the reason ford does not have specs for new or used is that they do not recommend used gears. the service manual is for installing new gears. my point is if you are using used gears i would want them to run in same place they were broken in at and the only way you can do that is to measure the backlash on the gear set before you remove it. i have built many gear set some used & a lot more that were new & i have never had one let loose. is a differential worth gambling? that is your choice.

 

I have no complaints about acceleration with 3.55s and the TR-3650. The gears are actually 3.545 if you take the # of ring gear teeth and divide by the # of pinion gear teeth.

 

Yao,

I'm assuming that you will be putting 3.55's in an auto? If I'm assuming correctly I don't think you are gonna see any noticable difference from the stock 3.31's to the 3.55's. I really think you should go with 3.73's. I went with Ford Racing 3.73's in my auto and noticed a good bit of difference and my milage stayed about the same. They are also gonna be safe when I get a Whipple installed here in the (hopefully near) future. I truely think you will be disappointed in 3.55's in your auto. Just my opinion. Good luck in whatever you decide tho!

 

Go with the 3:73's. I also agree that the 3:55 will not be enough of a change. People alot smarter than I am think this is the best gear choice for the auto. 4:10's are the best choice for the manual.
Scott

 

3.73 FTW !!!

Don't do 3.55 - a total waste !!

 

thanks for the feedback guys.

i guess one of the reasons is this:
http://www.mustangmonthly.com/featur...fications.html

shelby hertz edition did a 3.55 on their auto. GT

also, i want to really keep it slight subtle kick to response since i want to truly cruise at 75 mph at a decently low RPM.

lets face it, i wont be racing all the time. infact hardly at all.

also, alternative auto did some tests with auto. GT's and determined that 3.55 is probably the best choice.

http://www.alternativeauto.com/misc/...pressions.html

let me know your thoughts..

thanks!

 

Lidio is the one who told me to go with 3.73's. I did tell him I wanted a noticable difference and I also told him a supercharger was hopefully in the future. Maybe he told us different because of our different needs. Again, good luck with whatever you do.