One person said our 4.0L has a 3.29 gear and someone else said we had a 3.31 gear... which one is it??? And anyone who has a 3.73, does it work really well? Does it make a big difference rather? Thanks again as always for the help from you guys!

 

3.31 in both auto and manual.

and yes 3.73s are just awesome, i love mine (installed when i did the truetrac)

 

We have 3:31. I'm getting my 3:73's installed next week, tell you then

 

i saw 3.53 gears for sale. im like ughh that makes no sense. that would be almost no difference.

 

3.53 where?

 

3.53's would be great for forced induction.

And... the 3.73's are super keen!

 

3.73's here, been working good for me so far....though I am open minded about changing them....

..as for 3.53's.....did Ford do a change up on us..LOL.

 

I am assuming the upside is more torque from a dig... but, you run higher RPM's at higher speeds.... is this really a downside? Because if you run higher RPMs at higher speeds, you should be in the meatier part of the engines operating zone. For instance, supposed you are cruising down the highway at 65 MPH, and running at 2100 RPMs in overdrive.... now if you punch the accelerator, will you get a better response out of the 3.73 because you will be running at 2350-2400 RPMs? Or, will the response at 65 MPH be worse because the 3.73 help at low speed and hurt at high speed..

Bottom line... what's the upside for the 3.73's, at all speeds, and where are the downsides?

 

Ditto, on all points.

 

Go with the 3.73's and upgrade your diff to a t-lok (traction lock) or other posi-trak type diff. Be sure and get the bearings, seals, and shims kit, those parts are not allways in stock for the 7.5 inch diff that's in the V6 mustangs.

I have noticed dramatic improvement in drivability both street and hiway. Lots of power available even when going 70mph, punch it the little 4.0 just pulls to the max. I have the speed limiter set at 120, and it will pull hard all the way past 110mph. If you have the automatic, you can deselect over-drive manualy, then using the engine to brake/slow down from the higher speeds, saves your brakes from over heating too. With the 3.73's your final drive ration is not in the overdrive range, someone here posted the math and showed the results, just don't remember who, sorry. I'm getting about 19mpg, mix city/hiway driving with a heavy foot

I had ford do the install, specs call for backlash of .010, which is tight. I have some gear noise, but it's not as bad now, gears wearing in is slow with the synth oil ford uses, plus most of the 3.73 gear sets are made by motive for ford racing specs, I think these are more subject to gear whine. Some one here on forum used a set of 3.73 gears out of a ranger pickup from salvage yard, if I was to do this again, thats what I would look into, those are production gear sets, allready worn in and probably very good bargin.

Have fun and drive safe.