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Thread: Rear End change

  1. #1
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    Default Rear End change

    I have an 80 vette with the alunminum rear end which is on the weak side according to the folks that know. I'd like to put a cast iron rear end in there. Are there years of earlier vettes that will just swap in there with no real hassle?

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    Member GTR1999's Avatar
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    Those dana's have aluminum bearing caps that often fail with the stock 200 hp engines. Abusing them is crap shoot, although many have put 400 hp to them without breaking them. They were not good units.

    The iron units are better and can be built much better. They weight 100 lbs with axles and cover. They will bolt to the stock 80-82 cover so the rear mount is not an issue. The front bracket, 1/2 shafts, rods all have to come from a 63-79 with the later front brackets preferred. The iron units all had their weak areas, the 63-68 had weak posi's the 69-79 posi case are better. The 71-79's use 10-17 spiders, better then the 10-18 used in the 65-70. Forget the 63-64's posi are total junk. Look for a 71-79 308 diff if you go in that direction, you will probably have to have the DS shortened as well. This is a pretty straight forward mod but it will cost a lot to do it right. If going in this direction I sure wouldn't use a stock unit or stock rebuilt one. Build a custom one that will last.
    A 12 bolt won't work with the 80-82 cover if that is another consideration. Then you'll have to use a HD cover and some mount fabricating. The cost of a lot of this work can easily run more then the value of many 80-82 vettes. Something to think about.
    I've built custom diffs just for this mod and they work out well.
    If I can help let me know. Good Luck with the job.
    Gary
    GTR1999

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    Member GTR1999's Avatar
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    Another thought as well, I don't touch those units as I don't like them but my friend rebuilds the 80-82 and will fit a steel cap to them. These are the best built 80-82 around, there's no way you're going to break the steel cap. The posi still isn't as strong as the iron.

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    Member Rebelrob's Avatar
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    I have a posi differential from a 73. Are you saying that will bolt in no problem on the 82, but i have to use different half shafts and other parts to make it fit?

    Quote Originally Posted by GTR1999 View Post
    Another thought as well, I don't touch those units as I don't like them but my friend rebuilds the 80-82 and will fit a steel cap to them. These are the best built 80-82 around, there's no way you're going to break the steel cap. The posi still isn't as strong as the iron.

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    To do the swap you need to :
    Change halfshafts
    Change spindle flanges
    Change strut rods
    Change strut rod bracket
    Halfshaft u-bolts
    Front diff mount bracket
    Driveshaft
    The cast iron diff bolts directly to the batwing.
    The 80-82 Dana diffs have several flaws in their design. The caps are made out of aluminum and have a large notch for the bolt. This is where they always crack. Also the left cap supports all the side loading from the carrier in comparison to the iron diff and the 84-up Danas that use the case for support. Lastly, the mounting pads for the caps are not machined. They are left "as cast".
    My steel cap has additional material and is machined to use the case for support. All the Danas are different inside because of the sand casting and bearing support. This is why you cannot buy just a replacement cap. The cap and case are machined together.
    In comparison the Dana and iron diff are nearly equal in size and strength on internal componets. The Dana uses a smaller rear pinion bearing and a different design clutchpack. The iron diff will always be stronger than an aluminum diff. 400 HP should not be a problem with the modified Dana. I wouldn't trust the case integrity for high hp applications.
    Mike
    Tracdogg2


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    Dang, nothing is ever eash is it... So much are the same body style and swappable parts from 68-82. That was the overview I was given.
    Not sure if you have read, but I am planning on installing a 454. I will have to change the compression to make it streetable. I will stay with the same differential then, but plan on putting maybe some 3:35 gears or similar.
    You talk about modified, not sure what that means. If you stick new gears into it and put it all back together.
    Thanks for the info. This is good to know.

    R


    Quote Originally Posted by Stingray6974 View Post
    To do the swap you need to :
    Change halfshafts
    Change spindle flanges
    Change strut rods
    Change strut rod bracket
    Halfshaft u-bolts
    Front diff mount bracket
    Driveshaft
    The cast iron diff bolts directly to the batwing.
    The 80-82 Dana diffs have several flaws in their design. The caps are made out of aluminum and have a large notch for the bolt. This is where they always crack. Also the left cap supports all the side loading from the carrier in comparison to the iron diff and the 84-up Danas that use the case for support. Lastly, the mounting pads for the caps are not machined. They are left "as cast".
    My steel cap has additional material and is machined to use the case for support. All the Danas are different inside because of the sand casting and bearing support. This is why you cannot buy just a replacement cap. The cap and case are machined together.
    In comparison the Dana and iron diff are nearly equal in size and strength on internal componets. The Dana uses a smaller rear pinion bearing and a different design clutchpack. The iron diff will always be stronger than an aluminum diff. 400 HP should not be a problem with the modified Dana. I wouldn't trust the case integrity for high hp applications.
    Mike
    Tracdogg2


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    Member GTR1999's Avatar
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    If you stay with the 82 diff have Mike build it with a steel cap. Sounds like you're near each other so that should work out well.
    Gary
    GTR1999

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    Mike?? tell me who and where he is and I will contact him.
    I would like to discuss this in more detail.

    Thanks,
    R


    Quote Originally Posted by GTR1999 View Post
    If you stay with the 82 diff have Mike build it with a steel cap. Sounds like you're near each other so that should work out well.

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    Member Stingray6974's Avatar
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    Quote Originally Posted by Rebelrob View Post
    Mike?? tell me who and where he is and I will contact him.
    I would like to discuss this in more detail.

    Thanks,
    R
    Give me a call 214-717-8379 Mike

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    Quote Originally Posted by try2pas View Post
    I have an 80 vette with the alunminum rear end which is on the weak side according to the folks that know.
    I've never had a problem with my rear end. And I've definitely given it all the ZZ4 has to offer. Drag strips, top speed runs, whatever...have never fazed it.

  11. #11
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    What are the specs of a zz4?? size, hp, torque, etc?
    How many miles are on your rearend? do you have stock gears?


    Quote Originally Posted by Evolution1980 View Post
    I've never had a problem with my rear end. And I've definitely given it all the ZZ4 has to offer. Drag strips, top speed runs, whatever...have never fazed it.

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    Quote Originally Posted by Rebelrob View Post
    What are the specs of a zz4?? size, hp, torque, etc?
    How many miles are on your rearend? do you have stock gears?
    350ci, 355HP @ 5250rpm, 405ft/lb @ 3500rpm
    Over 100K on the rear end
    Stock gears.

    Engine Info

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    I see , wow, good deal, lots of miles back there.

    What about your 700r4, Ive got the stock one in mine. Have you rebuilt this one or had any problems with it?
    I don't think the 80's came with a 700r4

    My concern is I am planning to install a 454. So I am concerned about the torque and HP this will produce to the stock drive train.

    thx,
    R

    Quote Originally Posted by Evolution1980 View Post
    350ci, 355HP @ 5250rpm, 405ft/lb @ 3500rpm
    Over 100K on the rear end
    Stock gears.

    Engine Info

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    Quote Originally Posted by Rebelrob View Post
    What about your 700r4, Ive got the stock one in mine. Have you rebuilt this one or had any problems with it?
    I don't think the 80's came with a 700r4

    My concern is I am planning to install a 454. So I am concerned about the torque and HP this will produce to the stock drive train.
    I bought my 700R4 from BowTie Overdrives. At the time, it was "Level 3" transmission. I blew up the front pump a year or two ago. Supposedly this can only happen from improper installation in the car. I doubt it, as I'm convinced that the work I had done on the car was perfect. I think it was just a faulty pump to begin with. Other than that, no problems. However, the R&R to fix the front pump was $$$$. If I had to do it all over again, I'd scrap the automatic altogether and do a conversion to a 5 spd manual.
    I was expecting a lot more "oomph" going from the TH350 to the beefed up 700R4. (Taller first gear). I didn't really notice it. I've also heard the the 700R4 trans has some of the highest parasitic losses of all the various transmissions available. I can't confirm that, but it didn't make me happy to hear if it is true. As for overall strength, if you are going to a beefy 454, and want to stay with an auto, I'd consider a TH400 instead. Or a manual. Last on the list would be a stout 700R4.

    (I think the 700R4 made their Corvette appearance in 1982)

    If you are going the 454ci route, you're gonna need to do more than just the trans. Common things to replace/upgrade is the radiator, front suspension (heavier springs), and possibly upgrade your half-shafts / u-joints. With respect to the drivetrain and significant torque increases, just keep in mind that when you beef something up, the next weakest link will be the next part to fail.

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    Good to know. Thanks for the info.
    I think you were the one telling me also about your exhaust.
    I wish I could see a picture of somebodys 80-82 underneath with true dual exhaust.
    Thx,
    R

    Quote Originally Posted by Evolution1980 View Post
    I bought my 700R4 from BowTie Overdrives. At the time, it was "Level 3" transmission. I blew up the front pump a year or two ago. Supposedly this can only happen from improper installation in the car. I doubt it, as I'm convinced that the work I had done on the car was perfect. I think it was just a faulty pump to begin with. Other than that, no problems. However, the R&R to fix the front pump was $$$$. If I had to do it all over again, I'd scrap the automatic altogether and do a conversion to a 5 spd manual.
    I was expecting a lot more "oomph" going from the TH350 to the beefed up 700R4. (Taller first gear). I didn't really notice it. I've also heard the the 700R4 trans has some of the highest parasitic losses of all the various transmissions available. I can't confirm that, but it didn't make me happy to hear if it is true. As for overall strength, if you are going to a beefy 454, and want to stay with an auto, I'd consider a TH400 instead. Or a manual. Last on the list would be a stout 700R4.

    (I think the 700R4 made their Corvette appearance in 1982)

    If you are going the 454ci route, you're gonna need to do more than just the trans. Common things to replace/upgrade is the radiator, front suspension (heavier springs), and possibly upgrade your half-shafts / u-joints. With respect to the drivetrain and significant torque increases, just keep in mind that when you beef something up, the next weakest link will be the next part to fail.

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