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MG MGB Technical - Rear brakes wont bleed

Hi,

I was going to flush the brake lines with fresh fluid.

I was using a suction device to suck the fluid out at a constant rate.

It seems it only let me suck the fluid out that was Ill say locally traped in the line itself.

Is there some sort of sensor that is shut due to the 2 line servo system sensing a leak of some sorts? I tried doing the manual method of pumping the brakes, also unscrewing the bleed screw to see if the line is clogged, then attaching the suction device to the hole where the bleed screw is and nothing....

Front brakes are fine and bleed well.

No crimps in the lines. Rear brake hose is fine but I will double check.

What should I look for?

Thanks,

James
JRB Mr

I was going to suggest the flexible hose having collapsed, but you say it's OK.

You could try checking back along the line to see how far you are getting fluid.
Dave O'Neill2

Unless the flexible hose is new, it could have an internal crack that is allowing a flap to close it off when trying to bleed the brakes, or as Dave O. stated, is collapsing when a vacuum is pulled on it. Cheers - Dave D
David DuBois

Makes sense. Thanks guys. I will follow up once this weather clears.

-James
JRB Mr

When bleeding, sometimes the shuttle piston in the brake warning switch will slide over and close off either the front
or rear brake circuit.
Daniel Wong

As Daniel said, Remove the "brake fail" light warning switch while bleeding is usually enough. Replace it when finished. Denis
Denis4

Replace the flexible. If the back one has started to decompose, the front ones will be on the way too.
Whether you have a dual line M/c depends on the age of your B.
Allan Reeling

If you are using a suction device the brake failure shuttle shouldn't come into play as there should be no pressure difference between the circuits like there would be if using the pedal - assuming no problems with the master, that is.

FWIW the remote (from the master) failure switch doesn't need removing, just recentralising (by pedal bleeding first one circuit then the other until the light goes out) if the warning light *has* come on for any reason. The failure switch on the later boosted dual master needs to be unscrewed a few turns to prevent the shuttle latching with pedal bleeding.
PaulH Solihull

James
I assume the rear brake cylinders are both OK?
When I couldn't bleed mine I pulled them off and stripped them - they were full of sticky gunk - I cleaned them, checked bores and seals ok, flushed the lines with alcohol, and had no more problems (oh, and I replaced the flexible line too while I was at it)
John
John Minchin

Hi Everyone,

Well I loosened the switch and bled by pumping the brakes, all is well. Brakes are really firm and flushed with new fluid. Thanks! Hope everyone had a great memorial day weekend. More threads to start about my B as I had a lot of good weather and time on my side this weekend.

-James
JRB Mr

This thread was discussed between 24/05/2012 and 29/05/2012

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