trans change?
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New User
Joined: Oct 2008
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From: Florida
trans change?
I have a 2003 f250 with a 7.3 and a stock 4R100 tranny. Is there any advantange to change it out for a 5 or 6 speed tranny and can it be done without changing rears etc.??? Would I gain any power or fuel mileage if I can change it out? I've only had the truck for about 1 month and bought it used. Truck has 96,000 miles on it and I tow a 30' 5th wheel trlr that weighs about 11,000# and would like to up the mileage from the present 8.5 to 10.5 MPG when towing. Any help would be appreciated. The only mod I know about is the exhaust has been changed to a banks.
John
John
Post Fiend
Joined: Mar 2007
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From: Texas
With the 250, you should have a 3.73 rear end. I don't think RPM's at 11,000 pounds is your problem. I'd guess wind resistance plays a much larger role in your fuel mileage. You could add an aftermarket overdrive unit like Gearvendors or US Gear, but I don't know if you'd see enough savings to pay for the unit. Also if you get the RPM's too low, you'll fall out of the powerband and might end up with worse mileage.
Tell us what kind of mileage you're shooting for and maybe we can offer some suggestions.
Tell us what kind of mileage you're shooting for and maybe we can offer some suggestions.
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New User
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From: Florida
Thanks for the quick reply. Yes, the rear is a 3.73. In Florida, I was hoping to be able to get up to 14 mpg or a little better. The wind sure puts a lot of drag on the trlr and possibly a roof mounted deflector would help.
John
John
Post Fiend
Joined: Mar 2007
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From: Texas
I've pulled much heavier loads with my 350 with the 3.73 rear end, but I have a stick shift, and my loads don't have near the wind drag that your trailer does. Are you looking for 14 mpg on flat land, or are you including travel through some hills? Are you running in drive or overdrive when pulling? What RPM's are you turning and at what speed to get 10 mpg? Is the banks exhaust a 4" that goes from the turbo back to the rear?
Hopefully others will start chiming in soon, since I can pick whatever gear I want, as often as I want with my stick shift. A better intake, some gauges to keep an eye on things, some tranny mods to firm up the shifts, and a DP-Tuner might help you some, but we'll need someone with an auto and experience with a travel trailer to give you a better idea.
Hopefully others will start chiming in soon, since I can pick whatever gear I want, as often as I want with my stick shift. A better intake, some gauges to keep an eye on things, some tranny mods to firm up the shifts, and a DP-Tuner might help you some, but we'll need someone with an auto and experience with a travel trailer to give you a better idea.
Frmr Ford Trans Engr
Joined: Aug 1999
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From: SE Florida
The only way you're going to get 14 MPG on this rig is to tow at 50-55MPH.
Changing the auto for a manual isn't going to get you much, if any, fuel economy. The overdrive ratio on the auto is 0.71:1. On both the five and six speeds the overdrive ratio is 0.72:1. Since the auto has a lockup torque converter at highway speeds there is no slip in the torque converter, so the manual will run slightly higher RPM than the auto. There is a slight loss running the pump in the auto, but it's no more than 10 lb-ft, so it's loss on fuel economy is too slight to measure.
Lead Driver
Joined: Dec 2006
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From: San Diego, CA
There is less power loss through a manual than a slushbox, but I don't think the marginal power gains at the rear wheel will really be that noticeable in your economy considering the weight of the truck (and load you are pulling) combined with the wind wall that the SD is. The price of the swap alone I think would make it not worthwhile. IMO there are way too many other mods that you can do to improve performance/economy that would be more of a benefit (intake, programmer, etc...) and cost less in the long run in addition to driving slower like Kovalsky said.
Post Fiend
Joined: Feb 2007
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From: Blairsville,Ga
for towing economy I actually think the 3.73 rear end gear is a handycap,to be in the RPM sweet spot your speed has to be 68 to 70 mph with stock tires
A slower speed will be less wind resistance but will be out of the power band
I find if I can keep RPMs between 1800 and 2000 that is where best fuel milage is
A slower speed will be less wind resistance but will be out of the power band
I find if I can keep RPMs between 1800 and 2000 that is where best fuel milage is
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Lead Driver
Joined: Dec 2006
Posts: 7,093
Likes: 147
From: San Diego, CA
for towing economy I actually think the 3.73 rear end gear is a handycap,to be in the RPM sweet spot your speed has to be 68 to 70 mph with stock tires
A slower speed will be less wind resistance but will be out of the power band
I find if I can keep RPMs between 1800 and 2000 that is where best fuel milage is
A slower speed will be less wind resistance but will be out of the power band
I find if I can keep RPMs between 1800 and 2000 that is where best fuel milage is
FYI: the '03 peak torque is 525lb-ft at 1600rpm (around 420 at the wheel*) and peak HP is 250 (275 for the 6 speed) at 2800rpm (around 214 at the wheel*).
*the wheel stats come from this month's Diesel Power article's baseline of a stock '02 4x4.
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)?That would definately help out on the power AND the milage.
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New User
Joined: Oct 2008
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From: Florida
Thanks to all for the replies and information. I will definately look into some mods to help the situation but after the first of the year. Too many outlays and not enough income for a few months. On the way home on Thurs. I keep the tack at approx. 1600-1750 RPM's which put the speedo at about 62 MPH so I have to fuel up before too many non towing miles are put on this tank of fuel so I can check the mileage at that speed. All the miles on this tank of fuel will be on almost level ground from Birmingham Al. to Boynton Beach, Fl. by way of Disney World in Orlando. Thanks again for all of the input.
John B
John B
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Joined: Mar 2004
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From: West Coast/L.A. Area
Seems like I run about 1750 rpms at between 55 and 60 mph in OD on my 4R100 and I've got a 4:10 rear end. I also get between 10 and 12 mpg running an Edge Evo on tow mode pulling a 15K lb 5th wheel 12'9" high. Something doesn't sound quite right?
Postmaster
Joined: Nov 2003
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From: Utah County, UT
I usually try to tow around 65mph with my trailer. Speed and slippage are probably taking your mileage down to the 8mpg range. If I run 65 semi flat land with no extra head wind, I can get around 11 to 11.5. If there is a head wind it starts to drop to closer to 10mpg. If there is a tail wind, I will tow in OD and pull at 70, for what ever reason it pulls really good at 70 in OD vs 65 in OD. difference of 200rpm 1800 vs 2000. Closer to the sweet spot I presume.
What are the ratios for a 6speed? if it breaks it up sooner between 4th 5th and 6th, vs the auto of 3rd or 4th(OD). I would think you'd be able to find that sweet spot easier for the desired speed. Best milage towing I have gotten was 12.5 with a tail wind, enough traffic that I set it at 60mph.
What are the ratios for a 6speed? if it breaks it up sooner between 4th 5th and 6th, vs the auto of 3rd or 4th(OD). I would think you'd be able to find that sweet spot easier for the desired speed. Best milage towing I have gotten was 12.5 with a tail wind, enough traffic that I set it at 60mph.
Post Fiend
Joined: Feb 2007
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From: Blairsville,Ga
I have 4.10s and it really don't matter what size or weight enclosed trailer I hook behind it the milage is the same about 10 to 11.5 mpg towing around 65 mph
a few I know have trucks with 3.73s and theirs is about the same as mine towing a 16 - 18 ft enclosed trailers
a few I know have trucks with 3.73s and theirs is about the same as mine towing a 16 - 18 ft enclosed trailers
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From: Florida
I filled up the tanks today and the mileage towing at about 62 mph with no head wind in OD came up to 13.5 mpg. I had gotten the same mpg with an earlier tank of fuel, and thought it was a fluke but I guess with my set up and my driving habits the sweet spot for my truck is 62 - 65 MPH with my trlr.