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Thread: rear end rebuild questions

  1. #1

    rear end rebuild questions

    I am having my rear end in my 72 skylark rebuilt into 3.42, right now I have the stock one wheel wonder. I am having someone build up a core for me and then swapping them. My main concern is when I am reassembling the drive shaft into the transmission and differential how can I make sure everything stays balanced. I am also putting in new u joints. Is there anything else I need to look out for?

    Jake

  2. #2
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    If you plan to run the car at high speeds, you could have a driveshaft shop check the shaft for balance and run-out after you install the U-joints. As for installing the shaft in the car, the shaft orientation at the transmission splines or rear end yoke normally isn't critical.

    Ray
    Last edited by raycow; 03-18-2013 at 09:41 AM.

  3. #3
    Replacing the u joints shouldn't be a problem with balance, I am not going to be running the car at high speeds. The car will be a mild performance car at about 350-400 hp, three speed automatic and 3.42 rear end. Just a nice street car. I thought when you re install the drive shaft it needed to be installed in the correct way(at the transmission and at the differential) because it needs to be balanced? Everything I read says to mark rear differential and transmission for proper installment to keep balance.

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    Quote Originally Posted by J-Man View Post
    I thought when you re install the drive shaft it needed to be installed in the correct way(at the transmission and at the differential) because it needs to be balanced? Everything I read says to mark rear differential and transmission for proper installment to keep balance.
    The only time I ever ran into that problem was on a Chevy with a 2 piece shaft and 3 U-joints. Never on a 1 piece shaft.

    The driveline is not balanced as an assembly. At the factory, shafts are balanced before they are installed on the car. The only balancing the transmission gets concerns the converter and flexplate. The rear end doesn't get any balancing at all. On a 1 piece shaft there is no relationship between the shaft and trans or shaft and rear that you need to preserve.

    You may be thinking of another issue, which is alignment of the trans and rear end to get matching U-joint angles at both ends. This can definitely cause vibration if you get it wrong.

    Ray

  5. #5
    So when I take the drive shaft out and re install it the orientation of the drive shaft to the transmission and to the differential does not matter and will not have any off balance or effect on the car?
    Don't mean to be blunt or anything.

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    Quote Originally Posted by J-Man View Post
    So when I take the drive shaft out and re install it the orientation of the drive shaft to the transmission and to the differential does not matter and will not have any off balance or effect on the car?
    That's my take on it and that's what I have always done. Of course because of Murphy's Law, something WILL go wrong for you, but I just don't know what that is yet.

    Seriously though, the rear end would be easy enough to mark, because the shaft can go on only two ways. On the other hand, trying to line up a specific transmission spline would be more trouble than it is worth.

    BTW, one orientation that I DO observe is on manual transmission cars. I always mark the pressure plate before I take it off the flywheel.

    Ray

  7. #7
    Got to love Murphy's law. Well I can't mark the rear end because I am taking it completely out and putting a different one in. That is my main concern with the project. I have an automatic transmission too. But from what your laying down it shouldn't matter when I put everything back together. Right?

    Jake

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    Quote Originally Posted by J-Man View Post
    But from what your laying down it shouldn't matter when I put everything back together. Right?
    Jake
    No, it really shouldn't matter as long as you take normal precautions like cleaning the yoke and making sure the U-joint is fully seated in it. Please post again and let us know how it works out.

    Ray

  9. #9
    Thank you for your help! The plan is to start this project in a couple of months because I am finishing up my semester of college then it's a summer project. I will post once it is done. Thanks again.

    Jake

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