Ive got a 1977 F660, 4WD truck that was used as a brush fire rig. It's got 8600 original miles and is a great truck. However, it has granny gears and I'd like to modernize the axle ratios to something more driveable for use in my business. Rear axle is a Rockwell 8200-R-1188 D, Ford Axle code is 64J. Can I swap the differential or do I need new axles, etc? Where do I start?

 

Welcome to FTE

There is no such thing as an F660, it's an F600. 1st 3 digits of the VIN: F66 = F600 4WD (gas).

MODEL aka TYPE/GVW code stamped on the Warranty Plate:

F660 = F600 4WD (gas), 21,700 lbs. Gross Vehicle Weight Rating.

F661 = F600 4WD (gas), 24,000 lbs. Gross Vehicle Weight Rating.

64J: 64 = Rockwell-Timken model F-106 Rear Axle / 6.80-1 / 15,000 lbs. Rear Axle Capacity // J = 5,000 lbs. Capacity Ford Front Axle with Power Steering.

 

I suggest a good rockwell arvin merritor dealer... many ratios are available but the hard thing is sourcing them. My stock ratios were 6.17... which with the 46" xmls super singles was perfect for 65... with dually 20 " stockers... about 52-55

I have detroit lockers in both of mine.. rear was easy peasey... about 500... front was very hard to find and cost me over 1500... I think I have 5 k wrapped up in just the axles/tires now

I have the same axles in my firetruck... I also found the mud racers in the midwest had parts for them... as these axles were popular with them... google work is your best friend