Bleeding front brakes question from a noob

Wow, thanks for all the replies and the long detailed ones, really appreciate it. Pretty much have my questions answered, and some great tips I will use! Thanks again guys!!!

[NTECUK]

I've got into the habit of get as much of the old fluid out of the Master.
Suck it through with the vac bleeder.
If it's not as good as it should be ( my old zx6 is bad for this) then back bleed it.
But there's More chances of fluid spill if you get carried away.

[Bibio]

Originally Posted by Blueperson

Once you've finished cable-tie the brake lever to the bars (ie. brake on full) and leave it overnight to remove any stray bubbles of air

this does nothing apart from turn the big bubbles into little bubbles. there is nowhere for the air bubbles to go as the system is in 'compression' e.g. closed. the only way to get rid of air in a braking system is to bleed it out.

there are other reasons why this works but it has nothing to do with getting rid of air bubbles.

[aesmith]

I don't see the point in reverse bleeding if you're changing the fluid rather than filling after it's been drained out. Just pump through the system normally, and take care topping up the reservoir as the fluid can trap bubbles if you pour it in too fast.

[SV650rules]

Highest part of master cylinder (which is highest part of system) is open to reservoir when piston is in its normal position (as soon as piston moves forward the equalisation port is closed off), that is to allow fluid in and air out. Decent hydraulic systems are designed to be self-bleeding.

[Blapper]

Originally Posted by SV650rules

This company sells a non-return valve, wonder what their returns policy has to say about non-return stuff LOL - Also I often wonder if you should ever buy a battery that is shipped free of charge.

http://www.ebay.co.uk/itm/New-Motorc...3D161657955017

https://www.youtube.com/watch?v=1iSN2vc5-b0


The problem I see with reverse bleeding, especially on ABS systems is that dirty fluid from slave cylinders and lines is being forced back into the system not sucked out, there should be filters in ABS system and these could get blocked by crud, which in any case may be pushed back into system once brakes are used again. The dirtiest most contaminated fluid is likely to be in lower parts of system.

IMHO maybe a combination is best, get clean fluid into system by sucking from the bleed nipples on calipers (or squeezing brake lever / undo nipple etc, or with non-return valve as in link above) and then use reverse bleeding as a more effective way of getting any remaining air bubbles out.

Getting air into an ABS system actuator is not normally good news as it can be devilish hard to get it out again.

Good point. My ol' curvy don't have that new-fangled ABS stuff...

Originally Posted by aesmith

I don't see the point in reverse bleeding if you're changing the fluid rather than filling after it's been drained out. Just pump through the system normally, and take care topping up the reservoir as the fluid can trap bubbles if you pour it in too fast.

It's all about preventing air getting past the thread of the bleed nipple.

Originally Posted by Bibio

this does nothing apart from turn the big bubbles into little bubbles. there is nowhere for the air bubbles to go as the system is in 'compression' e.g. closed. the only way to get rid of air in a braking system is to bleed it out.

there are other reasons why this works but it has nothing to do with getting rid of air bubbles.

Yeah, weirdest thing. You would think that the air bubbles would be better off rising naturally up through the tiny hole that allows fluid to make up for pad wear etc. (which can only happen when the lever is out) and I don't understand how loads of small bubbles gives a less spongy lever than one big one, but it does work. I was sure it was BS until I tried it!

[Bibio]

Originally Posted by Blapper

I don't understand how loads of small bubbles gives a less spongy lever than one big one,

simple. with a large bubble you have fluid either side of the bubble (large bubble makes up a chamber) and when you pull the brake lever the fluid above gets compressed then compresses the bubble which gives less compression of the fluid below. with lots of tiny bubbles you have fluid surrounding the bubbles (no chamber) so gives a direct path for the fluid to compress. the tiny bubbles still compress so gives less performance than no bubbles.

another thing (especially so with curvy rear brakes) is to crack the banjo bolt at the MC on the pull then close just like bleeding at a nipple. its know for air to get trapped at banjo bolt unions more so than in the lines.

best thing to do is let the braking system settle in then do a second bleed.

if you dont have a proper bleeding kit and just using a tube and jar you must make sure that the tube at the jar is submersed in fluid or you will draw air unless you do the 'pull,open,close' method on the lever/nipple.

always have a bucket of water and a wet rag handy when bleeding brakes, brake fluid is hygroscopic and water neutralises/dilutes it enough not to cause damage to paint if you have a spill.

[Bibio]

if your changing the pads on your bike then bets are that the callipers are needing serviced as well. no amount of new pads or fluid change will improve braking performance if you have sticking callipers.

[SV650rules]

You can use a mityvac to both suck or blow fluid, so can be used to reverse fill as well. I bought a mityvac for use on cars for one man bleeding - but to stop air being sucked past threads you have to either put teflon tape on threads of nipple or another way I found (on cars) is to take nipple out and put a couple of fat 'O' rings around the thread (they end up between caliper face and the slight shoulder on nipple where hex meets thread), when you unscrew the nipple these act as a seal to stop air getting into fluid you are sucking out, and also when nipple tightened down they seal off the thread area from water and other crud.

[Bibio]

been using PTFE tape on nipple threads since the 80's. you need to know which way to wind the tape on or it all just bunches up as you put the nipple back in. PTFE tape serves two purposes, one is to seal the threads to stop leaks and the other is to stop the threads from seizing.

never thought about using o'rings.