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Old 03-04-2011, 03:03 PM   #1
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Brake booster leak

99 TJ 2.5 liter , 33" MTs 4"lift 153k miles

I just noticed while under the hood that there is grease leaking from where the booster and master cylinder connect. Also grease all around booster from the bottom

What needs to be replaced? Both items ?, a seal? Is it brake fluid leaking?
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Old 03-04-2011, 10:29 PM   #2
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Is it grease or brake fluid?

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Old 03-04-2011, 11:28 PM   #3
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Brake fluid will wash off with plain water, grease and oil won't.
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Old 03-05-2011, 09:24 AM   #4
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Originally Posted by 01TJSE
Is it grease or brake fluid?
It's thick looking like grease , but i think its because its full of dirt stuck on it. I guess I'll clean it off and then see if anything leaks out.
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Old 03-05-2011, 03:29 PM   #5
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Yes, ur master cylinder is leaking and u need a new booster and master cylinder. Some would say u can drain the booster and replace / rebuild the master cylinder. I would advise against this because, let's face it, it's ur brakes. I prefer to error on the side of caution in this situation.
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Old 03-05-2011, 08:50 PM   #6
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replace the master ,you don't need a new booster ,iv'e never seen a booster fill with brake fluid .
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Old 03-05-2011, 09:32 PM   #7
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If fluid is leaking out of the back of the master cylinder, where would it go? Think about it. Unbolt the master cylinder, take a flashlight and shine it in the hole. Lemme know if u see something floating around.
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Old 03-05-2011, 09:37 PM   #8
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Originally Posted by Nailhead432
If fluid is leaking out of the back of the master cylinder, where would it go? Think about it. Unbolt the master cylinder, take a flashlight and shine it in the hole. Lemme know if u see something floating around.
I'm no chemical engineer, but I do know that when rubber components that are not designed to come in contact with brake fluid end up exposed to it, they swell. Keep that in mind when that diaphragm inside ur booster deteriorates and u lose u power brakes, not to mention ur huge vacuum leak. Error with caution. It's ur BRAKES!
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Old 03-05-2011, 09:39 PM   #9
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If fluid is leaking out of the back of the master cylinder, where would it go? Think about it. Unbolt the master cylinder, take a flashlight and shine it in the hole. Lemme know if u see something floating around.
it go's on your floor if its leaking that bad. most of the time its a very small leak and drains out right were it is now ,inbetween the master and the booster
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Old 03-05-2011, 09:46 PM   #10
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I'm no chemical engineer, but I do know that when rubber components that are not designed to come in contact with brake fluid end up exposed to it, they swell. Keep that in mind when that diaphragm inside ur booster deteriorates and u lose u power brakes, not to mention ur huge vacuum leak. Error with caution. It's ur BRAKES!
if the boot inside the booster is rotted out then yes it could leak into the booster but i have never seen this happen ,possible yes , likely no , but yes it could happen , as you told him yes look into the front of the booster and see if the boot rotted out and filled the booster , sorry if i was un-clear in my post
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Old 03-05-2011, 09:51 PM   #11
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How? How does brake fluid leaking out of the back of ur master cylinder, which has a flange that fits into the back of ur booster, and a seal against ur booster, going to leak onto the ground or the floorboard of ur vehicle? If u have replaced these before, u need to call ur customer up and have them come back into the shop. It's highly dangerous doing what u mentioned, and I'm just trying to advise the guy to fis his jeep the right way. I know it's not cheap, but neither are funerals.
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Old 03-05-2011, 09:57 PM   #12
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To 4x4junkie, if u choose only to replace ur master cylinder and not the booster, ur tale tale sign that ur booster is about to go out is a hissing under ur dash. U may also notice that ur pedal seems to be a little tighter. Ur vehicle will still stop fine for a while, and a slightly firmer pedal may lead u to believe that ur brakes are working better when in fact ur booster is losing it's ability to assist u with depressing ur brake pedal. Be careful on ur choices.
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Old 03-06-2011, 07:09 PM   #13
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How? How does brake fluid leaking out of the back of ur master cylinder, which has a flange that fits into the back of ur booster, and a seal against ur booster, going to leak onto the ground or the floorboard of ur vehicle? If u have replaced these before, u need to call ur customer up and have them come back into the shop. It's highly dangerous doing what u mentioned, and I'm just trying to advise the guy to fis his jeep the right way. I know it's not cheap, but neither are funerals.
OMG !
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Old 03-06-2011, 07:33 PM   #14
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How does it leak out between the MC and booster?
Good logical question -

It runs down the little channel cut into the MC made so it doesn't get back in the booster.
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Old 03-06-2011, 07:45 PM   #15
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How does it leak out between the MC and booster?
Good logical question -

It runs down the little channel cut into the MC made so it doesn't get back in the booster.
thank you !
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Old 03-07-2011, 10:24 AM   #16
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Ok guys, to make it a little clear , it's not actually dripping to ground like an engine oil leak. I just noticed a small build up of thick grease at the connection between the 2 parts. it seems like a very small leak.
I just wiped it clean and I will check for any signs of leakage in a few days.

I will definitely get both new parts if I decide to change it out.
Thanks for the info!!

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