What exactly (I know it basicly is like a differental) will a posi do and how much will it cost me (2000, 3.0 supercab)?

What will changing my gears do and how much will this cost?

A posi rear end is gm's version of limited slip. Fords version is called a traction lock. It's a limited slip that uses clutchs to get the power to the wheel that has the traction. An open rear (probably what you have unless it's a tracloc) sends the power to the wheel that is getting less traction (takes the easy way out). It provides less tire wear and fish tailing on slick surfaces than a tracloc but sacrifices traction. Another option is to install a locker for around $400. You can get a powertrax no slip for $404 from summitracing.com or jegs.com. It can be installed easily yourself, giving you even more benefit than the tracloc and it hasn't any clutches to wear out like the tracloc, which usually wear out after about 60k or so. The powertrax or other locker will lock both rear wheels together when the traction is needed giving you the most traction possible.

As for changing gears, you can get higher or lower gears.

The lower the number the higher the gearing.
for example if you have 3.08 rear gearing vs. 4.10 rear gearing
the 3.08 will provide a higher top end, better fuel economy, engine turns less rpm's at a given speed, but, you have less get up and go.

the 4.10 will provide more get up and go, lower top end but much better low end, worse fuel economy, and the engine will turn more rpms at the same mph as the 3.08's.

I have 3.73 in mine and I swear by them. I think they have just enough bottom end but not enough to hurt gas milage like the 4.10's would. If I did more offroading I would probably opt for the 4.10's as if I did mostly highway driving I would opt for the 3.55's or something around that for better fuel economy. I do a little of both so that's why I like the 3.73's.
As for the price of swapping out rear gears I hav no clue since I haven't done it.
hope this helps.

Finally, I have seen the light... can I get an amen????? Can I get a Hallelujia???

what?

In "laymans terms", or fuktard terms, whichever you prefer... "I understand", And now I know what I need to put in my truck... Sorry I got all religious and confusing Drizzt.

Have a 98 Ranger, ext cab, 3.0L, 4spd auto, with 3.73 factory open rear. The good news is that the new Traction-Lok (Ford spelling) is great. The bad news is that I wasted a huge amount of money trying to go to 4.10 gears.

The new gears would not give a correct pattern with the marking paste no matter what was tried, period. Two excellent, experienced mechanics that teach mechanics at a university were baffled and the help from Reider Racing was the same input I got locally. Gears were outrageously noisy no matter what we did! We had Precision Gears which are a three cut Gleason. Go with Ford Motorsport if you want gears!!!

New bearings, etc.

Facts, the rear ABS sensor gives the input to the engine computer for the vehicle speed, so if you leave off the excitor ring off the carrier, you of course have no rear ABS, no speedometer, no odometer and not any info to tell the auto trans to shift!!!

Also, the computer does not know that you have changed gears. So, if you have wide open throttle, you go way past redline before shifting, which is not good at all!

So, check all of that out real well before changing gear ratio! Cost me a lot of money from wasted money, missed work with truck being on the rack, etc.

The 4.10's actually gave it improved performance all the way around, including the appearance of better mileage around town because it required less throttle to get moving! This was the experience on my Grand Marquis wagon and my F-150. In both cases I went from 3.08 to 3.55 and got better mileage around town and highway mileage stayed the same.

I have had a locker in my F-150 for a couple of years. Better than an open rear end, but the best is a Tru-Trac gear driven limited slip unit. They are in 8.8" but not 7.5" sizes. I really like them better than any other unit, period. Traction-Lok is my close second favorite.

The locker was noisy in ratcheting in all the turns, could give squirrely handing in curvy roads, and was a nightmare to get out when we replaced it. Also, it caused faster tire wear.

Hope that helps you some. Take care, ><> Ed

I think I'm just not going to mess with lockers or anything - but I might go to 3.55 or 3.73 gears.

What about trackion bars??

Traction bars will help if you're having a problem with wheel hop. On a nice level road, they sometimes will allow both wheels to spin like a limited slip will. Not all the time, just sometimes. Once you break on tire loose, the other one won't hook up with just traction bars.