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Old Aug 29, 2010, 10:19 AM   #1
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Weird problem- brake pedal softens and hardens randomly

Hi guys!

My car has been in the shop for a couple of weeks. Now that I have it back the brakes are acting real weird. While I'm driving one minute the brakes are firm and work fine and then the next time I go to hit the brakes, the pedal goes all the way down to the floor. I bled the brakes not too long ago so I doubt there's air in the system. Also it would be soft the whole time instead of hard and soft back and forth. Anybody have any ideas? Thanks

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Old Aug 29, 2010, 10:21 AM   #2
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what was the car in the shop for? and did you bleed the breaks in the correct order and way?

order is in the following how to..

http://www.joe250.com/cars/evo8/brak...ebleeding.html

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Old Aug 30, 2010, 10:35 AM   #3
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the car was in the body shop for a new bumper but it was there fo a while. Really strange problem. It's also quite scary when you go to hit the brakes and the pedal goe to the floor.
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Old Aug 30, 2010, 10:40 AM   #4
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Check for fluid around the back of the brake pedal, could be a seal in the master cylinder failing too. I've seen this caused by air and a failing master cylinder. How are the brakes when the car is off?
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Old Aug 30, 2010, 04:56 PM   #5
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05blue8, thanks for your insight. When the car is off, the pedal is completely firm and normal. Only when driving does the pedal get weird hard and soft. Does this sound like a seal or master cylinder? Thanks bro

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Old Sep 1, 2010, 06:11 AM   #6
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Check for fluid leaks around the master cylinder and along all the lines. I had brake failure recently when the crossover tube (the little tube on the bottom of the front calipers) loosened with high temperatures, brakes were fine one moment, soft and goofy next.

Next, make sure your pads are installed properly. If you have a pad that is cocked and sometimes frees and sometimes sticks, it can cause funky brake feeling.

Finally, rebleed your brakes once you ensure you have NO LEAKS and everything is installed correctly. It can take numerous times of bleeding to get all the air out. We have the Motive Brake Bleeder and find that doing them the old fashion way works the best.

If you still have a funky pedal, I would seriously start looking at the master cylinder or maybe the brake booster has a vacuum leak. That could make the pedal rock hard, but not super soft.

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Old Sep 1, 2010, 08:53 AM   #7
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thanks dan! To clarify, it's not that the pedal gets soft. It's that the pedal goes all the way down to the floor.
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Old Sep 1, 2010, 01:19 PM   #8
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Try this, put light pressure on the brake pedal, but not enough to actually engage the brakes. If the pedal sinks to the floor then you just have pedal sink cause by one of the cups inside the master cylinder. You wont have a leak cause the fluid just goes back up to the resevoir.

If the problem is you pump it and its hard then it sits a while (or youre cruising a while) then its very soft, then its air in the system.
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Old Sep 1, 2010, 03:53 PM   #9
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Unless you're losing brake fluid somewhere like a caliper or line it sounds like your master is on it's way out.
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Old Sep 1, 2010, 05:53 PM   #10
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On my 1G DSM I had this happen several times over a period of a few weeks. Then it never happened again. I know it was the cup rubber in the master not expanding for some reason. So, anyway, I'd say master cylinder.
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Old Sep 1, 2010, 06:11 PM   #11
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I agree that it is most likely the master cylinder. Is there any chance that some crud got into your fluid reservoir? There may be something that is intermittently getting between a piston seal and the cylinder wall, allowing backflow of fluid. If this is the case, you have to take the MC out of the car, take it apart, clean the components, then put back together. Probably best to throw a rebuild kit into it if you're going to do this.
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Old Sep 1, 2010, 10:37 PM   #12
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how much does the MC rebuild kit go for?
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Old Sep 2, 2010, 07:35 AM   #13
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Best to just call the auto parts store on that one. Sometimes rebuild kits are more expensive than rebuilds after you give your core back. I know it sounds weird, but you just gotta call and check both ways.

Another option, check the board for someone parting out their car and nab theirs.
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Old Sep 3, 2010, 05:34 AM   #14
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Check the insides of all your wheels to make sure there is no fluid on them .Also check inside car on floor mat under brake pedal to look for any kind of leak.also check under hood by master cylinder to look for wetness.Keep an eye on the level of brake fluid in resorvoir as you drive your car to see if it drops.Mark the outside with a marker and keep checking to determine if its going somewhere.If not sounds like the porportional valve.
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Old Sep 3, 2010, 05:34 AM
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