Rear Ends

[JoeyCleland]

I have 3 questions about the 11.25 dana 80 in the back of my 2000 dually

1. is it 35 or 37 spline axles
2. it has a Limited slip and 4.10 gears now. If I go to 3.54 gears what all will I have to buy in addition to the R&P? New Case? New LSD?
3. is any body here running a 2wd Dually with gears that low and if so how do they like them?

Thanks
Joey

[MrJohnWayne]

Not sure on the splines. They are really easy to pull out anc check though. 8 bolts with an o-ring seal and the axel is out.

As long as the gear is made for a certain carrier (i.e. 3.xx - 4.xx) you should not have to change the carrier.

[JoeyCleland]

Yeah but I know on the open diff there is a carrier break between the 3.73and 4.10 gears. But with most posi's there is no carrier, the posi is the carrier. I was just wondering if there is only 1 LSD put into the f350's will I need a carrier at all, Will I have to replace the LSD too?
Joey

[MrJohnWayne]

If there is a carrier break between 3.73 and 4.10 regardless of posi, limited slip etc you will probably have to change it out, unless some aftermaket company makes a set of gears that high to fit a 4.10 carrier. I'm not sure though.

Precision Gear - Dana 80 Ring and Pinion Gear Sets

From what I gather here the carrier should be the same, but the housing is different if you were going from 3.73 lower to a 4.10. Since you already have 4.10 I think you will be fine.

[jfines@cox.net]

Not to change the subject, But won't that kill your fuel milage?

If you were worried about economy I would stay with the 4.10.

I have a friend with the same truck as me, except he has training wheels, and he has the LSD. He hates it. cause of economy. He is at 13 Mpg. And I am sitting at about 18-19 Mpg.

[MrJohnWayne]

IMO it will probably increase just a little but I don't know. It will require more power to get it rolling but with the torque these motors have it shouldnt be too bad.

[jfines@cox.net]

OK maybe I'm wrong. The gear ratio's confuse me. Is it, the lower number, for more torque and higher number for faster speeds? or the other way around.

[MrJohnWayne]

You have it backwards. The lower (numerically) the number the higher the speed(or lower rpms at same cruising speed) The higher the number the overall speed (higher cruising rpms)

Does that make sence?

[jfines@cox.net]

Yeah, I thought it sounded weird to me. To many numbers and ratio's floating around in my head.

Thanks

[JoeyCleland]

With the 4.10's Im pulling about 2300rpm at 70mph with the 3.54 I would be pulling right at 2000. That will make a pretty good improvement in mileage. plus the engine will get less wear and tear, and it will run quieter at 2000 vs 2300. Any of you guys with a 4x4, big tires and 3.73's wanna swap for some 4.10's??