Advice needed

[motolover]

so i am a complete newbie when it comes to rear ends, i have a 66 c10 with a 454 and a th400 tranny the only modifications to the motor are headers, edelbrock 750cfm carb and a edelbrock rpm air gap intake. i have a 12 bolt rear end that i am going to be putting in the truck but it has 2.56 gears. will that work for my application? i am also thinking about going posi but i have no idea where to start. any advice is appreciated.

[The Rocknrod]

You can use the original truck 12 bolt and put a new posi and new gears in it. I got my whole set up from Quick Performance.

[mongocanfly]

That's a awful high gear...what size tires you running..??..
Like rockn said..gears and locker can be easily changed by a competent shop...
If you could find a axle already setup, it would be your cheapest way out..building a whole axle wont be cheap

[motolover]

16 inch wheels, the other question i have is online all i can find is 3 series posi carriers, will a 3 series carrier fit into my 2 series?

[mongocanfly]

not rim size...tire size....tire dia plays into the ratios you have with a t400 and 2.56s..
heres a rpm calc..
http://www.csgnetwork.com/multirpmcalc.html
punch the numbers in down at the bottom, and itll show you rpms at whatever mph you normally run
for instance
t400 is 1:1 final
gear is 2.56
say your tire dia is 28in
at 55 mph youd be turning 1690 rpm..

yes a series 3 will work but gear ratios will have to be in the 3.08-3.90 range

[SkinnyG]

That will be using a Series 2 carrier, for which there is no limited slip available (though there might be a "lunchbox locker," I have not checked).

There are plenty of Series 3 limited slips, but you'd need to buy gears. You could go up to (but not including) 3.73 gears, but I would recommend 3.08 or 3.42 for the stock cammed (or small cammed) big block and no overdrive.

I am a huge fan of the Detroit TrueTrack differential on a street vehicle, but they start at 3.73 gears and up (Series-4 carrier). To keep the gears sensible, I'd pick a clutch type limited slip. It will be fine.

I would avoid a "locker" on a street vehicle entirely, but possibly consider it if you do a lot of drag racing or off-road. They tend to be noisy and abrupt and somewhat unpredictable. Awesome grip though. Lockers are best at "straight" or "sideways."

[motolover]

thank you for the insight, i didnt know 3.73 would not work in my rear end. i would like to drive the truck mostly street maybe a bit of highway but id still like some good bottem end torque. would you recomend 3.08s or 3.42 for that?

[Wrenchbender Ret]

You don't say what you want to do with the truck. For normal driving & highway driving 2:56 gears will work real good with a 454 engine & stock cam. Gas mileage will be respectable. Like previously mentioned tire size plays a part in it too.
George

[SkinnyG]

It is said that 3.42 is a good balance between pulling and highway if you have no overdrive, but you have a big block, so you got torque! I'd lean towards 3.08's for the mileage - the 454 will pull anything just fine.

If you ever change the cam, make sure you pick something that starts making power 1000rpm or below. Keep the rpm range low to maximize your torque and mpg.

"Snotty" cams require a snowball effect of modifications (valve springs, compression, converter, ignition tuning, carb tuning....), and then you need to cruise 3000rpm just so the cam is "working."

[LostMy65]

Rpm chart. Orange is optimum.

[SkinnyG]

Optimum for what motor? If the motor is all done by 4000rpm, cruising at 2400 is too high. If the motor doesn't start making power until 3000, there is no point cruising at 2400.

This chart is using 55mph as cruise.

Having said that, 2400 is a decent "ballpark" or "rule of thumb" cruising rpm for most V8s.....

[LostMy65]

Sorry, I don't remember, but I think it's for a basic 350.
I guess a 283 would need to be higher in the rpm's and big block could be lower. I guess the chart is good to calculate tire size to gears to rpm. (but without overdrive)

[pdxhall]

I have new axles and bearings in my 66 stock 12 bolt. If I go to a posi setup will I need to change the axles. mine are the clip type.

[SkinnyG]

The axles you have should work fine.