brakes while the wheel's out. There's no rotor to stop the pads, so they keep moving until they bump into each other. That means they've moved a long way, so the seal has slipped and they only retract a little way. It then becomes hard to separate them, because they're so close together.
What do you do when you push 1 piston back, and the other one just comes out because of it? Tried to use 2 tyre levers to hold 1 inside, and push the other inside as well but I failed. Im going crazy here
Edit: apparently it had too much oil for fresh pads
I have lost count of how many piston seals I have replaced when they get deformed .
Not gonna lie, I _absolutely_ thought it was the clip doing all the work here. Consider me informed!
Thats why I run Sram Guide calipers - they retract themselves! Lol
Mtb: disc brakes are so simple and easy to adjust
Roadies: I can’t tech.
It's even worse when you have the pads removed, then the piston pops out entirely, and it floods the floor with fluid, lol.
And if you don't have a PS-1 you can always just use a tire lever.
I'm surprised you didn't talk about resetting pistons during a pad replacement, and opening up the system at the lever to give the fluid somewhere to go.
I also like to teach people to use the right tool to spread pistons during brake service. Cracked ceramic pistons on Shimano brakes make for a very bad day at the shop.
Yeah man. I open up the system each time I put in new pads to push back the pistons. One time I didn’t open up the system and pushed back the pistons, I blew my bladder.
No need to open the system when you always use a bleed block when bleeding. If you bleeded without a bleed block you might habe to much oil in your system. And yes, then you have to either open it or see what breaks first (usually the membrane in the brake lever).
@@GokkunGuru You did not use a bleed block.
As long as you don't fully open/seat the pistons back in to the caliper, no need to open the system. Inviting trouble with potential air in the system
with a flat brake disk the pads can float quite close to the disk, ready to make contact w/ little travel at the lever...
a little trick to reposition the pads as close to the disk as possible on a regular basis: use rubber bands to keep the brake lever pulled in overnight. you need just enough pressure for the pads to touch the disk and w/ time the caliper piston will slightly slide thru the square seal closing the gap between the pads and the disk. in the morning the brakes will feel firm -given there's no air in the system.
So... to lubricate the pistons is pointless.
Not only pointless, I read somewhere it's even detrimental. You want a bit of friction between the square seal and piston whereas with lubrication, the advancing piston doesn't flex the seal. It just slides out and does not retract.
Any thin tough metal would do, why buy the tool unless you're a repair shop
The tool itself is a clue that you can also use an old rotor. While I don't have this one, many of the times I have purchased Park Tool tools they were chosen over cheaper options to support the production of high quality repair help videos that have been of great help to me.
Good information but except for the diagrams the explanation with the cut away parts was completely wasted because you couldn’t actually see anything except for his fingers sometimes. If you’re going to use something like the cut away parts for gods sake please position the camera above where we can actually see what you’re doing!
I struggled to get past the first two minutes of this, never use dot fluid in mineral brakes, it will destroy them.
Mineral oil also has a higher boiling point than dot fluid
And don't do the bleed nipple or sealing screw tight. They will shear or strip the thread.
I think you commented on the wrong video... he didn't bleed the brakes here... what video were you watchjng?
You struggled to comprehend what he was actually discussing in this vid. LOL
I've never understood why people get so worked up ab this...spread the pads and move on!
You talk to people like they are school children. And, your explanation as to why the pads retract isn’t even correct.
Says the internet basement dummy 😀
OK, what's the correct explanation?