I have an open differential with the 3.15 gears and was wondering what was the best way to go locked. Have been looking at the Eaton Powertrax or the Auburn mini spools or would it be better to swap out the whole center section for a limited slip? I really don't want to swap out gear ratios right now due to getting great gas mileage right now, but I want to be able to get more traction when I need it for towing. This is on a 2-wheel drive '09 truck. Also how do I find out which rear end I have, the 28 spline or the 31 spline?

 

I guess I have no-takers for advice on this one.

 

If you are only wanting more traction for towing on roads get a limited slip unit. lockers aren't good for high traction areas because they dont let your tires spin at different rates when turning. This will significantly shorten your rear tire life span if you drive on paved roads most of the time(which I assume you do). Look into swapping out a whole axle from a truck that already has LS and the same gear ratio as you (not sure if 3.15 and LS was a factory option, but you can research that). then you can sell your stock axle. This is probably the cheapest route and less labor intensive than setting up gears.

 

A little more $$ but look into an Eaton/Detroit Tru-Trac unit. Install it and forget it..no clutches and no anti-slip juice ever!

 

Concur with "Woods-Rider". I used to have a 86 FS Bronco that was equipped with an "Air-Locker" unit, but you really needed to be on dirt, sand or ice for it not to jam up in the case. Although it was called an "Air-Locker" it used engine vacuum to activate the locking mechanisms totally. I used to call it "Tonka-Truck 4x4 Mode".
Essentially it was removed because it would cause too many problems in mixed use driving. (For me).

 

Woods-Rider, do you know if the rear axles are much different from the '04-'08 compared to the '09s? Probably not gonna be able to find a LS with my 3.15 ring gears as Ford didn't make them, may have to go up to a 3.55. That seems to be the only axles around here I can find.

Sam1947, will try to look at Eatons site for the Tru-tracs.

 

I would suggest either a standard Ford limited slip (if you go cheaper), or a true trac gear driven limited slip for what you are doing.
A ford limited slip is going to be clutch based. It will wear out over time but they hold up okay in normal driving and will increase traction.
A true trac is gear driven and won't wear out. It will be capable of sending more power to the tire on slippery terrain. Any limited slip will be (nearly) useless if one tire is completely off the ground.

The ring & pinion are separate from the carrier. You can buy a limited slip or locking carrier and install it with whatever gears you have in there right now.

There are different types of lockers out there. A selectable (arb) is something that you only engage when you absolutely need, like you are sitting somewhere with one tire spinning and the other not. It is disengaged normally during driving.
A spool locks both ends together and will not differentiate speeds in turns, you don't want that unless you are installing it in a strictly off road truck generally.
The other is an "automatic" locker, like a Detroit. It is locked when you are on the throttle generally, but will differentiate speeds during a turn if you are coasting or light on the throttle. I have a detroit in my F150, it's clunky, can be loud, it's harder on tires, I love it. lol. But the average person would hate it.