Brake rebuild: Photo how-to guide: YZ400F

[motorbyclist]

Feel free to make any corrections or ask any questions

Right, so here's my how-to on replacing all the seals in a floating caliper hydraulic brake setup, but is basically the same process across the entire hydraulic caliper type range.

I'm not a brake expert, and this was my first time, but it's not difficult and I'm not entirely stupid either so hopefully by making all the mistakes I can prevent others from doing the same. Think of this as a handy reference

I did this without disconnecting the lines as I'm a lazy bugger and there's no real cause to. If you DO separate the lines the copper washers at the joints are actually gaskets and should be replaced. If you seem to have a pressure leak somewhere these may be the cause - Ive seen spurts of fluid come out before but it might not be so obvious.

For the record, brake fluid DOES strip paint, and can do so very quickly in some cases. As with most things it's not good for skin either but after spending a day in contact with the stuff I'm still ok.... I meant to wear latex gloves to see if they survived but never got round to it.
Look at the pictures in part six (a few posts down the page) for a very handy tip when it comes to safely pouring brake fluid.

Always use the specified grade of brake fluid from a fresh (unopened) container - Brake fluid is hydrophillic; it loves moisture and will draw it in from the air around it.
If the new fluid is a different colour to the old stuff this helps you see when you've bled all the fluid through

Also, while my yamaha manual gave full instructions on how to do this, I ignored them and read afterwards - there was more about safety warnings and 'replace with new' than actual instructions...

Foreword: Brake Bleeding, because your brakes are spongy or soft and/or the fluid is old
Brakes can become spongy or soft over time for any number of reasons, including air bubbles and old fluid. Old fluid can be particularly dangerous as water may does get in over time and if it boils from the heat of braking your brakes will lock solid.
So if you are simply bleeding your brakes, without any seal work or replacing the pads, you need should not even remove the calipers - just fit a clear tube to the nipple and route it to a receptacle then use the 'as per the manual' method: open nipple - pull lever - close nipple - release lever - repeat - don't forget to keep topping up the reservoir!

The clear tube lets you see the bubbles coming out and keeps things clean. Afterwards give the area a thorough clean with soapy water to stop the paint peeling off. The nipple is operated like a tap, a quarter turn anticlockwise is enough to open it, and just nip it tight to close. When you're done tighten it properly but don't go overboard.
Brakes will always be slightly soft when using standard brake lines as they will expand/stretch under pressure, and more so as the lines age. Stainless steel braided lines or even just a harder rubber line will improve the 'feel' of your brakes dramatically.
If you do elect to remove the calipers first, ensure that the pistons can not accidentally push out or you will have a bit of work ahead of you

Part One: The Problem - Brakes Lose Pressure

So to begin, I did this for a number of reasons, and on two of the same bike.
My bike, which I did first, had nothing 'wrong' with it but a squishy feel due to not being bled or having fluid replaced for years - a job which should be done annually - but now being eleven years old I decided I should do it while parts were still around, and seeing as I had to do my brother's bike anyway this way we could compare between working brakes and buggered brakes if anything got difficult.
My brother's bike had a problem whereby the system would loose pressure while sitting and while in use. He had bled the system several times to no avail and then his fork seals went and dumped fork oil all over his brakes anyway. I'm told oil is not good to brake seals, just as brake fluid is Not Good to everything else.

[motorbyclist]

Part Two: Get all the bits together

You will need:
Allen keys
Screwdriver
Ring Spanners
Circlip Pliers

Soapy water
Clean containers
Toothbrush - mum wont mind

Brake fluid - Fresh and of the right sort, DOT4 in my case

Seals - one oil/pressure seal and one dust seal per piston
Master cylinder kit - or just seals, but I was forced to buy the whole kit as one

Parts diagram/Manual - this helps in correctly disassembling things that may otherwise seem stuck, and helps when reassembling things. It also gives the proper name for parts so people know what you're talking about.

Patience - I hate bleeding, both brakes and fingers, especially when at the same time, but it pays to do it right the first time.



You may want:
PVC tube - to fit over bleed nipples, this makes bleeding easier and tidier
Big ol' Syringe - as above, but try not to get brake fluid on the livestock and vice versa
Anti-seize - this makes the next time you change your pads so much easier
Impact Driver - cause the last guy didn't use anti-seize
Scribe - or any other 'pointy stabby scratchy' thing
Clean containers
A clamp or vice to hold things - obedient children will suffice

[motorbyclist]

Part Three: Pull the bugger off and clean it up

Well as you can see I believe in maintaining a protective layer of dirt on my bike, but even road bikes will have a lot of baked on brake dust on their calipers.


What can often happen is when we replace brake pads, we just push the pistons back in without cleaning them first: this basically forces crap past the seals and into the caliper itself, ruining the seals and the pistons in the process! You may also note I need new pads.

So before we do anything, we are going to remove the pads. Being the Pro that I am, I seem to have landed my caliper on a rock and dented it so that there is material blocking the cover grub screw over the pad pin. Fixed with a file to remove some material and careful application of an impact driver.

Remember to take note of which side of which disc each pad comes from, as it's grooves will match it's disc face.

Now we clean the pistons - commandeer Mum's toothbrush and get at it with some soapy water. It will help to remove everything you can which will come off with a bit of wiggling. Also give the master cylinder and reservoir a good clean - in my case they are the one unit but most road bikes over 250cc will have a separate reservoir (and probably not need much cleaning).



Now remove the lid from our reservoir and push the now clean pistons in just enough so we can clean the rest of the caliper - this will cause the reservoir to overflow so be ready. I do it this way as I like to keep water from entering anywhere I want brake fluid, and the pistons are very effective at doing just that. Don't worry about the seals we're replacing them anyway, but if we aren't you shouldn't push these in as far as I have - in fact if you go all the way the pistons may not be able to come out again as no fluid will get behind them.



Now clean!

[motorbyclist]

Part Four: The Piston Seals

Now, once everything is clean and reasonably dry, we can pop out the pistons. The manual tells me to use compressed air and "proceed with caution" followed by over a page of warnings. I will not, as I have a perfectly good pump secured in my vice, and no air compressor to speak of anyway. MY method of removal is to pump the brake lever until both the pistons can be removed by hand. If we just do the one piston it has to be replaced before we can do the next so this is ultimately your choice but do try to put the pistons back in where they came from. Once the pistons are out far enough they should come free with a bit of a wiggle and tug**. "Far enough" will be around where the pistons would meet the opposing side of the caliper and fluid leaks out from around them.

**My brother had significantly more difficulty due to the damaged seals jamming things up.

On these calipers the pistons are made of a crumbly ceramic that does NOT like pliers, as the previous mechanic has obviously found out. I imagine this ceramic is used as it will not expand with heat and is very hard so should not wear too much and cannot be easily scratched. Evidently they HAVE worn, as a result of never being cleaned since I got the bike and me just pushing them back in, but I can't possibly afford to even look up a price. Meanwhile, my road bike has metal pistons that still do NOT like pliers on their mating surface for obvious reasons, but are going to be much easier and cheaper to repair/replace.


Here we can see all the crap that has collected in the bottom of my brake system that will not be readily bled out - one of the sources of this crap is just forcing the pistons back without cleaning. You might also see that my dust seals are a bit raggedy.


To remove the old seals, I just stab them with a scribe and pull them out - they're buggered anyway - but you can use your fingernail.

Now there's a lot of crud in there behind the seals, so get another toothbrush and some brake fluid and clean the thing out. Some would suggest I do something about the wear in there, but again I'm on a budget and the piston is clearly buggered anyway so it's not going to get much worse - the manual instructs me to replace the entire assembly. I know this isn't perfect but it will have to do.


Now just pop those seals back in and you're away. Fill with fluid, open the bleed nipple, and gently push the pistons back into the holes they came from.


Done.

[motorbyclist]

Part Five: The Master Cylinder Job

This is surprisingly easy - the most difficult part is removing the bloody lever! Yes those are two locking nuts and not a solid piece, the manual tells us.

So just pull the rubber boot out with pliers or stab it with your scribe - there is nothing holding it but a tight fit - and get in there with circlip pliers to remove the circlip.

Now do NOT triumphantly hold the part up in the air, or the circlip pliers will spontaneously explode and you will spend the next 30 minutes looking for the small spring responsible.

After I did mine and watching my brother do his, I then spotted you can do it all without removing the lever anyway!

Now, I used my pliers to gently hook behind the socket there and pull it out - again there is nothing holding it but the seals pressing against the cylinder. My brother found his one pushed in too far to reach behind and would not return, so I pushed it right the way in and released, and the spring behind pushed it right the way out.


Compare the old kit with the new kit, and the manual, and put the seals on where they belong. In my brother's case it would appear the 'master cylinder cup (primary)' seal had a nick out of it, which meant whenever he applied the brakes the fluid just went around the seal rather than going down the brake line. Problem Found.


We can install the new master cylinder kit by just pushing it back in. Then just put pushrod/lever back in and push slightly to get the circlip in place.
Now my kit came with a small vial of oil. I assume this was to keep the seals? Either way I put this in before pushing the boot back in assuming it's a safe oil to keep the secondary cup seal from the elements.

Done.



You may note on my brake lever I use a wire to ensure I do not lose the small circlip holding it, as the clip is worryingly easy to remove. Curiously, the circlip really does nothing to hold the lever in place nor does it hold the pin in place.....

[motorbyclist]

Part Six: Bleeding the brakes, clean, and put her back together!

Right, now we bleed the brakes. I like to use a large syringe to both suck bubbles out of the bottom and push them out of the top, but there is nothing wrong with the good old fashioned, 'as per the manual', "open nipple - pull lever - close nipple - release lever - repeat" method even if it is a bit tedious.


Once this is done to our satisfaction, we can now clean everything with soapy water and put it back on.

Now is a good chance to get a rag and some brake-cleen and clean up that disc.

If you have any anti-seize I suggest you use it on the pad pin and caliper mounting bolts to save any future grief.





Easy!

[motorbyclist]

Part Seven: Afterword

Most important to any repair is that you test that you have in fact fixed the problem - go ride! (carefully)



I welcome any and all corrections.

All useful photos can be found in my album here



Now obviously brakes are important, and advice given over the internet is worth as much as the paper it is printed on, so I accept no responsibility for any damages etc resulting from this thread. If you are unsure of any of the steps and how they relate to your particular brakes, do ask for help from knowledgeable forum members or your local qualified mechanic.

[motorbyclist]

Done!

Time for a ride I think

[mdbobbo]

great piece motorByclist,
A good informative overvew of brake overhaul just what I needed, doing our own repairs is so much easier with a read though, it's been twenty years and then it was on a car not a bike, I especially like the syringe to suck the air out of the bottom, makes life a lot easier and quicker, especaillly as I've emptied all the old fluid out already. nice work thanks.

[The Pastor]

done!

Time for a ride i think

when i remove the pistons, what i do is keep the brake fluid system intact, but removing the cailipers and pads so its sorta just hanging there, then i use the brake lever to pump out the pistons, a bit messy but its easy as

[bekker]

Great write up man.

I've done a far bit of this recently but you always learn something new, like the syringe to suck the air out. But by far my favourite bit and something that will help me greatly in future are the holes in the top of the fluid bottle! I can't believe I've struggled for years with those bloody seals! Genius! Thanks for the post.

Cheers

[motorbyclist]

cheers guys! It's always good to hear that these threads do get read

RM, could you be a bit more descriptive?

by far my favourite bit and something that will help me greatly in future are the holes in the top of the fluid bottle!

Haha yeah I picked that one up from my highschool part time job signwriting - we would stab holes in the tins of paint so we could pour/mix without all the mess and just tape up the holes when done

(and knocking over the tin wasn't an instant disaster)

[motorbyclist]

No my skin didn't peel off or turn to cancer after all that brake fluid, but since posting this thread I've worked a bit with a qualified mechanic who reckons gloves really are worth it in the long term; especially if you're in frequent contact with these chemicals. Go whichever way you want but that stuff does strip paint.

ALSO:

My RVF400 has brakes that develop a dead zone. This is because the seals are old and are sticking to the pistons without sliding, so when a pull the lever, the rubber stretches to push the pads but on release it retracts. Until I fix this, what I can do is pull/pump on the lever with both hands, as much as i dare, for a minute or so - this forces the pistons to slide somewhat and take up the dead space.

[The Pastor]

to pop the pistons out i just unblot the calipers take the pads out then pump the brakes to push out the pistons

[CookMySock]

A great read, and some useful tips for oldies and newbies alike. Nice work!

Observations ;

I have never replaced copper washers, and I have never had one leak.

Modern paint doesn't mind brake fluid, but to be safe flush spills with water - do not rub with a cloth.

Pop caliper pistons out as RM suggests - remove caliper and pads, pump lever. If you use compressed air you must damp the calipers with a thick cloth.. much safer using the lever.

I wouldn't put water near any part of the process for any reason, unless you are going to bake everything dry afterwards.

Unless the seals are completely stuffed, they can often be returned to service to get you out of a bind. But seals cost almost nothing - replace them all.

Reassemble all suspect areas with coppercoat antiseize or similar, particularly under rubber boots where they will corrode heavily and lock up.


Steve