Has Anyone Swapped the 4.30 Rear End for the 3.73 in an F-450? - Ford Powerstroke Diesel Forum
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Old 10-25-2013, 03:43 AM
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Has Anyone Swapped the 4.30 Rear End for the 3.73 in an F-450?

I was going to post this in the "Powertrain Problems" area... but it really isn't a problem, per se.

I was just wondering if it was possible... and if so, how difficult it would be... to remove the 4.30 rear end from my F-450, and replace it with the 3.73 rear end that is used in the F-350 DRW trucks?

Since I tow a 5th wheel toy hauler RV, and often visit campgrounds where I have to back the rig into the site... I opted for the F-450 because of the wider front-end geometry and the resulting better turning radius. But, of course, the F-450 is only offered with the 4.30 rear end.

Even if I fully load my rig, it'd only weigh no more than 18,000 lbs, and for that, I don't think I need the 4.30... especially when the 3.55 rear end in my old F-250 pulled 15,000 lbs. just fine.

Since the F-350 DRW models are offered with the 3.73 rear, I'm thinking it shouldn't be that difficult. Just a simple swap and the reprogramming of the computer... but, of course, that's just a guess.

I love everything about my truck, except for that 4.30 rear. It's killing me in gas mileage. I just pulled an EMPTY 8x16 enclosed trailer that weighs about 3000 lbs. from NC to MS yesterday... and only got 10 mpg with the cruise control set right at the 70 mph speed limit for well over 80% of the trip. It's obviously much worse when pulling my RV... somewhere in the 7-to-8 mpg range.

Considering I plan on pulling the RV around 20,000 miles per year... getting 1 or 2 more mpg by installing the 3.73 rear would probably pay off in the long run.

Knowing that I can't be the only person who's ever thought of this, I was just wondering... has anyone already done this, and can give me an idea of what to expect?

Thanks...
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Old 10-25-2013, 04:44 AM
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Yep, I feel your pain, , , check my sig below.

I have not inquired lately, but I think the F450 only came as a 4X4 when I got mine. That would mean changing the front axle too and there goes the wide front end??

You are correct that the fuel savings would soon pay for the change though.

BTW - our campers are almost identical if you park them side by side.
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Old 10-25-2013, 05:08 AM
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Quote:
Originally Posted by mowdoc View Post
...I have not inquired lately, but I think the F450 only came as a 4X4 when I got mine. That would mean changing the front axle too and there goes the wide front end??...
Hmmm... ok, I admit that I hadn't thought about the front end gears. I guess changing one w/o the other would create a problem if engaged.

But, since you can get the F-350 DRW in a 4x4... unless the actual pumpkin housings are different... why couldn't a 3.73 gear set be placed into the housings?

Or, if that's not feasible, I'd be willing to lose the 4x4 capabilities to get the 3.73 rear. I hardly ever use 4x4 anyway... and it's not like I'm going to take this big 22-foot long beast mudding thru the swamps.

I guess I'm just thinking back to my older car days, when we used to swap out different rear-end gear sets into the housings all the time. I know that our vehicles are better now overall... but things were simpler back then, and no axle changes were needed.
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Old 10-25-2013, 01:12 PM
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You might try calling a reputable shop in your area to see about swapping your gears. I traded out 3.55s to 4.10s on a Dodge a few years ago and it was $1000 per axle for ring and pinion and new bearings, labor etc.
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Old 10-25-2013, 03:14 PM
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Yep your looking at close to 2K for a job like that, and could get much higher!
There's a chance you cant even put a 3.73 on a 4.30 carrier...I'm really not sure on every axle but you may need new carriers also?
I would also assume you'll need some sort of a programmer to set your MPH.
And finding a good shop that does A1 work is a must!!
I've been doing gear changes for years as a 2nd income and
IMO it aint worth the cost to gain a few MPG, besides you'll lose a little TQ also.
Gene
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Old 10-27-2013, 12:18 AM
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X2 on the wide front axle turning radius. With double cab and long bed it takes a lot of ground to crank that 40' 5er around backwards.

Loaded i am a bit over 26k; 16 of that being the 5er. Despite Ford's 5er Tow ratings and GCVWR, this pretty much maxes out rear axle WR, and GVWR. I have often thought what you are thinking, but even the interstate in western Virginia, PA, and WV can get things pretty hot (240) from time to time on long uphill pulls in 5th. That is when i decide it would be a dumb idea; really dumb if you go out to the Rockies and add altitude to the equation. My 5er is pretty square fronted and is right at 13'6". In a stiff head wind I notice a 10+ increase in boost to maintain speed versus calm. I think this would be worse with 373's.

GearVendors makes a nice overdrive, but the recommend not using when towing. Payback ends up being 80k+ miles running empty. Several years ago i saw that someone went through the process of cutting his drive shaft as part of the install and advised folks to buy a new one piece driveshaft.

The 350 dually rear axle has a significantly higher weight rating than a 450, so the carrier may well be different.

If you will always be going 70 a wind deflector might be of some help - it will keep the bugs off the front of the trailer.

Fuel addiditive helps, especially where cetane rating is not posted on the pump. Virginia seems to have great fuel, but a lot of places do not. I think California is the only state requiring a minimum cetane of 45; and these trucks were designed for 50. You may have gotten the first loads of winter fuel - always a bit fewer mpg's but no gelling. Bio mix ratios (especially zero to 10-20) can make a big difference in mpgs.

I believe our larger than 350 dually tire diameter helps us a bit in final drive, but we are still 200+ rps higher than a 350. Putting a 3.73 into your drive wheels, you would turn slower than a 350.

Wouldn't it be great if the "old" heavy 450 coming back in March has a dual speed rear end? The 19.5 tires will still max out at 80 mph or so.
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Old 10-27-2013, 06:41 AM
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Pyle bros

If your in the Houston area check out Pyles bros in Baytown tx. They specialize in setting up rear ends in trucks and racing applications...
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Old 10-29-2013, 06:58 PM
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I have a 2012 F350 dually pulling a 21,000 lb goose neck. At best i get about 8.5 at 65 mph. And I don't have near the wind resistance. Don't think you would ever regain the money invested.
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Old 10-30-2013, 06:57 PM
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Keep your gears, 4:30 are great for towing. Get a gear splitter. Like gear vender or someone else. Then you have the best of both worlds and about the same price as the swap.
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Old 10-31-2013, 08:30 AM
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Quote:
Originally Posted by ATCguy View Post
I was just wondering if it was possible... and if so, how difficult it would be... to remove the 4.30 rear end from my F-450, and replace it with the 3.73 rear end that is used in the F-350 DRW trucks?
I have a 350 DRW. My TH averages about 17K, highest ever was 19 (CAT scales).

I averaged prior to the latest trans flash - 55 = 11.5 mpg, 65 = 9.5 mpg

After the flash I get 9-9.5 regardless of speed up to 65-68
Personally, I wouldn't bother with the gear swap. You would be better slowing down.

There is a good chance that changing out the ring and pinion will give you little gain, no gain or lost mpg.

Odds are you truck will work harder trying to push that shoebox through the air at 70 with the 3.73 then it does with the 4.30's.

On a side note, a couple of camping buddies that have 2013 450's are getting better mileage then they got with their 2011 350 DRW's.

Looking forward to seeing what the 2015 brings to the table - should have bought the wide axle in the first place.
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