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View Full Version : What rear gears should I purchase? Please help



NYTRANSAM
04-08-2012, 12:51 PM
Hi All,

Im restoring a 68 Firebird and putting a Ls1 motor and 460 auto trans in it. Im looking into purchasing a rear, Most likely a 12 bolt. What type of rear should I look into and what gears should I run. (Stock, Moser, 9")? Im building a driver that will not see a track, I want to be able to drive at highway speed but I also would like some low end torque. some people say 4:10, others say 3:73, It is all foreign to me. What are you running? and what would satisfy my needs?
Thanks

Chevelle598bb
04-08-2012, 02:57 PM
What size rear tire are you running?

astroracer
04-08-2012, 04:45 PM
If you were running a 6 spd I would go with 4:10's The 4L60 will like the the 3:73's. I am running a set in my '02 collector edition and they run just fine at highway speeds and really improved the seat of the pants over the stock 3:42's.

JEFFTATE
04-08-2012, 05:50 PM
The 4L60 has a 3.05 1st gear ratio .
A good rule of thumb for most heavy production line / musclecars is that you want a 10 to 1 total gear multiplication in 1st gear for pulling the car of the line .
With a 3.05 first gear in the trans and 3.42 gears in the rear end , you will have a 10.431 total ratio . That's pretty good for take -off in a street car ..
I would use a 3.42 for a street car .
The 3.42 , coupled with the .70 overdrive in the 4L60 , will give you enough take off multiplication and good gas mileage and lower rpms for highway cruising .
If you want a little more umph for take-off , go to a 3.73 , then your mulitplication in 1st will be 11.37 to 1 ..

Also if you plan on using a big cam in you engine , make sure you choose a rear gear that will be in the cams comfort zone at highway speeds ..
Big cams tend to work at higher rpm ranges , and you don't want the car to lug in overdrive ...

andrewb70
04-08-2012, 05:52 PM
I vote is for something around the 3.42 range, which is actually what the stock new GTO gearing was. That being said, I think anything between a 3.3x and 3.5x will work well.

Andrew

NYTRANSAM
04-08-2012, 05:59 PM
Thanks for your advice. What spline do I need?

JEFFTATE
04-09-2012, 06:14 PM
What spline are you talking about ???
Axle splines?
Transmission output shaft splines ???

NYTRANSAM
04-09-2012, 06:33 PM
What spline are you talking about ???
Axle splines?
Transmission output shaft splines ???

Axle Spline

ProdigyCustoms
04-09-2012, 06:58 PM
You will be fine with a 30 spline C Clip rear up to 450HP. If your going to use the car like most of us and do, a lot more for cruises to the ice Cream Stand and raise a little hell at stop lights and back roads, then you will long distance interstate trips you will most likely like a 3.73 gear for the stop light to stop light fun.

If you planing on doing a lot of 200 mile trips, I would look at 3.31 to 3.50

Bolt in axles would be a nice upgrade for a little more then $100, but not required at your horsepower levels