68 Deville posi rear end swap?
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, 68 Deville posi rear end swap? in Past Cadillac Vehicle Discussion; The car: '68 Sedan Deville with Holley Street Avenger carb, dual flowmasters, ignition/wires, edlebrock air filter, B&M shift kit. Primarily ...
  1. #1
    SERvo is offline Cadillac Owners Member
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    68 Deville posi rear end swap?

    The car: '68 Sedan Deville with Holley Street Avenger carb, dual flowmasters, ignition/wires, edlebrock air filter, B&M shift kit. Primarily used as a weekend hotrod for cruises and general mayhem around Las Vegas.

    The problem: I'm looking for a posi diff or whole rear end to swap into this car. I've Googled my brains out with terms like "C-body posi" "14-bolt posi", etc, etc. All I get is truck posi info from 4x4 sites. An Eaton posi is waaaay out of my price range, and I'm pretty sure they don't even make one for this particular 14 bolt rear anyway. Seems there are two 14 bolt units made, the ever available truck/SUV one and my ancient pumpkin. My current burnout situation is embarrassing, resulting in one track from the passenger side tire so I'm assuming I don't have the optional Controlled Differential offered on this year Deville. Headwork, modded intake, cam, headers are in the works, so I'd like to put power to two wheels, ya know?

    So.....
    Can anyone tell me if there is a 70s, 80s, or 90s car that I can find at the salvage yard with a GM posi rear end (and disc brakes if possible!) that will bolt in to the '68 frame? As long as it bolts up to the arms, I can live with gear ratio changes if they're not too sluggish.

    Any info my dear gear gurus?

    I appreciate any help you guys can provide. If you need numbers from anywhere on my sled to better inform you of what it's equipped with, let me know.

    Thanks,
    Ryan in Sin City

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    JTraik is offline Cadillac Owners Enthusiast
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    Re: 68 Deville posi rear end swap?

    This is a topic that I have been very interested in myself. My suggestion would be to go to the cadillaclasalleclub.org forum and ask the guys there. I have heard there is like one or two people that is even capable of working on these particular rear-ends mainly because the ring gear is riveted onto the carrier, making it almost impossible to service/rebuild.

    Your real concern should be to go and find a posi carrier that will fit in the housing... after-market preferably (one that will be serviceable in the future) However if you really desire to do so, you can hit up the junkyards and look for the little posi tag that goes around the fill hole on the pumpkin!

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    jayoldschool's Avatar
    jayoldschool is offline GM RWD V8 addict
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    Re: 68 Deville posi rear end swap?

    Your best bet would be one of the disc rear ends out of a 94-96 Impala SS or Caprice 9C1 (police package). There is a SLIGHT difference in width. To get this under your car may require cutting off the mounts and redoing them to work with your trailing arms. Measure the width of your rear, then get over to the impalassforum.com to see if it is close to yours. Note that if you want to get one with factory posi, look for option G80. It was standard in the SS, optional in the 9C1. Even if you get a core, gearsets and posis are readily available and affordable.

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    SERvo is offline Cadillac Owners Member
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    Re: 68 Deville posi rear end swap?

    Thanks for the responses. I'll do some measuring and see what I come up with. It's not a priority on my project list yet, but I'll be sure to come back and report what I find out as I work on it. I've had such a hard time finding info, I'd like to save someone else the trouble.
    You rock.

    If anyone else has info, please share.
    R

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    JTraik is offline Cadillac Owners Enthusiast
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    Re: 68 Deville posi rear end swap?

    Quote Originally Posted by jayoldschool View Post
    Your best bet would be one of the disc rear ends out of a 94-96 Impala SS or Caprice 9C1 (police package). There is a SLIGHT difference in width. To get this under your car may require cutting off the mounts and redoing them to work with your trailing arms. Measure the width of your rear, then get over to the impalassforum.com to see if it is close to yours. Note that if you want to get one with factory posi, look for option G80. It was standard in the SS, optional in the 9C1. Even if you get a core, gearsets and posis are readily available and affordable.
    That rearend is a childs toy compared to the stock Cadillac one. The stock rear-end is suitable for a dumptruck, the stout third-member design... thick axle shafts and actual press-on bearings... yeah press on bearings, not the cheap roller type. Also remember the stock Cadillac rear-end has an offset pinion shaft to proper line up with the tranny tailshaft.
    The Ape Man and The Ape Man like this.

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    jayoldschool is offline GM RWD V8 addict
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    Re: 68 Deville posi rear end swap?

    I just remembered: check with Powertrax to see if they have an application that will work! You would get to keep your stock rear, your non-posi housing, and you wouldn't have to rebuild/reshim anything. If they have something, this would be by far the easiest option.

    I have no doubt that the Cad housing is stouter than the 8.5 "corporate" rear in the B/D bodies. That 8.5 is plenty strong, however, and has no problem standing up to hp/torque numbers over 400 at the wheels in a 4500-5000lb car. You've got a 93 - when is the last time you heard of someone grenading the 8.5?

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    JTraik is offline Cadillac Owners Enthusiast
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    Re: 68 Deville posi rear end swap?

    Quote Originally Posted by jayoldschool View Post
    I have no doubt that the Cad housing is stouter than the 8.5 "corporate" rear in the B/D bodies. That 8.5 is plenty strong, however, and has no problem standing up to hp/torque numbers over 400 at the wheels in a 4500-5000lb car. You've got a 93 - when is the last time you heard of someone grenading the 8.5?
    I have had my 8.5" apart several times and used to have the 3.42 posi setup. Just comparing apples to apples here... that Cadillac rear-end is a brick shithouse compared to my 8.5" And again you have an issue with a straight drive-line.

    My question is... will the 12 bolt Pontiac rear-ends that are found in Caddies a couple years after '68... will those swap into a '68? I personally don't see why they wouldn't, and I am pretty sure those rear-ends are quite serviceable??? Problem there is... after 69' they stopped using these high quality rear-ends and went to the non-thirdmember style housing with the roller bearing setup with the axle shaft as the inner race .

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    Mechanicville is offline Cadillac Owners Member
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    Re: 68 Deville posi rear end swap?

    I'm wondering what happened here... I'm measuring my 68 rear in the morning and gonna hit my local salvage yards for a posi unit..

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    SERvo is offline Cadillac Owners Member
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    Re: 68 Deville posi rear end swap?

    I never pursued the idea any further than the info in this thread, honestly. We had a kid, car project slowed down and I've since sold the car and moved. I miss that '68.

    Even though I'm not involved with this forum much anymore, I'd encourage this thread to continue with your posts to see if there is a solution. Best of luck!
    ryan

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 68 Deville posi rear end swap?

    There was a guy on ebay last year selling ring and pinions and posi units for just about any GM vehicle. He even had a posi for those 8.75 rear axles.

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    caddywarewood is offline Cadillac Owners Member
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    Re: 68 Deville posi rear end swap?

    im kinda of an cadillac newby but are the 1977 deville come stock with an posi rear end

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    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: 68 Deville posi rear end swap?

    Quote Originally Posted by caddywarewood View Post
    im kinda of an cadillac newby but are the 1977 deville come stock with an posi rear end
    You could get a 77 with a posi but it was optional.

    Axle for a 68 would be the 3.15:1 posi found up to 1976. Post 76 things got a whole lot smaller. IO've only seen one 3.15 posi in the flesh. Unfortunately for me it belonged to the guy in the next lane at Raceway Park in Englishtown.

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    caddywarewood is offline Cadillac Owners Member
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    Re: 68 Deville posi rear end swap?

    wow so my caddy is a rear because it has the posi rear end on it

  15. #14
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: 68 Deville posi rear end swap?

    Quote Originally Posted by caddywarewood View Post
    wow so my caddy is a rear because it has the posi rear end on it
    Not really. Just the option is hard to find.

  16. #15
    caddywarewood is offline Cadillac Owners Member
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    Re: 68 Deville posi rear end swap?

    what is the benefits of positraction rear end

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