hye07

Hi guys, this is actually my first time here. Anyway, I just bought and 07 v6 mustang with 20k miles. A couple of days after i bought it I noticed the speedometer was completely off. At low speeds it was off by 5 miles but at higher speeds it was off by 15 miles. I took it to a shop to see what the problem is and they told me the differential was changed to one from a gt, I think the 3.73. I know absolutely nothing about cars. Is this a good or bad thing. The guy I bought from has done absolutely nothing else to the car.

Alec

The 05-09 V6 has a 7.5" open rear with 3.31 gears (at least for autos, I think 3.55 for manuals). The open rear will only gives one wheel power and is the reason for one wheel burnouts.

The GTs have a stronger 8.8" rear and usually come with a 3.55 gear. Gears can be swapped out, like yours probably were. 4.10 and 3.73 gears will make the car pull harder and accelerate faster, but slightly affect gas mileage and top end. The 8.8" rear also comes with a t-lok, or limited slip differential(LSD) which gives power to both rear wheels

Changing gears affects the speedo. This can be changed with a handheld tuner. I'd suggest a CAI/tune package from American Muscle. Gives you great performance gains and comes with a custom tune and the handheld. Something like this: http://www.americanmuscle.com/jlt-sct-0509v6-kit.html

Bottom line, yes it's a good thing. I have a 8.8 with 3.73s in my garage, just haven't had the time to install.

jimkaray

My first question would be just to confirm that you are running a stock tire size. Assuming the shop is competent and actually checked it out then the rear swap is likely, but it could be just the gears were changed. Take a look at the rear cover and see which shape it matches.

On the left is the 7.5" and the right is the 8.8.
Next would be to look for the tag on the rear that identifies it. Unless its missing or changed its the quickest way to know what's in there.


Although the focus is on trucks theRangerStation has lots of good on the two rears. the above images are from their site.

hye07

Thanks for all the help guys, really appreciate it.
1. Yes it is running stock tires
2. It is in fact an 8.8" with 3.73 gear ratio

I wasn't planning on tuning the car or anything but now that this has been done what else can I add to it to make it better?

jimkaray

Choose a custom tune shop and order your tune & CAI package and you won't regret it. Sticky and plenty of threads on the subject to keep you busy researching while the turkey digests.

Alec

There are endless mods you can do for the car. What do you want to make "better"? Suspension? Looks? Power? Exhaust? Braking? Etc

Tuning is one of the best bang for you buck mods you can do along with a CAI.

hye07

Thank you very much for your help guys, seriously, I knew nothing about differentials and tuning when i woke up now I know exactly what to do. I am definetely getting the CAI/tune package from american muscle.