Update on rear end ratio change to 3.42
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2004-2007 Cadillac CTS-V General Discussion Discussion, Update on rear end ratio change to 3.42 in Cadillac CTS-V Series Forum - 2004 - 2007; The 3.42 rear was installed Friday. No issues like leaks or bearing noise so far. My cost for the install ...
  1. #1
    Rey
    Rey is offline Cadillac Owners Fanatic
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    Update on rear end ratio change to 3.42

    The 3.42 rear was installed Friday. No issues like leaks or bearing noise so far. My cost for the install was $400. The gearset cost $300. Altogether, my cost for this changeover was about $1000.

    I really like the 3.42. First gear engages very smoothly, perhaps more smooth than the 3.73, if that is possible. I can engage first gear on level and slight hills with my foot off the throttle. The first 50 feet of a launch is not as hard.

    5th gear is now just right for light pedal in-town cruising. Sixth can still be engaged at less than 40 mph. 6th gear stomp at highway speeds is slower, but the motor has plenty of torque to pull 6th at any speed.

    The change is about 9-10% across the board. Before 2000 rpm = 71 mph. Now, 1750 rpm. = 72 mph. Speed confirmed by GPS.

    The 3.42 pinon has 12 teeth on a 41 tooth ring gear whereas the 3.73 pinion has 11 teeth on a 41 tooth ring gear (gear pitches are different). The 3.42 gear is definitely quieter than the 3.73 because of the increased gear contact area.

    It is too early to tell about gas mileage. I need to recalibrate the speedo/odometer, but my sense is that gas mileage will increase as it now shows 27 mpg. @ GPS speed of 65 MPH, which was what it got before the gear change at the same GPS speed.

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    c5racr1 is offline Cadillac Owners Enthusiast
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    Re: Update on rear end ratio change to 3.42

    where did you get the parts? who set it up and all? I would like to do the same thing to my spare diff?

  4. #3
    50 4Ever's Avatar
    50 4Ever is offline Cadillac Owners Connoisseur
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    Re: Update on rear end ratio change to 3.42

    Before you recalibrate the spedo check with someone that can verify where the spedo pickup is on the CTS-V. I know for a fact that a Corvette uses a wheel sensor and counts revs to determine speed so changing gears has no effect. But changing tire sizes does and must be programmed in by a hand held tuner or someone that does tunes. I would imagine the Corvette and the CTS-V are similar besause of the computers needed to control the LS6 & LS2 engines. If I was Cadillac I sure wouldn't start from scratch.

    Tust my thoughts...

    About Gas mileage: I took a trip to Texas in June in the Corvette, I reset my Average Fuel Mileage in Sacramento and when I pulled into Amarillo Texas the mileage was 32.0, and that was driving 75 - 80 most of the way. The Corvette is an LS1 manual with 3.42 gears.

  5. #4
    lunarx's Avatar
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    Re: Update on rear end ratio change to 3.42

    I like the idea of this.
    Please keep us posted.

  6. #5
    japx is offline Cadillac Owners Member
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    Re: Update on rear end ratio change to 3.42

    Folks:
    Part numbers and who performed the switch. This is the single best MOD one can do to the V. The 3.73 rear is way to high for the LS2/LS6 power curve.... My 05 GTO has a 3.46 dif. and is a far superior setup for the LS2/LS6......

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    Re: Update on rear end ratio change to 3.42

    THE best mod? C'mon......

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    Re: Update on rear end ratio change to 3.42

    Quote Originally Posted by japx View Post
    Folks:
    Part numbers and who performed the switch. This is the single best MOD one can do to the V. The 3.73 rear is way to high for the LS2/LS6 power curve.... My 05 GTO has a 3.46 dif. and is a far superior setup for the LS2/LS6......
    I seem to remember V's beating gto's..stock vs stock....so eh, best mod...HAH

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    Re: Update on rear end ratio change to 3.42

    Quote Originally Posted by japx View Post
    Folks:
    Part numbers and who performed the switch. This is the single best MOD one can do to the V....
    to make it more competitive for the GTO to race against....


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    Re: Update on rear end ratio change to 3.42

    I must be missing something here? ? ?

    We usual change the gear ratios in the rear for either better acceleration (stkshkr has 4.10) or mileage. I already get 28 MPG (Highway driving, of course) in 6th gear. I can't imagine 6th even being usable with the 3.42. I'm not the devil's advocate, just curious and obviously uninformed.
    Please educate me! !

  11. #10
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    Re: Update on rear end ratio change to 3.42

    [QUOTE=50 4Ever;1176065]Before you recalibrate the spedo check with someone that can verify where the spedo pickup is on the CTS-V. I know for a fact that a Corvette uses a wheel sensor and counts revs to determine speed so changing gears has no effect.

    the speedo pick up is at the transmission on cts-v as i just had speedo issues and that is what they replaced at the transmission. fyi.

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    Rey
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    Re: Update on rear end ratio change to 3.42

    The part mumber for a 3.42 ring and pinion gear set is #89058650, GMPD price is $280.52. List price is $473.21.
    I did the gear change at www.tpis.com. I have known owner, Myron Cottrell, for 50 years (so, I'm a geezer). I bought a spare 2006 3.73 rear end on eBay. I got it cheep because it was mis-listed into the CTS section. I shipped it to TPIS. I had the original OEM container, which really helped. This rear weighs about 73 lb, and packaging properly is a problem. Shipping cost was about $70 from Oregon to Minnesota. Last month my wife and I were in Minnesota, and I did the change over with Myron.
    Shipping these rear ends back and forth is a major problem as a typical cardboard box will not hold it well. My sense is that there is a very small market for rear end gear changes; and because the change turned out to be basically simple with no shims required, I think any competent local shop can do the job - provided they have access to a GM shop manual. The major unexpected glitch was the essential requirement to heat the case around the pinion shaft in order to gain clearances to realease the pinion. This takes a couple of propane torches and about 20 minutes.
    Why did I do the change? It is highly personal, but I felt low gear was too low for my driving style. I found myself starting often in second. Then, I thought this motor could pull a higher 6th gear, which has proven to be correct (again, my tastes).
    I should also mention that a couple of years ago I changed the dual-mass flywheel/clutch to a OEM single mass Z06 flywheel/clutch. At this point my driveline is basically Corvette.
    What is the optimum gear ratio? I think it depends on what you want. For drag racing, I haven't heard of anyone going deeper than stock. Myron Cottrell is considering a 3.23 rear in his personal CTS-V. I think he wants a first gear that will run to 60 mph at 7000 rpm. For me, the 3.42 represents a moderate change with no extremes.

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    Re: Update on rear end ratio change to 3.42

    Quote Originally Posted by 50 4Ever View Post
    Before you recalibrate the spedo check with someone that can verify where the spedo pickup is on the CTS-V. I know for a fact that a Corvette uses a wheel sensor and counts revs to determine speed so changing gears has no effect. But changing tire sizes does and must be programmed in by a hand held tuner or someone that does tunes. I would imagine the Corvette and the CTS-V are similar besause of the computers needed to control the LS6 & LS2 engines. If I was Cadillac I sure wouldn't start from scratch.

    Tust my thoughts...

    About Gas mileage: I took a trip to Texas in June in the Corvette, I reset my Average Fuel Mileage in Sacramento and when I pulled into Amarillo Texas the mileage was 32.0, and that was driving 75 - 80 most of the way. The Corvette is an LS1 manual with 3.42 gears.
    I used to get low 30s mpg in my C5 coupe too, and even got 38mph when I was bringing it back from the dealership when it was nice and tight and I was driving 65mph with no traffic. But keep in mind that the great milage isn't 100% because of the more reasonable gearing. The C5 coupe has a .28 coefficient of drag, which is *awesome*, especially at highway speeds. I don't know what the V's Cd is, but I'm sure that giant square ass is an aerodynamic drag chute, so I wouldn't be surprised if it was .34/.35 or so. The faster you go, the more of an effect your Cd has, so while keeping your rpms lower will have *some* effect, it won't have as big an effect as it does on a C5.

    -B

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    c5racr1 is offline Cadillac Owners Enthusiast
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    Re: Update on rear end ratio change to 3.42

    I think this is the way for me to go. i have a crate ls7 and the shit points are 7200, I should be right at 60 mph with this set up, but more importantly my motor made 480 lb/ft on the rear wheel dyno, and 491hp, so i don't really need the 3.73 ratio. I also believe that the 3.42 is going to be a stronger ring due to less teeth. I plan on getting the ring and pinon cryo treated before the install just fo addes insurance. I did this with a old 7.5 ten bolt f-car and never had a problem. thanks for the help. I hope the pinon cutting process is self explanitory! if not a may have to lean on you or myron for help. (i met myron while i was working for troy design tech aka wheel to wheel in the 90's while they were campagining the firebirds in imsa for pontiac).

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    Rey
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    Re: Update on rear end ratio change to 3.42

    It is interesting to note that the 3.73 and 3.42 ring gears both have 41 teeth, but pitch is different. The pinon on the 3.73 has 11 teeth, and the 3.42 has 12 teeth.

    Cutting the "extension" off the 3.42 pinion is a no brainer, as it will be readily apparent when you campare it to the 3.73 pinion. I don't think a hacksaw or even a bandsaw will cut it. We used a cut-off wheel.

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    z06bigbird is offline Cadillac Owners Connoisseur
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    Re: Update on rear end ratio change to 3.42

    Quote Originally Posted by 50 4Ever View Post
    Before you recalibrate the spedo check with someone that can verify where the spedo pickup is on the CTS-V. I know for a fact that a Corvette uses a wheel sensor and counts revs to determine speed so changing gears has no effect. But changing tire sizes does and must be programmed in by a hand held tuner or someone that does tunes. I would imagine the Corvette and the CTS-V are similar besause of the computers needed to control the LS6 & LS2 engines. If I was Cadillac I sure wouldn't start from scratch.

    Tust my thoughts...

    About Gas mileage: I took a trip to Texas in June in the Corvette, I reset my Average Fuel Mileage in Sacramento and when I pulled into Amarillo Texas the mileage was 32.0, and that was driving 75 - 80 most of the way. The Corvette is an LS1 manual with 3.42 gears.
    'Tust my tots' You're good--I like that. LOL

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