Changing gear ratio 4.56 on a 66 F-250 - Hiboy

[Oldman]

I want to change my gear ratio from the stock 4.56 to something that will allow me a little more speed. I can only do 55 in 4th and the rpm is high. What could i use instead? 3.42 - 3.73? Please advise. Thanks.

[tomsrod]

Not 100% sure, but I think you have to change the front differential to the same ratio.

[ICEMAN6166]

Not 100% sure, but I think you have to change the front differential to the same ratio.

yes front and rear both need to be the same for 4x4

not many choices, most 3/4 ton 4x4s were 4.56 or 4.10

[robert porterfield]

if you have a dana 44 front and dana 60 rear, the fastest aval ratio's is 3.54, this requires a ring gear case change because of the
'ratio breaks" the 60 break is between 4.56 and 4.10, the 44 is between 3.73 and 3.92....hope this helps.....

[Oldman]

Thanks for the replies. I am not versed in axle ratios, as my son is going to do the work. He was contemplating what gear ratios I could use. In reading on the net about the F-250 the gear ratios for this truck were only 4.56:1 I don't know if I have dana 40 on the front and dana 60 on the rear. I have a 300CID 6 cyl engine and thought this may play a part in what gear ratio I could use. Did the 66 F-250 have both dana 60 or was the front dana 40 and the rear dana 60? Would you recommend 3.50:1?

I am wanting to change the gear ratio so I can get a little more speed and lower rpm. Thanks.

[Oldman]

Okay, I made so errors in my reply. How do I tell if I have dana 44 on the front and dana 60 on ther rear. I was told I have dana 60 on the rear. Does the ring gear case mean I have to change the differential case? I know I am showing my ignorance but I would like to know the skinny before my son works ont he differentials. Thanks

[robert porterfield]

if truck still has factory axles in both ends, i'm going out on a limb here, it should have a 44 and a 60....the case in question is the one the ring gear phisicaly bolts too, some refer to it as the diff case....not entire axle hsg... if you are running a "factory" tall tire, i.e. 7.50x16 or simialer 3.54 ratio works out not bad, however might "pull" on that 300 little bit on long hill, may have to down shift.....i switched my 4x4 from 4.56 to 4.10....helped but wish i would have went more, wound up about same at 65 mph now....

[Oldman]

Thanks for the information. I will pass this on to my son. It is a great truck except it is not fun to drive long distances because of the low gear ratio. I want a little more utility out of it. Appreciate the help.

[Tech]

4:10's
460
C-6
33" tall street tires
It easily does 70+ and isn't bad on the freeway
Just not terribly economical.

[HiBoy63]

I agree with Tech taller tires help drop the ratio somewhat. There are tire gear ratio calculaters around on the net at some web sites. Not sure which ones try google for that info.

[ICEMAN6166]

4:10's
460
C-6
33" tall street tires
It easily does 70+ and isn't bad on the freeway
Just not terribly economical.

my 66 f250 4x4
4.56, d60 rear, front spicer 2444 front (early 44)
292
T98 4 speed
265-16 tires

easily does 70+, in fact likes 73 it seems to be the sweet spot.thats right around 3400 rpm.
almost impossible to break it loose on the ice in 2wd
dont care about economy it does what it was designed to do very well.

wifes 66 f 100 4x4
3.50 9 inch rear , 44 front
300 6, np 435 4 speed
235-15 tires
18 mpg and will hit 100 mph but very easy to slide the @$$ end around in snow and ice

[Oldman]

Thanks for all the advice. I am a bit confused thought. I have 7.50x16 tires and a 6cy 300 cid engine. I know very little about gear ratio. Is 3.54 better or 4.10? I am just looking for more speed, say 60 -65 mph without having the rpm up so damn high. The gear ratio I have now is 4.56 and is doesn't give me much range. I won't be mudding and I certainly won't be driving like a bat out of hell. I bought this truck with the intent of hauling grapes in 55 gallon barrells, about 2000lbs each time, about twice a year. The remainder of the time I will be hauling lumber for projects and occassional load of hay. I don't want to sell this truck but I am thinking an F-100 would be better? I like this truck and want to keep it. Any thoughts?

[ICEMAN6166]

neither ratio is "better" specifically
it all depends on what you want
if you are like me and dont care about the rpm in relation to road speed and ratio then drive as is.
changing gear ratios on a 4x4 you will spend more time and $ that you likely wont ever get back in the long run.
the 4.56 will easily pull a trailer of 55 gal barrels full and the bed full too. 3.54 will work harder to do that but gas mileage will be higher and rpm lower.

you have to take into consideration these were built as work trucks not like todays 4x4 for everyday soccer mom trips.

[factorystock]

The 4.56 ring and pinion gears can be swapped out for a 4.10 ring and pinion set. Any higher ratio such as 3.54 and 3.73 require the carriers to be swapped out also. A carrier is what the ring gear rides on. This work should be done by an experienced gear shop only, because it requires special tools to pull the Dana apart and precise measurements need to be made when reassembled.

[Tech]

Craigslist some taller tires and see if it is enough to make the noise tolerable. Is it that it won't go faster or you don't like to run it that hard?
350 ratio = highway use
450 ratio = heavy towing use

[Blackwaterforge]

The easiest solution might be a 5-speed overdrive transmission.

[Oldman]

I don't like the rpm to be so high. I don't do that much hauling or pulling a trailer. I guess the best answer I have is I don't like that it only goes 55mph and I feel I am taching the rpm higher than I should. I like the idea of five speed and what little I know about changing this, it sounds easier than changing the gears. If I understand correctly putting in a five speed I wouldn't have to change the gears - correct?

I have also thought of selling this truck and buying a truck that serves more of what I want. I bought this truck five years ago, did some work on it, though my mechanic says everything mechanical is is good shape. The county govt. I bought it from did a lot of maintenance on it. The body is in good shape. It needs to be repainted because the original color has faded. The bottom line is I have $$ in this and really don't think I could sell it for I paid for it. I thought of trading with someone for a F-100 but... I don't know what I would be getting. Does anyone know where I can get a five speed for this year and model? Thanks.

[frank66]

I have the same truck as you, except mine is 2 wheel drive. I swapped out the 4.56's for 3.73's. And as factorystock said, I had to swap out the carrier and this made it expensive. The truck still had more than enough torque to tow my racecar, but the rpms were still higher than I wanted. I wish I would have gone with 3.54's instead.

[Jarrod]

Here is a cool site to calculate ring gear vs tire size vs desired RPM and all that jazz. Like everyone said already, on Dana 60 and Dana 44, the carrier must be changed if you move to a higer (numerically lower) ratio than 4:10:1

http://www.snoman.com/HTML/axlecalc_5a.html

[oldtrucks]

Oldman

Keep looking around on craigslist and the local salvage yards for complete axles front and rear with the ratios you are looking for. Much eaisier to do a complete axle swap than a ring and pinion swap, IMHO. Price won't be much different but you wind up with spare parts.
My work truck has 4:10 dana 70 rear and 4:09 dana44 front I run 3400 rpm at 70 mph and have plenty of power. That shouldn't strain your 6. I'm running a 429 and that seems to be it's sweet spot. My tire size is 285/75 R16 basicly a 32 inch tire.
A 5 speed swap is a good idea too, it will give you a better gear split and bring your highway rpm down. They are pretty expensive but probably about the same as either a front and rear gear change or front and rear axle swap.