Diff Swap 05 STS
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Cadillac STS Forum - 2005 through 2012 Discussion, Diff Swap 05 STS in Past Cadillac Vehicle Discussion; Hey everybody just looking for anybody's thought on this as I'm not 100% certain I should go for it. I ...
  1. #1
    Cadzilla8's Avatar
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    Diff Swap 05 STS

    Hey everybody just looking for anybody's thought on this as I'm not 100% certain I should go for it. I have a v8 sts rwd with 2.73 gears and no posi. I want to get the 3.42 diff with posi. Hoping to get some better traction at quick acceleration and faster acceleration. Looking for some thoughts of if I should tinker with this or not and keep why I have.

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    EChas3's Avatar
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    Re: Diff Swap 05 STS

    I'd try tires, first. You're not still on the OEM Michelins are you?

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    Subsailor613's Avatar
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    Cool Re: Diff Swap 05 STS

    You'll probably have to swap the whole 3 rd member, as I have
    read, that Cadillac, to save on weight, actually welded the ring gear
    to the carrier, to eliminate the weight of the bolts.
    This should show how much has been done to increase MPG,
    as I am sure they went through the engine also !
    The 3.42 gears WILL reduce your total MPG some,
    Guessing 3 or 4 MPG or more ?
    As I have 3.23 w/Posi, and I miss the mileage of my prior 2.7 gears.
    (Upgrade from 2005 to 2006 STS)
    With 3.23 I get 15 and 25, almost 26
    I like the knowledge of having Posi, but dearly miss the MPG.
    17 and 27 almost 28.
    You ONLY street race, once in a while, but MPG is forever.
    Some models DID have larger REAR tires, than the fronts.
    Happy Motoring

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    Cadzilla8's Avatar
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    Re: Diff Swap 05 STS

    Yeah sorta been rethinking it. The 3.42 gears would be more about a speed think and a performance upgrade. The posi would be a safety thing. True that amount of time im seriously going to demand on the car that i would need it is so minute. I do break traction every now and then in the rain or when driving like an A hole and its sorta weird when 1 wheel spins.

    ----------

    As for tires I have Michelin energy lx4 those might be the same as oem ones not sure what the car came with and I know the owner before me always replaced tires with same thing. Plenty of thread left though

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    EChas3's Avatar
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    Re: Diff Swap 05 STS

    My wife's car came with those tires. They are optimized for mileage and treadlife at the cost of road noise and traction on any pavement that isn't clean. dry & warm. With just 20,000 miles on them, I considered them dangerous.

    The car did get 25 MPG at 80 MPH on a tank of regular gas with them.

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    Re: Diff Swap 05 STS

    Where the problems come up is getting everything electronic and related to speed to work. Everything interacts from the speedometer to the EMU to the fuel mileage computer, ABS, and stability system. Good luck! The EMU is programmed serially with one long digital word that somebody that knows all the secrets can construct. According to "The Old GM Guru" this process can sometimes cost GM five to six figures.
    Don't mess with Binky Bear!


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    ddgm is offline Cadillac Owners Fanatic
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    Re: Diff Swap 05 STS

    I was thinking of going the other way. I used to drive from Ontario, Canada to Fort Myers, Florida for the winter and was looking for a 2.73
    hoping to improve MPG. I have the 3.42 with POSI. However I bought another vehicle to leave down there and am going to fly back & forth.
    I did see a complete carrier on ebay for $300 with the 2.73. I would be interested to hear the results if you decide to do this, just to satisfy my curiosity.

    Doug
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    Charles Warren's Avatar
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    Re: Diff Swap 05 STS

    How do you know what gears you have?

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    Re: Diff Swap 05 STS

    Quote Originally Posted by Charles Warren View Post
    How do you know what gears you have?
    Look at the tag on the bottom of the spare tire cover in the trunk. One of the RPO codes will denote your final drive ratio.
    Don't mess with Binky Bear!


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    Charles Warren's Avatar
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    Re: Diff Swap 05 STS

    Quote Originally Posted by dkozloski View Post
    Look at the tag on the bottom of the spare tire cover in the trunk. One of the RPO codes will denote your final drive ratio.
    i think i have 3:23 limited slip. and i know cts has open differential

  12. #11
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    Re: Diff Swap 05 STS

    Anybody know the difference between "Limited Slip and Positraction" ?
    Thanks

  13. #12
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    Re: Diff Swap 05 STS

    This might be a useful video for those that aren't experts in diffs ... the video was made by / for toyota.



    From what i've read (not sure how accurate it is) is that positraction is GM's name for limited slip differentials.
    So they are the same thing LSD = Posi.
    Compared to the 3 open differentials in the AWD models
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    Re: Diff Swap 05 STS

    but our diffs are not lockers if they were they would be louder than what they are thats a question and a guesstimation lol

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    Charles Warren's Avatar
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    Re: Diff Swap 05 STS

    forgot to add if your in park and your car is in the air/wheels off the ground and you turn 1 wheel one direction and the opposite wheel goes the opposite direction then you dont have a posi. my gtp has a posi diff and ive noticed before we put a posi diff in it it did this but after we put the diff in it made both wheels turn the same direction and locked that direction when the gears clicked
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  16. #15
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    Re: Diff Swap 05 STS

    I would LOVE to get a 2.7 rear end with Posi-Traction.
    After having a 2.7 and a 3.23, Yes, I would give up
    a little performance for gas mileage.
    Is there such a setup, and would it fit a 06 ?

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