Brake bleeding for dummies (and me)

[mick_dundee]

Anyone care to slap up a post on the go to whoa, pitfalls etc of brake bleeding, my fronts are spongy as and time to lose the old shit fluid and replace with some decent stuff.

TIA

Mick, aka "The Dummy!"

[Slow and wobbly]

I'm home tomorrow Mick.

[MickLC]

Get the wobbly bugger to give you a run through in person seeing as he's offered and be really patient with the 9's brakes as they seem to take an age and some really good technique to get bled properly....but it's worth persisting

[Saki]

K well here is my version of it. There is a "by the book" way then there is my cut down lazy way but both sitll good. Tried, tested and still here so obviously works way, on all my bikes and all my cars!

1. Locate the master cylinder as the res that holds all the fluid will be there.
2. Locate Brake caliper and further on, locate bleed nipple.
3. Open preferably with a ring spanner, the bleed nipple, with the lid off the fluid res.
4. Once bleed nipple on brake caliper is open, continue to pump the front brake lever as if you where apply the brakes. When doing this on each "pump" fluid will stream out of the bleed nipple.
5. Keep pumping until there is nothing left coming out so the res is empty and the lines are empty.
6. Fill the res with a small amount of fluid and again continue to pump, this will help drain any old fluid out, continue this step until all old/dirty fluid is out.
7. Fill the res now with enough fluid now to get the continuous stream of clean fluid flowing, you DO NOT want any air bubbles or pops, just a nice even flow.
8. Once the clean fluid is flowing nicely (i stress this point as its most important), have your spanner ready to tighten the nipple.
8a. REMEMBER TO KEEP TOPPING UP THE MASTER RES WITH CLEAN FLUID, IF NOT YOU WILL GET AIR IN THE FLOW AND START AGAIN.
9. Close the nipple enough so the fluid will still flow out, but only requires a small enough turn to be tightly closed (so no air gets in or fluid gets out)
10. Again pump the brake lever, but be aware of how much travel u have left in the pump of the lever, watch closely to the stream flowing, when you feel the brake lever get half way through the flow, quickly tighten the nipple.

11. Tightening part way through the smooth flow will ensure the next thing to come out of the brake lines is fluid, not air.
12. If you have dual brake calipers, then goto step 4. However the old fluid will most likely be drained from the other set of lines, so again let the even smooth, airless flow of fluid through the nipple, untill half travel of the lever then tighten the nipple.

13. Once your finished tightening both and your happy that if you opened the nipple again and squized the lever again fluid would smoothly flow out, with the lid off the master res, continue to pump the brake lever and until the brakes start to feel firm.

14. Keep pumping.......... once its now feels like strong brake pressure ensure there is enough fluid, lid on, tighen and screw up. and Done.

15. Before you ride, find a straight flat bit of road and walk along with the bike applying the brakes to ensure that it will stop. You will have an idea of how the brakes felt before, so they should feel the same or stronger. Any less, there is sitll air in the system.

Hope this helps.

[Slow and wobbly]

On this topic, and since I'm in a favourable mood why do people have so much trouble bleeding brakes?
It, to me, is a very simple operation and they are a very basic hydraulic system. I know there are some systems that can trap air due to their design but I have yet to find a system a can't flush and bleed within 10mins. I don't understand the compressing the lever and leave overnight philosophy at all as this places the piston / actuator in the closed position and would seem to do nothing at all to allow air within the system to retreat to the reservoir.

[dilligaf]

did this guys maintenance course a while ago and he goes through it
http://www.madbiker.com.au/maintenance%20courses.htm
bugger made it look easy

think he's one of our sponsors but he's not on the list.

[mike-s]

Remember that when you compress the master cyl there is a slight bypass/return that is activated, that is why when you squeeze the master cyl with the lid removed you have to do it gently, otherwise you'll get a fountain of brake fluid shooting into the air. I can confirm that zip tying the brake closed overnight (or longer if you have time, or, erm, forget ) also helps with loosing any fine air bubbles.

Another thing to remember when you replace the hosing or want to do a full flush, sometimes its worth flushing a bit at the master cyl's banjo bolt to help prime (if you've just drained the lot/new hosing) or just want to be thorough and remove as much old shit as possible.

[Gosling1]

On this topic, and since I'm in a favourable mood why do people have so much trouble bleeding brakes?
It, to me, is a very simple operation and they are a very basic hydraulic system. I know there are some systems that can trap air due to their design but I have yet to find a system a can't flush and bleed within 10mins. I don't understand the compressing the lever and leave overnight philosophy at all as this places the piston / actuator in the closed position and would seem to do nothing at all to allow air within the system to retreat to the reservoir.

Often, and especially with older bikes - brake caliper pistons can get stuck, air can get trapped behind the piston, the seal in the master cylinder may be a bit dodgy - there are *heaps* of reasons why people have trouble bleeding brakes......that, and also the fact that some of them are complete twats ....

But yes, it *should* be quite a simple job - and as long as all the operating parts are in perfect nick, it generally is...

The bypass valve in the m/c piston assembly allows any air trapped in the system to return to the m/c.....what compressing the lever overnight does, is pressurise the entire hydraulic system and it literally *forces* small bubbles of trapped air out from where they are trapped, and they will slowly rise through the lines and back up into the m/c.......

I know when I did this on the MFP12, before a track day in '07, the feel of the brakes improved heaps, and it has never diminished since.

The easiest way to bleed brakes quickly is using the banjo bolt at the m/c end. Pull the lever in, and give this bolt a quick undo-and-do-up action with a ring spanner of the correct size. Its necessary to sacrifice a big towel that is placed under/around the entire brake area, to catch any fluid. Its easy to hear the trapped air escaping as soon as you 'crack' the banjo fitting......

Trapped air naturally rises in a hydraulic system - trying to push it all the way out of a tiny bleed nipple at the lower end is a pain in the arse and takes forever. Doing it with the banjo bolt snap/unsnap method, I generally get good lever pressure within a minute. If this method doesn't get good lever pressure, then I just take the calipers off one at a time, take out the pads, and use a small G-clamp to push the pistons right back into the calipers....this method will often push a shitload of fluid out of the m/c, so be prepared. This method is also *guaranteed* to remove air-pockets behind the piston...

[jonoZRX]

some of them are complete twats ....

I think that was my problem

take the calipers off one at a time, take out the pads, and use a small G-clamp to push the pistons right back into the calipers....this method will often push a shitload of fluid out of the m/c, so be prepared. This method is also *guaranteed* to remove air-pockets behind the piston...

I did this on Gos' advice and it worked like a charm. There must have been an air pocket, it felt like a completely new set of brakes afterwards.

[mick_dundee]

On this topic, and since I'm in a favourable mood why do people have so much trouble bleeding brakes?
It, to me, is a very simple operation and they are a very basic hydraulic system. I know there are some systems that can trap air due to their design but I have yet to find a system a can't flush and bleed within 10mins. I don't understand the compressing the lever and leave overnight philosophy at all as this places the piston / actuator in the closed position and would seem to do nothing at all to allow air within the system to retreat to the reservoir.

Emphasis on yet as he found one tonight, my 9 Wasn't quite just drain, pump, refill as the theory suggests it should be huh wobbles

[Slow and wobbly]

Ok.... so Micks bike is cantankerous. I new that from the first time I changed the oil in the bugger .
After doing the usual and flushing the old fluid out and bleeding off both calipers I still could not ain a reasonable feel at the lever. Since the option of tying up the lever and waiting 24hrs was not feasible I tried another method I have seen - but never had to apply. I rapidly pumped the lever for several minutes until I saw air bubbles appear in the reservoir and the feel at the lever greatly increased.
Over to the boffins to explain how this works. It is a method I have seen used in workshops where they also do not have time to wait overnight. It works.

[robracer]

Adrian I have done dozens & Dozens of brake bleeds including new lines & starting from scratch, & thought I had seen it all, but FMD the radial MC on the six was a doozey. the only way I could get the fluid to move from the reservoir was to use a syringe to pump fluid into the master cylinder through the top bleed nipple I have never encounted an air lock like this in any master cylinder before & just to confirm I had the MC off twice & had to repeat the process each time to get any movement of fluid.
NB the brembo Radial I had, which is a similar set up, did not need this much attention to get the ball rolling

[Blurr]

Adrian I have done dozens & Dozens of brake bleeds including new lines & starting from scratch, & thought I had seen it all, but FMD the radial MC on the six was a doozey. the only way I could get the fluid to move from the reservoir was to use a syringe to pump fluid into the master cylinder through the top bleed nipple I have never encounted an air lock like this in any master cylinder before & just to confirm I had the MC off twice & had to repeat the process each time to get any movement of fluid.
NB the brembo Radial I had, which is a similar set up, did not need this much attention to get the ball rolling

+1 the mc on disco's mc took a while to get all the air out. There was an air bubble that seems to work up the line from the calipers instead of he other way around

meant that i had to bleed the calipers for a while to chase the bubble up to the mc before I could bleed that properly!!!! 10r was much easier

[hoffy]

Adrian I have done dozens & Dozens of brake bleeds including new lines & starting from scratch, & thought I had seen it all, but FMD the radial MC on the six was a doozey. the only way I could get the fluid to move from the reservoir was to use a syringe to pump fluid into the master cylinder through the top bleed nipple I have never encounted an air lock like this in any master cylinder before & just to confirm I had the MC off twice & had to repeat the process each time to get any movement of fluid.
NB the brembo Radial I had, which is a similar set up, did not need this much attention to get the ball rolling

fark all this fancy shit, the 12R MC is off a GPZ900 !

[MickLC]

Ok.... so Micks bike is cantankerous. I new that from the first time I changed the oil in the bugger .
After doing the usual and flushing the old fluid out and bleeding off both calipers I still could not ain a reasonable feel at the lever. Since the option of tying up the lever and waiting 24hrs was not feasible I tried another method I have seen - but never had to apply. I rapidly pumped the lever for several minutes until I saw air bubbles appear in the reservoir and the feel at the lever greatly increased.
Over to the boffins to explain how this works. It is a method I have seen used in workshops where they also do not have time to wait overnight. It works.

I did try to warn you