I have a 55 f100 with 289 automatic. Took out for a spin and so low geared it needs another gear...anyways thinking of changing the ratio in rearend..Has 392 ratio now...what ratio wpuld be best for cruisin and if i wanted to drive on interstate? Thanks

 

3.0s or 3.55s are both good...3.55 is probably better if you are interested in having a little more performance. 3.0 is better for MPG.

 

I have the 3.92 in my truck....was gong to change to a 3.55 also but requires a new carrier. So I am putting that off for a later date.

 

I would think a 3.50 would be correct but without knowing your current RPM or desired RPM it is just a guess. Here is a RPM calculator that may help.
Engine RPM Calculator

 

With a 3.92 ratio, the OP's 1955 F100 has its original Spicer/Dana 44.

Where will the OP find a 3.00 or 3.50 or 3.55 ring & pinion for this rear axle?

 

Whatso a good rpm for say if I wanted to drive on interstate but still scoot around town.where can I buy ring and pinion for Dana 44 to make 3.08 or 3.50?

 

Indybeer,What do you mean a new carrier? Like housing?

 

Ring gear bolts to the case. No Spicer/Dana rear axle has a carrier.

Case shown as 4205 in pic.

 

What you're calling a "case" is most commonly referred to as the "carrier".

This shows the reason for changing the carrier when you go below 3.92. The flange on the carrier (or the ring gear) would get so thin as the pinion diameter gets larger, that it wouldn't have any strength.

 

Oh ok...So if I change to a 3.08 then I have to purchase new carrier also.? Thanks everyone

 

OR you could just go get a truck 9" complete axle. Then you can change gear ratios by exchanging the entire center (it bolts in).

 

What he said!

 

I thought a place called Randy's is making g gears for the Dana 44?

 

I have found several places online that have the two differential carriers and ring and pinions that fit the Dana 44.

Once I get my truck on the road I will look at changing my gear ratio.

 

What trans you are running is also important on your choice . Road engine speed IMO should be around 2500 max less for mileage but also depending on your engine set up .