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Old 08-22-2012, 11:47 PM   #1
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Brakes gone soft?? No brakes?? 986 Boxster

NO Brakes ??

At the weekend me nd my brother replced the top mount bush on the nearside front (UK Right hand drive) Didnt fully drop the hub etc just un done the top 3 bolts and tilted the strut out of the wing to replace.. all was fine until drove it off the ramps and onto the forcourt..

The brakes went soft and need a full pump to the floor before having any brakes??

Sounds like air got into the system but we never opened the lines??

I have now replaced the hard brake pipe from the calliper to the flexi ( it looked as if that could of twisted and deformed so to rule that out I just replcaed it ) and now bled the brakes until there is no air out of that corner.. but still the brake pedal needs pumping until it has bressure?

I have checked to ensure the disc is flush and not pushing the pads back not that

Could the master cylinder just go like that?

PLEASE HELP!!
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Old 08-23-2012, 01:21 AM   #2
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What is the symtoms of a failing master cylinder?

what is symtoms of a failing booster? (servo)
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Old 08-23-2012, 03:46 AM   #3
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The symptoms you describe sounds a lot like a dual circuit master cylinder that has failed on one circuit.
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Old 08-23-2012, 04:04 AM   #4
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So I need a new master cylinder?

Thanks for getting bac to me -
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Old 08-23-2012, 04:18 AM   #5
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Do some more checking before you run out and buy expensive parts.
When I was in automotive school, my instructor said a good mechanic will change what is broken, a bad mechanic will just start changing parts until he fixes it by a process of elimination.
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Old 08-23-2012, 04:25 AM   #6
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Sounds a very fair outlook -

So I am a progressive learner.. worked on cars for over 10 year but only had brake issues this once? all other where just a simple case of fitting new pads etc and doing the normal bleeding? at the moment I have a problem and I need to know where to start as a process of elimation into what is wrong by testing?

Thanks
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Old 08-23-2012, 04:05 PM   #7
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Well, I suppose the first thing to do is to check all four corners for any signs of leaking.
I've never had to test a master cylinder before, they either worked or didn't. I would think that if you disconnected the brake lines from the master cylinder and put in some screwed in plug fittings, and then applied pressure to the brake pedal, it should have a solid pedal pressure since the brake fluid can't go anywhere. If it goes to the floor, you have your answer. Not sure how you would get the plugs in without introducing air in the system, but maybe you could screw them in partially and then bleed the air out like you would with a caliper. You would have to make some sort of accommodation to catch all the fluid that would be spilling all over. You don't want to get it all over the car and ruin the paint.
Someone with more recent experience may want to chime in if my process is flawed.

Edit: I suppose you could remove it from the car and test it on the bench. That way you won't get brake fluid all over the place. If it is bad, then you already have half the job done.
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Last edited by Spinnaker; 08-23-2012 at 04:13 PM.
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Old 08-23-2012, 05:44 PM   #8
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Replace the rubber brake hose and pressure bleed all four wheels.
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