New Dually Gears
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New Dually Gears
I want to change the Rear Differential Gears on my 85 Dually with a 460. I don't know what to go to. Right now it has 4:11 gears in it. I sold my race car but kept the trailer to store my Fairlane in. I'll tow with it maybe at tops TWICE a year. I want to be able to drive it more around town & on the highway more, but with gas prices what they are & with the gears it has I can't hardly afford to drive it! It has 245/75r16 tires on it now & if I remember correctly I think it tachs at around 2500-3000 RPM at 55 mph. I have a friend that will sell me a Gear Vendors Overdrive unit for around $600 but I still have to buy all the adapters to get it to fit my C-6 because it came off a Turbo 350. I was thinking about going to a 3:73 gear but I had a friend last night told me to go to a 3:55 gear, I'm worried if I do that, it will be to high of gear for the 460. What do you guys think? I want to be able to cruise with it & get a little bit better gas mileage. I will tow with it but it will probably be twice a year TOPS!
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Joined: Apr 2004
Posts: 34,499
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Expect the rear axle change to run $200+ for gears, plus several hours of labor at whatever rate prevails in your area. Some here have been quoted $1000 or more to swap gears.
The GV for $600 plus the parts to make it work sounds better to me.
You have 30" tires with that size.
So, your mph per 1000 rpms is as follows:
4.11: 22
3.73: 24
3.55: 25
Put another way, at 55mph:
4.11: 2532 rpm
3.73: 2298 rpm
3.55: 2187 rpm
Note this does not add TC slip of approx 200 rpm, depending on your TC.
You can try other combos at:
Novak Conversions - Gearing & Gearing Math for Jeeps
Plugging in the .78 GV ratio with your 4.11s:
28 mph per 1000 rpms, and
1975 rpms at 55 mph.
The GV for $600 plus the parts to make it work sounds better to me.
You have 30" tires with that size.
So, your mph per 1000 rpms is as follows:
4.11: 22
3.73: 24
3.55: 25
Put another way, at 55mph:
4.11: 2532 rpm
3.73: 2298 rpm
3.55: 2187 rpm
Note this does not add TC slip of approx 200 rpm, depending on your TC.
You can try other combos at:
Novak Conversions - Gearing & Gearing Math for Jeeps
Plugging in the .78 GV ratio with your 4.11s:
28 mph per 1000 rpms, and
1975 rpms at 55 mph.
Posting Guru
Joined: Jul 2008
Posts: 1,250
Likes: 1
I would go with the gear vendor unit. I've have a 95 F250 with a 460 with 3.55 gears. It's always been great for highway/interstate driving, but I'm afraid it's going to feel weak when pulling a camper. I have a gear vendor unit from a 2wd C6 truck, and I'm looking to get the adapters for it to be installed on my truck and then someday regear to at least 4.10. Overall, I think the gear vendor unit is a better option because you'll keep the 4.10 gears for towing when needed, but you should be sitting really well for highway RPM.
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