change rear ratio

The early 48 & 49 F1 pickups had the 3.78 rear (Dana 41). The Dana 44 had the 3.92. Randy's Ring & Pinion has stuff for Dana 44. These old rear axles aren't all that difficult work on. The only special tooling used in them was the pinion depth measuring set up but that can be worked around with the right measuring equipment. I've even seen those old measuring tool sets on flea-pay. The 3.92 gear set was used in the Mercury cars with R10 electric overdrive and it works well with OD.
 
The Merc Dana 44 axle only needs some spring pad work to be a bolt in. Ron's sounds like one for a Merc-O-Matic trans. The 9-inch axles are good but they are heavy and have a bit of offset.
 
thank you rotorwrench, does 2000 rpm at 55 mph seem like too much of a load for my 239? what would the correct rpm be at that speed?
 
MII said:
thank you rotorwrench, does 2000 rpm at 55 mph seem like too much of a load for my 239? what would the correct rpm be at that speed?
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I don't know how to equate load into it other than starting out in first gear. To me, it's more about engine sound or noise level since I don't run a tach. My old Mercs will go 70 MPH with the engine running at a decent rpm and lower noise level but that's due to the R10 overdrive. If I was running 70 in 3rd gear, it would be winding a bit too much for my taste. With overdrive, the gas mileage is better too. To more or less equal that in 3rd gear (no overdrive) a person would likely need a 3.54 or lower ratio. This could make it lug a bit off the line in 1st gear if the ratio is too low a number.
 
I just installed a overdrive in my 50 today, its a world of a difference. At 60 the engine sound is like it used to at 45. If changing to a overdrive is a option you might want to give it a look.
 
I would opt for a later Ford 9" out of a '57-66 Ford F100. The common gear ratio for '57-66 is 3.73 which is a good average ratio with 28" tires (235/75R 15). The HD trans you have is most likely geared low so an OD would be a good choice.. If you opt for a high speed differential, you will be in the gears (shifting) all the time with the engine out of it's RPM range.
The Ford F100's of the 50'-60's that had OD transmissions had 3.89 gear ratio's with 3 on the tree trans..
My father had a '53 F-1 with the V8, three spd OD which he bought new. I loved that truck. It ran great in town or on the highway. When we had to pull something, we'd disengage the OD which gave us plenty of pulling power. Dad pulled a 35' house trailer with the truck for years.
 
thanks for the info blucar, but I don't understand overdrive is it in the differential or the transmission ?
 
They can be mounted to transmissions or in the case of the old Columbia set up, it's mounted in the rear axle like a 2-speed axle. There are torque tube drive types like the Mitchell for the older cars & trucks that have that type of drive.

For the late F1 pickups with open drive, there are several transmission possibilities. The old 49 thru early 51 Mercury cars had a column shift type R10 overdrive transmission available. The Ford version is similar but has the smaller 1-inch 10-spline input shaft. The electric operating solenoid can be a problem on the F1s. The T5 transmissions are available and can be made to fit. There are still some of the Ford/Tremec T170 RTS 4-speed overdrive transmissions as used in 84 to early 87 F150 & Bronco trucks but they are getting harder to find. There are others but these are the most common ones used on open drive flathead powered vehicles like the F1.
 
Here's one for a 53.
 

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