Brakes not working after changing pads

[Chrisjlm]

Hello,

I changed the pads on my Yamaha xt 125 today, I can’t afford to pay someone to do it properly so I had to do it myself. After putting it back together I applied the brakes several times to push out the brake pistons into the correct posistion. The rear one is working just very weak and not road worthy. The front is almost non existent.

I’m sure it’s done properly and everything is as it should be.
Also when doing the front it leaked a lot of brake fluid so I was thinking this could be a reason?
But again I’m new to bikes and can’t afford to get a professional at the moment.

Thanks in advance.
Chris

[MCN]

1) Leaked fluid from where?
If some bell-end has topped up the brake reservoir as the pads wore down then the extra fluid will be displaced and 'leak' out when the pads push the pistons back in.
Or was the leak from the caliper? If it's from the caliper then you have a different Problem Houston

2) Did you fit O.E.M. pads or the 'exact' equivalent after-market pads.

Some pads are harder and therefore do not 'bite' as much on the disc.

They need a lot of heat to allow them be efficient.

3) Did you abrade the discs to remove old pad material from the surface?
The pad material is smeared over the disc as it disintegrates during braking. (Energy Exchange/Conversion stuff). This can prevent new pads from 'bedding in'.
You can bed-in (or burn-in) new pads by loading the brakes. It needs to be done gradually to prevent sudden temperature changes harming the pads and cetera.
You can google that shit.

You may know Hee-Haw about bikes but at least you spelled 'Brakes' properly which, in my book, is a good fcuking place to begin.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Hong Kong Phooey]

If you lost fluid you probably gained air.
Have you tried bleeding the air out?

Did fluid contaminate the disks or face of the pads?

I think you need to get someone who knows what they're doing to hold your hand if this is your first time, I promise they'll be gentle.
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[Chrisjlm]

[kramdra]

[Riejufixing]

[Evil Hans]

[Teflon-Mike]

Most brake fails occus shortly after DIY maintenance... this is why.

Pads are pushed against disk by pistons, caliper pistons pushed by hydraulic fluid, hydraulic fluid pushed by master-cylinder pistons, master-cyl piston pished by brake lever.

Hydraulic discs brakes are notionally 'Self Adjusting'. As the pads wear thinnner, they need to be moved closer to the disc, that means that the piston that pushes them needs to be shoved further out of the caliper... if the caliper piston is to move further out the caliper, the 'space' made by it coming out has to be filled with extra brake fluid,,,, its the only thing around that can fill that space, hence you have a 'reservoir' of the stuff on the master cylinder on the handle-bars (or close to the master cylinder some-where, on a rear brake)

NOW.... as pads wear out.... the pad material turns to dust... nasty stuff; they have taken the asbestos which causes caner out of the things these days, but I'm not sure whats left is much better. When mixed with water, and UK roads tend to be wet a lot of the time, so the brake dust first tends to stick around, second get wet; the 'stuff' in the dust then turns the water acidic, and that rather helps the brake pistons rust rather faster than they would anyway.

THIS is good reason to very thou roughly clean the brakes regularly with warm soapy water... sod the shiny paintwork and crome... that aint going to get covered by especially rot-fast slime!

Howebler... you now have a load of rather nasty acidic slime gunking stuff up around the brake... that on its own wont help matters much, but it will help rot the caliper piston, which is especially unhelpful.... these tend to be mild steel coated in chrome; the piston doesn't rust like a nail, and turn red, it sort of 'pits' where a reaction finds a spot on the chrome it can work on; eventually the surface of the piston gets rather rough, and starts to act like sand-paper on the rubber seals of the caliper. The 'past' that helped pistons rust does like-wise, being a mix of road grit, rust and brake sludge, it acts a bit like the grinding past you use on valves and stuff, to wear thins away...

Eventually, the rust gets under the chrome, and teh chrome starts to flake, adding little knives to the grinding paste, as well as leaving the mild steel piston exposed to even more rust, and even rougher than before.

See comment about regular washing of the brakes.....

Oh kay... brake is self adjusting... so to all extents and purposes its out of sight and out of mind, and no one sees any point ion even touching it, let alone cleaning it, till it dont work.... and they hear the horrible noise of metal rubbing on metal when they apply brakes, cos there's no brake pad left....

SO... new brake pads are obviousely needed... Right-ho... simple job, no need to pay a mechanic, can DIY.... wheres the Haynes Manual... oh bugger that, not paying £15 for a book, and I know what needs doing anyway, its OBVIOUSE.... y-e-r-s.....

Clips are found, pad pins located, old pads dropped out..... New pads, gleefully pried from the pastic blister pack and compared to the old backing plates that have dropped out! "ooh, look at meat on them!" Right, lets wop-em-in.... and the first pad goes in a treat, and then... Eh! Bludy things too thick! Why wont it fit!

At this point the old pads are fished out the dust-bin, if they got that far, the new ones pulled back out to see if they are different thicknesses for either side or 'something', and mush head scratching ensues....

Eventually the light of realisation dawns, and 'Oh! Pistons need pushing back in!" There was a tool to do this in Halfoprds... £20 though, wasn't paying that.... where's the screw-driver....

I SHOULD mention at this point that a screwdriver is a precision decide for doing and undoing SCREWS!!!! It is NOT, repeat, NOT a general purpose pry-bar, lever and pointy thing!!!! Misusing tools does rather annoy me!!!! But still....

Using a more appropriate tool.... the caliper piston(s) can be pushed back in.... Hey! In go the brake pads.....

And within a week.... the brakes not working and probably pissing brake fluid....

IS THIS sort of where we came in?

Y-e-r-s.. remember that caliper cleaning? Didn't say it just for lols.

Rushing to get the job done, not bothering to buy or read the Haynes... these pistons get shoved back in the caliper with whatever brute-force-and-instruments-and-ignorance is needed.... BUT... along with the pistons goes so much of that horrible brake slime... remember, the stuff that works like a cross between rust-quick and grinding-paste....

There are normally two, if not three rubber seals around a brake piston. The outermost seal is a wiper; its job to keep the 'worst' grime off the piston and wipe it clean of fluid as it comes out. Next is the piston 'seal' itself, that is there to keep the fluid in the caliper; B-U-T, also has the job of 'twisting' a bit as the piston comes out, and then twisting back, when the pressure is taken off, to pull it back a bit.. not all the way, just enough to take it off the disc. This is the cleaver bit about the self adjusting.

HOWEVER... that crap that has been made by the brake dust and rain-water and road-grime... is now dragged in behind the primary wiper-seal as you brutally shove piston 'in' to make room for thicker new pad. You ALSO, shove the piston back inside the caliper, and the bit of metal that has, for however long been hanging outside the seals, getting dirty, getting pitted and corroding... has now been shoved back INSIDE the seals.....

If the seals WERE OK before... if the bit of piston running on them was not bad, or even brand new unblemished chrome that had lived all its life under protective coating of hydraulic fluid.... NOW you have pitted corroded piston inside the caliper, and the bit rubbing on the seals the horrible nasty bit that has been rusting and pitting and flaking outside for however long....

IF the caliper dont leak fluid straight away.... it wont be long before it does, as that sand-paper-rough old bit of poston starts working on the seals....

Meanwhile... them seals are the springs that pull the piston back off the disc... any 'gunk' gets in there during the shove'em-back-in-with-effin-screwdriver!!!! Sorry, I need a moment just thinking about it... where was I? Oh yeah... piston shoved back in brutally, with whatever gunk was hanging around it, that hunk now gets into the seal groves as they twist... and stop-em twisting... as well as gumming stuff up.

Worth noting that particularly on small bikes they use a form of caliper known as a 'Floating' caliper, it only has pistons that move in and out on one side, so they have to move twice as far, the caliper-body itself on pins that let it slide forwards and backwards, so as the pistons come out from the front and 'push' pad against disc, the caliper is shoved side-ways on teh float-pins, and 'pulls' the other pad against the disc from t'other side.

Yeah... them pins is mild steel, and that brake dust gathers on them too, water turns it to corrode-kwick slime... and the caliper first starts to get rather lazt and NOT float, pushing brake pads against disc from just the one side... look at your old brake pads is one still got some material left on it where other hasn't? Yup, that's a stickly caliper mount.... But, the float mounts usually have gromet seals on them, the dust gets in there, THESE all need taking off, taking apart stripping and cleaning properly from time to time, especially like when you change brake pads!!!!

SO..... back to you..... THAT is sort of how this kind of problem occurs, and more oft it's done by monkees who know no better, worse its going to be when any-one comes to try sort it.

Answer is.... take the caliper off... inspect everything, especially the state of the pistons. Sof the fluid, that is likely LONG due a change.....

Decide how much of a full and proper caliper overhaul you need or can get away with.

New seal kits are around "7 a piston, new pistons around £15, and you might be lucky and only have a single piston caliper that needs the one of each.

Some folk try and penny-pinch and re-use the old pistons...... SOME even the old piston seals!!!!!

A work of warning on that one; NEVER re-use brake seals!!!!

Brake fluid actually has an agent in it called a 'seal-sweller'; The rubber of the seal absorbs it, making the seal soft, but also 'grow' so its a bit tighter around whatever it was sealing.

Old used seals, because of the seal sweller are then almost impossible to re-fit.. they are too big and too soft.. And even if you DO manage to get them back in.... they wont swell no-more, so they wont 'seal'.. they is pennies in comparison to the parts for the rest of the job, let alone the time, which if it was paid for would be the most expensive bit, so juts DONT stint on them, and dont risk the boat for a hapeth of tar!

Pistons, similarly tend to be fairly 'cheap' in comparison to even the brake pads, let alone what a pro-mechanic would charge for the job, so even there, to my mind, in for a penny, in for a pound, DONT short change the job.... a-n-d stanless steel after-market pistons are often no more expensive than OEM mild and chrome, and less prone to rust... so for the small extra, worth the while still, to my mind.

More hapeth of tar! New float pins and caliper pin seals are usually pennies on the job, why not order them too, whilst getting the pistons and seals... A-N-D what the heck, may as well order a new bleed-nipple and nipple cap whilst you are at it.....

NIPPLES! Cause much consternation... especially when our Snowie with her 38DD's is bending over brakes.... sorry.. what was I saying?

Oh yes; BLEED nipples... probably siezed solid, these things also live under coating of that rust-kwik slime... and even more chance brakes have never been bled, let alone had fluid changed, to need them loostening... if they aren't already shered from someone having the idea to be a bit diligent... and giving up.... they probably will be by the time you get that far......

New nipple? Means you cab wack in an E-Z shear stuf extractor to get the nub out the hole, and have a new one to fill it after you have sworn at the crappy e-bay or motorfactors stud-extractors.... BUT... nice shiney nipple..... oh dear did I just type that... my mind seems to be wandering again.....

Back on track.... overhauled, with nice new seals, nice new float pins, lots of coppa-slip, and then bled through with nice new fluid....

BRAKES should be good as new, work wonderfully, and do so for an awful long time.....

As long as you remember to WASH the ruddy things from time to time, not leave it till you hear metal scraping on metal to do anything down there!!!

A-N-D... if you have followed advice.... when you need to adjust the headlamp for the MOT... your screwdriver will still be straight AND have a decent tip on it and NOIT be sop want to chew the screws and make even more work for you! You have been warned!

For what its worth, these days, I presume a full overhaul will be needed if the pads need changing.... on most stuff I touch I'm not wrong... on my own bikes, most of which I've had over a decade, I probably dont... but means bits I dont use are on the shelf for next time.... hen I probably DO!

And on a Learner-Legal? These things tend to be owned either by no-nuffin learnaers and miser miler commuters, they generally suffer the most from at best 'lazy' mechanics, ranging through no mechanics, to dire mechanics... its almost inevitable that if you need touch brakes on these things, tyhey will need the LOT, doing from the top, once and almost for all... and IF you can get away with anything along the way, call it a bonus; EVEN doing a full overhaul DIY with a little care and attension is a saving over paying some-one else to possible bodge it... so its all win....

And POVERTY is no excuse... if you cant afford new brake caliper-seals and pads and fluid, let alone a new hose, how the heck you gonna afford petrol?

Old adage, before you start, make sure you can stop! Its far more important, and far less painful!
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Pjay]

Good lord Tef, if time is money, that post would cost him more to read than a professional to fix his brakes.
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struan80 - I'll go first - satisfied tick 1

[Pete.]

[Ste]

[andyscooter]

[bikenut]

safety critical.....no manual and you now know of cmsnl for the exploded views which can only help....what year is your bike ??

2 caliper pistons, one either side of the disc ??

Caliper parts held together via bolts, so a seal is in the passage that connects the haudraulic units together.........

see cmsnl and learn.

contaminated pads are now scrap but in the real world some ( SOME BUT NOT LOTS ) of contamination can be cleaned with water and detergent, and even boiled, but get new pads and be sure.

You know how to bleed brakes ??

get a manual, there may be one on here.
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nuts about bikes

[Riejufixing]

Single-sided on these things. May need to hold the caliper above the master cylinder to ease bleeding.

[-]

[bacon]

Just start from the beginning. Watch YouTube videos and read some guides on how to bleed brakes.

It's rather simple once you understand what you have in front of you. If you have removed/loosened a bolt(s) that holds he two halves of a caliper together then you will have most likely allowed air to get into the system. Did you split the caliper? Or just loosen the bolts off?

If you just loosened them I would:

*Get a bottle of fresh brake fluid.
*Re-torque the caliper bolts back up to spec.
*Remove the pad pin/spring.
*Remove the pads.
*Unbolt the caliper from the fork leg.
*Clean the whole thing with soapy water like Tef suggested, I prefer to douse everything in brake cleaner personally. But use whatever you like. Ensure you clean around the pistons. Use a toothbrush.
*Apply a smear of red rubber grease over the exposed piston.
*Open your brake fluid reservoir, keep an eye on the level during the next step.
*Push the brake pistons back in until they are flush. Check the reservoir while doing this, if it gets close to overflowing, remove some fluid.
*Use some wire wool, or perhaps some scotchbrite and clean up the pad pin etc.
*Refit the caliper to the fork leg.
*Clean or replace the brake pads, I've never contaminated pads before so I'll let others chime in here.
*Fit the brake pads with copper grease on the back of them to prevent squeel.
*Apply some copper grease to the slide pin, fit the pin and pad spring to the caliper to hold the pads in place.

*Then bleed them properly, I would get a cheap bleed kit, it's simply a bit of tubing with a one way valve, costs about £10.

Put a ring spanner onto the bleed nipple, fit the tube with the one way valve in the correct direction.

Ensure the master cylinder always has fluid in it from this step on.

Open the bleed nipple, pump the lever, topping up fluid as you go.

When it seems full, close the bleed nipple, you now need to purge the air out of the line.

Pump the brake lever several times and then hold the lever down, crack the bleed nipple allowing air/fluid to pass through, shut the nipple and release the lever. Top up brake fluid.

Repeat until you no longer have any air bubbles coming from the bleed tube.

Last bit to bleed is your master cylinder, what I do is this:

Get a ring spanner to fit over the banjo bolt, get a rag and cover the banjo bolt and hold onto the spanner with one hand, it might help to get the bolt slightly loosened before you start this. But don't allow air in yet.

Pump the brake lever and hold it down as before, crack the banjo bolt and quickly close it again before the lever hits the bar. Repeat until you have just fluid coming out. Hard to tell. So just do it a couple of times. Don't spill any on your tank. Ensure the rag is soaking up the brake fluid as you do it.

Top up the brake reservoir and voila, you are done.

[bacon]

[Pete.]

[Nobby the Bastard]

[MCN]

[MCN]

[Pete.]

[MCN]

[Sister Sledge]

'A precise study could provide interesting results/findings.'

Interestingly, a bloke on Youtube managed to get platinum from road dirt. Nothing to do with brake fluid on pads but just thought I'd mention it!

https://www.youtube.com/watch?v=v5GPWJPLcHg

A local garage here burns spilt fluid off brake pads using oxy acetylene (gently)

[Riejufixing]