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Old 01-25-2012, 08:51 AM   #1
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Knocking noise

My 89 2.5 5-speed has developed a knocking noise. I only hear it inside the vehicle, loudest just in front of the gear shifter. Only does it at a idle after warm and the sound goes away if I release the clutch a little and put some resistance on the drive line.

Any clues where to start looking? Recently I have changed the oil, brake booster (which makes it idle much better and quiter, so perhaps the noise has always been there, just able to hear it now), and changed the rear diff lube.

Thanks

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Old 01-25-2012, 04:09 PM   #2
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Almost sounds like it could be related to the throwout bearing or clutch..

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Old 01-25-2012, 05:05 PM   #3
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Kinda what I was thinking but the clutch feels great.
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Old 01-25-2012, 05:15 PM   #4
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my wifes 95 YJ does the same thing. I am going to go ahead and replace clutch, throw out bearing, and p plate while im in there. Ive found over the years that once your in there you might as well replace it all. so you dont have to pull the trans twice.
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Old 01-25-2012, 06:37 PM   #5
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You might also check underneath, could be exhaust or drivetrain hitting something if you only hear it at idle and then can make it go away.....may have a broken motor mount
Could also be loose bolt on flywheel??
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/w steel half door and slider windows
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Old 01-25-2012, 06:59 PM   #6
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If the weather plays nice this weekend I plan on getting it up on jack stands to change out the front diff fluid. Will be a good time to look and see what I can find
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Old 01-27-2012, 01:02 AM   #7
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Tips from the Beas

Sounds to me like the U-joint of the front drive shaft closest to the transfer case may be bad. It can also be a rod bearing. To see if it is a rod bearing, pop the hood and have the wife, girlfriend, or even the dog put a foot on the brake, pull it into gear and give it some gas. You should hear a low end knock. May be a lifter collapse too. If the sound is comming from the engine, it could be just about anything and you will need to pull the motor and open it up. You did replace the pump and the noise quietened a bit, so I really can't say, because you actually have added more vacume to the motor and there is a little more pull on all intake and exhaust parts. I would start with a U-joint.

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Old 01-27-2012, 12:11 PM   #8
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I dont see how it could be a u-joint since it only makes the noise when I am sitting still. It is a 5 speed so there should not be any pressure on the joint when I am sitting still at a idle. As for rod knock I hope not. A engine rebuild is just not in the cards right now.
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Old 01-27-2012, 12:59 PM   #9
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Throw out bearing for sure. Depending upon how loud/bad it is, you should be alright for quite some time. Had an s-10 that did the exact same thing. Think I put 40,000 miles on it after the noise first started!
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Old 01-27-2012, 09:17 PM   #10
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Quote:
Originally Posted by jay_in_cgohio View Post
My 89 2.5 5-speed has developed a knocking noise. I only hear it inside the vehicle, loudest just in front of the gear shifter. Only does it at a idle after warm and the sound goes away if I release the clutch a little and put some resistance on the drive line.

Any clues where to start looking? Recently I have changed the oil, brake booster (which makes it idle much better and quiter, so perhaps the noise has always been there, just able to hear it now), and changed the rear diff lube.

Thanks
What was wrong with your brake booster? Mine is causing my engine to increase idle about 400rpm when I push on the brake.
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Old 01-27-2012, 09:57 PM   #11
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The diaphragm in the booster breaks causing a vacuum leak that raises the idle. When you take it off to it over and see if brake fluid comes out the master cylinder side. If it does change the master also. Brake fluid is what usually causes the diaphragm to break in the first place.
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Old 01-27-2012, 10:26 PM   #12
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For what it cost I would just change them both out. The part was 89 dollars at oreilys auto parts. I knew it was bad cause when I would press on the brake I could hear a strong air sound coming from where the booster is located. SImple test to check your is start the engine, let it run for a minute or so. Do not touch the brake during this time. Turn the engine off, again...dont touch the brake. After the engine has stopped press the brake. Did you hear air? If so chances are it is the booster. Now go to the booster and pull the check valve out. Any air or suction sound? If not then your booster is bad. Replace booster and at that price get a new master cylinder with it.

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