Jerry, Thank you for the education. I hope others are learning something from what has been shared here as well. Maybe the MPG will improve somewhere close to 14% as well. If so, that would be 28 more miles per 20 gallons of fuel if it was getting 10 MPG. I don't recall the tank size on the truck. I'll check on that. I'm guessing that a lot of other variables would need to be factored in. As they say a little knowledge can be dangerous. It seems that a 14% reduction in RPM's would generally speaking help extend the life of the engine. Although the engine / transmission might need to downshift more frequently and for longer durations especially when towing, pulling speep hills etc.
I have a '66 F250 that had 4.11's, turning nearly 2800 rpm at 65MPH. Pulled a set of 3.54's out of a '68 F250 and swapped the ring and pinion out. That was a great move in my opinion. RPM at 65MPH dropped to 2300. I have a 390 4V and a NP435. Unloaded it is getting 14mpg driving 65MPH.
I pull a 7000 lb trailer from time to time...the 3.54 does great.
Krh427, It sounds like the 4.11 to 3.54 swap is working out great for you. Your experience will give me a good basis for comparison. I don't know how a NP435 compares to a cruise-o-matic. My speedometer will be off until I replace the gear. When I get my truck back I'll drive next to my wife or one of my children at 65MPH on a level road and see what my RPM's turn out to be. I'll report that back here. Hearing about your experience is very encouraging. Thank's for sharing!
If you have a gps it will give you a pretty close call on what your speed is and then you can adjust until you have the propper setup.
1965 F100 4x4 for fun. Name Gentelman Jim
1963 F250 4x4 for restore. Name Beast
1998 F150 4x4 for daily use. Name Birthday Boy
2001 Ford 4x4 Explorer Sport Trac (nice but sucks on MPG its underpowered)
If you went with a rear end from a 1970-72 Camper Special, you could go for a 3:73 and also get
better drums (I think from 2" to 2.5"...). The yoke spline count is a bit different, I just did a conversion
Where can you buy the correct conversion u-joint? I'm thinking of doing the same rear end swap to my '66 f250.
I got my conversion u-joint for my 1972 Dana 60 / 1966 F250 Driveshaft from a drive-line shop that services
transmissions and diffs and builds drive-shafts-the original diff was a 10 spline and the '72 diff. yoke is a 29, so this
does the job nicely.
I'm sure you could find one at any driveline/tranny specialist shop. Mine was a sealed (no grease fitting) "Brute Force"
model number 1=0134BF.
Mine likes 55mph. I realize these were made for work/hauling and I love my 250, just wish it had a bit more cruising oomph. With the 3 speed cruiseomatic tranny it always seems like it needs to shift into 4th, but never does(:
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