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Old 03-20-2017, 11:24 AM
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Overdrive add-on to 5-speed auto possible?

Hi all,
Sorry if this is a repeat thread/subject, but I have been unable to find it separately...
I travel weekly 600+ miles on the freeway, and I usually see 3400-3600 rpm at highway speeds (79-83MPH). Can anyone tell me if it is possible to modify the stock automatic transmission on a 2006 G35 Sedan, in order to add a 6th gear or overdrive and get RPMs down?!
Thanks!
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Old 03-20-2017, 01:18 PM
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5th gear is OD. Sounds like your car is sticking in 4th unless the last owner installed a different differential.
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Old 03-20-2017, 02:28 PM
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Originally Posted by ScraggleRock View Post
5th gear is OD. Sounds like your car is sticking in 4th unless the last owner installed a different differential.
Yeah could be sticking
OP should try throwing the gear selector into manual mode to see what gear shows up on the dash. Or try manually shifting from 0mph and count the gears to ensure when you select for 5th it really is shifting.
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Old 03-20-2017, 05:13 PM
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Really the only thing you can do is lower the final drive gearing in the rear diff. I believe the 2006 is 3.5:1 for the auto. In stock form, the 6MT crusies at lower RPMs, but that is to be expected since it has a 6th gear.

If you drive that much and like the G you may want to see if you can trade up to a G sedan with the 7AT in it. It gets better highways MPGs. I think that was available in 09 for the G sedans.
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Old 03-20-2017, 06:55 PM
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Originally Posted by BradMD_96 View Post
Yeah could be sticking
OP should try throwing the gear selector into manual mode to see what gear shows up on the dash. Or try manually shifting from 0mph and count the gears to ensure when you select for 5th it really is shifting.
Yes, it is shifting up to 5th in manual mode and stays properly in gear when I take it out of manual mode (even a drop in RPM going into 5th). Thanks for the note!
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Old 03-20-2017, 10:46 PM
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I believe the 5th gear hwy speed should be very similar to the 6mt tho (~82mph at 3krpm). Are you sure someone didn't swap to a more stout diff? There's no way Infiniti would have made cruising speeds 3600rpm.
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Old 03-21-2017, 02:23 AM
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Quote:
Originally Posted by bdflyer View Post
Hi all,
Sorry if this is a repeat thread/subject, but I have been unable to find it separately...
I travel weekly 600+ miles on the freeway, and I usually see 3400-3600 rpm at highway speeds (79-83MPH). Can anyone tell me if it is possible to modify the stock automatic transmission on a 2006 G35 Sedan, in order to add a 6th gear or overdrive and get RPMs down?!
Thanks!
Already addressed. Also you posted in the V36 (which starts with the 07 sedans) forums so please start new threads in their correct places. You'll get better help that way.

Quote:
Originally Posted by miltoda View Post
Really the only thing you can do is lower the final drive gearing in the rear diff. I believe the 2006 is 3.5:1 for the auto. In stock form, the 6MT crusies at lower RPMs, but that is to be expected since it has a 6th gear.

If you drive that much and like the G you may want to see if you can trade up to a G sedan with the 7AT in it. It gets better highways MPGs. I think that was available in 09 for the G sedans.
The 05-06 automatics were 3.3.1 and the 05-06 sedan 6MT's were 3.5.1. The second gens added the 3.7.1 but more gears so cruising RPMs were kept in check.


Quote:
Originally Posted by ScraggleRock View Post
I believe the 5th gear hwy speed should be very similar to the 6mt tho (~82mph at 3krpm). Are you sure someone didn't swap to a more stout diff? There's no way Infiniti would have made cruising speeds 3600rpm.
My 05 with the stock diff cruised at 80 running about 2800 RPMs. When I swapped in a 3.5 that raised to 3200 so I suspect you might have a 3.7 or higher or something's seriously wrong with yours if it's still stock.

My 06 GTO with the 6MT runs at 1800 RPM's in 6th gear and gets 24 MPG even with the LS2 singing away. Good times.......
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