Gearing change for my bump.

[two-bit]

I'm seriously thinking about changing my rear-end gears when i put in the
Power-Lock unit.
My truck is currently running 4:10-1. At 60mph the 360 i have in it is really starting to work (9 mpg). I want to change that.
I have two FE blocks to work with my built 390 and the stock 360.
I was thinking about going to a 3:55-1 gear ratio. I'm afraid if i do that the 360 won't pull it when i load her up, ie: 4000lbs plus.
I know in my 69 F-100 the 390 could get 15 mpg with a T-18 and 3:25-1 in a 9 inch and had LOTS of power to spare.
My final thought is to run the 3:55-1 rear end in the D70 w/Power Lock, the NP435 that came with the truck, and my 390.
Not sure how i'll ever get the speedo right. I also saw a O/D trans in my local salvage yard that has a seperate bell. Its in a 80's something Ford pick-up. The shifter knob says 1, 2, 3, O/D. Any one know anything about those trannys.
What do you guys think???
Good idea, bad idea, no idea??
Thanks everyone, Two-bit

[REDNECKMOBILE]

Your final thought is the way I would go, you'll have plenty of power and a drive train that can take it.

[FLATBEDFORD]

My '96 has 3:55's in it and a 351 5spd. I wish it had 4:10's. With any substantial load I find I want a gear somewhere between 3rd and 4th at 55-60 mph. My bump has 4:10's and 4th has plenty of power at cruising speed. In a 1 ton truck that actually carries 1 ton and then some, I'd stay with the 4:10's. My '96 only makes about 8-10 mpg with a big load. about the same as the bump. The 351 and the 360 have similar torque and horsepower ratings, and the trucks weigh about the same. I wouldn't expect much fuel effeciency with an F350 even empty. Buy a little car instead for when you're only carrying yourself.

[ICEMAN6166]

an f350 actually rides better with a good load.
i would not go less than 3.73 if you still want to pull/carry a load, but i prefer the 4.10 in those and 4.56 is the better for extreme heavy towing.you are not going to get drastically improved mileage on any f250 or f350 that you would get from an f100 with a 9 inch and 3.50 or 3.25.

i wont even get in a small car, to ride or drive.if i have to i can ride in a little ranger but i would rather not.

[Jake11]

3.73 or 4.11's Got to keep it at around 2500rpm's if it's got a load
on it. If you lug it you'll hurt the motor.

[19674x4]

i wouldn't go lower than 3.73's. Ihad 3yds of 3" minus rock in my 67 one day and i was really glad i had 4.56's 352, np-435 , and a d-60. It was still sluggish but with anything lower than a 4.00 or 3.73 it would have had to wind the engine up to much.

[two-bit]

OK, did some math, (scary thought), and decieded to go with 3:73 gears.
I doesn't look like i'll ever find and O/D trans that will hook-up to an FE that can take it.
I looked into the O/D four speed Ford was using in the mid-eighties.
Yuck, aluminum case, remote shift, and heard they had bearing problems.
I don't need that.
Guess i will stick with NP 435. Getting 3:73 in the tail will help it un-wind.
Might help with fuel cost on the open road some too!!!
Thanks for the advice.
Two-bit

[two-bit]

I am not at all suprised by that comment
LOL

[two-bit]

I got my locker
Will be setting up my rear end with new gears and different chunk.
No more "one wheeled wonder".
Does anyone remember the name of the stuff you use as a "paint" when resetting your ring and pinion? I know its out there, i just can't remember the name of it.
Thanks
Two-bit