C7 rear end gear change question
Thread Starter
Dig
Joined: Jan 2006
Posts: 5,460
Likes: 1,125
From: Port Saint Lucie FLORIDA & HONDURAS
C7 rear end gear change question
I have the A8. Has anyone with the A8 trans replaced the 2.41 rear with a 7 speed 3:42 gear ? Performance should be spectacular never mind adding a 3500-4000 stall. Maybe I'm wrong since I do not see any doing these. Also, if I did add a GM (bought from them) 3:42 rear.... Would that void my cars warranty?
Pro
Joined: Jan 2013
Posts: 567
Likes: 28
From: Arizona
I have the A8. Has anyone with the A8 trans replaced the 2.41 rear with a 7 speed 3:42 gear ? Performance should be spectacular never mind adding a 3500-4000 stall. Maybe I'm wrong since I do not see any doing these. Also, if I did add a GM (bought from them) 3:42 rear.... Would that void my cars warranty?
I have the AFM disabled with the Trifecta tune and found the car cruises in Touring mode at 1800 rpm at 70 mph in 7th gear and at 2200 rpm at 70 mph in Sport mode in 6th gear. I can cruise at 1400 rpm at 70 mph if I shift to M, which keeps the car in 8th gear, so long as I don't accelerate hardly at all.
Since disabling the AFM, I can't really get into the throttle more than 1/4 safely on the streets or even the freeway.
Safety Car
Joined: Jan 2006
Posts: 3,940
Likes: 42
From: shavertown Pa.
What you need to find out is will the 390 gear set work in your carrier, or find someone that builds gears for the carrier in your car.
In the past they use different carriers for the lighter geared rears and a heavier gear will not fit into the space in the carrier.
In the past they use different carriers for the lighter geared rears and a heavier gear will not fit into the space in the carrier.
Melting Slicks
Joined: Nov 2013
Posts: 2,016
Likes: 73
From: Texas
Going from a 2.41 to a 3.42 would be impressive, nearly a 30% increase in gearing. Can you say “light them up?!”
Right from the get go, when I was ordering my 2014 with the A6, I wondered why couldn’t you get the A6 Z51 gears which were 2.73? Can’t see why not, they passed emissions with the Z51 package and obviously GM considers them to be sufficiently durable. Nothing hard to do on the assembly line. Don
Right from the get go, when I was ordering my 2014 with the A6, I wondered why couldn’t you get the A6 Z51 gears which were 2.73? Can’t see why not, they passed emissions with the Z51 package and obviously GM considers them to be sufficiently durable. Nothing hard to do on the assembly line. Don
Last edited by W88fixer; Aug 10, 2015 at 04:44 PM.
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
The A8 transmission gears are already very steep, the car gets up into the power band quickly.
Your car won't make any more power with new gears, and it won't weigh any less. It will probably not be any faster at all, it'll just shift more often (and A8's already shift a lot).
Rear end gears are kinda like ignition timing in the way that if your car needs it, it'll make a HUGE difference. But if your car already has enough, adding more really won't help at all.
Your car won't make any more power with new gears, and it won't weigh any less. It will probably not be any faster at all, it'll just shift more often (and A8's already shift a lot).
Rear end gears are kinda like ignition timing in the way that if your car needs it, it'll make a HUGE difference. But if your car already has enough, adding more really won't help at all.
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Race Director
Joined: Dec 2006
Posts: 12,354
Likes: 2,892
From: Fort Worth, Texas
Curious how much power you're making or plan to make and what tire running/run?
At stock 6600 rpm limit and 28" tire, 5th gear would be limited to 126mph. Though 6th is actually 1:1, it wouldn't be optimized for 1/4. Unless you're making some serious power and then the gearing wouldn't be as beneficial I'm afraid. The starting line overall ratio with a8, 3.42 gears and 28" tire would not be much steeper than a6, 3.42 and 25.5" tire which some c6s ran iirc.
On a side note a gtr has a 4.06 first gear and 3.70 rear gear, which is only slightly less overall than a 4.56 and 3.42 combo.
At stock 6600 rpm limit and 28" tire, 5th gear would be limited to 126mph. Though 6th is actually 1:1, it wouldn't be optimized for 1/4. Unless you're making some serious power and then the gearing wouldn't be as beneficial I'm afraid. The starting line overall ratio with a8, 3.42 gears and 28" tire would not be much steeper than a6, 3.42 and 25.5" tire which some c6s ran iirc.
On a side note a gtr has a 4.06 first gear and 3.70 rear gear, which is only slightly less overall than a 4.56 and 3.42 combo.
Last edited by PRE-Z06; Aug 10, 2015 at 11:14 PM.
Race Director
Joined: Jul 2007
Posts: 10,959
Likes: 2,641
From: Texas Hill Country
Curious how much power you're making or plan to make and what tire running/run?
At stock 6600 rpm limit and 28" tire, 5th gear would be limited to 126mph. Though 6th is actually 1:1, it wouldn't be optimized for 1/4. Unless you're making some serious power and then the gearing wouldn't be as beneficial I'm afraid. The starting line overall ratio with a8, 3.42 gears and 28" tire would not be much steeper than a6, 3.42 and 25.5" tire which some c6s ran iirc.
On a side note a gtr has a 4.06 first gear and 3.70 rear gear, which is only slightly less overall than a 4.56 and 3.42 combo.
At stock 6600 rpm limit and 28" tire, 5th gear would be limited to 126mph. Though 6th is actually 1:1, it wouldn't be optimized for 1/4. Unless you're making some serious power and then the gearing wouldn't be as beneficial I'm afraid. The starting line overall ratio with a8, 3.42 gears and 28" tire would not be much steeper than a6, 3.42 and 25.5" tire which some c6s ran iirc.
On a side note a gtr has a 4.06 first gear and 3.70 rear gear, which is only slightly less overall than a 4.56 and 3.42 combo.
Race Director
Joined: Dec 2006
Posts: 12,354
Likes: 2,892
From: Fort Worth, Texas
The gtr runs an almost 28" tall tire, so it's not steeper than an a8 with 3.42...I'm aware it's heavier and awd, but I assume he's talking about maximizing track times on a sticky tire being he mentioned a higher stall converter as well and isn't concerned about hooking up on the street with street tires. Atleast I know that wasn't the case when my uncle had 4.88s in his '69 camaro lol
Melting Slicks
Joined: Nov 2014
Posts: 2,204
Likes: 17
From: Fayetteville North Carolina
St. Jude Donor '15
I just don't see how it's needed. My A8 has been 1.68 60' bone stock on stock tires, I'm sure with drag radials it would do a little better.
Also 123 I have an NX kit on my car if you have questions about the install hit me up. The NOS brand 15982 is a really nice addition.
Also 123 I have an NX kit on my car if you have questions about the install hit me up. The NOS brand 15982 is a really nice addition.
Race Director
Joined: Jul 2007
Posts: 10,959
Likes: 2,641
From: Texas Hill Country
The gtr runs an almost 28" tall tire, so it's not steeper than an a8 with 3.42...I'm aware it's heavier and awd, but I assume he's talking about maximizing track times on a sticky tire being he mentioned a higher stall converter as well and isn't concerned about hooking up on the street with street tires. Atleast I know that wasn't the case when my uncle had 4.88s in his '69 camaro lol
I run 5.83's in my cobalt and it is 3000 lbs with a 550 hp NA 327 at 8000 RPMs....
Thread Starter
Dig
Joined: Jan 2006
Posts: 5,460
Likes: 1,125
From: Port Saint Lucie FLORIDA & HONDURAS
I just don't see how it's needed. My A8 has been 1.68 60' bone stock on stock tires, I'm sure with drag radials it would do a little better.
Also 123 I have an NX kit on my car if you have questions about the install hit me up. The NOS brand 15982 is a really nice addition.
Also 123 I have an NX kit on my car if you have questions about the install hit me up. The NOS brand 15982 is a really nice addition.
