I have a 01 Screw with the 5.4, tow package, 3.55 ls, ORP. My
question is I tow a new 4500 lb Terry Dakota 29' travel trailer
out here in Colorado and wanted to know if a 3.73 LS would
be worth installing for better towing performance.

During our vacation the truck did great pulling this 29' trailer
up and down mountains (up to 11,300') but with the 3.55
rear end, the 17" tires I was in 1st gear at 3800 rpms during
most climbs over mountain passes...(up to 50 miniutes for each
climb) (no over heating...)

DO you guys think this change is worth it ...going from a 3.55
to a 3.73 rear end...Also any idea what this may cost to have
Ford Dealer to the switch ??

Thx, TMeyers-Colorado
2001 Supercrew XLT
5.4
ORP, tow package
upgraded radiator
K&N FIPK
Gibson SideSwept cat bacl
2,980 miles

 

If you needed 3800 RPM in first gear to make those grades, a 5% change would net you 4,000 RPM at the same speed and grade.

You'd never notice that difference.

You are likely to notice the difference in direct drive at cruise -- and especially in OD at cruise speed.

You obviously overtook every 18-wheeler going up that grade -- so it was the grade and altitude -- clearly an unusual climb -- that your truck was able to negotiate probably quite well with that gear/RPM.

You didn't mention whether that was WOT or not -- so it is hard to guess as to whether you could have pulled the grade in second gear with a reasonable change in axle ratio.

If your transmission was able to lock the torque convertor during that climb, the only issue that you'd have is the extra heat generated by the transmission as it went thru the planetary gears -- which wouldn't be much less in second gear than in first.

If the climb was with a locked torque convertor -- and at part throttle -- your set-up was probably doing quite well and should be of no concern unless you're doing it many times a day, every day.

 

Thanks for the reply...I was not at WOT...but just mantaining a
good rpm/mph...I was doing 35mph in first at around 3700-3900
rpm's if I remember correctly. I shifted to 1st and held it there so
how do you know if the TQ was locked up or not ?????..How
do you tell ???...SHifting to 2nd gear bogged down my speed
and I actually lost speed at WOT...so I would drop it in first and
it seemed to hold 35 mph with no problem...Fully loaded I was
towing 6000 lbs (trailer, people, gear, bikes.ect...)...
I love this truck and hate to alter anything that was factory
installed but I was wondering if the 3.73 would help me get
to 2nd gear in the same situation...The water temp never
moved....but my power steering pump was whinning big time.
After the screw cooled off going down the passes the PS pump
would quite down to a whisper...does this sound normal for
a hot PS pump ?...I was passed by turbo diesel's quite often.
Mostly by Ford Powerstokes on the steep grades...Man those
thing can haul a$$ with a heavey load !!!!!!!!!

Thx, TMeyers-Colorado
2001 Screw

 

TMyers, while I can't answer your question for you, are you familiar with the colorado chapter of f-150s? E-mail me mattadams@pcisys.com if you are interested in joining.

 

Have you considered a Superchips? I'm sure it would be cheaper than switching gears.

 

Hey TM,

My $0.02 worth is that the 3.73 gear would help but only the 5% mentioned and that may be enough to get you into 2nd under the mentioned conditions, but that depends on your transmission setup (i.e. shift kit or stock).

I seriously doubt the converter was locked up in 1st gear.

The power steering noise was probably due to running the engine at almost 4K RPMs under the uphill condition and the noise is just less at a lower RPM when almost coasting down the hills.

The chip mentioned may help to get more power and hence burn more fuel to go faster, but the gears and wheel OD are what control the overall engine RPM and not the engine's computer and it's settings.

Again, only my $0.02 worth.
Good luck though with your issue.

DaveMan

 

the converter will never lock up in 1st gear

 

I switched to 4.10's and found the truck tows my trailer much better with the new gears. It will stay in 3rd where it used to downshift to 2nd. The change also gave me more power when travelling solo in OD.

I don't think going to a 3.73 is worth the effort.

Ian

 

Another way to accomplish the same goal would to buy a set of used 16" wheels and go to a smaller od tire. Re-install the 17's when you get back home for better mileage etc. Take a look at
www.dakota-truck.net/TIRECALC/tirecalc.html
www.tirerack.com has charts giving diameters and revs per mile as well as load ratings for most tire sizes.
I have a '98 F-250 LD with a 5.4 (235 hp), 3.73 gears and 255/70/16 tires. I pulled my 25ft Alumalite travel trailer over Wolf Creek Pass with no problem. I haven't tried Monarch Pass yet!
Good Luck

 

IMO it is not worth swaping ratios to go up only one ratio. If your going to do it, get 4.10's. It's going to cost around $1000 to get the front and rear done. Plus, I'm sure you will loose 1-2 mpg without the trailer.

I like Model A's idea the best, but the change may not be large enough to make a big difference. It's simple math to know what the differance will be (even more simple with the calculator below).

 

Hi T Meyers,

We have basically the same vehicle but with a SuperCab instead of the Super Crew cab, a 2001 5.4 Lariat with the ORP, and with the ORP (Offroad Package), the factory tires are right about 32", the tallest you can get from the factory on an F-150. Those 32" tires with 3.55 gears allow nowhere near enough torque multiplication to tow much of anything, especially up any kind of grade. Sure, it will do it, but not with any real comfort or efficiently.

With ours, at 80 mph in Overdrive, we're turning about 2000 rpm, and far less at "normal" towing speeds of about 65 mph; that's nowhere near enough for just the vehicle weight alone, as it's alwsy downshifting at the drop of the proverbial hat, without towing anything. (Note: no mods on this F-150 yet, as we were accumulating all the stock data for the before & after)

We're going to be towing our project Lightning with this vehicle, so with the Lightning & trailer & tools weight, we'll be pulling an easy 6500-7000 lbs., and probably should go ahead and do 4.56's, but we'll try the 4.10's most likely.

Changing to 3.73's will not be worthwhile, I agree with all the posters who said that, as it will get you only a 5.07% change, so you need to go with a 4.10 gear ratio. With the ORP, that means it's a 4X4, so you have to do the gear ratio change front & rear, an expensive proposition. So if you're going to go that route, definitely go for the 4.10's.

Though I wouldn't take this route, another choice would be to install the smallest tires & wheel package from the factory on these F-150's, the 16" setup, which would give you a 30.4 " tall tire, and that would effectively give you roughly 5% more torque multiplication without doing the gear ratio change. Me personally, I'm in favor of doing the gear ratio change, as that would net you a 15.49% change ((4.10-3.55)/3.55) but you do have that other option.

When you do either one, change tire size or gear ratio, the speedo calibration will be thrown off of course, affecting speedo & odo as well as shift points a bit. A Ford dealer can recalibrate that for you, but *only* for tires sizes & gear ratios offered on that exact same vehicle from the factory. Since 4.10's are not offered, then you'll need to go to the aftermarket to get your speedometer recalibrated, whiich will automatically bring the odometer & shift points right back into line, as it's all VSS-dependant.

You've already received some good advice here of course, I'm just dropping in with a couple of quick comments, and by now you may well alreday be well aware of all of this.

Best of luck whatever you decide,

 

TMeyers,

I have 4.56 gears in my 97 f150 and turn 2950 rpm @ 80mph.
I used to have 3.55 gears and ran 2200 rpm @ 80mph. I have 265 70 17's for wheels and tires and also live in colorado where elevation is a factor.

 

I have a 2001 F150, Lariat, Supercab, 4x4, short box 7700 gvw
I pull a 24' Frontier 5th wheel trailer, my truck and trailer
are about 350 lbs of max gvw for the unit (13500 lbs)
I have 3.73 gears, 5.4 triton v8, auto trans and the trailer
towing packager..heavy rad (yes I checked it ) trans cooler etc
I have done some heavy pulling this summer and also had to
shift into 1st gear....3500 rpm and could only get 40 - 45 mph at the best, the mountain I was going up was 1744 Meters (multipy by 3 for feet), This rig is a beauty...did not over heat, no noises
from the P/S pump....I would say to stay where you are with what you have
Happy Camping

 

What the other posters said about tire size is important. Here's a link to a Tire Size Calculator that's fun to play with.

http://www.powerdog.com/tiresize.cgi

List the various tire sizes in the box:

Example.
265/70-17
235/70R16 ....click on Compute Sizes.

The first listed tire size is charted for 60MPH. In this case, the difference for the smaller tire is -8.4%. The diameter of the large tire is 31.6" versus the smaller 29" tire (OEM for my 2003 F150.

It would be interesting to hear from someone who has actually downsized tires for the purpose of towing.

 

The problem with downsizing tires is the possibility of exceeding their load rating.