I'm finally confident enough to report my findings and impressions regarding the replacement of my rear differential to enhance my tow vehicle's performance (and my own safety).

The background: I have a 2012 Ford E-350 V10 Extended with a rear 3.73 non-LSD that was having trouble pulling a 9,500 lb travel trailer. Part of the issue was an improper weight distribution set-up (the saddles were set on the a-frame to work with a regular length E-350). But the tall rear gear just wasn't allowing the truck to accelerate with any alacrity. At all. Very. Poor. Acceleration.

I trolled this forum and posted some questions, called and spoke to experts in the field, figured out how much it'd cost me, balanced the risks and then got an earful of warnings from my mechanic who warned me *not* to do it!

After much pontification, I finally took the plunge and ordered a Yukon 4.30 LSD gear set from Randy's Ring & Pinion, then ordered the SCT Tuner from Mike at 5-Star.

My Ford dealer couldn't (or wouldn't?) recalibrate my truck to run with a 4.30 gear -- because Ford didn't offer it. They would recalibrate it for a 4.10 for $187. That's why I bought the SCT Tuner.

Anyway, I took the truck to a very well respected transmission shop, King Transmission in Elmhurst, IL, and their surgeons performed the transplant.

My tuner wasn't ready to tune the truck when I picked it up two days later. So I had to drive around with the speedo showing 10 mph faster than what I was really doing. The guys from King said to drive her gently for 500 miles to break her in, so I did. It was hard to tell any difference in off-the-line performance.

When I got the tuner ready with the files (Mike gave me a 92 octane tune, an 87 octane tune and an 87 octane factory tune with a 4.30 rear so I could taker her in for warranty work), I had put about 150 miles on the truck and I pushed her a little bit to feel her out.

It felt a tiny bit more spritely off the line, but suddenly I had a power band under heavy acceleration that spanned 45 mph to the truck's 90 mph cut-off. Seriously. It felt like a 737 on takeoff. I've never felt this brick accelerate so aggressively and continuously to 90 mph. I'm used to feeling the van begin to feel the effects of wind resistance and air intake limitations above 75 or so. I was grinning.

A few weeks later I hooked up the 9,500 lb RV, had Pete's RV in Joliet re-adjust the weight distribution system, and headed up to Copper Harbor, Michigan, for some adventure and rest. The van pulled flawlessly. It towed the trailer up inclines without drama or strain. It passed vehicles on 2-lane roads with power to spare. It returned 9.5 mpg doing 60 mph -- which is 0.6 mpg better than my old Excursion V10 with a 4.10 rear diff could manage.

Without the trailer, my highway mileage at 60 mph was around 16.5 mpg. At 70 mph, I was getting 14.7. Both figures are significantly higher than factory tune. I suspect 87 octane would return slightly less.

At 55 mph, I was turning 1,500 rpms with the 3.73. Now I'm turning 1,900.

The verdict?

I feel like the 4.30 is the perfect gear for my van and my RV towing needs. When towing at 60 mph, it seems to keep the V10 closer to its peak torque and peak operating efficiency than the 4.10 (which was my second option). I'm really glad I made the choice, and I would highly recommend this mod to other E-350 V10 owners if they're unhappy with their truck's tow capabilities.

I'd especially recommend this mod to guys who are planning trips through mountainous regions of the US.

All told, this mod cost me about $2,000. To me, that's a lot of money. But the peace of mind it gave me when towing, and the reduction of stress that resulted, made it worth every penny.

Special thanks to Mike at 5-Star for all his advice and patience. I haven't had better customer service anywhere! And kudos to Randy's Ring & Pinion -- they know their stuff and their expertise helped me make the right decision. Lastly, King Transmission in Elmhurst is top notch. Car guys every one. Look 'em up if you need trans work, I was thoroughly impressed by their expertise -- and their prices.

Lastly, thanks to all of your forum folks. The knowledge base here is unreal. Thanks!!

 

That's very cool I'm glad to hear a success story. Exactly what rpm are you running at 65mph? And 70mph? (Does your van have the same 5speed automatic as my 07 E350 v10?)

However 14.7mpg at 70mph seems like a miscalculation... No offense but you should doubt that result and recalculate it repeatedly.
I suppose I could be wrong though... I just know that I average about 11.5 to 13mpg with about 50-60% highway driving (mostly at 65mph/2,000rpm stock 3.73 gears, and 1,000lbs cargo)

 

I'll have to check my notes for rpms at 65 and 70; yes, my van has the 5 speed, and yes, I double-checked my mpg at 70 mph.

I filled up with premium (92 octane) and reset the trip computer. Drove 70 mph consistently for a few hours, then stopped to fill up again. My computer showed 14.9 mpg, but when I divided trip computer miles by the amount of fuel I poured into the tank, I got 14.7. No kidding. I was shocked, too.

More shocking is the 16.5 mpg that the computer showed when I was consistently driving 60 mph. I figure I'm prolly getting 16 or so.

I've never scene fuel economy like that from a V10 super duty van. Especially one with a 4.30 rear.

Where's the tradeoff? Better towing, better performance, better mpg...

 

Did you ever get the speedometer corrected?

I wonder if the 92 octane fuel with the 5star tune is what improve the fuel economy.

I am very curious what your RPM is at 70 mph and 65 mph. Please find out, do it for me :-)
I am way too analytical to do the gear change without knowing ahead of time.

 

Yes, the SCT Tuner corrected the speedo (Ford Dealer wouldn't recalibrate it for me), and yes, I think the premium fuel may have added 0.5 mpg to the equation.

I'll find my notes on rpms and post again.

 

RPM at 65mph = 2,100
RPM at 70mph = 2,250