Bleeding brakes - what I am I doing wrong?

[plenty]

New to this to please bear with me...

I am trying to completely flush and bleed my brakes. My system is almost drained of fluid as I had previously taken apart the calipers and hoses to refurb/change the calipers and upgrade to steel hoses.

Bought a Gunson Eezi-Bleeder so that I can do this solo. Inflated a tyre to 20 psi as recommended to act as the pressure source.

What is happening is the master reservoir fills right up to overflowing but no fluid comes out of the valve when I undo a bleed nipple. Have tried pumping the pedal repeatedly (it goes to the floor) but this makes no difference. When I close the nipple there is again no difference and pumping the pedal also does nothing - the reservoir stays full.

Connecting the Eezi-Bleeder to the tyre also makes no difference - the fluid is not pushing through the reservoir, as if there is a blockage somewhere.

No doubt I am making an elementary mistake?

[spdpug98]

Sounds to me like there must be blockage somewhere in the master cylinder or pipework close to the MC, I have just used exactly the same bleeder when I put a complete new system on the car I just built and it worked fine.

If the resevoir is filling up when you pressurise the system (connect to the tyre) then it is working correctly, all you should have to do then is open the bleed nipples on the callipers.

Just a thought, do you have bleed nipples with a large hex head and a small hex head, if so then it is the small one you need to undo

Edited by spdpug98 on Monday 6th July 21:53

[GreenV8S]

The reservoir is only connected to the brake circuit in the last fraction of an inch of its travel. If there's gunk in the master cylinder stopping it retracting fully, or the pushrod adjuster is done up too tight, the piston won't come back far enough to open the port to the reservoir and you'll get the symptoms you're seeing.

I suggest you make sure the load is right off the pushrod and try again.

[plenty]

spdpug98 said:

Just a thought, do you have bleed nipples with a large hex head and a small hex head, if so then it is the small one you need to undo

The caliper nipples have 11 mm hex heads.

System worked fine before draining and replacing the hoses and calipers. I don't suppose it could be the calipers could it? I suppose if that were the problem then I would eventually get a firm pedal - however the pedal goes to the floor indicating the system is not filling with fluid.

GreenV8S said:

The reservoir is only connected to the brake circuit in the last fraction of an inch of its travel. If there's gunk in the master cylinder stopping it retracting fully, or the pushrod adjuster is done up too tight, the piston won't come back far enough to open the port to the reservoir and you'll get the symptoms you're seeing.

I suggest you make sure the load is right off the pushrod and try again.

Thanks. Before I start messing with the cylinder gubbins - the system took about one litre of fluid before clogging up like this. Is this consistent with your diagnosis?

[spdpug98]

Are you not getting any fluid out of any of the calipers 'front or rear'. It does sound like there is still a lot of air in the system if the pedal is going to the floor, I would guess that the bleeder must be working if you have put 1L through already

I had a similar problem in the past when my system had no leaks but was continually getting air in the system, this turned out to be one of the seals within the MC allowing air in on the return stroke and not pulling the fluid down from the resivoir....but I was getting fluid out at the calipers.

[GreenV8S]

plenty said:

Thanks. Before I start messing with the cylinder gubbins - the system took about one litre of fluid before clogging up like this. Is this consistent with your diagnosis?

Perhaps. If the system was initially OK you would be able to get fluid into it, but if something changed to stop the piston retracting fully then this could cause the problem. If the master cylinder isn't new then bleeding the brakes by pumping the pedal can sometimes damage the seals because they run out of the normal worn area of the bore. That might lead to this sort of problem.

I suggest you make sure all the load is off the pushrod (for example by slackening off the mounting bolts a few turns) and see if that helps. If so, it supports this theory.

If that doesn't help, I suggest the next step is to slacken off one of the unions at the m/c and see if you can get fluid out either pumping the pedal or via the eezibleed. If you can, the m/c is allowing fluid through and I think you're looking for a blockage further downstream.

[plenty]

Well it turned out to be something elementary after all - a gunked up nipple. Should have tried another nipple before rushing to post a question. D'oh!

Thanks to all who gave advice.

[spdpug98]

plenty said:

Well it turned out to be something elementary after all - a gunked up nipple. Should have tried another nipple before rushing to post a question. D'oh!

Thanks to all who gave advice.

Glad you got it sorted!