I have an 09 F150 SC with a 5.4 engine and a 3.31 differential. I want to tow a pull-behind travel trailer weighing 6500 pounds. I'm prepared to re-gear to a 3.73 differential. Is this a realistic way to go? Will my truck handle a trailer of this weight? I've priced trading for a F250 and it's scary.

 

3.73s should be fine. Is 6500lb the total wet weight of the trailer, or just the listed weight empty? If you're going to be doing it a lot, look into a weight-distributing hitch also.

 

i would say the 3.31 would be fine behind that 5.4

 

Go ahead an slap the 3:73s under it. I have an o8 stx with a 4.6 with 3:55 and I beleive I could hook a Radio Flyer wagon to it, and it would know its there

 

haha... my 02 f150 4.2 has open diff 3.55s and my 08 has ls3.73s.... and i quite often pull very heavy loads.... my 08 pulls and 18 foot fish and ski bass boat like a ragdoll... but ive pulled a case bachoe with my 02.... it wasnt very safe but i had to tow it about 45 miles on the backroads very easy... pulled it better than it stopped it

 

Your truck is rated somewhere around 83-8400# for towing. You don't NEED to re-gear for the truck's sake, unless you're towing all day/every day. I'd stick with what you got. Then you're not burning as much gas and turning as high an RPM when you're not towing (which I'd assume is most of the time).

I'd compare that to adding extra leaf springs to the front of a truck and screwing up the ride quality all year long to compensate for a snowplow that's only on the truck for a few days out of the year.

You'll have no problem towing up to your rating, and doing it regularly.

I can tell you that my '08 SCAB with 3.55's and a 5.4 is rated to tow 8400#, and I pretty regularly tow between 6500-8000, without issue. Engine and tranny stay pretty cool, and it has enough "get-up" to keep me happy.

I'm with AK on the weight distributing hitch too, but that's regardless of the gearing.

You really can't compare the STX to the 5.4 for 2 reasons...
1. There's a 50+ horsepower difference between these engines.
2. The '09 5.4 trucks are a 6-speed tow-haul tranny with a super-low 1st gear. That's how reach a high tow rating with that high of a gear. The STX is a 4 speed, (i think rated for about 6800 towing).

Remember, if you have 4wd, you have to regear the front too, and that MORE THAN doubles the price. (more labor)

 

Thanks for all the input! Technically, the dry weight of the travel trailer we're considering is 6210 pounds. No doubt we'll be adding a few hundred pounds to that. I've been pulling a trailer about half that size and I do have a load distributor hitch. Even with the smaller trailer, the truck shifts a lot on the hills and even on flat country with a head wind.

 

shut the overdrive off

 

If you are planning to tow at or near your truck's weight limits, you need to scale your truck for its weights configured as you plan to tow. Full tank of gas, all passangers and gear, etc. You need its front and rear axle weights as well as the total weight. Measure each of these individually to account for scale error. Don't just add the front and rear weights.

After you know exactly how much the truck weighs, you need to look up the following three ratings for your truck, they should all be on the data lable:

1) GCWR: Gross Combined Weight Rating, this how much total weight the truck and trailer(s) can weigh and still be safe.

2) GVWR: Gross Vehicle Weight Rating, this is how much your truck can weigh, including the weight the tounge or pin of the trailer puts on the truck.

3) GAWR: Gross Axle Weight Rating, this is how much you can have on each axle and still be safe. The rear axle's rating is the important one for towing.

Now its time for some math, or as the English say "Maths."

Subtract your truck's actual weight from the GCWR. This is the max pull of your truck in its current setup. You will likely be impressed with this number. The numbers to come won't be so optimistic. For example, my truck has a GCWR of 13,500 and I estimate its road weight at 5,500 loaded out, giving me a max pull of 7,000 lbs trailer weight.

Subtract your truck's weight from the GVWR. This is the max payload of the truck, including the tounge weight of the trailer and the weight of the hitch. For example, my truck GVWR is 6,500 and using the previous weight, I have 1,000 lbs payload left. Assuming the nominal 10% trailer weight on the tounge, at max pull, I should have around 700lbs on the tounge, leaving me 300lbs for the hitch and any extra cargo.

Subtract your truck's rear axle weight from your rear GAWR. If this number is lower then your GVWR based payload, adjust your tounge or pin weight down accordingly. Staying with the previous example, if my rear GAWR is 3,550 and the non trailer weight is 2,850 in the rear, and my hitch setup weighs 100 lbs, I better drop the tounge weight to 600 to not over load the axle. Keeping the 10% tounge weight, that means my trailer weight just dropped to 6,000lbs.

Changing the axle ration doesn't usually do anything to change any of the ratings above, but it can make the truck acclerate better.

Also note, air bags, helper springs, and weight distributing hitches don't increase the GCWR, GVWR, or GAWR. They can, however, help push the weight from the back to the front to help if you are over the rear GAWR but under the GVWR.

The last thing to do after doing all this math and properly setting up your rig is to scale it once again and actually confirm your weights. You may need adjust the WD hitch or air bags (if equipped) to adjust axle weights.

One last note: all vehicles are designed with a factor of safety in their weight ratings. This doesn't mean double up your GVWR, it does mean you could get away with putting 1100lbs total weight into a truck with only 1000lbs payload left without too mutch trouble every once and a while. I believe Platninum Sean does something like this. Note, if the weighmaster catches you doing this, it will be a ticket.