no pressure In rear brakes

[glang]

It sounds as if the piston comes out as you operate the lever but then returns to its original position when the levers released so it never gets to take up its correct place close enough to the disc. Can you try pumping the pedal quickly and repeatedly in an attempt to get it to stay forwards?

[Red Herring]

The most effective tool for bleeding a rear brake is a large medical syringe and a short length of suitable clear pipe.

The issue you have encountered is that neither the bleed nipple or feed into the master cylinder are at the highest part of the system, this is usually either the top of the master cylinder at the banjo, or about midway along the brake hose towards the rear caliper. Due to the limited amount of fluid moved with each stroke of the brake pedal any air in the system will have time between strokes to go back to whence it came, rather than towards either end.

To overcome this open the bleed nipple and attach the empty closed syringe to it. Then draw the syringe back whilst operating the brake pedal up and down rapidly. It helps if you have an extra pair of hands available for this...... Keep the lid off the reservoir as you should see the level drop rapidly as the fluid is sucked through the system to the syringe and you may need to top it up. Basically the vacuum you are creating with the syringe is overcoming the suction from the master cylinder when it is on it's return stroke thus preventing the air getting pulled back. When you are getting more fluid than air into the syringe (you will always get some air as it will suck it in from the bleed nipple threads) close the nipple and hold the syringe up vertically so that any air in the pipe or syringe can rise up out of the pipe. Then open the bleed nipple again and compress the syringe pushing some of the fluid back into the caliper and creating pressure in the system. Don't do it to hard otherwise the pipe will blow off and fluid goes everywhere, but what you want to do is create enough pressure to push the pistons and pads out. Again you can encourage this by rattling the brake pedal but basically what you are trying to do is eliminate the back suction that the master cylinder creates when you release the brake as this is what is pulling your freshly greased and free moving pistons away from the pads and stopping you getting any pressure! Finally tighten the bleed nipple and hopefully you now have a functioning brake....!

[SV650rules]

Best way to bleed brakes is Mityvac - use it on cars and bikes.......

[Red Herring]

Sure, Mityvac make some great kit but it costs a hell of a lot more than a simple syringe and because it does vacumn only it's not a lot of use at pushing the pistons out onto the pads......

[aburamjan]

Originally Posted by Red Herring

The most effective tool for bleeding a rear brake is a large medical syringe and a short length of suitable clear pipe.

The issue you have encountered is that neither the bleed nipple or feed into the master cylinder are at the highest part of the system, this is usually either the top of the master cylinder at the banjo, or about midway along the brake hose towards the rear caliper. Due to the limited amount of fluid moved with each stroke of the brake pedal any air in the system will have time between strokes to go back to whence it came, rather than towards either end.

To overcome this open the bleed nipple and attach the empty closed syringe to it. Then draw the syringe back whilst operating the brake pedal up and down rapidly. It helps if you have an extra pair of hands available for this...... Keep the lid off the reservoir as you should see the level drop rapidly as the fluid is sucked through the system to the syringe and you may need to top it up. Basically the vacuum you are creating with the syringe is overcoming the suction from the master cylinder when it is on it's return stroke thus preventing the air getting pulled back. When you are getting more fluid than air into the syringe (you will always get some air as it will suck it in from the bleed nipple threads) close the nipple and hold the syringe up vertically so that any air in the pipe or syringe can rise up out of the pipe. Then open the bleed nipple again and compress the syringe pushing some of the fluid back into the caliper and creating pressure in the system. Don't do it to hard otherwise the pipe will blow off and fluid goes everywhere, but what you want to do is create enough pressure to push the pistons and pads out. Again you can encourage this by rattling the brake pedal but basically what you are trying to do is eliminate the back suction that the master cylinder creates when you release the brake as this is what is pulling your freshly greased and free moving pistons away from the pads and stopping you getting any pressure! Finally tighten the bleed nipple and hopefully you now have a functioning brake....!

thanks for the very detailed reply. there is no air bubbles coming out when I bleed it so I would have though there's no air bubbles left. however, I will definetly give this a go.

[aburamjan]

Originally Posted by Red Herring

Sure, Mityvac make some great kit but it costs a hell of a lot more than a simple syringe and because it does vacumn only it's not a lot of use at pushing the pistons out onto the pads......

I do have a pump I picked up off Amazon for like £20 I tried out but it seems to suck a lot of air in because the air bubbles don't seem to reduce even after using a half a litre of brake fluid.

[SV650rules]

Originally Posted by Red Herring

Sure, Mityvac make some great kit but it costs a hell of a lot more than a simple syringe and because it does vacumn only it's not a lot of use at pushing the pistons out onto the pads......

Mityvac does pressure and vacuum ( well the one I have does ) just flick the lever to suck or blow... can get down to one hell of a vacuum ( 30 in Hg - 1 bar ) and up to 2 bar pressure.... had one for many years - paid for itself many times over. The reservoir can be filled with brake fluid and can blow fluid into cylinder as well as suck it out, and what is in the reservoir never gets near the mityvac seals.

[SV650rules]

Originally Posted by aburamjan

I do have a pump I picked up off Amazon for like £20 I tried out but it seems to suck a lot of air in because the air bubbles don't seem to reduce even after using a half a litre of brake fluid.

The air gets past thread on brake bleed nipple.

Wrap PTFE tape around thread of nipple and it stops a lot of the air getting past thread.

[Red Herring]

Originally Posted by SV650rules

Mityvac does pressure and vacuum ( well the one I have does ) just flick the lever to suck or blow... can get down to one hell of a vacuum ( 30 in Hg - 1 bar ) and up to 2 bar pressure.... had one for many years - paid for itself many times over. The reservoir can be filled with brake fluid and can blow fluid into cylinder as well as suck it out, and what is in the reservoir never gets near the mityvac seals.

Sounds like a great tool.

[embee]

I have a suck/blow Mityvac too, a very useful tool. They also do suck only versions, quite a lot cheaper. I empty the reservoir of old fluid first using it, refill with fresh stuff, then bleed at the caliper. The big advantage is that you can get a continuous flow to draw the fluid through the system to hopefully purge all the air.
As said, air does get in past the nipple threads while bleeding, but in reality this doesn't matter because while you are pumping it the low pressure in the bleed line is always drawing fluid out of the brake system so no air can get back in while it is still flowing. Make sure you tighten up the nipple while the flow is still coming out.
I've never had any issues getting a firm brake using it. Just make absolutely sure you don't empty the reservoir while using it as this will take air directly into the system and you'll have to start again.
It makes the process so easy it means you tend to do it more often, keeping the fluid fresh.
There are alternative very similar items to the Mityvac, I don't have any experience of them so can't comment, but it's not rocket science so they're probably perfectly good. Mityvacs are used in industry and are good quality tools, well worth the money IMHO.
The one niggle is the small plastic vac bottles which come with them are very light and always fall over with the vac tubes attached. I made a steel holder for it using a square plate (old scaffold tube foot) and a slotted tube welded to it, the slot lets you see how much fluid is in it so you don't overfill and pull fluid into the pump.