andylancaster3000
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| posted on 6/9/10 at 02:42 PM |
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M' Bike disc brake problems...
Hi all,
Thought I'd ask here as I'm sure there some 'bikey' people with far more than an ounce of mechanical knowledge.
I have some Hayes 9 hfx brakes that are proving impossible to bleed, same front and rear. The rears had not been working for a little while so I
bought a working 2nd hand assembly (lever, hose and caliper), thinking I might have a knackered seal on the old one, only to find I couldn't
bleed that properly either. Having once thought I'd managed it I re-bleb the front only to have both levers then end up coming back the the bar
with no braking 30-40 brake applications after attempting to bleed them.
What am I doing wrong?! Tried numerous methods including injecting fluid with a syringe from either end, the conventional pump it through with the
lever, holding the caliper above the etc. The most odd thing is that initially after bleeding the lever will come up nice and firm but slowly becoming
spongy to the point of no braking.
Any help greatly appreciated!
Andy
[Edited on 6/9/10 by andylancaster3000]
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dinosaurjuice
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| posted on 6/9/10 at 02:50 PM |
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Try pushing fluid from caliper to lever with a syringe, can be a bit messy but usually brings them back to life.
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lewis
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| posted on 6/9/10 at 03:00 PM |
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I'm sure a bike shop would not charge much for a brake bleed it's obviously a air lock can you put the bike on something vibrating? The
hoses are so small any tiny bit of air will cause it.
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MikeCapon
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| posted on 6/9/10 at 03:01 PM |
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Bleed the system as best you can and then pull the lever in, secure in place with a tie wrap / ratchet strap or otherwise. Leave overnight and try.
This may help.
Cheers,
Mike
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andylancaster3000
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| posted on 6/9/10 at 03:03 PM |
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quote:
Originally posted by dinosaurjuice
Try pushing fluid from caliper to lever with a syringe, can be a bit messy but usually brings them back to life.
Have tried this but will give it another go.
Nearest bike shop worth going to wants £20 an end to do it. I'd rather persever a little more before it comes to that. 
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tony-devon
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| posted on 6/9/10 at 03:13 PM |
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as mentioned, cable tie back, but if its possible try gently heating the caliper and brake line
Im not talking melting things, just hair dryer or hot air gun on low setting etc
hot air will rise much better
I have used this method on motorbikes that people have spent days trying to bleed, and always worked for me
heavy is good, heavy is reliable, and if it breaks, hit them with it
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02GF74
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| posted on 6/9/10 at 03:16 PM |
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I was unable to get air out of a caliper as I was using the calipr in unconventional fashion - fitted before the seat stay as opposed to after.
This meant the bleed screw was below the pistons so no amount of pumping would shift the air.
You probably don't have/shouldn't have that problem but first step is to mount the caliper so the bleed screw is at highest point.
If this cannot be done on the bike then place a 3 mm or so plate between the pistons so they don't pop out. You may thrid hand to pull the
lever, hold the caliper and undo/do up the bleed screw.
(note 5 mm aquatics air line is idea to fit over the bleed screw).
Undo the bolt holding the lever to the bars so that when the reservoir lid is removed it is horizontal - this allows max amount of brake fluid to be
in it (this applies to Magura Marta and Shimano brakes - can't say I know your model but I have seen levers with a small screw to which is
fitted a tube and bottle of fluid, kinda like a remove reservoir - as on Formula disc brakes).
When reservoir is full, pull lever, undo bleed screw, let fluid/air out, do up bleed screw, release lever.
Do this many times ensuring that the fluid level does not get so low as to draw in air - you can get 2-4 strokes before this happens.
On Magura calipers, there is no bleed screw but a socket aka grub screw (I use Shimano bleed screw which although does not have the same shaped cone
end, will work as long as it is not done up to tightly).
Once the above it done, refit the reservoir lid or replace the filler screw, put bike on side so that caliper sits horzontally and ideally above the
reservoir, quickly whip out the bleed nipple and replace the socket screw.
if the seals were gone, they would leak.
ah, just read this bit:
The most odd thing is that initially after bleeding the lever will come up nice and firm but slowly becoming spongy to the point of no braking.
only way that can happen is for air to get into the system - entry points are reservoir, hose-reservoir, hole in hose, hose-caliper, caliper seals.
if there joins wer not air tight, I would imagine you would see fluid leakage.
... when you come to bleed them, do you see air bulbes coming out of the caliper?
there is also instructions here -
[Edited on 6/9/10 by 02GF74]
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dazzx10r
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| posted on 6/9/10 at 05:11 PM |
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They are a nightmare to bleed, but the best solution that I have found to work was to remove the brake system complete and clamp the caliper into the
vice with the brake cylinder at a lower point and bleed it with the bleed screw at the highest point. I think you can buy the hayes brake bleeding kit
off the net.
just found this on youtube;http://www.youtube.com/watch?v=KpdTKzgoVGk
[Edited on 6/9/10 by dazzx10r]
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Daddylonglegs
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| posted on 6/9/10 at 06:44 PM |
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I'm not familiar with the make, but I've had success with other types in the past by trying to get the caliper in a position where the
bleed nipple is at the highest point. I know this can help with certain Hondas and may be of use in your case.
Just an idea.
It looks like the Midget is winning at the moment......
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