have a 97 F350 crew Cab 4x4 7.3 with 3.54 gears,pulling a Gooseneck 32ft 10ton tandem axle dually trailer weighing 6700lbs, with 2 jeeps and a ATV , having to pull in 3rd only 60mph OD won't hold at all ,live in Florida so pretty flat, Have 35" tires so that doesn't help takes me about to a 3.33 ,I have had a few diesels and my first was 99 F350 4x4 dually stock tires and I pulled a 12 ton inverted 5th wheel with equipment on it, truck and traile empty weighed 20600lbs, so i was pushing 32000lbs, i don't know what gear ratio this truck had but i got 16mpg empty just truck and never droped below 10mpg loaded and could drive in OD even in hilly areas like northern Florida, I want this truck to pull like it did, Had a 2005 F350 with the tow boss package and it pulled great too but the 4.30 gear was terrable on fuel 13 empty and 9 or 10 pulling justa 30ft boat, my Excursions 2002,2003 last 7.3 with the 3.73 gears always went in and out of OD didn't do great either on milage loaded but 16-18 empty, so what would you suggest, a 4.10 is what I am thinking. And would tranny be alright and torque converter. Thanks kinda lenthy but I try and explain things.

 

IMO...having good fuel mileage and 35" tires in a sentence is just not going to happen. You need to decide if mpg's is more important when loaded or unloaded?

However...for the weight (when towing) and year of 7.3L...IMHO...I believe the 4.30 is the best option. That is only due to size of tire. Getting the rpm's back where they belong...will help your tranny keep heat down...and improve mpg's while towing.

Good luck...with whatever you decide.


biz

 

Unloaded mostly I only pull about once a month, why do the new engines or 99 get such better fuel mileage, is there that much differance in the them.

 

3.54 is not enough gear for that truck. It should have at least the 4.10.

Toyman

 

I agree and I think 4.30 is to much, and the tires are only about 3 inches taller than stock. I mostly just don't want to run in 3rd gear, while pulling.

 

35" tires and 4.10's would get you to ~3.70 gearing (in 3rd gear...i.e. direct drive)

35" tires and 4.30's would get you to ~3.88 gearing (in 3rd gear...i.e. direct drive)

Sounds like you are wanting to get back to the 3.73 effective ratio...so going 4.10's in the rear with those tires would put you back at that gearing.

If you haven't seen this tire size calculator...it is very handy! https://www.ford-trucks.com/calculat...re_sizes/a-er/

joe.

 

Problem is X-Hemi is that he wants to tow in OD...and not be in 3rd...as your numbers suggest.

Here are the number that I ran...

Recommended RPM while @60mph in a Ford Diesel (Turbo) = 1400-2200rpm
----------------------
Gear Ratio = 4.30
Tire Size = 35"
Speed = 60mph
Total RPM = 1734 (AOD)

------------------------------

Gear Ratio = 4.10
Tire Size = 35"
Speed = 60mph
Total RPM = 1653 (AOD)
-----------------------------


So...what the numbers suggest...is that there is not a significant difference between 4.10 and 4.30...other than while towing you will have a better chance at staying in AOD. So...IMO...I still believe the 4.30 is the better overall choice here.


biz


PS...Source is from Randy's Ring & Pinion http://www.ringpinion.com/Calc_RPM.aspx

 

Biz,

Thanks!

I missed the OD part...

I posted about 3rd gear as that is a 1:1 gearing on the trans with our 4R100.

FINAL drive ratio is a combination of tire size, transmisison gearing AND rear end ratio...my point about 3rd gear was that 3rd gear is where the transmission is taken out of the equation and only tires and rear end gears are in effect...in order to calculate true final drive ratio in OD...you'd have to multiply that ratio by ~.73 or something to that effect...so in OD final ratio is even taller thru OD...that's all...

joe.

 

Just one point, it's a 4x4 so the gears will have to be changed in both the front and rear diffs. I just didn't see this mentioned anywhere, and thought it should be bought out.

 

I think I am going with the 4.30 for over drive pulling, don't know how the equate but should put me into the 3.73 range, and yes bothj front and rear have to be changed.

 

sorry this may not belong here but i just got a f350 dually 4x4 crew cab,wondering if any one could tell me my gear ratio ,code is f2 it is a 6.0 liter,2003.what kind of mph i might get.

 

Axle Type
31 — 3.73 non-limited slip, F-250/Excursion
C1 — 3.73 limited slip, F-250/Excursion
32 — 4.10 non-limited slip, F-250
C2 — 4.10 limited slip, F-250/Excursion
33 — 4.30 non-limited slip, F-250
C3 — 4.30 limited slip, F-250/Excursion
36 — 4.56 non-limited slip, F-250
C6 — 4.56 limited slip, F-250
41 — 3.73 non-limited slip, F-350 (single rear wheels)
D1 — 3.73 limited slip, F-350 (single rear wheels)
42 — 4.10 non-limited slip, F-350 (single rear wheels)
D2 — 4.10 limited slip, F-350 (single rear wheels)
43 — 4.30 non-limited slip, F-350 (single rear wheels)
D3 — 4.30 limited slip, F-350 (single rear wheels)
46 — 4.56 non-limited slip, F-350 (single rear wheels)
D6 — 4.56 limited slip, F-350 (single rear wheels)
61 — 3.73 non-limited slip, F-350 (dual rear wheels)
F1 — 3.73 limited slip, F-350 (dual rear wheels)
62 — 4.10 non-limited slip, F-350 (dual rear wheels)
F2 — 4.10 limited slip, F-350 (dual rear wheels)
63 — 4.30 non-limited slip, F-350 (dual rear wheels)
66 — 4.56 non-limited slip, F-350 (dual rear wheels)
F6 — 4.56 limited slip, F-350 (dual rear wheels)
81 — 3.73 non-limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
E1 — 3.73 limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
82 — 4.10 non-limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
E2 — 4.10 limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
83 — 4.30 non-limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
E3 — 4.30 limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
86 — 4.56 non-limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
E6 — 4.56 limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
88 — 4.88 non-limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
EW — 4.88 limited slip, F-350 Chassis Cab, narrow frame (dual rear wheels)
G3 — 4.30 limited slip, F-450 Chassis Cab
73 — 4.30 non-limited slip, F-450 Chassis Cab
78 — 4.88 non-limited slip, F-450 Chassis Cab
G8 — 4.88 limited slip, F-450 Chassis Cab
75 — 5.38 non-limited slip, F-450 Chassis Cab
G5 — 5.38 limited slip, F-450 Chassis Cab
GW — 4.10 limited slip, F-450 Chassis Cab
98 — 4.88 non-limited slip, F-550 Chassis Cab
K8 — 4.88 limited slip, F-550 Chassis Cab
95 — 5.38 non-limited slip, F-550 Chassis Cab
K5 — 5.38 limited slip, F-550 Chassis Cab
KW — 4.10 limited slip, F-550 Chassis Cab

 

I'd say you need to drop the gearing a bit, 4.10 would probably do you fine. But i have to tell you that its better for it to tow in 3rd. There is no trans that is gonna like towing in OD and if it starts shifting lots it will burn the trans up. Thats why there is the O/D OFF or tow/haul button. Ford didn't make these trannys to tow in overdrive with lots of weight or in hilly area. The only time i ever to in o/d is with a really light load on some long flat open areas.

And ya the MPG's might be worse but its better for you tranny and you may not have to get gears so low that it kills your empty mileage that you will be getting for the other 97% of the time.

Oh and i tow with a 2004 f250 kingranch PSD when i have to a heavy load. Not the truck in my sig.

Good Luck

 

thanks x_hemi_guy for the info new to this side of diesel ,last two trucks were 7.3 idi for 10 years this is new to me

 

So witha 4.30 I end up with a 3.73 or close for OD, and I know towing in OD is suposed to be NO,NO but if RMPS and torque convertor is kept locked up the should not be a problem? Also adding a cooler from a 6.0 truck I found on Ebay, Am I crazy with this set-up?