I have a 1966 Ford F250 Custom Cab with the Axle 25 – 4:56Gear Ratio. I also have the original Cruisomatic3 Speed A/T in the truck. I would liketo change out the Rear End to a Dana 60 w/ a 3.54 Gear Ratio. Does anyone know if I will have any issuesdoing this? Will this easy up on theEngine RPM’s and allow me to get her on the highway without hitting 4500 RPM’s@ 65 MPH?




Axle: 25 (4:56 Gear Ratio)

 

I started looking into doing the same thing on my '64. I haven't done it yet. You will need a different carrier for 4.1 and higher gears along with the 3.54 ring and pinion. The big factor is the axle spline count. As I understand it, it should not be a problem for '66 and latter years but maybe for my '64.
john

 

There is a break in the carrier size for the D60's 4.56 and up and 4.10 and down (numerically). So you'll need a new rear end in order to get 3.54 gears.

I was looking for quite a while to find a 3.54 geared rear end to replace my 4.10 gears for the same reason you're looking.

I ended up getting a 78 F250 donor truck that gave up it's front suspension, PS and steering column to my 66 F250. The donor had a Dana 61 rear end with 3.08 gears, which may be a bit taller than I wanted, but will do for now. I need to move the spring perches and shock mounts to account for the narrower frame on my 66. I'll let you know how it goes.

Here's an article that explains carrier breaks:

Thick Gears vs. Thin Gears and Axle Carrier Breaks Explained

Regards,
Corey

 

Rick--what state are you in? I know someone parting out a 1971 or '72 I think that has one a 3.54 for $425 drum to drum. Best to buy the whole thing and be done with it. I found a 1970 3.54 to replace the 4.88 in my '62.

 

Rick: If you tell me what size tires you have on the back (either the Pxxx/xx, or inches diameter), I can run the numbers & tell you what RPM it is/will be turning @ 60 & 65 MPH with the present & future gear ratio.

James

 

Hoss73Ford - I live in Rhode Island


James Western Canada - P255/70/16 Tires


Thanks you for the help - Greatly Appreciated

 

Rick: Your tire height works out to about 29.055"

With 4.56 gear

~3170 @ 60 MPH

~3430@ 65 MPH

With 3.54 gear

~2460@ 60 MPH

~ 2670 @ 65 MPH

(and I will be sending you a PM shortly)

**looks like you're not set up for PM's, so I sent you an email

 

I would love to go to a 3.08 or 2.73.I would consider 3.25 as well.This truck is a freeway truck.