Gearing questions
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Gearing questions
Ok so my 1997 F250 CCSB PSD is fairly stock for now with the TTB Dana50 front axle. It has the E4OD trans and 332k miles on the odometer. I am fixing to start a SuperDuty spring and axle swap. Right now my truck is geared 3.55 with 305/70-16 tires. When I do the spring/axle swap I am also going to lift it at the same time to fit 37-38" tires. SuperDuty axles come geared 3.73, 4.10, 4.30 and of course other ratios are available from the numerous aftermarket sources. Question is what would you go with and why?
Postmaster
Joined: Sep 2007
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From: Medford Oregon
My 97 has 3.55's and is great for overall daily driving and fuel mileage is good. My 99 has 3.73's and I like the slightly higher RPM's and get same fuel mileage as the 97. Both vehicles are automatics.
1. 3.55's are great if not pulling heavy loads and running on fairly flat Terran. With the automatic you can always take it out of overdrive if necessary.
2. 3.73's are a great compromise between 3.55's and 4.10's. A bit increase in RPM's when cruising but nothing crazy. Takes the hills better without down shifting.
3. 4.10's are the work horses if pulling heavy. I simply don't like the higher RPM's for daily driving, but that's just me and I don't pull heavy.
If I'm not mistaken you will lose the emergency brake on the rear axle swap so take that into account. I had considered replacing the gears in the front and rear ends from 3.55 to 3.77 in the 97, not by myself as I don't have the tools or knowledge. The cost didn't seem to out outrageous to have a qualified shop do it though. Although the SD disk brakes on the rear end are nice. You only mentioned the front end but assuming rear end also. I'm no expert in this area so will let others chime in with more knowledge.
1. 3.55's are great if not pulling heavy loads and running on fairly flat Terran. With the automatic you can always take it out of overdrive if necessary.
2. 3.73's are a great compromise between 3.55's and 4.10's. A bit increase in RPM's when cruising but nothing crazy. Takes the hills better without down shifting.
3. 4.10's are the work horses if pulling heavy. I simply don't like the higher RPM's for daily driving, but that's just me and I don't pull heavy.
If I'm not mistaken you will lose the emergency brake on the rear axle swap so take that into account. I had considered replacing the gears in the front and rear ends from 3.55 to 3.77 in the 97, not by myself as I don't have the tools or knowledge. The cost didn't seem to out outrageous to have a qualified shop do it though. Although the SD disk brakes on the rear end are nice. You only mentioned the front end but assuming rear end also. I'm no expert in this area so will let others chime in with more knowledge.
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You can keep the parking brake on the SuperDuty axles, just have to change some cables around. I was leaning closer to 4.30, maybe even 4.56, hoping it would help me with towing, especially with 37-38" tires.
Fleet Owner
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Tuned
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go here Engine RPM / Engine Speed Calculator and you can determine which gear will work the best. A good cruising RPM while towing with my truck seems to be about 1800-2000 RPM. Looks like a 4.56 with 37" tires will put you at just about 1731 rpm at 55mph, and just over 2000 rpm at 65 mph. If you are towing light then go with a 4.30 for slightly better cruising rpm.
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I don't own a 5th wheel. All my towing is bumper pull, towing the 4 wheelers and the mobile fire house/room thing for the fire department.
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