please help. brake lever with no resistance

[pompousporcup...]

I've had a nightmare trying to bleed my gpz brakes and am at the end of my tether. Please help confirm diagnosis

I substituted a known working caliper to my bike as the other was sticking. Big piston was fairly seized

I've tried 3 methods now. The pump the lever squeeze and hold - open the nipple, close the nipple release which saw fluid come out as expected. Couldn't get a steady stream with the one way valve type tube.

Tried leaving the bleed nipple open and pumping the brakes with the one way valve but this didn't seem to do much as the fluid kept going back in, never a consistent stream.

Tried the open bleed nipple, pull lever - close nipple and release method without success. Same problem.

Also tried the above without the one way valve...clear tube from bleed nipple with the other end submerged in some fluid..nope.

Assuming an air lock at the top of the system, Today I went and got some syringes from the local pets and home, although only 20ml ones, and used some new clear tube to back bleed the system. Sure enough bubbles came out the MC and I flushed the rest of the old fluid out this way... Still no effing resistance on the lever

I then bled it the conventional way to release any bubbles but there weren't any.

Wtf is wrong? Crappy MC?


Fwiw I've bled many a car system without issue so know what is meant to happen but this has me stumped.

Edited for android failures.

[Just_James]

Had the same issue recently (on completely different bike) with trying to bleed a front brake from dry after rebuild. Did everything just like you've tried and literally spent hours getting nowhere!
Tried the trick of clamping the lever closed with a cable tie and leaving overnight to let air escape which helped a little but never got a decent feel to the lever.

Ended up buying a cheap (around £13 iirc) vacuum bleeder kit off the bay and that it had it sorted in minutes! Very worthwhile investment in a handy bit of kit
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[pompousporcup...]

I've tied the lever 3/4 closed now to leave over night. Is it worth closing it all the way?

It's disheartening. This is the third night Ive tried to get this done with only a little time after work. 1.5 hours a night

[Fisty]

Bleed the master cylinder first. Crack the banjo bolt on the m/c and bleed it like you would a caliper.
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[pompousporcup...]

[Fisty]

Yup. Then do the rest of the system again.
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[pompousporcup...]

Ok, thanks fisty. Will give it a go and report back.

I've ordered the 15quid vacuum bleeder as well just in case as i'm still waiting on new discs and time to rebuild the other caliper, so this will need tobe done in a few months time. It stopped being fun after the first couple of hours

[MCN]

[pompousporcup...]

[MCN]

[skatefreak]

Been here as well.
After about 2-3 hours of getting no where fast I just got mighty Pi$$ed off at it. Put the cover loosely on the master cylinder and furiously moved the lever back and forth as fast as humanly possible...

Went proper potato tantrum on it and low and be hold, job jobbed

That was from a completely dry calliper though.

Never had the trusty old Compress, Open bleed, Close bleed, decompress, repeat fail :\

-Jvr

[MCN]

The problem on bike brakes is that to provide for powerful braking effect the master cylinder piston square area is tiny compared to the wheel cylinder/calliper piston square area. This is to provide the mechanical (hydraulic leverage) advantage. As gears do in a transmission.

It's like trying to fill a swimming pool with a bucket (sort of). It will get full but maybe sometime next week.

[chris-red]

I've never failed to bleed brakes by simply opening the nipple, attaching a tube from the nipple to a pot of waste fluid, making sure you keep it under the fluid level, then squeezing the lever repeatedly.
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[stinkwheel]

Bleeding at the banjos will almost certainly sort it out.

Wrap a cloth round the banjo, start pulling the lever then open and close the banjo quickly before the lever reaches the end of its travel.

If you hear a sharting noise, that's air coming out. Keep at it until you're just getting fluid.
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[bikenut]

you do realize that if the m/cylinder is full of fluid with the cover off, and the brake hose goes down hill to the caliper, and the caliper bleed nipple is open, then the fluid will flow down into the caliper all by its self??

that is assuming the bleed nipple and the tiny recouperating port in the m/c aint blocked! and there is some free play tween brake lever and m/c piston!!!

always get the m/c to pump fluid first.........suitable rag paint protection, thumb ( or finger, or screwed devise ) over pressure hole, and gently pump, then cover hole ( so fluid drawn into pressure swept volume chamber ) and watch fluid drawn into that CHAMBER, THEN PUMP........then fit hose etc and watch it syphon from the caliper bleed nipple. when no bubbles, bleed the conventional way.

do not let the fluid tank ( htf do you spell reservuar ) run out of fluid.

of all the bike brakes I have bled I have never had a problem doing it this way.....htf do you think they do it in the factory!! ( pressure bleeding probably ) wait overnight??
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[MCN]

[pompousporcup...]

Thanks all.

Bled the upper banjo bolt, heard the described sharting noise and FINALLY started getting resistance in the lever. Also noticed little bubbles coming out in the reservoir at each pull of the lever so did about 30 pulls...job jobbed

Its not perfect but stops me from 60 in the distance it did previously but I think the pads are half warn. Will hopefully see tomorrow if the binding has gone but it seems to coast better now from the short test run
left the lever tied down over night for good measure.

Yaay for riding again.

[MCN]

[pompousporcup...]

that's a good point, hadn't considered that.
Leaving it over night got a bit more resistance in the lever so it now nearly matches my buddies cbf6. Seems to stop well enough for my riding style. Fix one thing, another breaks..