Your rear has a Limited Slif Differential. Trust me when I say this is fine for most people.

With 4.10s, you'll be able to break it loose a little easier but it's not gonna happen unless your mashing the throttle and alot of it depends on what kind of rubber your wheels are wearing.

Overdrive works like this. It's only on when you're NOT mashing the throttle and you're traveling at a decent speed (like say 55). It's a quieter and more fuel efficient gear. When you go to pass someone and you press the pedal, it may usually downshift and you'll hear the engine sound louder (more RPMs). It'll return to O/D as soon as you're driving regularly.

Now, how 4.10s will affect your car is simple, it'll budge more in any gear, at a given RPM. This is good however it also shortens the range of each gear. This is why people are recommending much moves than 4.10s. It will give you a distinct seat-of-the-pants improvement and it will speed your car up with very few trade-offs.

Gas milage will only suffer on long trips where sustained driving in O/D at say, 70 mph will utilize slightly more gas. This is because your engine is turning at a higher RPM in every gear. This tradeoff is mild and acceptable to the majority of performance minded enthusiests. Ford wanted to list better highway miles-per-gallon when then advertised and sold the car which is probably the only reason they choose such a small gear in the first place. Gears "Wake the car up"

 

You can leave the OD on as you will finish the 1/4 mile still in 3rd anyways and you will not be all over when you hit it unless you are stopped with the steering wheel turned, then you will slide the car sideways. It's limited slip so when you take a corner the inner wheel turns slower than the outer wheel so the rear stays stable and does not cause tire problems. I found it really made my automatic which is also a heavy convertible much more driveable and responsive. It will climb hills and stay in OD instead of downsifting. The tuner is great also and the deal I got also comes with new bearings for the carrier and more, just get 3 quarts of good synthetic gear oil and you will need a pinion shim kit(about $10.) and the carrier shim kit was $20. Mark

 

Ok so the only time I turn my O/D off is when I am full throttle correct? otherwise I just leave it on?

 

is this a good package with the gears and tuner??

http://www.rpmoutlet.com/newv8m.htm

 

oh **** not another gear thread [sm=headbang.gif]

 

4.56!! I had a set of 4.56 gears in a saleen. quite fun

 

Get 4.10's and a tuner....

 

That's the kit I just got. I chose the Predator tuner on their advice as they said it was more user friendly and from another thread I read it seems a fellow is having trouble with his SCT tuner.
All you will need with that kit is pinion shims and carrier bearing shim kit if you change the bearings which are supplied with the install kit and of course 2 quarts of good synthetic gear oil and a bottle or 2 of posi additive. I used MOBIL 1 75W-90 but now Ford recommends 75W-140 weight oil which I would have gotten. There is a lot of negative material you can read about Motive gears but it's really the installer's set-up that counts. All I get a is a slight whine, more like a whistle, between 40 & 50 MPH.
If you have trouble in your area finding the pinion shim or carrier shim kit I can get both for you around $30. If you are already happy with the Superchips tune you have you could sell the tuner you get in the package and get the gearset for free though you may need the tuner for some other things which would require that you remove the superchips chip first. I set my auto's shifts for quicker, harder shifting and changed some shift points. A '99-'04 GT isn't going to be a really quick car. However the gears enhanced the driveability of mine. I still have an exhaust to install and will note what the outcome of that is when done. Feel free to PM me with any questions I may help answer. mark

 

Do the supporting suspension modifications and a good tire setup, go with 4.10's.

 

No offense but don't read it if bothers you so much! Some may gain from this thread. Oh and btw before you mention the dreaded search feature have you tried it lately? It seems to be acting up like a middle school’er reaching puberty! 05SDI