Ford F350 Differential Swap-Out Questions & Other Upgrades

[DR Buck]

I'm considering swapping the differential gearing in my 2003 F-350.  It currently has 3.73 gearing and I want to go to 4.30 for towing larger loads.  Ford increased the towing capacity in later model F250s and 350s by 4000 lbs going to the 4.30 gearing along with some other changes.   I've already had my transmission rebuilt and beefed up for heavier towing and I am in the process of upgrading the suspension.   I will most likely rebuild with new ring and pinion gears and not swap out the entire axles.    I haven't messed with differentials since back in the old days (circa 1973 and earlier), and then 2 wheel drive only.

1 -  I'm assuming I need to change both front and rear differentials on my 4 WD?
2 -  If I stay with the stock tire size how do I recalibrate the speedometer
3 -  What am I missing?   (besides the cash to do this  :D)

[bill m]

Speedometer comes off of the transmission. Will need a new gear for in there.

[snowstorm]

what motor do you have? if its diesel with the 5sp auto it will already tow anything you can put behind it. the v10's did use a 430 rear. the speedo can be recaled with a computer it has a tone ring in the rear end. 4x4 you must change front and rear ring gears

[snowstorm]

Speedometer comes off of the transmission. Will need a new gear for in there.

no it dosent tone ring on the ring gear in the rear end. ford hasnt used a speedo cable in a lot of years

[snowstorm]

the only difference between a f250 and a 350 single rear wheel is one extra spring in the rear

[snowstorm]

how big are you towing? if you have a gas motor and 4 sp auto i am sure you know not to tow in overdrive. you will spend a lot of cash changing gears and may not gain enought to be worth it. if you want to tow big go diesel. and no the 6.0 is not junk...i own 2 of them. they can be a very good motor

[Dan_Shade]

just drive around in low range.    ;D

[DR Buck]

The engine is a 7.3 diesel.   I have had the transmission (4R100) valve body & torque converter replaced with a hi-preformance after market kit made specifically for towing and snow plowing.

2003 F 350 SRW has a tow rating of 13000 lbs.   Later models using the 6.0 with the 4.30 differential are rated at 17500 lbs towing.

[Dan_Shade]

to add a somewhat useful post, a differential is a differential...

I'm assuming that the rear is a limited slip, the front may/may not be an open diff. 

getting the gears set is the same regardless of make/manufacturer: you need to get the pinion depth right, and then move the ring gear left/right to get the right backlash.  I have a pinion depth gauge and a tool that I made to hold the pinion flange if it has one.  On my 2004 F250, the rear has a flange, and the front a yoke for the u-joint.

Do you have an impact wrench?  this makes it much easier.   I don't know if the pinion bearing is preloaded by a crush sleeve or not. 

Back in the day when I was drag racing, I took a pinion bearing and honed it out so it would slide on/off of the pinion gear to get the depth right with different shims.  There was a company that sold a stackable shim set for the carrier which would move the diff left/right....  you would measure the two carrier bearing shims, and set up the stack for the same combined thickness, then use the marking compound to get the mesh right.

you will need to do something to fix the speedo

it's gonna cost some bucks to swap. 

[DR Buck]

it's gonna cost some bucks to swap.

That's what I'm afraid of.  Looking at ring & pinion kits on line cost is going to be around $500 - $600  for each differential.   I just spent over $500 for a set of Sumo Springs & 4 Bilstein shocks, and another $250 for a K&N performance air filter upgrade.  Then there is the Banks engine exhaust brake I want to add at another $1300.      Maybe I should consider a new truck. 

[1270d]

Im pretty sure you can recal the speedo with certain programmers.  The 7.3 is a bombproof engine.  My last worktruck with a 7.3 got parked after 240000 "highway" miles.  .ie.  plowing bush road all winter for log trucks, hauling fuel and supplies everyday and generally spending most of its life on rough, dusty, muddy, gravel roads.  Ford super duty's are some tough tough trucks.   Others may be also, but this is where my experience lies.

[snowstorm]

The engine is a 7.3 diesel.   I have had the transmission (4R100) valve body & torque converter replaced with a hi-preformance after market kit made specifically for towing and snow plowing.

2003 F 350 SRW has a tow rating of 13000 lbs.   Later models using the 6.0 with the 4.30 differential are rated at 17500 lbs towing.

6.0 has more hp and tq than 7.3 but they peak at a higher rpm. the 7.3 has more lugging power. the 5sp auto has a lower first gear it mat shift a lot but it works really well. cheapest way to gear it down buy shorter tires. neither ford or ih approved an exhaust brake. reason being the motor uses hydra lifters and the brake could over power them causing vales to hit things they shouldnt

[lumberjack48]

I would drop the tire size, a friend of mine had a KW, 450 Cat, with 22,5 rubber, it was under powered getting going on the landing and in hills. He dropped the drivers to 10,00 20, it was like a different truck, solved the problem.

[clww]

If it were me, I'd go with the same size tires and change both (since it's 4X4) pumpkins to 4.56 ratios.

[DR Buck]

It's looking more like I will be holding off on the differential change for a while.   I think I'll just wait until I pick up the new 5th wheel and see how well it pulls with just the transmission and suspension upgrades.  I am still planning on adding the Banks engine exhaust braking, probably over the winter after I stockpile some cash.

If it were me, I'd go with the same size tires and change both (since it's 4X4) pumpkins to 4.56 ratios.   

I wonder what the 4.56 will do to my fuel mileage?   What I've read indicated going to 4.30  could drop it as much as 2 mpg.

[Cypressstump]

Best thing you can do is join - Powerstroke.org

Some of the most informative info on the web about our powerstrokes.  You may want to ask specifically about the engine brake, as already mentioned, they have been know to cause undue damage.

It's a great site to learn about these diesels.

[Bobus2003]

Alot of guys just re-wire the EBPV (Exhaust Back Pressure Valve) to function as a Engine Brake if you want it. I personally hate the EBPV so I take it out of the turbo.

How big of loads are you trying to Haul/tow? I have towed well into the 43/44K lbs Gross area many times with my 7.3l 6spd w/3.73's and I did the same with my 6.0l 6spd with 3.73's.. In my honest opinion its the Tranny thats the limiting factor, not the rear end gears

[DR Buck]

How big of loads are you trying to Haul/tow? I have towed well into the 43/44K lbs Gross area many times with my 7.3l 6spd w/3.73's and I did the same with my 6.0l 6spd with 3.73's.. In my honest opinion its the Tranny thats the limiting factor, not the rear end gears

I've already taken care of the transmission with the rebuild I had done this summer.   As I said I'm goin to hold off on the differential change at least for a while.   Though I will still probably add the engine brake.   I will be towing a 5th wheel toy hauler that is 13K dry and has a gross of 16K.  I don't want to rely only on the vehicle and trailer electric brakes when towing in mountain areas.   I'd rather have the engine brake slow the rig down on long grades than risk heating up my pads and rotors.

Finished installing the Sumo springs and new Bilstein shocks last night.  Almost ready to go pick up the new Toy-hauler.  8)