Spongey brakes

blue_painted · Nova Slayer Joined: 04 Aug 2015 Karma :

I've had the Bonnie's front caliper refurbed - new seals, pistons etc. - but now I can't get the brakes right.

I've bled half a bottle of brake fluid through and I see no air bubbles in the outflow any more. My best guess is there's air behind the pistons so the next step is to push them right back and clamp them there and go through bleeding bleeding again.

But am I missing anything?
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GP-100 -> CB250RS -> CBX550F2 (pause) KR1S -> RD350YPVS -> ZX6-R (pause) CD200 ->Mash 400 -> T100 (current) & (R1100RT scrapped pile o' shite) (CB250 Nighthawk - SORN in shed) Meteor 350 (current)

sickpup · Old Timer Joined: 21 Apr 2004 Karma :

Polarbear · Super Spammer Joined: 24 Feb 2007 Karma :

I've found that that last little bit of air can be a right bitch to get out.

The old trick of cable tying the brake on over night works in most cases for me.
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Triumph Trophy Launch Edition

blue_painted · Nova Slayer Joined: 04 Aug 2015 Karma :

- · Super Spammer Joined: 22 Oct 2013 Karma :

Another idea is to fill a thump pump oil can with brake fluid, attach a hose to the bleed nipple and slowly pump fluid in from the bottom, opening the lever at the top to allow air to escape.

It pushed air up the system from the bottom instead of trying to bleed downhill. Air tends to rise, not fall.
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TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

Easy-X · Super Spammer Joined: 08 Mar 2019 Karma :

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

You also sometimes get a small bubble sat behind the top banjo bolt at the top of the brake line. Putting a rag under it (to catch any fluid) and "bleeding" the top banjo bolt in the same way you would the calliper sometimes rewards you with a little fart of bubbles.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

- · Super Spammer Joined: 22 Oct 2013 Karma :

xX-Alex-Xx · World Chat Champion Joined: 12 Sep 2019 Karma :

Vacuum pump for the bleed, and cable-ties holding the brake lever back ovenight has always worked for me.

When I did the GSR's brake lines this year (convert from rubber to braided), the lever still felt a bit spongy after the change, but the brakes worked a LOAD better even with the feel. Just an excuse to upgrade to a radial master Laughing

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DILLIGAF

Hong Kong Phooey · World Chat Champion Joined: 30 Apr 2016 Karma :

Unbolt caliper, raise and tilt/rotate while bleeding.

Clamping lever to bar works, but you may get better results doing it a few nights in a row after riding it during the day.
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~~'81 CG125, '97 FZS600~~ : '99 CBR600F4, '09 KTM RC8

steve the grease · Crazy Courier Joined: 26 Jan 2018 Karma :

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

Robby's lazy method for bleeding brakes after draining the system.

Put everything back together. Do up all of the joints, bleed nipples, as if you were going to ride it.

Open the master cylinder lid. Fill with fluid.

Keep working the brake lever for 10 minutes. Watch lots of little bubbles appear in the master cylinder.

Go and make a cup of tea. Go back to the garage.

Keep working the lever whilst drinking tea. By the time the tea is finished, the lever should be fairly firm.

Put a pipe on the bleed nipple and crack it off to bleed out the last little bit of air.

Top up the master cylinder, lid back on, job done.

Hong Kong Phooey · World Chat Champion Joined: 30 Apr 2016 Karma :

blue_painted · Nova Slayer Joined: 04 Aug 2015 Karma :

Well then .... this is what I did ...

1. Hooked the caliper to the bar-end (was already unmounted) bleed nipple uppermost

2. Bled and tapped (handy piece of wood) - got quite a few biggish bubbles

Put the caliper back - still spongey but no longer "as fuck" ...

3. Cable-tied and left over night

Feels good now but other crap (doing accounts) means I can't test it yet.

Thanks all for the help and advice. Very Happy

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GP-100 -> CB250RS -> CBX550F2 (pause) KR1S -> RD350YPVS -> ZX6-R (pause) CD200 ->Mash 400 -> T100 (current) & (R1100RT scrapped pile o' shite) (CB250 Nighthawk - SORN in shed) Meteor 350 (current)

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

steve the grease · Crazy Courier Joined: 26 Jan 2018 Karma :

JackButler · Traffic Copper Joined: 11 Nov 2019 Karma :

Robby's (the dirty old man) technique is probably closer to how it's done at the factory & is the technique of choice by many who strip & re-build brakes regular.

Nip everything up, fill the reservoir, then pump the lever like mad. IME you'll start to feel the pressure build after just a few mins, meanwhile the level in the reservoir keeps dropping & the fluid looks like champagne. I generally have to refill the reservoir 3-4X on a dry system. Finally, when you have pressure & the pistons are out you can start cracking the bleed nipples.

If this doesn't happen then there is something else wrong.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

At a mechanics they fill the reservoir, put a clear hose on the nipple, crack it open and go do something else for half an hour. they top up the reservoir if they are walking past.

Gravity does the rest.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.