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Trouble bleeding brakes


Chrisjlm
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Iv’e just bought a bike as a tiny project and it doesn’t have any pressure in the front brakes at all.

I took the Calipers of the forks and pushed the pistons back into posistion; put back onto the bike and hooked up a one way brake valve kit.


When attempting to bleed them no amount of pumps will release any fluid from the nipple although a small amount did come out when first loosening it.


Any ideas?

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Hi and welcome to the forum


What bike is it?


It sounds like you may have air in the master cylinder try cracking the banjo bolt at the M/C to release the air

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They can be an absolute **** to bleed, took forever to bleed them on the ER5.


I found sucking some fluid through with a vacuum pump first then putting a U shaped pipe on the bleed nipple going up then down made things easier as it will retain some brake fluid so when you depress brake lever you'll see fluid and air come out, air will float to the top then when you release without doing up bleed nipple air can't get sucked back in so just keep pumping away and forget about the nipple then (calm down six30).

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As mentioned above, try bleeding at the M/C first as there can be a surprising amount of air trapped in the cylinder piston. Once you've done that, the easiest way that I've found is to use a syringe and plastic tubing on the caliper bleed nipple to push fluid up through the system, just keep a keen eye on the level in the m/c to make sure it doesn't overflow.


Have you checked the pistons, piston seals and the calipers generally? If they're looking a bit grim it could be time to overhaul them and replace all the seals etc.

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Iv’e just bought a bike as a tiny project and it doesn’t have any pressure in the front brakes at all.

I took the Calipers of the forks and pushed the pistons back into posistion; put back onto the bike and hooked up a one way brake valve kit.


When attempting to bleed them no amount of pumps will release any fluid from the nipple although a small amount did come out when first loosening it.


Any ideas?

Yeah - crudded up nipple. Have you tried a new one?

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Before you can bleed a brake system you have to fill all of it with brake fluid . A master cylinder WILL NOT fill a system . It is designed to apply pressure at one end which is multiplied at the other end by the area of the piston . It is not designed to shift any significant volume of fluid down the brake line . The way I fill a brake system involves no devices or gadgets . All I do is attach a metre of clear PVC tubing from B&Q to the bleed nipple , fill the master cylinder right up , open the bleed nipple , put the other end of the tube in my mouth and suck . When I can see at least a foot of brake fluid in the tube, stop sucking , close the bleed nipple and with the tubing still in place begin the bleeding process . This consists of squeeze the lever, open the nipple , close the nipple , release the lever and repeat . Works for me every time. HOWEVER this whole exercise will be a complete waste of time if you have not thoroughly serviced your callipers . If you don't clean all the crap and mineralisation out from behind the seals you will never achieve responsive braking with minimal lever travel. Pumping the pistons out , removing all visible dirt and then pushing them back in again is a complete waste of time and effort. Trust me on this , I got this wrong for years until the penny dropped 😉

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Okay so bleeding the master cylinder did the trick, got the fluid flowing, shit load of air as expected.

Problem now is fluid is leaking from the Caliper, can’t tell if it’s coming from the pistons, or the seam where either side of the Caliper meets.


Having said that I’d swear it wasn’t coming from the piston seals?


I’ve stopped bleeding as it’s pointless with more fluid leaking from the Caliper then what is coming through the nipple.

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have you had the calipers in half too? you may have trapped the O ring between the two halves

 

Yep , my first thought too . Maybe its missed out altogether. You didn't accidentally loosen the wrong bolts when you removed the calliper by any chance ?

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Okay so bleeding the master cylinder did the trick, got the fluid flowing, shit load of air as expected.

Problem now is fluid is leaking from the Caliper, can’t tell if it’s coming from the pistons, or the seam where either side of the Caliper meets.


Having said that I’d swear it wasn’t coming from the piston seals?


I’ve stopped bleeding as it’s pointless with more fluid leaking from the Caliper then what is coming through the nipple.

 

Have you checked all of the caliper and hose bolts are torqued to spec? I thought I had tightened mine sufficiently, but there was another 1/4 turn needed on the new banjo bolt and bleed nipple to completely seal them.

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