77 Drive train upgrade

[ratliffusmc]

I am looking to do a buget upgrade from my C4/Dana-20 configuration. I am wanting to have off road reliability with improved gas milage. Any guidance would be great.

 

[oleguy74]

welcome aboard...first what tire size do you have?current gear ratio?engine?first if you have 3.50 rears and 30" tires,good combo.if 3.50 rears and 33" tires,you should go to at least 4.11 gears.taller tires lower gears.with that said,a 4r70w od trans and 4.56 gears and 33"tires would be a good way to go.final drive would be about 3.60.now depending on your engine and fuel system,carbd or fi results will variy.remember the bronco is not very streamlined.most carbed 351's will get 8-12 depending on gears and tires and most of all how you drive.302's -5.0's generaly do a little beter.

 

[ratliffusmc]

welcome aboard...first what tire size do you have?current gear ratio?engine?first if you have 3.50 rears and 30" tires,good combo.if 3.50 rears and 33" tires,you should go to at least 4.11 gears.taller tires lower gears.with that said,a 4r70w od trans and 4.56 gears and 33"tires would be a good way to go.final drive would be about 3.60.now depending on your engine and fuel system,carbd or fi results will variy.remember the bronco is not very streamlined.most carbed 351's will get 8-12 depending on gears and tires and most of all how you drive.302's -5.0's generaly do a little beter.

 

[ratliffusmc]

Thanks for the quick reply. The fundamentals are... Professionally rebuilt carb'd302 bored .030 with GT 40 heads, 2.5 suspension lift, currently 3.50:1 gears (from ID tags). I plan on running 33 BFG AT's. So I guess to install 4.11:1 gears and a 4R70w.

Will it match up to the Dana 20 or should I swap that out also?

Is there any special needs to install and operate the 4R70 od transmission?

thank you,

Curt

 

[S_bolt19]

Your expensive alteranative is to go with a 5 speed tranny swap. It isn't as easy as doing the dif. gears, but you will get better mileage out of it because it the 5-speeds have a highway gear. Try this gear calculator, it is outdated, but you can play around with it to figure out what you are going to need as far as tranny & R&P gears.

http://web.archive.org/web/20050204061805/...onco+gears.html

 

[oleguy74]

the 4r70w has od.if you have a auto now,cheaper than the 5 speed.i am assuming s-bolt is talking a manual trans.if not we are saying the same thing.

 

[S_bolt19]

Yeah, I am talking about doing the NV 5 speed manual swap.