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Old 10-14-2009, 12:19 AM   #1 (permalink)
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Final drive ratio changes?

Can you alter the rear gearing on these cars? I'm used to being able to pop open the pumpkin and swap in a ring & pinion - these things look a bit more complex....
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Old 10-14-2009, 12:29 AM   #2 (permalink)
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rear diff

Well, as I understand it, this is the same rear diff as in the CTS, so there might a couple of different ratios available. The RL and 2.4 have different ratios.

Its not setup like a 10 bolt chevy, obviously, here's a picture of a 2.4 rear.


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Old 10-14-2009, 12:38 AM   #3 (permalink)
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Interesting. Given that I've seen 1,000HP conversion kits out there I assume these are fairly sturdy - more that I would have imagined from visual inspection. I'd say the same for the stock axle shafts.
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Old 10-14-2009, 08:21 AM   #4 (permalink)
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The Getrag differential is used in a couple other makes and models from GM. So your choices are 3.23, 3.42, 3.73(Redline/GXP), or 3.91 (stock base).

Otherwise you can play with tire aspect ratio.

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Last edited by NormSky; 11-22-2009 at 10:42 AM.
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Old 10-14-2009, 08:47 AM   #5 (permalink)
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Can we tune to compensate for tire size changes?
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Old 10-26-2009, 02:08 PM   #6 (permalink)
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Is there a 4.10 available,maybe from CTS?
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Old 10-26-2009, 02:13 PM   #7 (permalink)
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Is there a 4.10 available,maybe from CTS?
GOOD GRIEF, isn't first gear short enough already?
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Old 10-26-2009, 02:22 PM   #8 (permalink)
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Quote:
MEGAS : Is there a 4.10 available,maybe from CTS?
Getrag lists 3.91 as the shortest ratio.
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Old 10-26-2009, 07:08 PM   #9 (permalink)
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GOOD GRIEF, isn't first gear short enough already?
I'd have thought so!

No point rowing around when you have massive torque like these cars have.

I use a 4.55 on the race car (25" diameter tires) and have even run 5.125, which gives you a top speed of about 90 MPH but you get there VERY quickly - good for hill climbs, but for the street you really want something a lot more relaxed.

The GXP has great pull low down plus decent top end. I would certainly change some of the transmission gear ratios, but not the diff.
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Old 10-26-2009, 08:08 PM   #10 (permalink)
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I would think 3.91 would be a great compromise for the street between acceleration, top speed, and mileage. I ran 4.10's on my Mustang w/26" tires and ended up dropping back to 3.73 - 3.91 would have been great. (after I turbo'd I went back to 3.56)
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Old 10-27-2009, 02:22 AM   #11 (permalink)
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IMHO when 4th gear nets a top speed of approx. 138 miles ,then it's too long,not to mention 5th gear.
I think 4th and 5th are long but the only way to close gaps is FGR.

3.91?Can you pinpoint me a link for this?
Thank you.
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Old 10-27-2009, 04:43 AM   #12 (permalink)
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I would say 4th gear is way too long for my tastes, I would love to loose most of the top speed but to eliminate that lazy ration of 4th gear.
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Old 10-27-2009, 11:06 AM   #13 (permalink)
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MEGAS : .... 3.91?Can you pinpoint me a link for this? .....
I went to the Getrag website to find a link, and discovered that the 645 Drive Axle is no longer listed as a product.

There is a 650, which is now listed as fitting the Cadillac SRX and STS:

GETRAG Corporate Group - 650
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Old 10-27-2009, 11:46 AM   #14 (permalink)
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Quote:
Originally Posted by NormSky View Post
The Getrag differential is used in a couple other makes and models from GM. So your choices are 3.23, 3.42, 3.73(Redline/GXP), or 3.73(stock base).

Otherwise you can play with tire aspect ratio.

Norm
I think you made a typo, this was from another posting here and confirmed -

====

Second, the 2.0 final drive ratio is 3.73, vs. 3.91 on the 2.4.

-=====

I have both '07 rears on my cars and have not had time to inspect them for various mounting differences, but considering leaving the 3.91. Another poster on that thread indicated the BCM can be programmed for the different rear end ratio w/o issue, but it does need to be done if swapping things around.

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Old 10-28-2009, 04:31 AM   #15 (permalink)
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Originally Posted by JRinKY View Post
I went to the Getrag website to find a link, and discovered that the 645 Drive Axle is no longer listed as a product.

There is a 650, which is now listed as fitting the Cadillac SRX and STS:

GETRAG Corporate Group - 650

GETRAG Corporate Group - 645

it does exist
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