Rear brake air-bubbled?

[ldnz]

Having trouble with the back brakes on a 96 zx6r. When the bike is upright (off its stand) or moving there is absolutely no resistance in the back brake lever. Its doesn't really feel like an air bubble, its not just spongy. When the bike is on its stand if I pump the rear brake twice it seems to fill up and work exactly as it should.

Whats going on? There is no sign of any fluid leak/hose damage, when its on the stand they work fine, and theres plenty of fluid in the reseviour (sp?).

I've undone the bleed bolt thingy and pumped the lever down with fluid coming out, held it there then retightened it a couple of times, but being the brake expert i'm not I don't know if thats really the correct procedure.

Any thoughts?

[surfer]

Blimey, this sounds a strange one.

The only thing that I can think of is to get a brake bleed kit and some brake fluid and do a proper bleed job. A jam jar and a bit of hose will do it if you don't want to fork out for a kit (Repco or somewhere like that and they aren't expensive).

Good luck

[xwhatsit]

Well, the difference between it working and not working is to do with the stand being up or down. I take it it's a side stand you're talking about? Maybe it's pinching the hydraulic line or something. Does the brake actually work when the side stand is down?

Maybe it's to do with the bike being on an angle when it's on the stand. Hydraulic fluid draining from one place to another?

This looks interesting.

[bugjuice]

get a vacuum suction thing goin, suck the fluid thru. There could be a little bugger just stuck somewhere ya can't get. Most garages have something that should fix it, else it'll mean stripping/dismantling bits, if you want to do it yourself.

Also just check the condition of the hosing leading to the caliper. Also, if it's had a good life, the internals might be starting to give a little. Not a hard or expensive job to replace..

[Flyingpony]

Having trouble with the back brakes on a 96 zx6r. When the bike is upright (off its stand) or moving there is absolutely no resistance in the back brake lever. Its doesn't really feel like an air bubble, its not just spongy. When the bike is on its stand if I pump the rear brake twice it seems to fill up and work exactly as it should.

Whats going on? There is no sign of any fluid leak/hose damage, when its on the stand they work fine, and theres plenty of fluid in the reseviour (sp?).

I've undone the bleed bolt thingy and pumped the lever down with fluid coming out, held it there then retightened it a couple of times, but being the brake expert i'm not I don't know if thats really the correct procedure.

Any thoughts?

Sounds like you've got an air bubble in the brake line. My bike had the same symptoms, the brakes would engage but not really bite and the pedal didn't feel spongy. Even had a bike shop look at it and they said, "No air bubble in there, must be something else".

Anyway, after a proper bleed at home where a couple nice air bubbles emerged, they were back to normal functionality.

So, bleed the brakes properly a.k.a. not as you described above - that'll only encourage more air bubbles to enter the line, and see how the brakes work then.

Believe brake fluid it meant to be replaced every 12-24 months to keep it in prime condition.

[ldnz]

Cheers folks. I took it into the shop (kwaka place off barrys pt rd?) and they had a go at bleeding them. Mechanic was concerned it was more than just an air bubble because there was stuff all flow out the bleed nipple. Have ordered a seal kit but may have to fit it myself as the shop is all booked up. Any experts reckon they could give me a hand?

[Denniso]

The fastest way I've found to bleed bike brakes is to get a large syringe from a vet supply bout 60ml dont want the needle , connect to this a suitable hose that will go onto the bleed nipple fill this with brake fluid (suck it out of a new clean bottle of good brake fluid , dont mix silicon & mineral fluid ) make sure no air bubbles in syringe & connect to brake nipple , loosen nipple & push fluid in , this pushes out the old fluid and air , make sure that the resivar dosent overflow ( take off top beforhand and clean out old fluid from it , keep an eye on the level as you pump in the new fluid) As long as everything else is good this will get rid of any air bubbles well because you are pushing the air the way it wants to go , up .Dont forget to tighten up the bleed nipple before you take off the hose from syringe.

[ldnz]

Well one cylinder seal kit and 30 mins of swearing at a circlip (blah blah...proper technique....blah...proper tools....blah blah blah not multimeter probes....) later I have a semi working back brake. Semi in that it seems to function ok, no sponginess in pedal, piston moving etc. But its gutless. Completely. Contributes absolutely nothing to slowing the bike down, however it will happily hold the bike on a moderately steep hill.

Whats going on? I assume it could be either - an air bubble still there, or b, pads that just aren't gripping? Do pads go crap if they aren't used in ages?

[imdying]

Pads can crap out, but if you're not sure what's wrong, take it to a professional.

[surfer]

Well one cylinder seal kit and 30 mins of swearing at a circlip (blah blah...proper technique....blah...proper tools....blah blah blah not multimeter probes....) later I have a semi working back brake. Semi in that it seems to function ok, no sponginess in pedal, piston moving etc. But its gutless. Completely. Contributes absolutely nothing to slowing the bike down, however it will happily hold the bike on a moderately steep hill.

Whats going on? I assume it could be either - an air bubble still there, or b, pads that just aren't gripping? Do pads go crap if they aren't used in ages?

Sounds like you need to check the wear on your brake pads.

Did you use a kit for bleeding your brakes? Use it again as it sounds like you have a few small air bubbles left in there. It can be a real pain to get them all out. Give it another 15 minutes and see what happens.

Good luck

[Dai]

Once you have filled the reservoir, replace the cap.

Over night apply the brakes and tie them off so that the brakes arre on all the time. This will cause the bubbles to rise.

in the morning bleed of the air and seal.

[ldnz]

Cheers. Went for a ride and they got better and better. But still don't seem great. I don't know what I should be expecting though - its one tiny piston trying to haul a very sticky large tyre. Should it be able to lock the wheel? Way less braking equipment than the KR.

[Kwaka14]

It should be able to lock the rear wheel, when you did the seal kit and pads I assume you cleaned the caliper and the disc before you put the new pads on? The new pads will also take a while to "bed in" particularly if your disc is a bit worn as the pad needs to both cure (happens with heat from friction applying the brake over the first 100ks or so) and also to contour themselves to the wear of your disc (which is the slowly gets better and better part).

[imdying]

You should be able lock the rear wheel pretty easily at 50km/h on a 96 ZX6R.

[ldnz]

Haven't done the pads - old but still have a little left on them. Have only changed the seals in the cylinder. Haven't touched the caliper. Might have to have a look for some new ones!

[imdying]

Perhaps the caliper is siezed (even partially). Very common.

[ldnz]

In part 5492 of the great rear brake saga our gallant hero gets off his bike and kicks the shit out of it after discovering the banjo bolt on the caliper missing and the hose dangling, while half way to new plymouth. Not detered by the absence of any rear brake function the 1000k round trip was safely completed.

On closer inspection the dodgy as bracket kittyhawk had had made up for the muffler was catching on the caliper banjo bolt when going over big bumps etc. No sign of damage on the caliper (bar the missing bolt..) however the bracket has a big bolt width and 30 mm long chunk missing. Quite impressive when its 3 mm odd aluminium.

I believe this was a good portion of what was wrong with my brakes, as it must have been leaking in air slowly for quite a while. Off to Spectrum tomorrow to order the proper bracket and grab a new bolt. Bloody hell kittyhawk...