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GTO rearend

This is a discussion on GTO rearend within the GTO forums, part of the Vehicle Specific category; Has anyone had issues with their rearend and rebuilt it themself? I ask as I need to know what kills ...

  1. #1
    Smiles for 9.5 Years cammed goat's Avatar
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    Phantom Black Metallic
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    GTO rearend

    Has anyone had issues with their rearend and rebuilt it themself? I ask as I need to know what kills the rear on these cars. I have read about GTOs running 6-900RWHP on their cars on the factory Dana/3:46 combo. But my car, with 343RWHP is eating them alive. How can this be? I know the shop I took my car to used Torco gear oil and diff additive. I have also used Lucas with CRC additive. I don't go doing crazy ass burnouts nor drive at batshit crazy speeds but there has to be an issue somewhere. Also, where does that vent from the diff run to? I know there is a box above the rearend that my vent hose goes into. Could there be something clogged in the hose/box causing pressure build up blowing the pinion and axle seals? I also run staggered 18s. I just don't get how my car is chewing up rears when others are running more RWHP and their rears are still running strong.

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    Grand Imperial Wizard Sarge's Avatar
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    I know some came from Aussie Land "out of line"...apperantly the trannie mount was not right. There is a bulletin out on it...lemme see what I can find....I do remember that particualr issue though.

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    Member Texas Jack's Avatar
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    Cyclone Grey
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    Sorry Cammed, Hopefully this forum can give you a heads up, thats' has to be so frustrating for you and others that have this problem.

  4. #4
    Smiles for 9.5 Years cammed goat's Avatar
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    It just baffles my mind how my car eats these rears like nothing. It's a mystery. Kinda like my car gets a rear and the car says "NO!!!"

  5. #5
    Smiles for 9.5 Years cammed goat's Avatar
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    Now that I think of it...last time I was under my car, I noticed some wetness around the output shaft in the trans. Could the driveshaft be cocked a little?

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    Member Texas Jack's Avatar
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    I would almost bet something is out of line in the drive train, pinion angle, trans mount like Sarge said, rear cradle..............maybe we will get to the bottom of it!!!!

  7. #7
    Smiles for 9.5 Years cammed goat's Avatar
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    Can the rear cradle be adjusted? I have looked under my car for any slotted holes and I have found nothing.

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    Member JAX04's Avatar
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    Why do i seem to recall all four bolts that hold in it are slotted?? seems like i remember that for some reason

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    Grand Imperial Wizard Sarge's Avatar
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    Yes the cradle can be aligned. And I am like Jax04 here....I remember some such crap like that....

  10. #10
    Smiles for 9.5 Years cammed goat's Avatar
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    OK. I heard back from the shop and the manager told me there was an issue with the casting causing the pinion seal leak. Was there a TSB for this issue? The manager told me, in his opinion, the rear "should have never been rebuilt". Is this flaw really noticeable? I have never cracked open a rear for these cars before.

  11. #11
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    Quote Originally Posted by cammed goat View Post
    Can the rear cradle be adjusted? I have looked under my car for any slotted holes and I have found nothing.
    The rear cradle can be adjusted and quite frequently is not centered from the factory. The front cradle bolts and the rear differential mount bolts are loosened to do this. There are 4 alignment holes, 2 in the cradle and 2 on the "chassis" where a rear cradle alignment fixture is seated to set the alignment.

    The exhaust needs to be dropped. Then the 2 front cradle bolts loosened and then the 4 rear differential mounting bolts are loosened. The cradle and the diff mount are jockeyed around until all 4 pins on the fixture are in the 4 holes in the chassis & cradle. Tighten everything back up with the fixture in place.

    While you are under there, look to see if the transmission is off center just a bit. Check the spacing of the 4 bolt heads vs the transmission casting. The spacing should be equal left to right at the front and the back. I've seen a couple that were off center from the factory. Not normally a huge issue, but it never hurts to make sure everything is straight.
    Dan Morris

  12. #12
    Smiles for 9.5 Years cammed goat's Avatar
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    Quote Originally Posted by PartsGedder View Post
    The rear cradle can be adjusted and quite frequently is not centered from the factory. The front cradle bolts and the rear differential mount bolts are loosened to do this. There are 4 alignment holes, 2 in the cradle and 2 on the "chassis" where a rear cradle alignment fixture is seated to set the alignment.

    The exhaust needs to be dropped. Then the 2 front cradle bolts loosened and then the 4 rear differential mounting bolts are loosened. The cradle and the diff mount are jockeyed around until all 4 pins on the fixture are in the 4 holes in the chassis & cradle. Tighten everything back up with the fixture in place.

    While you are under there, look to see if the transmission is off center just a bit. Check the spacing of the 4 bolt heads vs the transmission casting. The spacing should be equal left to right at the front and the back. I've seen a couple that were off center from the factory. Not normally a huge issue, but it never hurts to make sure everything is straight.
    So could I use metal punches as "guide pins" in order to make the necessary adjustments?

  13. #13
    Grand Imperial Wizard Sarge's Avatar
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    No. It is a special tool that aligns the cradle. Sold by Pedders. We have a few shops around here with them. Check with Pedders who near you has the tool.
    http://forums.peddersusa.com/showthread.php?t=449

  14. #14
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    The rear cradle fixture was a necessary tool purchase for GM/Pontiac dealers. They are at some GM dealerships. It looks like this.

    Most of them don't know they have it. Check the GM dealers around you. You will probably need to show them what they are looking for as they may have never used it or it's been tucked away.

    Cheers,
    Dan

  15. #15
    Fast Cars & Trucks 2006GTO's Avatar
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    Post 2006 GTO Rear End

    My 2006 has only 12,900 miles and they had to replace the entire rear end at the local GM dealer. It developed a whine and got louder and louder. There must be some sort of issue with these because GM had to send the dealer 2 to get 1 good one which still has a slight whine between 45 & 50 mph. They will not do a rebuild at a GM dealer only a replacement don't know why. The only good thing about it is they paid for the rear end even though it was out of warranty.

  16. #16
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    Dana/3:46 combo dana being the maker and 3:46 being the ratio?

  17. #17
    Member Texas Jack's Avatar
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    Quote Originally Posted by wilsonbri88 View Post
    Dana/3:46 combo dana being the maker and 3:46 being the ratio?
    You are correct, my friend.

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