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Disc brake newbie advice

tc1992tc1992 Posts: 62
edited August 2017 in Workshop
I have a bike with disc brakes (Tektro Mira) for the first time. The front brake has needs the brake pulling in almost all the way before it starts gripping, so i think it is time far a replacement . . i think that must be the reason.

With caliper brakes it is easy to see how worn they are, but with disc brakes, is the only way to see how worn they are to take them out?

Another thing is i have been using my hex-key on the little silver disc thing (on the right) to move the pads in as instructed over time as they have worn down. I watched a video on youtube and it was saying that you should do this on both sides, but i do not see any way to make adjustments from the left. Am i missing something, should i definitely be able to make this adjustment from the left side as well?

looking at the videos on youtube, i know i have to push the where the pads are attached back into their sockets with the end of a screwdriver before putting the new pads in. Do i need to do anything with the silver adjustment disc eg turn it with my hex-key so that it is fully "out" again?

Finally does anyone know what sort of pads do i need as replacement, i emailed Tektro just now. There are a few different shapes available, i think it is the rectangular ones i need to go for, something like this . .

http://www.ebay.co.uk/itm/Shimano-Disc- ... SwX61ZDGuC

thanks for any help

Posts

  • Man Of LardMan Of Lard Posts: 903
    Some mechanical discs only move on one side. Otherwise adjustment has to be made through the spokes.

    Take your current pass out, photograph them, measure them and you should be able to work out which of the 837 designs of pads they are (somewhere like EBC brakes have a gallery of them to compare against)

    Upon replacing pads, yes you have to wind the wear adjustment screw(s) back out again.
  • dj58dj58 Posts: 2,193
    I've no experience of mechanical disc brakes, however if these are the model brakes you have?
    https://www.tektro.com/products.php?p=28 also shows type of pads.
    The specs. says they are single sided hub (side A), pad adjustment using 5mm allen wrench, and use the cable barrel aduster to adjust pad clearance on side B. See section 3 Removing the pads of the Installation instructions pdf document.
    https://www.tektro.com/upload/Product/F ... 9uWPB9.PDF
  • tc1992tc1992 Posts: 62
    thanks Man Of Lard and DJ . . so it looks like i need the E10.11 going off the website. yes that is my model . . that's useful info about the barrel adjuster, which i have used, adjusting the left side pad, it makes sense.
  • k-dogk-dog Posts: 1,652
    And you don't have to push anything in when you change the pads - that's to reset the pistons on hydraulics. Cable discs you just wind out the adjuster (which as you correctly say is to adjust for the pad wearing down - so when you put in new pads you'll have to wind it out again).
    I'm left handed, if that matters.
  • fenixfenix Posts: 5,437
    Rim brakes seem so much easier to fathom...
  • tc1992tc1992 Posts: 62
    k-dog . . .ok, got it. the videos i watched did not mention any difference between hydraulic and cable. I honestly thought they were all hydraulic (though i had no idea where the oil was stored on mine). I take it it's only the hydraulic that are "self adjusting".

    fenix - yes really seems that way
  • awaveyawavey Posts: 2,368
    Fenix wrote:
    Rim brakes seem so much easier to fathom...

    agreed, contemplating a disc brake pad change myself as turning the adjustment barrel is no longer provide much stopping power down descents, mine are at least double sided adjustment, but I learnt that about 5months after Id been merrily just adjusting the one side :roll:

    and its a nightmare, once you work out what type of pad shape youve got, then youve got to work out whether you want sintered or organic pads !? or if EBC which colour :? then hope the shop has them in stock, and someones done a nice youtube video to show you how to do it because they dont come with instructions, I know mine have a cotter pin too which is bound to either get dropped never to be found again, or be so fiddly to be impossible to refit.

    a rim brake block change seems effortlessly simple in comparison.even when cycle republic sold me blocks that werent like for like replacements on my boardman, it was still dead simple to correct the setup to get them to work, if I get the wrong types of pad I think Im stuffed
  • tc1992tc1992 Posts: 62
    awavey, my advice to you is go to your brakes manafacturee's website. FInd out which pad model is associated with your brake, and put that as a search into ebay, and i am pretty sure something will come up. Email any sellers before buying to check compatibility
  • pilot_petepilot_pete Posts: 2,120
    Awavey

    Anything you have not taken the time to understand appears complicated if you compare it to something you are familiar with. Disc brakes, be they hydraulic or cable or not very complicated once you understand the basics.

    Cable discs use a cable to operate either one, or both pistons to clamp the rotor. If only one moves the other needs to be set using the adjuster to be by close to, but not touching the disc whilst the brake is 'off'. When you operate the brake the single moving piston moves towards the rotor and bends the rotor slightly as the force applied pushes it up against the static pad.

    With dual operating Pistons they need to be set with the rotor between them and the force is applied equally to both when the brake is operated and the disc is sandwiched between them.

    If your lever pulls all the way to the bars and you don't get sufficient stopping force it could be a few things causing this;

    1. Over time the cable can stretch slightly. You may well be pulling up the slack as you operate the brake before the pads come into contact with the rotor. You can take this slack up by releasing the cable clamp bolt on the operating lever arm at the caliper, pull through the slack and if necessary hold the lever arm in position just before the pads contact the rotor. Reclamp the cable and use the barrel adjuster to fine tune the gap between pad(s) and rotor. If you set the barrel adjuster with some adjustment both in and out before clamping the cable this allows for fine adjustment either way.

    2. Pads worn excessively. The pads may have worn down excessively with not enough material remaining to offer braking force to the rotor when applied. These are usually very simple to change once you have identified and purchased the correct or compatible new pads. With the wheel removed some require a threaded pin to be removed which holds the pads in the caliper. Others don't, you simply squeeze them together and pull them out of the slot where the rotor sits. Most have a bit of sprung metal which holds the pads away from the disc rotor when the brakes are off. Replacement is usually just the opposite of removal.

    3. Pads not adjusted for wear. This has been alluded to before and is the adjustment of either one or both pads to allow for the material wearing away and thus the gap opening up between pad and rotor which leads to excessive play at the lever and a longer pull before pad contact.

    4. Check the calipers are correctly aligned; the two mounting bolts allow for a little adjustment to ensure the caliper is set in the correct position; the rotor should run directly through the middle of the slot in the caliper with the same gap either side and square to the rotor.

    5. Sticky lever or cable which is rarer but can lead to less than optimal braking performance. Clean or change as required.

    So that's cable operated discs and each element can be related to a caliper brake on exactly the same way - pads are equivalent to blocks, which are held away from the rim a set distance to allow them not to foul but close enough to allow the cable to pull them in far enough against the spring to clamp the rim. The Spring returns them to this position after each operation and the cable barrel adjuster will need periodic adjustment to allow for brake block wear. The brake must be set in the correct position using the bolt(s) before the cable is clamped to ensure both blocks contact the rim at the same time. The blocks must be set using their respective mounting nut to ensure they contact the rim in the correct orientation with perhaps a little toe in. See, just as complicated (or not) as a disc brake.

    Now hydraulic discs....they really are pretty simple...!

    PP
  • +1 to Pilot Pete. They're pretty straightforward once you do a bit of tinkering; I've had Tektro Lyras and Avid BB7s and set up is usually simply as described (although getting the pads in with the retainer spring in the BB7s can be a bit of a challenge). My only issue stems from a bent frame thanks to a crash, which means there's always a little bit of rotor rub (but that's just a bit of resistance training, right?). I've also found finding the right pad not too much of a bother once you find a part number - although lots of places also have a list of what is compatible with what e.g the drop down menu here.

    My history with rim brakes, however, is full of squeaks, squeals, brown trouser moments and much swearing. I don't recall ever being satisfied with rim brakes - although I fully accept plenty of people are, it's just I never got on with them.

    My advice would be get the bike up on a stand, shine a light on the calipers and pull the cables, twiddle the knobs until you know what everything does and how it moves. Then take the wheel off, change the pads, reset the calipers as described above and put it all back together. If you properly mess it up, there's always the LBS...
  • tc1992tc1992 Posts: 62
    good posts, i did not know that the rotor was slightly bent onto the pad, thought it was just gripped.

    can someone tell me specifically about this . . is the barrel adjuster really a last resort thing that i should be using? I'm pretty sure that i have single operator (as opposed to dual operator) set up. I have the adjuster (little silver disc with adjusted by hex key), through the spokes on the right, and also the barrel adjuster. Looking at them it certainly looks like only one side moves when i apply the break. So i have been using the adjuster on the right quite easily as they have worn down. But my question is should i also use the barrel adjuster as well as the, as the brakes wear down, or, as i said, is the barrel adjuster a last resort thing (ie only use the main adjuster on the right till they are really down to the end of their days) ?

    The other thing is with rim brakes you can easily see how worn they are, is the only way to see how worn a disc pad is, is to take it out and look at it?
  • awaveyawavey Posts: 2,368
    happy to hold my hand up and admit it wasnt anywhere near as nightmarish as I thought, it just looks more complicated than it is, following PistolPetes advice (top advice), I picked some pads that I thought should fit online, found some instructions to follow, and yeah its embarrassingly simple and I was so close to just paying and letting the LBS sort it out , but I just removed the cotter pin, removed the retaining bolt and the pads easily pulled out, then fitting the new ones was just do the steps in reverse, whilst remembering to back the piston adjustment back off as the new ones wont fit otherwise, quickest bike job I think Ive ever completed.

    old pads measured <1mm on one side (literally only just thicker than the spring prongs), ~1mm on the other, which highlights I suspect my uneven adjustment for 5months, but I suspect the pads were only just in contact with the disc, hence some braking but not feeling there was enough bite.

    Id admit Im rubbish at fettling rim brakes, its just Ive borrowed rim brake bikes where the brake bite feel was spot on for me, so I know its possible to get it right, Ive just never had that feel on a disc brake...yet :)
  • dj58dj58 Posts: 2,193
    awavey wrote:
    happy to hold my hand up and admit it wasnt anywhere near as nightmarish as I thought, it just looks more complicated than it is, following PistolPetes advice (top advice), I picked some pads that I thought should fit online, found some instructions to follow, and yeah its embarrassingly simple and I was so close to just paying and letting the LBS sort it out , but I just removed the cotter pin, removed the retaining bolt and the pads easily pulled out, then fitting the new ones was just do the steps in reverse, whilst remembering to back the piston adjustment back off as the new ones wont fit otherwise, quickest bike job I think Ive ever completed.

    Meanwhile Pete's had a change of occupation from pilot to gun slinger :shock:
  • pilot_petepilot_pete Posts: 2,120
    DJ58 wrote:
    awavey wrote:
    happy to hold my hand up and admit it wasnt anywhere near as nightmarish as I thought, it just looks more complicated than it is, following PistolPetes advice (top advice), I picked some pads that I thought should fit online, found some instructions to follow, and yeah its embarrassingly simple and I was so close to just paying and letting the LBS sort it out , but I just removed the cotter pin, removed the retaining bolt and the pads easily pulled out, then fitting the new ones was just do the steps in reverse, whilst remembering to back the piston adjustment back off as the new ones wont fit otherwise, quickest bike job I think Ive ever completed.

    Meanwhile Pete's had a change of occupation from pilot to gun slinger :shock:

    Yeah, so watch your step if you're going to Tenerife on Saturday with your wife and kids ok :evil: :lol:

    Glad to hear the pad change went well. Just remember to bed them in with a few hard brakes before tackling a steep hill!

    PP
  • pilot_petepilot_pete Posts: 2,120
    tc1992 wrote:
    good posts, i did not know that the rotor was slightly bent onto the pad, thought it was just gripped.

    can someone tell me specifically about this . . is the barrel adjuster really a last resort thing that i should be using? I'm pretty sure that i have single operator (as opposed to dual operator) set up. I have the adjuster (little silver disc with adjusted by hex key), through the spokes on the right, and also the barrel adjuster. Looking at them it certainly looks like only one side moves when i apply the break. So i have been using the adjuster on the right quite easily as they have worn down. But my question is should i also use the barrel adjuster as well as the, as the brakes wear down, or, as i said, is the barrel adjuster a last resort thing (ie only use the main adjuster on the right till they are really down to the end of their days) ?

    The other thing is with rim brakes you can easily see how worn they are, is the only way to see how worn a disc pad is, is to take it out and look at it?

    Hi TC

    As I alluded to in my previous post, with a single moving pad, the first step is to set the caliper orientation up correctly with the small amount of play allowed when you loosen the mounting bolts. Make sure the disc rotor sits in the middle of the slot with an even gap either side. Tighten the mounting bolts to the specified torque when you have the caliper in the correct position.

    Now adjust the static pad so it is nice and close to the rotor, but not touching. Some people recommend a thin business card be slipped in and used as a feeler gauge to set the gap. If you have them, you could of course use a feeler gauge! However, it is easy enough to do by eye. Once adjusted, spin the wheel and (possibly with a light source) make sure the rotor does not touch the pad as the wheel spins.

    Now adjust the barrel adjuster (or equivalent where the cable enters the caliper) most of the way in, but leave a little further adjustment just to allow for fine tuning.

    Loosen the cable clamp bolt and pull through the slack in the cable. What you may find is that the operating arm (where the cable is clamped) could spring back. If you operate the arm using your fingers you can get it to the position just before the pad touches the rotor. Hold it in that position as you pull up the slack in the cable and nip up the cable clamp bolt.

    Operate the lever gently to feel where the biting point is. Now pull the brake fully and see where the lever stops in relation to the bar. The biting point/ point at which you get full brake operation can be tweaked using the (barrel) adjuster to (in effect) either lengthen or shorten the outer cable. Screwing the adjuster in will in effect shorten the outer cable thus allowing a fraction more of the inner cable 'through', which moves the adjustable pad slightly away from the rotor, and turning the adjuster outover does the opposite; bringing the pad a little closer to the rotor.

    Assuming your rotor is not bent at all (and there is no play in your wheel bearings!), you should be able to get the static pad at a suitable distance from the rotor, and then the adjustable pad similarly to get a lever that does not touch the bar before full braking force is applied, a biting point which feels right for you and also a wheel that spins freely without either pad contacting the rotor and causing that annoying tinkering sound when the brake is off.

    Hope this helps.

    PP

    p.s. One thing to check on a used caliper is that the pads move freely in the caliper (in and out). I have had BB5 pads which have seized in the caliper due to build up of crud, road grime and worn off pad material. This just required stripping, cleaning and a fine rub with some wet and dry paper to clean up the inside surface and remove the slight corrosion that was present. This got the brake working like new again.
  • tc1992tc1992 Posts: 62
    Hi Pete

    thanks for the detailed post . . and i'm sure it will help, i'm going to have a go at this in a couple of hours and i will use your post as guidance. I guess it's one of those things that becomes easy with after a few goes
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