Morning all. Hope all your trucks serve you well. I got tons of trucks but still not happy with my setup yet.

I'm looking at a F450 7.3 (2003), flatbed. Seller said once runs around 70 MPH engine's revving up with higher pitch sound (RPM @ around 2000 vs around 1800 for 60-65MPH). I'll test drive it tomorrow. But was wondering if the forum can shed any light as if there is any difference to the setup in F450 cab & chassis truck versus the engines installed in regular trucks? Is gear ratio having anything to do with it?

I'd like to use this truck mostly to haul stuff, pull trailer 80% of the time (20% would be my 6.7L) - which is @ 60-65MPH max. But I'd also like to use it for my daily driver (50-60%) for light duty work too. So being able to run 70-75MPH empty/mostly empty loaded is pretty important to me.

Thanks.

 

F-450/550 2wd chassis used 4.30 gears and lower. 4x4 chassis came with 4.88 or 5.38 gears
F-350's normally came with 3.55, 3.73 or 4.10 gears.
These lower gears make the engine rev higher and limit top speeds to 70-75 mph flat out.
After swapping in a lower rpm 5.9 Cummins in my 04 F-450 it would only run 69 mph flat out.
You can swap in higher gears up to 3.73 in the Dana S110 rear axle but it'll cost, ring and pinion, bearing kit plus tune ring will set you back $1500-2000 plus labor.
If it's 4x4 you have the front gears to change as well, I did my own work but still spent a lot of coin swapping from 4.88's to 3.73's, overall for what I do with the truck it was worth it.

 

 

 

My 99 F450 came with 4.88 gearing so I swapped to 4.10 when I installed my locker for this reason. Is it 2wd or 4x4? If 2wd with the Dana 80 axle it is not to bad to do.

 

Ford sales literature shows the F-450 pickup available with 3.55, 410, 4.30 gears, I believe they have a Dana 80 rear axle
Older cab and chassis used a much larger Dana 110 rear axle, not sure what the newer cab and chassis use.

 

 

I'm guessing your 2wd came with a Dana 80 axle, haven't looked at a 2wd pickup in years.

 

Yes dana 80 chassis cab though. Not sure when the 450 pickups came about. I have always wondered if someone has a list for what all rear axles came with what. Looking at 99-03 chassis cab trucks I have seen either the dana 80 or the a larger dana axle that the differential comes out the front S135 possibly? Don't remember. I have seen 450's and 550's with either one. I never could figure out why some had the 80 and others the larger one. possibly a 2wd vs 4x4 thing? No clue.

 

I do not think 4.10 would be factory in the 450 in 2003. In my opinion 4.10 is a good compromise gear ratio. 4.88 was too low for me when driving unloaded. Is the truck an automatic or manual transmission?

You can check rear end ratio a few ways:

1. Door tag code for rear axle. This will tell you what it should be.
2. Part numbers on rear axle itself. This will tell you what it should be.
3. Assuming 225/70/19.5 tires and in overdrive Rpm at 70 should be 2600 with 4.88 --------- 2184 with 4.10 ----------- 1987 with 3.73 Need to use a scan tool to verify rpm. My dash tach is off about 100 rpm at 2000 according to several scan tools. (snap on, laptop at friends shop, and torque pro all agree with each other) This will tell you what it is.
4. Jack up in neutral, mark the driveshaft and spin the rear wheels 10 turns. Driveshaft will spin either 49 with 4.88 --------- 41 with 4.10 ----------- 37 with 3.73 This will tell you what it is.
5. Get a drain pan, pop the cover off and look at the numbers stamped in the ring gear or count the teeth on the pinion gear. This will tell you what it is.

 

 

 

Driving empty around 55-60 I went from about 14.5 to 16.5 mostly to and from work 55 mph speed limit. I have had it up to 75 or 80 with both gears no problems. Never stayed that fast long enough to compare any mileage.

The dana 80 has a carrier break between 3.73 and 4.10. 2 different carriers are used in the rearend depending on the gear ratio. The locker I bought was for 4.10 and numerically higher. I had a 250 with 3.73 and an automatic and felt 3.73 would be too tall for my needs with the 450. I don't spend much time over 65.

 

Take a look at your other thread. I think you will have trouble with the CA dmv with this being a 450 I don't think you will be able to get license plates for it in a couple years.

 

my 2010 f-450 drw has a dana 110 axle in the rear and the front axle is different as well...aka super 60???

the computer for the 2008 thru 2010 f-450/f-550 diesel are flashed for 25 hp less than f-250/350