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Old 02-26-2009, 05:07 PM   #1
tonyvlx
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Default How to tell if i have a Bad Brake Master Cylinder??

93 Toyota Camry
With the car running the brake pedal goes straight to the floor when pressed. I checked for leaks and found nothing. I checked fluid and it was a bit low, so i topped it up and with the car running again pressing the pedal, same thing. Oddly enough the fluid is at the full level. Would u guys think its the master cylinder??? Any help would be appreciated. Thanks
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Old 02-26-2009, 05:09 PM   #2
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

what does it do with the engine off?
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Old 02-26-2009, 05:23 PM   #3
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

with the engine off, the pedal still goes straight to the floor but it is much more stiffer while pressing it.
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Old 02-26-2009, 05:24 PM   #4
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

then yes it sounds like your master cyl is bad.
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Old 02-26-2009, 05:55 PM   #5
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

Make sure there's no air in the system. A scratched Banjo washer ended up costing me $35.00 in diagnostic fees; that's not bad though because all the other shops in town wanted $95 for an inspection and to bleed brakes.
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Old 02-26-2009, 08:19 PM   #6
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

The best test that I know of to determine if a master cylinder is bad, is to put plugs in each of the outlets, and step on the brake pedal. If the master cylinder is defective, the pedal will sink to the floor. If it is good, it will be rock hard. You can purchase the plugs at the auto parts store.
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Old 02-26-2009, 08:27 PM   #7
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

If this is a new problem and no leaks odds of air is slim. I would say master. If you or someone had recently had the brake hydraulic system open for any reason then you could have air in lines or a caliper and or wheel cyl.

Have someone pump the pedal and look carefully to make sure you don't have any leaks before deciding to replace the master and if you end up replacing the master then make sure you bench bead before installing, then rebleed the entire system
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Old 02-26-2009, 10:38 PM   #8
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

Start by bleeding the system (if all four will bleed) sometimes a failed master will lose half the circuit entirely. See if it does bleed, if the pedal feels normal again? A balooning brake hose can give you a bad pedal, a leaking wheel cylinder(if it has rear drums) can leak and suck in air if faulty. Look for leaks and bleed, then give us more info...
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Old 02-26-2009, 11:24 PM   #9
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

I'm wondering if the pedal started sinking all of a sudden or AFTER having brake work done.
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Old 02-27-2009, 12:08 AM   #10
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

Follow what junkman suggested, good way to to judge master cyl.
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Old 03-03-2009, 01:21 PM   #11
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

quick test. hit the pedal as in a panic stop. the pedal could be firm. now push the pedal nice and easy. it will probably go to the floor. what happens when you hit the pedal hard, the quick movement of fluid will expand the rubber cup seal in the master cylinder and prevent the fluid from by-passing, thus holding pedal firm. when pushing pedal slow, the fluid just moves past the seal cup. that was a long way of saying what has already been said, bad master cylinder.
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Old 03-03-2009, 01:34 PM   #12
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

Check the steel brake lines for rust in that vintage. I had a corolla from that area and there was no detectable leak and I even changed the MC, but the pedal was still really low. Finally took it to a shop and they said the lines were rusted in places, but we were all dumbfounded over why it didn't show. Even they had to look close. Lines replaced for $100 and good as new.
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Old 04-16-2011, 12:56 AM   #13
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

Hey everyone and an apology for puttin this thread up. Supposed to be, im planning to start a new thread in other discussions but im afraid no one will pay attention onto it. until i came to this one. I badly need some sort of help. So guys please pay attention to this. Any help will be highly appreciated. So, this morning I changed over my stock front brake lines to Goodridge Braided lines.Taking the old ones off and replacing them with the new ones was no hassle,in fact it was piss easy! Now my problem is this (sorry to re-hash and old chestnut) when I proceed to bleed the Master Cylinder I'm not getting any resistance in the lever.It just pulls straight to the bar. I been bleeding for over a hour without any success,the amount of brake fluid in the resovoir hasn't changed one bit. Could my master cylinder be damaged?
My brakes were fine yesterday,but today I can't get' em to work! This is really giving me the shits as I don't have a car my R6 is my only mode of transport,look like I'm walking to work tomorrow!!




Last edited by clarkandrew45; 05-04-2011 at 01:38 AM.
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Old 04-16-2011, 08:11 AM   #14
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

Any time you bleed a system with a used master cylinder you want to make sure you don't stroke the master cylinder through it's whole length of travel. The reason is that crap and rust builds up on the inner walls where the piston seals don't normally wipe. When you run the piston through a full stroke you drive the seals over and through this stuff and it tears them up. As Junkman stated above, you need to disconnect the lines on the master and plug 'em and test it that way. You might have just drained the prime out of the master, fill it up and while the lines are off, plug the ports with your thumbs and have a helper stroke the cylinder through a few times. It's messy but it works.
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Old 04-16-2011, 09:05 AM   #15
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

Re the OP, I would pull all 4 wheels and just make sure everything is/looks OK.
Also, I have seen a few cars with a bad wheel bearing and the caliper piston was pushing the rotor about an inch or more, and letting the pedal go to the floor.
Thanks,
Tony
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Old 11-02-2011, 02:04 PM   #16
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

does anybody know how to get the resevoir off the master cylinder
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Old 11-02-2011, 04:18 PM   #17
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Default Re: How to tell if i have a Bad Brake Master Cylinder??

Quote:
Originally Posted by TheBigDog View Post
does anybody know how to get the resevoir off the master cylinder
Usually has a screw of roll pin through a plastic tab from the reservoir, you remove it then pull the reservoir up out from the master cylinder.
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