I have a 2001 super crew with a 5" lift and 35" tires. It currently has 3:55's in it but i am looking to put 4:10's in it. I want to know if any one has put 4:10's in there late model F-150. I think that 4:10's will give me back the power i have lost. I was also told actually riase m mpg, because right now it takes a lotmore power to accelerate then it should. And I am wondering what kinda rpm's i should expect with 4:10 compared to 3:55?

Any help or feed back would be appreciated, thanks

 

Choosing an axle ratio is fairly involved. Of most importance is knowing the speed and load and performance at that speed you expect.

For example:

You may want to run fully loaded at a cruise speed of 65 MPH with reasonable power to take 4% grades without downshifting.

That might mean that you want to keep higher in your HP range -- say 2600 RPM or so.

If you want to do that in Direct drive -- you'd need one axle ratio -- which will give you the option of using OD when unloaded to gain gas mileage. But you'd be sacrificing a gear for towing.

You could also choose an axle ratio that would give you that 2600 RPM in OD -- which would give you greater flexibility (more gear/rpm choices) at lower speeds -- but would eliminate your option for light loads at slower (OD) engine speeds.

You'll notice that for most applications the 3.55 ratio gives you the ability to use second gear (automatic tranny) for anything between 15 and 55 MPH -- wich gives a pretty good towing gear for taking steep grades.

When you move towards higher ratio (like 4.10, 4.56, etc), you lose the ability to run 55 in second -- which puts you into direct -- at considerably lower HP (RPM) range.

Many people still don't like to tow in OD (the Y2K manual does not recommend using direct instead of OD) -- however the way the tranny controller is set up it allows the tranny to preserve itself by downshifting at smaller throttle settings than I'd prefer.

There is little difference between 3.73 and 3.55 ratios (I had the 3.55 in a 97 and have the 3.73 in the Y2K -- and the tire size differences in the two trucks nearly perfectly offset the gain in gearing (sigh).

To make an intelligent choice of gearing, you really need to examine your torque/hp needs at the speed you wish to gear for. It is not easy. Ford has done a remarkable job of mating the gear ratio for the 5.4 at 3.55 or 3.73 -- and/but I'd prefer a 4.10 for the way I tow (13,500 GCW at 70mph in OD).

I am at 2,000 RPM at 70 -- which provides mediocre HP. If I were using the truck for towing more then the 10% that I do, I'd be swapping gears to get the RPM up a bit.

As a compromize, the 3.73 is fair (note: the 4.10 will be used in the 7700 series in 2002 -- which would put me at 2200 RPM at 70 in OD. Better, but not good).

I really prefer towing at 60 to 65 MPH, but the Wife-o-Meter complains when the world passes us.

What are your towing performance requirements?

 

I agree with Y2K, except that I can run 55 in 2nd with my 4.10's. As I recall, it puts me at about 4000 rpm.

I love my 4.10's and wish Ford had made them available from the factory.

Ian

 

I agree. You're making nice HP at 4,000 -- and it's not an excessive RPM and a decent speed to be taking a grade.

Q: On such a pull, does your torque convertor ever finally lock up?

I haven't needed second gear for much of a pull yet -- and if it will lockup the TC, then it will keep the heat buildup (due to TC churning) to a minimum.

 

I have never noticed the TC locking in 2nd. A few people here have stated that it will lock when the selector is in the "2" position but mine doesn't seem to. I haven't needed to be in second for more than about 5 minutes straight when towing though. Before I got the 4.10's I was in second on every hill (when towing).

I am going to add a bigger trans cooler and a temp gauge to my trans because I am a bit concerned about the heat. The factory cooler is pretty small. I have been meaning to use the factory diagnostics to watch trans temp when towing, but haven't tried yet.

On the Ford Diesel website there are instructions on how to manually lock the TCC by jumpering the wiring harness through a switch. I was thinking of trying this because I would like to be able to lock it in second or when going downhill.

Ian

 

I am not concerned about the heat. They test these things in AZ up a grade in very hot conditions with no fan fully loaded -- and they pass Ford's spec's. While nobody recommends THAT kind of operation (and I'll never be pulling up a grade in AZ without my fan), I doubt that I'll overtax the cooling system.

I have thought about monitoring the diag for the temp -- but cannot remember how to enable it (lemme see, was it coffey in the left cup holder while rolling down the window -- or was it Pepsi in my left hand while whistling and pushing the button as I start the engine? -- remind me). I've even thought of relocating the temperature sensor directly to the transmission instead of the air (damn - I can tell when it's hot out without that temperature gage) -- but doubt that it would read high enuff for it to be useful (perhaps in Celcius -- but then just how hot IS 25 or 125C -- not being a kid -- nor growing up in GB, it's about useless to me unless it's -40 or 0 or 100 C).

I'm heading off to Jamaica tomorrow -- so I won't be reading your post for a week or so -- so thanks, in advance, for your post.

PS -- from what gear ratio did you change? I checked mine at 3,600 rpm at 55 with a locked TC in 2nd today -- bet it would be an additional 500-600 at WOT.

 

Ian N,
Which manufacture did you go thru for your gears and are you happy with them. I am thinking of going to the 410s. I have the 355s now. I do tow sometimes but really I went from 16 inch stock to 17 inch performance tires and want to get back to a more favarable rpm range for performance. Jacobs Ignition, superchip and a gear change seem to be the best performance changes for the dollar. Just one left.

 

WLF: Mine are Precision Gear (good enough for NASCAR, good enough for me). I am very happy with them. I heard that Ford will be making 4.10's available in the 7700 pkg, so the gears might be available from Ford soon. I had 3.55 from the factory.

Y2K: Check out http://www.mustangworld.com/ourpics/fcar/dtcodes.htm for the display setup. I haven't tried it yet but Neal says it works.

I will check my RPM at 55 in second to give you the real number in the next few days. I have the ORP package so YMMV if you have smaller wheels and tires.

Ian

 

Ian N,
Precision Gear it is (good enough for me also).
Although I have a 4x2, I bought the ORP wheels and tires off a 98 Expy. I have since changed the tires for the Nittos I have now. They are about the same height but have a wider tire patch (and greatly improved performance). If you ever want to change tires to improve wet weather driving and all around performence then go for the NITTO 404s. They were rated #1 in a test done by Truck-in mag on 20 inch tires and they are just as good in the 17 inch size...
THANKS