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post #1 of 10 (permalink) Old 18th January 2013 Thread Starter
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Angry Flipped Seals on master cylinder - Megane

Hi guys, first post, the most helplful website on the internet

I changed the front pads on my megane yesterday used the procedure in the haynes manual, have done them before on a peugeot and had no problems so gave it a go.

after i finished i noticed that the brake pedal now goes all the way to the floor under pressure

called my mechanic and told him what i did he said i did everything right and maybe they just need bedding in, but would the pedal travel all the way to the floor until they are bed in? they used to be savage and now i cant even lock the wheels up.

got quite concerned so even called the AA, guy came and bled the brakes said there was no air in the system, no leaks to be seen.

Is it possible i flipped the seals in the master cylinder? what would be the symptoms?

Thanks guys
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post #2 of 10 (permalink) Old 19th January 2013
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Re: Flipped Seals on master cylinder - Megane

Going by your description of the pedal movement, I'd suggest that points to you having flipped the seals as you suspect.
I'm sure some of our more "hands on" people will be along soon to assist.


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post #3 of 10 (permalink) Old 19th January 2013
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Re: Flipped Seals on master cylinder - Megane

If it's not the master cylinder, perhaps you have somehow lost pressure/vacuum from the brake servo unit?? Or is a brake piston stuck?
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post #4 of 10 (permalink) Old 19th January 2013
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Re: Flipped Seals on master cylinder - Megane

In my experience I have never actually seen master cylinder seals flip although it would be great to see a photo of such.

With the servo empty how much brake free travel is there in the brake pedal and is it firm when pressed?

It may be the caliper pistons keep retracting and not remaining in position against the back of the pads. If you clamp the front flexi hoses and the pedal improves then this would prove if the problem is at the master cylinder or at the caliper.

I have came across this problem on a few occasions. Once on a Megane and another on a Honda Accord. I dismantled the master cylinder on the Megane numerous times but could find no fault. I them clamped each flexi-hose and the pedal was fantastic. I then got someone to fully depress the brake pedal and then clamped the hoses and got them to release the brake pedal slowly and watched the brake level drop. I repeated this 3-4 times at each wheel and the brake pedal returned to normal. This had the effect of preventing the caliper pistons retracting.

You can use a pair of vice grips as a clamp as long as you use a heavy piece or cardboard or the like in the jaws to prevent damage to the rubber pipe.
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post #5 of 10 (permalink) Old 19th January 2013
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Re: Flipped Seals on master cylinder - Megane

To keep this fault from happening which does happen on quite a few times on different vehicles To counteract this problem the bleed nipple on caliper piston has to be slacked off
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