I've been collecting up all the parts I need to convert to a dually, and scored large. I got the complete set up, frame down, including the frame off of an 04 F350 Dually. I figure I will use my springs since they are the same except for the helper coil spring thing the 04 has. I don't want that. My questions are, I noticed that my rear axle is thinner than the dually, and the spacer block on the dually is about half the height of my block. Mine is stock by the way. So should I use the dually block or my block under the springs. I image even with the thicker axle it will be lower if I use the dually block?? Secondly the dually has 4:10 gears, mine is 3:73. Should I change out the gears to the 3:73? Or will it make little difference? I do remember during my high hp build , Jody asked me what gears I had for my programs. So I imagine I would have to get them changed?? Thirdly, I could not find a year match box. But I found a brand new never used box off an 05 dually, for a steal if it will fit?? Does that box fit? I thought up to 06 was similar and fit, but not sure. I have to get this thing now or it will be gone. For some reason older ford boxes are hot hear and you can't get them. Thanks for any help.

 

I would use what came with the set up exclusively. I'm not an Engineer and do not understand the process of design and safety margins.

I would use what came with the set up exclusively. I'm not an Engineer and do not understand the process of design and safety margins.


What was your motivation to go to a Dually? That, along with your needs will answer this question.

The predominate reason one purchases a Dually is pay load and torque.

The Taller Gear Set will allow the platform to perform.

Will you pay more in the long run with maintenance and fuel expenses? Yes.

Will you have problem pulling up to 15k lbs. up a 6% grade? No

Do your Tunes need augmenting? Yes.

Box? I assume you're referring to a Bed? Yes it will fit with some minor modifications and all the lines meet with the cab nicely.

 

I actually don't care which gears go in it. The reason I asked is I only have one issue with the 3.73 gears. The issue is , our speed limit here is 60kmh, the truck stays in 3rd gear at that speed and is just shy of changing to 4th. I figured the 4:10 would either make it shift into 4th at a different speed, or just lower the rpm at 60kmh. Minor I know, but it bugs me when I'm driving and its switching from 3 to 4 and back and forth because its hovering around the gear change zone at 60kmh. So I find myself going faster to keep it in 4th, and I have had several warnings for my slightly high speed. Figured the 4:10 might help on that. That said, I tow some big weight so don't want to kill my tranny.

 

The 4.10 gears will raise your RPM at any speed, not lower. Have you tried it as-is with the O/D off?

 

yes, when it really bugs me I shut off the od. And burn up fuel with the rpms too high. I was hoping the lower gear 410 would cause it to shift to 4 at that speed rather than use the od button and 3rd. Just want the rpm lower at 60kmh.

 

You definitely should care what gears are in your truck. Rear gear, and final drive ratios (trans gear ratio x axle ratio) can greatly alter a vehicles "personality" and will determine what it does well, what its marginally acceptable for, and what its a complete failure at. Also, if your truck is 4x4 (no signature or truck details, so we don't know what you have.), the front and rear gears MUST match, unless you like catastrophic driveline failures.

3.73's are a good compromise between off the line acceleration/pulling power and highway economy/general daily usability. 3.55's are more economy/cruising oriented. Think rarely loaded highway commuter. On the other hand 4.10's are good for getting heavy loads moving, with less stress on the driveline. They will, however, result in loss of fuel economy, particularly at higher highway speeds. Keep in mind, that dually rear (Dana 80?) is bigger, heavier, and has more parasitic horsepower loss then your outgoing single (10.5 sterling), plus the added weight of 2 more tires. All else being equal (ie sticking with the 3.73's) you will have less pulling power.

So, given that you pull heavy loads, and have already expressed a willingness to cower and obey before a mere piece of metal with silly numbers painted on it, even at the expense of possible tranny damage (hunting in/out of OD is not good for it.), then running the 4.10 gears in the dually rear may be your best option.
Keep in mind, you will need to get your ABS computer reprogrammed for the new gear ratio, lest your speedo be off and you run afoul of the highway overlords. You may also need some tuning updates, to account for the changes in the "operating envelope" (Where and how you'll want the power delivered), as well as changes in the tranny shift schedule.
Your tuner should be able to customize the shift schedule to accommodate desired characteristics. Shifting primarily off engine RPM is an antiquated and crude trans strategy. Modern electronically controlled transmissions use many more inputs and variables to determine shift points. Road speed is the "primary" one, with things like throttle position, engine load, rpm, engine and trans temps, etc... all influencing the final "decision" by the pcm.

As I said, I imagine your tuner should be able to stop the trans from hunting, by either raising the 3-4 shift point, to keep it in 3rd; or lowering it, to allow the trans to shift into 4th/OD a little sooner and stay there, depending on what you want.

 

This is the reason I keep my Superchip tuner. This problem is eliminated, no fishing for the right gear.

 

Huh?? I don't fish for gears either. The transmission does all that.?? Odd comment? Carguy jared my memory a bit, and I remember Jody telling me a year ago that he could change where the transmission shifts to pretty much anywhere. My bad, sorry, forgot about that. I'll stick with the 3:73 gears and get the programs changed. Its free. I feel stupid, sorry guys. I'm actually happy now. When I was told the 4:10 meant less speed, I was sad. I love that 140mph blast into work every day. Also I never realised I would need all the ABS, and speed sensor etc programmed. I think I'd be saving a bundle sticking with the 3:73 gears. Less programming.

 

About my signature. I made one, it was there, now its gone. Don't know what happened.