Video: Trail Doctor - How To Replace Your Disc Brake Pads

Nov 16, 2014
by Dan Milner  


Mentions: @yeticycles, @shimano



Posted In:
Videos Brakes



46 Comments

  • 12 0
 Well this isn't quite a tech tuesday, (where are they anyways?) but good job!
  • 10 0
 I already knew how to, but watched it anyway, because i knew it would be funny
  • 1 0
 Nice video as always, but I have a question: can you push pistons apart like that with all kind of brakes or just with the ones which have a reservoir (like shimano)? I always thought that it can damage the pump bladder on Formula-like brakes (especially given dot4 oil tends to increase its volume).
  • 2 0
 Not unless it's overfilled. Hydraulic fluid (and pretty much anything else) expands as it heats up, the system is designed to take up extra fluid and it should have used up some of the "slack" in the system to backfill as your pistons move in with pad wear.

But as always, if it feels sketchy, it's probably sketchy. Don't force the piston back in if it's not going with normal effort.
  • 1 0
 Yeah I tend to overfill my formula rx brakes because I have small hands and it's the only way to get the lever close enough to the handlebar and a firm bite point before they touch the grips.
  • 2 1
 Question: Every time my dad and I do this, the new brake pads always rub severely against the rotor, making it barely spin. We've tried the "holding the brake lever and loosening/tighening the actual brake" but it does very little. The only resort is to just ride it until the brake pads somehow loosen up or something.

Any suggestions? Big Grin
  • 3 0
 Try gently pushing the pistons back and then repeat what you said you already do
  • 1 1
 This probably means there is air in your system.. When you try to push the pistons in it instead compresses the air, which just expands back out. What brakes do you have?
  • 6 1
 bbtt04, that isn't necessarily the first assumption I would go with, but all the same it is possible.
kdstones: If you imagine the brake caliper, it has pistons behind the pads. and as the pads wear down, the pistons have to move farther and farther for the pads to actually contact the rotor. In reality, as the pads wear down, the pistons move out and eventually dont retract all the way, as the system is designed to push fluid, the vacuum as a result of releasing the lever is rarely enough to suck the pistons back in all the way. This works though because the resivoir at the lever has fluid to add to the system to make up for the extra space behind the currently extended pistons. When the pads are replaced, you now have extra pad material in the caliper, as well as the space taken up by the extended pistons meaning there will be very little clearance for the rotor and furthermore it will rub! When replacing pads you always want to gently push the pistons back into the caliper with a plastic tire lever (never reef on them with something metal cause you can crack the piston Razz ). If all goes well, the fluid that was originally in the resivoir should return to its place and the pads should have a little more room to sit without touching the rotor.
If the brakes were bled between the last pad replacement and now, chances are there is too much fluid in the system, and it might have to be burped/bled anyways Razz
  • 7 26
flag deepcovedave (Nov 17, 2014 at 18:55) (Below Threshold)
 Get your daddy's best credit cards - ram the cheap ones (American Express, Mastercard) in between the pads. Then insert your daddy's gold card (probably a Visa) in between the cheaper cards. You might need to insert his platinum card as well. Keep em in for a couple of minutes.

Pull them out and adjust the calliper. If that did not work, take your daddy's cc down to the LBS and buy a new bike.
  • 7 0
 @WhatsEnduro @Xyphota Actually I have done that many times, but to no avail. Actually a while ago, I was bleeding my brakes at home, and I couldn't even fit the plastic stopper in between the pistons even after pushing them out as hard as I could without damaging them... I had to shave down the plastic to finally fit it in there just to finish the bleed. So clearly it's must a piston issue, so is it possible that they are stuck/lodged out somehow?

@deepcovedave that sounds interesting, but if I were to do that, I would use my own credit card because I actually work hard at my own job thank you very much.
  • 2 0
 Assuming you are using the right bleed block that came with the brakes, than it is quite evident as you said that one of the pistons is probably seized. In a situation like this, you should try to verify that both the pistons are actually moving.
If you lightly squeeze the brake, they should both move (it is very common for one to move more than the other), If one is not moving at all, try to hold back the moving one with a tire lever and squeeze the lever so that all of the fluid is moving the stuck piston. All you are trying to do is see if it moves.
If it does not, dont be afraid to push really hard on it with a plastic tire lever. Unless it is an XTR/saint caliper with a ceramic piston, I promise you are not going to hurt the piston.
To answer your question, it is very possible for a piston to be sticky, even possibly a little crooked. If this is the case, pay close attention as to which part of the piston you are pushing on, try different parts, so that it will straighten itself out if it is crooked.

The end goal here is to push the piston all the way back into its bore. It should be absolutely flush with the rest of the caliper, regardless of brake.
  • 2 0
 It may be that there is too much fluid on the system, and you need to bleed a few drops so the pistons can recede. This will happen if the system was bled without the block or with a block that has been "shaved" this will allow too much fluid inside and a new set of pads will be pressed against the rotor until they loose some material.
  • 1 0
 Ok awesome, thanks for the help guys! I'll keep this all in mind the next time I run into trouble! Big Grin
  • 4 1
 i dont need to take my wheel off just a simple securing pin and bolt and there out
  • 2 1
 Yeah, what's with removing the wheel? Is there a reason for that with top loaded pads ?
  • 1 1
 Pads are expensive and can get thrashed/contaminated easily so for somebody new to bikes i would guess its probably best to take the wheel off. Also with new pads they usually need some adjusting so its best to take the wheel off anyway.
  • 12 1
 how are you going to push the pistons back in to place if you don't remove the wheel?
  • 1 0
 Yeah, you've either got to remove the wheel, or the caliper. One is much quicker than the other ;-)
  • 1 0
 It's probably a lot easier to check pad wear too.
  • 1 0
 You'll have trouble pushing the pistons back in with the wheel in place. And if you dont push them back in you wont be resetting them for the new (thicker) pad and they will likely rub. So pop that wheel out, and push on those pistons so you have nice working new pads the way they are meant to be.
  • 1 0
 Oh. So pushing the pistons back in is why. Makes sense. I've got a lot of random tools in my shop. One of those is just a 6 inch long thin piece of steel that I use to push the pistons back without wheel removal. After the old pads are out, the thin bar of steel fits between the rotor and piston. Both thumbs press against the caliper body while finger pull on the steel bar. Takes like 10 seconds. Probably easier for most people to just remove the wheel though.
  • 1 0
 you can just use a 9mm wrench, or even a tire lever to push the pistons back. Just some kind of leverage is needed.
  • 2 1
 If i need to change pads i don't remove the wheel as it takes around 15 mins to do so and 15 to put on again. I just remove the caliper as this takes seconds
  • 22 0
 30 minutes to remove and reinstall a wheel......?
  • 2 0
 yeah it has weird adjustable dropouts
  • 2 0
 What bike are these dropouts on? The only wheel I have ever had take literally 15 minutes to remove was a customer with a european cruiser, in which the fender, rack, chain protector, drum brake, and the bell crank were all attached to the axle of the rear wheel.
  • 1 1
 Duncon Cock. it has this little wheel on it that you need to turn on both sides to slide the wheel out
  • 1 0
 My road bike from the late 60's is kinda a pain with angled drop outs that slide in... I guess this was before they cared about the relation between the cassette and derailleur pulleys (think b-tension). But even that's not terrible with 2 adjustables.
  • 5 2
 He lost me when he waited to perform this on the trail...
  • 2 0
 yeah theres this idea called checking your pads before you ride. So your mechanic friends dont have to watch you do a 2.5 minute hack job on the side of the trail.
  • 1 0
 Ah, c'mon, Lets be real .. who checks their pads before every ride.. the first I know is actually when my lever is starting to pull in close to the grips and then I wait a little longer until I can hear metal on metal LOL. Actually the idea behind this series is a mix of easy tech how-to's and trailside repairs.. you know how to get out of trouble for free stuff... and we just thought it looked a lot nicer to film it out in the wilds instead of yet another boring in-the-workshop how to. After all you cant beat a little bush in the shot can you.
  • 1 0
 I ride fast and big! So yes I check my entire bike before riding. Those who do not are the ones ruining other's rides...
  • 1 1
 Follow all these steps and you will be a happy camper. Hell you will be a happy rider as well. Push in the pistons with the old pads in. Shift to lil cog. Sage advise to make the job go smooth.
  • 2 0
 Don't worry about breaking them in properly either, that's for losers...just change them and go rip!
  • 1 0
 If you struggle to work out how to change brake pads then I hope you have read the manual of 'How to ride a bike without stabilisers' very carefully.
  • 1 0
 Damn did someone do that episode already? It was next on my list. Ha ha. Actually they are intended to encourage middling riders who are a bit scared of tackling the tech side, to actually start taking notice of their bikes, how they feel and how to fix them if they are out on the trail. And I know there are a lot of average (and experienced) riders who dont (yet) do any of their own mechanics for confidence reasons. Hence the encouraging tone of my videos. You gotta start somewhere.
  • 3 0
 Sorted!
  • 2 1
 And off he rides with no mention of being careful for the first few stops until the new pads are burnt in a little?
  • 1 0
 You are dead right. Do a bit of braking to bed them in before hitting a descent straight and scorching them... so yes, there is actually so much more we can put in these little videos, but doing so would make them become the Ultimate Bible of Knowledge, and be so long and over-explained that the audience would switch off. I'm told by my Epictv powers that be that potential viewers actually look at the length of a video to decide if they're going to bother watching it. So instead I keep them short, sweet and to the point. Like my love life.
  • 1 0
 Agreed on the length of the videos, I am guilty of doing the same thing myself.
  • 2 0
 if you have less than 1.5 mm your gonna have a bad time
  • 1 0
 Or a lively one.
  • 1 0
 Cheers lads!
  • 1 4
 Yes, because all brake brands are the same.
  • 1 0
 The general theory is the same.. Any pro mechanic will tell you each brake has its own tweaks to do it right (and more importantly know when bleeds are needed!)

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