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post #1 of 6 (permalink) Old 17th August 2013 Thread Starter
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Pedal sinking to floor when engine is on

Hi all

Got a problem with my brake pedal going to the floor when engine is on.

Not sure if this bit is relevant but ill give you full story. One of my rear brake pads were low, so I changed rear pads, but like a numpty hammered the calipers in, after realising I had destroyed them I bought 2 used rear calipers and a whinding tool, and fitted the new cailpers. I did open the bleed nipples when hammering the calipers to let the fluid out.

Fitted it all fine, and bled all the calipers, though it took a while to getting fluid flowing out the nipples, was no resistance on brake pedal at all.

finally started to get fluid through and bled all the nipples, no air coming out the calipers.

Now the brake pedal is hard when engine is off, but when I start the engine the pedal slowing sinks to the floor with light pressure, I can pump it hard again, then will sink to the floor again

I had bled all the nipples a further 4 or 5 times over the past few days, took the car for a little run, jammed the breaks on. still the same

please help I don't want to catch the train to work for another week
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Pedal sinking to floor when engine is on Brakes/Hubs scotiaboy2k7 5 1664 17th August 2013 12:50 PM
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post #2 of 6 (permalink) Old 18th August 2013
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Re: Pedal sinking to floor when engine is on

try beeding one back and one front at the same time. Then repeat on the other side. You'll need two bleed tubes obviously.
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post #3 of 6 (permalink) Old 20th August 2013
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Re: Pedal sinking to floor when engine is on

I had this same issue. Worried me a lot. Van stopped brilliantly, handbrake great but slow sink only when engine running.

I ordered a new master cylinder but by the time it had arrived the brakes were well on their way back to being normal.

Still not sure of cause as all I had five was change pads on all corners and never opened the brake lines.

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post #4 of 6 (permalink) Old 26th August 2013
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Re: Pedal sinking to floor when engine is on

The 2004 Espace I had did this too. I had an independent garage check the system and they could not establish what was going on, I contacted two Renault dealers for advice and both stated it was the way the brake system operated, a valve was designed to relieve pressure to protect some component(s) in such situations.

This was my experiece but with braking systems, if you have a concern I would be conferring with a dealer to ascertain for definite what was occurring -
safety is a must.
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post #5 of 6 (permalink) Old 23rd May 2015
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Re: Pedal sinking to floor when engine is on

I think I have the same problem after re-seating the front pads on my Laguna II. I took off caliper cleaned and re-seated pads and re-built with no breaking into the fluid system. Started the engine and when pressed, pedal went straight to floor with little or no braking. pumped a couple of times and they came back a bit but after a few seconds pedal had gone again. No visible leaks, no air bubbles in master reservoir, and pedal goes rock hard as expected when engine off and pumped 3 or 4 times. When re-building, I only squeezed the piston back about 1-2mm, just enough to make sure I could bet it back in place with ease. Any advice?
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