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Old 05-02-2014, 09:51 PM   #1
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Noob ALERT!

91 YJ 4.0

This past Sunday I began to hear a hiss coming from my brake pedal. After a little searching, I have determined this is most likely the brake booster, or something further up the chain like the master cylinder.

What has me confused is that since then I have also slowly begun to lose pressure in my clutch and it is getting worse each day. Yesterday I had to kill my Jeep while at a stoplight just to get it back into gear. I just replaced the clutch, master cylinder, and slave cylinder less than 3 years ago.

I am pretty sure the two systems are unrelated, but for them to happen at the same time is really odd. Can losing pressure in my brake pedal impact my clutch performance?

I think tomorrow I will try to bleed the clutch lines and hope this solves that issue. What else should I do? Any advice is welcomed!!!!

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Old 05-02-2014, 10:04 PM   #2
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Look for fluid leaks, and air leaks on the booster.....check clutch fluid level,

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Old 05-02-2014, 10:07 PM   #3
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Originally Posted by jaredbgregory View Post
91 YJ 4.0 This past Sunday I began to hear a hiss coming from my brake pedal. After a little searching, I have determined this is most likely the brake booster, or something further up the chain like the master cylinder. What has me confused is that since then I have also slowly begun to lose pressure in my clutch and it is getting worse each day. Yesterday I had to kill my Jeep while at a stoplight just to get it back into gear. I just replaced the clutch, master cylinder, and slave cylinder less than 3 years ago. I am pretty sure the two systems are unrelated, but for them to happen at the same time is really odd. Can losing pressure in my brake pedal impact my clutch performance? I think tomorrow I will try to bleed the clutch lines and hope this solves that issue. What else should I do? Any advice is welcomed!!!!
No they are not related. Check the fluid for your clutch, it could be dirty and may require a flush. As for the hissing, if say maybe you have a leak in the main vacuum line going to the booster. Haynes manual has a way to test to see if your booster is still good. Something like pump the pedal with the jeep off and hold the pedal down when it won't go anymore. Then turn the jeep on and if the pedal goes down, it's good. Also spray the vacuum line with some throttle body cleaner and listen for the rpms to change, if they do, you got a leak.
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Old 05-03-2014, 06:08 AM   #4
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Look for fluid leaks, and air leaks on the booster.....check clutch fluid level,
x2, it may be something as simple as an air pocket that needs to be bled out
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Old 05-03-2014, 10:28 AM   #5
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x2, it may be something as simple as an air pocket that needs to be bled out
I've seen a lot of pictures on these forums of there being a dust boot on the pedal as it connects to the booster. Mine doesn't seem to have one.

That's not good...is it?
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Old 05-03-2014, 10:39 AM   #6
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What you have is all good. It has enough if a boot to keep engine bay air flow out. Nothing wrong in that picture.
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Old 05-03-2014, 12:50 PM   #7
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I would bet that if your clutch is fading, then it probably has a leaking slave cylinder.

3 years for a slave really isn't that bad of a time period, I have seen them last a lot less time than that. The replacement parts that you buy today aren't even close to lasting as long as the original, unless you spend $500 or so for a centerforce clutch kit. Then you get what you pay for.

And the hissing only when you step on the brake pedal is a sign of a failing booster. If the line going to the booster was bad, it would be hissing all the time, not just when you are on the brake pedal.
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Old 05-03-2014, 07:17 PM   #8
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I would bet that if your clutch is fading, then it probably has a leaking slave cylinder. 3 years for a slave really isn't that bad of a time period, I have seen them last a lot less time than that. The replacement parts that you buy today aren't even close to lasting as long as the original, unless you spend $500 or so for a centerforce clutch kit. Then you get what you pay for. And the hissing only when you step on the brake pedal is a sign of a failing booster. If the line going to the booster was bad, it would be hissing all the time, not just when you are on the brake pedal.
Okay, so I'm attempting to bleed the clutch and I don't know what I'm supposed to be twisting to loosen the bleed screw. Is it the small nipple on the end, the larger part in the middle, or the hex on the right side of the picture.
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Old 05-03-2014, 10:52 PM   #9
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Okay, so I'm attempting to bleed the clutch and I don't know what I'm supposed to be twisting to loosen the bleed screw. Is it the small nipple on the end, the larger part in the middle, or the hex on the right side of the picture.
Just the nipple. You have to hold the rest from moving.
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Old 05-05-2014, 11:36 PM   #10
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Thanks for the help! I got the clutch bled and it resolved my issue! YEAH for free fixes!

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