Looks like this thread has been hijacked. What started out as a differential question has evolved into an AOD answer.

I tried to answer the differential question without going into the AOD option, but I'm also in favor of the AOD option. If you have the cash, you might want to explore keeping the 3.50 gears and buying an AOD (Not AOD-E) out of a Fox Body. There is a kit available to do the swap. I'm about to do this to my '67.

http://www.transmissioncenter.org/cl...conversion.htm

AOD-E: Do you really want to install some sort of switch to be used for shifting into overdrive? Sounds lame.

Do you guys really manually shift your automatic transmissions on a regular basis? If so, why don't you have a standard transmission?

 

Sorry about the hijacking. My understanding of the AOD-E, gears 1, 2, and 3 each have their own shifter position and 4th is on a switch. I'm not afraid of putting a stand alone controller for the overdrive. And with the "improved" valve body 3 and 4 gear become grouped into the same position. At least with the AOD-E you could have control of each gear. And trust me, if I and the $ I would be all over switching to a 5 speed manual.

 

i dont mind the hijacking it just gives me more to think about since right now i have a C4 trans in my mustang with the I6 250 engine and i cant decide on what trans to go with when i install my 351w with some mods (rpm air gap intake, mild cam,headers and a 600 cfm carb) i cant remember if my C4 trans will hold up when i get this running until i upgrade my trans. i dont drive my cars slow. the other day i saw a AOD trans rated to 550hp on ebay sell for $800 and i thought of getting it since when i build my 408w, my power will be right under that.

 

just on the original subject. I predict that you will be a bit annoyed of the 3.5:1 when you are highway driving, but as soon as you change that to a 3.0:1 you will be bawling crying because everything else gets worse (the accelleration!). the 3.5:1 is a good match that you want to keep, just as all the others say, eventually you want to upgrade to overdrive. all depends on how much daily driving/highway driving you do.

I vote keep the 3.5 even with the non-overdrive gearbox i had i wouldn't have swapped to 3.0

 

Best advice I can give is for you to think "down the road" a little. IOW, put a little time into deciding if an overdrive of any sort will actually end up getting installed, and then make your axle choice with that in mind. Whether any OD tranny ends up being an AOD, Tremec, or whatever probably won't matter, as all the top gear ratios are about the same (except if you get something with a close-ratio 5th).

Without considering drag strip duty other than maybe "just to see what she'll do" . . .

For a direct drive in top gear manual tranny, 3.00 is a little on the tall side and 3.50 a little short, so if your final decision is to stick with a non-OD tranny maybe 3.25 or so is really what you're looking for.

FWIW, it's a little easier to put up with numerically lower axle ratios with non-lockup automatics, as there's a little slip across the torque converter (which lets the revs run just a little higher and lets the engine spool up a little quicker initially when you step on it a bit).

Between 3.50 and 3.80 is what you might want with an overdrive tranny 3.25 is "do-able", but you likely wouldn't use 5th anywhere but on the Interstate. You probably won't be able to use 100% WOT on the street in first gear, but you'll be fine with the next three gears and your cruising rpms will be low.


Norm

 

so far many people tell me my 3.50 is ok with my c4... ill try that then if i just dont like it ill get the AOD trans. as far as i know my mustang has the V8 suspension and trans because the year i have (1969) and the engine i have (250) comes with the V8 stuff right??? it currently has 5 lug hubs. now for my last important question on this, will my c4 trans hold up to a mildly moded 351w or do i have to upgrade the trans? (mild cam,mabey some rpm heads, air gap intake and headers) thank you guys for all the help.

 

You still haven't told us how you plan to drive your Mustang. If you're going to use it for normal driving, the C4 will be just fine. If you're plan is to melt the tires down at every intersection, then the transmission isn't the only think you'll be repairing.

 

melting the tires lol. my plans for this car is to drive around my town like taking my kids to school or to a restraunt with the wife and to my work once or twice a week that is about 6 miles away and to visit my mom or dad that live 109 miles from me diving 65mph or less since i dont have a aod trans. im not going to floor it at every light but i dont drive slow either. i dont want to find out if it will be ok by just using it because i dont want to be stranded somewhere with my kids and a blown trans. so what do you think?

 

I've heard that the C4 can be built to be very tough, as any of the transmissions in this thread can be. When I had a C4 with 3.73 gears in a truck 9" I got 13 MPG on country roads and mild driving. I really like the overdrive that's for sure and I'd never build a car without one. You get the benefits of putting more torque to the ground AND reduced RPMs (better MPG) on the freeway. If your going to stay auto, save up some money and get one that is performance built. I hear real good things about the Lentec AOD.

 

yeah i like the sound of more torque at the wheels and better mpg's im sure ill get a built AOD but i would like to use my c4 if it will hold up until i save up to get a built AOD.