I have a 71 ford f250 with a 390/c6 and i am going crazy trying to figure out if i can put a 4 speed or 5 speed?? Automatic in my truck..im getting tired of my truck screaming @65mph and killing gas.. Any help or advice would be greatly appreciated!-mike

 

You can bolt up an AOD or GM 700R with an adapter, about $700 last I checked. Plus better put some beef in that AOD for your application and even at that it would be a question mark. Probably ditto the 700R.

You could get an E4OD, big as a house and needs a $500 controller.

No easy answers with the FE motor.

Do the math, say you improved 20%. What would that mean and how long would your payback be?

 

Well it may be a while till i see payback but i would love to have the 4speed option due to the rpm being considerably high on the freeway And my love for speed.. Or would a different rear end be A better option for lower rpm. my truck currently has a dana 60 rear end with 8 lug set up.. what is a reccomended rear end for lower rpm yet durable enough to tow still?

 

Mike a FE powered 250 and mpgs don't drive on the same lane. You will be miles ahead to buy a gas sipper to drive and use the truck as needed.

From your description sounds like a high 3s rear end ratio. Those were drunken pullers not polite sippers. The Dana's are not as easy to work with like the 9s in the half tons.

Zackly why I keep my Taurus truck, much better mpgs.



John

 

My truck is my daily driver, you will never see me in a prius.. I am supposed to get a really decent tax check this year so i am trying to get an idea of the best mods to do to my truck so i can stretch that $109 a week fuel another day and/or be able to cruise at 70 without my truck screaming.. You were saying a 9inch rear end is easier to work with? I would gladly swap out this dana if that would help my situation.. But there are so many different ways to go its overwhelming on what to spend the $ on and make it worth it..

@jowilker: i love the quote at the bottom of your reply about hearing chevys rust, pure poetry lol

 

IIRC, the tallest gears for a Dana are 3.54. Find out what you have, and also, what tire are you running?

You don't want to swap in a 9 into an F250.

 

I have 235/75 16.5 i believe, standard for that truck i was told.. How do i find out what gearing i have in my rear end?

 

Might still be a ratio tag on one of the bolts holding the rear cover on. There is an axle code on the id plate found on the door or in the glove box.

Those tires are probably 30". With a 3.54 axle, you would be turning 2577 rpms at 65 mph. 25 mph per 1000 rpm.

If you currently have 4.10s, you are turning 2985 rpm at 65, or 22 mph per 1000 rpm.

 

Trans-go makes an adapter for the 7oR4, and probably others too. It can be built to handle a 390 without breaking the bank. I know a couple guts who did them and liked the set up. I'm not sure on mileage but overdrive and a lockup convertor has to put it better than the C-6 (which is the air sucking chest wound of efficiency)

 

Performance Automatic offers a "Street Smart" package to bolt-in a 4R70W to an FE... Bucks though.. The tranny alone is around $3,500 plus the converter, the controller, harnesses, etc. Last time I saw the ad it was.... $7,000 . Performance Automatic - 4R70W Street Smart Packages

How important is the OD gear again ?

Makes swapping to a TKO-500 5-speed manual comparatively "cheaper". Modern Driveline - TREMEC T5 / TKO / T56 Transmission Conversion

 

A Gear Vendors overdrive unit is about $3500. They bolt on the back of the transmission.

 

Mike Thanks for the flowers on the tag.

You are grown, fully capable to make your own choices, I'm sorry but a 71 FE powered 250 for a daily driver is not a good one when you are looking mpgs. I have owned trucks for 40 years, love to take my 66 out and play. It pulls hard, leaves many cars in the rear view. I say to folk, it will pass about everything on the road but a gas pump.

You will be miles ahead at the end of the day putting any money in a commuter car, keeping the ol truck for important guy things.


John

 

Wow thanks everyone for all your information, it is very helpful. @jowilker i appreciate the info lol i really have no choice, my truck is all the ex wife left me with and just payed off lawyers so now i have some $$, not enough for another vehicle but enough to put into my truck. @86e150six4mtod i didnt know that and i will check right now. I will just tweak the rear end cuz it seems that any tranny mod will be through the roof.. @alex from ga i did some research on the gear vendor mod and it would be the way to go but they are expensive for the time being and installers want a rediculous amount to put it on.. I have put one on the wish list though.. Thank you again to everyone for all the great info, i sencerely appreciate it!!

 

change the rear gears of your truck to a lower number uslly a few hundred for the gears brand new try to find the tag on the diff with the number most on the site can tell you what the ratio is from the or what rpms you are running in 1:1 on your trans at a seat speed hears a calculator to help
( Planet 4x4 - Gear and 4x4 Calculators ) i like my truck at 2000 rpms to cruse at that is just my thought or bigger diam. of the tire will lower rpms
too remember any of these will change the speedo

 

Dana 60: 3.54 introduced in 1966, 3.07 & 3.23 introduced in 1980.

The AXLE code is stamped on 2nd line, at the far right, of the Warranty Plate, located on the left door face below the latch.

The rear axle ID tag is located under one of the bolts that retains the inspection cover to the housing. Do not be surprised if it's missing.