Brakes non existent when engine is running.

Hi all. Had a bit of a brown trouser moment tonight taking my defender out, pedal just goes to the floor and the brakes do nothing. Resistance builds when pumping the pedal with the engine off, but doesnt get truly hard. When the engine starts the pedal goes down, but while running the brakes do nothing.

Any ideas of what i should be checking? Is it likely that the system just needs a good bleeding, or does it sound like a more expensive job?

Thanks,
Ben

Master cylinder would be my first call.

Loss of servo assistance could be leak on the servo unit

If it was the servo or master cylinder would i be able to spot a leak, or anything i could do to test and make sure thats what it is? Or is it just a case of replace the cheapest one first and hope that does it?

Thanks

Loss of servo assistance would give you a very heavy but full brake pedal, master cylinder internal seals often fail and give the symptoms you describe without any visible fluid leak.

Ok, cheers for that rob, looks like im going shopping tomorrow.

Maybe a wheel bearing, this happened to me, brake pedal just hit the floor bearing was very loose.

warrior said:

Maybe a wheel bearing, this happened to me, brake pedal just hit the floor bearing was very loose.

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That's an interesting one, I guess the disc was moving about so much it pushed the pads right back! Worth checking and then almost certainly a master cylinder, I had similar on my old 90 and there was no leak just the master cylinder seals failed and so pushing past the fluid but none made it out.

Defender Bits said:

That's an interesting one, I guess the disc was moving about so much it pushed the pads right back! Worth checking and then almost certainly a master cylinder, I had similar on my old 90 and there was no leak just the master cylinder seals failed and so pushing past the fluid but none made it out.

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If I pumped the pedel say twice it went solid as it should do, also if I turned one way gently and applied the brake and loaded the loose bearing I got no travel on my pedel.