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Joined: Apr 2007
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I have a 67 firebird 400 with a 3.08 posi; put new axles and bearings in it about 5 years ago because one of the axle seals was leaking. I was told the axles needed replaced at the time so they are new as well. Just some background there. I have had the car for 8 years and I believe I have always heard an occasional clunk from the rear, not a loud one, but I can hear it. One shop I use thinks that means the rear needs to be rebuilt, does that mean the rear needs rebuilt?
Last edited by jdoane; 09/21/15 11:23 PM.
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Joined: Jan 2012
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Hard to tell without breaking into it and looking at the gears and other items inside. Most likely you will need to rebuild it and you might have a broken tooth on one of the gears. If it does need to get rebuilt, it will only get worse down the road. I would have someone open it up and look at everything, it cant hurt and will most likely save you a lot of pain a later on.
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Joined: Feb 2004
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My thought is there should be a clunk when you take up the small amount of slack in the drivtrain. That would normal.
I had a rear that I tried to do the crushsleave preload myself and I didn't get it right at all. That made a really loud clunk we changing from Driver to reverse or vise versa. In that case I could duplicated the noise by jacking up the back and rolling the wheels back and forth.
A sound like that can be hard to diagnose on a forum.
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Joined: Sep 2015
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Sound more like a u-joint issue. The gears are set to have a certain amount of play and should last a couple of hundred of thousand miles before adjustment or replacement is required. The 3.08 is an awesome ratio to have BTW.
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Joined: Dec 2005
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Raise rear end and support axle with stands Then put trans in neutral.
May be able to tell where problem is by turning rear wheel, but best way is to turn driveshaft back and forth by hand.
You will hear exactly where noise is coming from.
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Joined: Dec 2005
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Forgot.
Drove my 1st 68 FB for 5 years and lots of 1/4 mile runs before developed a clunk from park to reverse, etc.
Turned out to be the cross shaft for the side gears had egg shaped the posi carrier along with a crack on each side.
Last edited by Region Warrior; 09/23/15 07:27 PM.
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Thanks folks, appreciate the information
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Joined: Apr 2007
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Quick update WRT the rear end in my car; I jacked it up and turned the wheels some in park and then again in neutral. The only clunk noise I heard was towards the front of the driveshaft where it connects up to the auto transmission, which I believe is pretty normal. I'm going to start a thread on this site (see link below) later on today when I have time just to gather some more info (looks like a great shop that has done awesome work for a lot of people). Thanks again folks- http://forum.jdrace.com/index.php
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Joined: Jan 2012
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Quick update WRT the rear end in my car; I jacked it up and turned the wheels some in park and then again in neutral. The only clunk noise I heard was towards the front of the driveshaft where it connects up to the auto transmission, which I believe is pretty normal. I'm going to start a thread on this site (see link below) later on today when I have time just to gather some more info (looks like a great shop that has done awesome work for a lot of people). Thanks again folks- http://forum.jdrace.com/index.php Yes, Jim at JDRace is very knowledgeable and can help you with any rear end problem. I bought my 8.5 with posi and 30 splined axles from him and he did a great job!
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