# F150 With 3.73 Or 4.10 Gears



## larrylisa7176

I have a 06 F150 and was just curious about 3.73 and 4.10 gears. Those of you that have switched to 4.10 gears are you towing in overdrive. I am curious as my truck is equipped with 3.55 gears and runs right at 2500 rpm with OD off at 60mph. I can only imagine the engine rpm difference with 4.10 gears.


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## Devildog

Larry I have the '05 F150 with 3.73, 4x4, and I usually tow with OD off here around SC & GA due to the interstates are up and down. I usually run around 60 to 65, and my RPM's are around 2000, maybe slightly more.

I did a lot of investigation before I purchased my truck back in September, and waited until I found one with the 3.73 and other options I wanted. Cannot complain so far, been on around 4 trips, including GA mountains, and no troubles yet. Let you know after my trip next weekend on the RPM's with the 3.73.


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## Oregon_Camper

I would think if you had 4:10 gears you would not have to use overdrive. The 3:73 gearing would almost require overdrive.


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## 2500Ram

Oregon_Camper said:


> I would think if you had 4:10 gears you would not have to use overdrive. The 3:73 gearing would almost require overdrive.
> [snapback]91147[/snapback]​


I think you got that back wards. With a 4:10 rear your RPM's are higher at hwy speed so it might be possible to tow in OD as long as it's not hunting between 3rd and 4th gear.

Bill.


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## Katrina

2500Ram said:


> Oregon_Camper said:
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> I would think if you had 4:10 gears you would not have to use overdrive.Â The 3:73 gearing would almost require overdrive.
> [snapback]91147[/snapback]​
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> I think you got that back wards. With a 4:10 rear your RPM's are higher at hwy speed so it might be possible to tow in OD as long as it's not hunting between 3rd and 4th gear.
> 
> Bill.
> [snapback]91152[/snapback]​
Click to expand...

What Bill said.


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## larrylisa7176

I found a online gear caculator and showed the following calculation with OD off for my truck with current size tires

3.55 gears at 60 mph 2500 rpm
3.73 gears at 60 mph 2700 rpm
4.10 gears at 60 mph 2900 rpm

Maybe its just me, it seems 2900 rpm is quite a bit at 60mph with the OD off which is why i was curious if those running 4.10 gears are towing in OD.


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## Oregon_Camper

Katrina said:


> 2500Ram said:
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> Oregon_Camper said:
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> I would think if you had 4:10 gears you would not have to use overdrive. The 3:73 gearing would almost require overdrive.
> [snapback]91147[/snapback]​
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> I think you got that back wards. With a 4:10 rear your RPM's are higher at hwy speed so it might be possible to tow in OD as long as it's not hunting between 3rd and 4th gear.
> 
> Bill.
> [snapback]91152[/snapback]​
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> Click to expand...
> 
> What Bill said.
> [snapback]91155[/snapback]​
Click to expand...

I stand corrected...


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## Moosegut

LL,

If you have the 3:55 and are thinking about changing to 4:10, 4:10 may not fit in your pumpkins. You may only be able to go up to 3:73 before you have to swap out the whole pumpkin. I was thinking about going up myself and a mechanic friend said it wouldn't be worth the money to just go up to the 3:73 and he didn't think I'd have room for the 4:10. I'd like to know what you find out for sure if you research this more. If I could change to 4:10 without changing the pumpkins, I'd consider it.

Scott


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## cookie9933

Moosegut said:


> 4:10 may not fit in your pumpkins. If I could change to 4:10 without changing the pumpkins, I'd consider it.
> [snapback]91241[/snapback]​


Pumpkins? Is that mechanical terminology, or have you been watching the Food Network? Or a colloquialism from Nascar Country?









Bill


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## Grunt0311

cookie9933 said:


> Moosegut said:
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> 4:10 may not fit in your pumpkins.Â If I could change to 4:10 without changing the pumpkins, I'd consider it.
> [snapback]91241[/snapback]​
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> Pumpkins? Is that mechanical terminology, or have you been watching the Food Network? Or a colloquialism from Nascar Country?
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> Bill
> [snapback]91250[/snapback]​
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LMAO!!!








To confuse it even more, I often refer to them as the "pigs"


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## Herbicidal

Moosegut said:


> LL,
> 
> If you have the 3:55 and are thinking about changing to 4:10, 4:10 may not fit in your pumpkins.Â You may only be able to go up to 3:73 before you have to swap out the whole pumpkin.Â I was thinking about going up myself and a mechanic friend said it wouldn't be worth the money to just go up to the 3:73 and he didn't think I'd have room for the 4:10.Â I'd like to know what you find out for sure if you research this more.Â If I could change to 4:10 without changing the pumpkins, I'd consider it.
> 
> Scott
> [snapback]91241[/snapback]​


Give these guys a call: Go Unitrax @ 800-622-4327. I bought my 4.88's from them and they were quite helpful, along with very good prices. Both sets of gears (I have a 4x4) ran me right around $425 shipped to my door. I could be wrong, but I would think the overall diameter of the (ring) gear would not change, just the number of teeth. As an example, my stock gears were 3.91's and the new gears fit in the melons







without issue.


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## ninemmbill

I have a 2004 F150 that came stock with the 3.55 gears. A couple of weeks ago I had a local shop swap out the stock 3.55 for 4.10 gears. There is no probelm fitting larger gears. The rear is a 9.75 inch and the front (if you have a 4x4) is a reverse cut 8.8. Total cost $1050.00 for all parts and labor.

As far a driving, the truck definitely feels more responsive. The truck has much more power from a start. I am still in the process of breaking in the gears so I can't give any type of towing report yet, but will let you know by early April.


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## LateralG

Towing with overdrive off is not a problem. In fact, it's advantageous. In third gear, (O/D off) the transmission is in "direct" ... straight through, no gearset involved. In overdrive, the power goes through an added gearset, reducing efficiency.

Going to the expense of changing to a 4.10:1 ratio would be a waste of money, and a step backward, if the result is the same RPM (not RPMs) at crusing speed in O/D as you now get in third gear.

Further, a reduction in fuel economy would result when not towing.

We can fine tune the RPM estimates if I know the overdrive ratio in your F-150. Please check the owners' manual. The 4-th gear (O/D) ratio should be somewhere around 0.7 to 0.8 :1


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## snsgraham

I did this very same thing on my '97 F-150 that had the 4.6. What a difference the 4.10 made on the truck, wow! OD was used quite a bit more and the towing was much more relaxed.
MPG did not change either, except when I was driving it like a Mustang GT!

Scott


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## larrylisa7176

So what would be considered a good 60mph cruising rpm without OD on?

I currently cruise at close to 2500rpm at 60mph with OD off which seems like a good reasonable cruising rpm. I can pull OD on the flatlands with no problem. At the slightest incline i turn the OD off.

I will be going to a longer heavier trailer here shortly and will try the trailer out before changing gears to 4.10 to see how it acts. My reasoning for going to 4.10 gears would be for better climbing power in the hills but dont want a cruising rpm of close to 2900 rpm with OD off at 60mph. If i can pull the flatlands in OD and turn the OD off when climbing that would be a plus.

Anyways i am just speculating and need to see how the new traler tows before i get paranoid about changing gears


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## LateralG

larrylisa7176 said:


> So what would be considered a good 60mph cruising rpm without OD on?
> 
> I currently cruise at close to 2500rpm at 60mph with OD off which seems like a good reasonable cruising rpm. I can pull OD on the flatlands with no problem. At the slightest incline i turn the OD off.
> 
> I will be going to a longer heavier trailer here shortly and will try the trailer out before changing gears to 4.10 to see how it acts. My reasoning for going to 4.10 gears would be for better climbing power in the hills but dont want a cruising rpm of close to 2900 rpm with OD off at 60mph. If i can pull the flatlands in OD and turn the OD off when climbing that would be a plus.
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> Anyways i am just speculating and need to see how the new traler tows before i get paranoid about changing gears
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Larry,
Do you know the RPM @ 60 MPH in OD? If so, we can calculate OD ratio.


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## larrylisa7176

Its right at 1800-1900 rpm


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## LateralG

Here's what you've got:

3-rd gear 3.55 gears at 60 mph 2500 rpm ..... OD 1850 rpm
3-rd gear 3.73 gears at 60 mph 2700 rpm ..... OD 2000 rpm
3-rd gear 4.10 gears at 60 mph 2900 rpm ..... OD 2150 rpm

If you go to 4.10 axle, you'll be turning 2150 rpm @ 60 mph in OD. That might be a bit low on the power curve & result in more gear-seeking by the transmission than you'd like. And when it downshifts, you'll be turning 2900 RPM.

If you stay with 3.55 axle, you'll be turning 1850 rpm @ 60 mph in OD. Definitely too low on the power curve. You'd have to be towing in third gear at 2500 rpm.

2500 rpm is a reasonable engine speed.

With the 3.55 you'll be towing in the more-efficient direct 3-rd gear, and you'll have the full advantage of the OD when not towing. A factor to consider is what % of the vehicle's life will be spent not towing. Another factor is what else you could be doing with the ~$1,000.


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## larrylisa7176

Big thanks. I am going to leave it for now and see how it does. The truck does just fine with the 21RS and will probably be fine with the bigger trailer also. Maybe i'll invest in a hensley instead of gears


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## 2500Ram

Moosegut said:


> LL,
> 
> If you have the 3:55 and are thinking about changing to 4:10, 4:10 may not fit in your pumpkins. You may only be able to go up to 3:73 before you have to swap out the whole pumpkin. I was thinking about going up myself and a mechanic friend said it wouldn't be worth the money to just go up to the 3:73 and he didn't think I'd have room for the 4:10. I'd like to know what you find out for sure if you research this more. If I could change to 4:10 without changing the pumpkins, I'd consider it.
> 
> Scott
> [snapback]91241[/snapback]​


Half correct, any gears will fit in the pumpkin/differential but in the 4x4 front Dana 44 you need to change the carrier out after 3:92 about $160 last I checked.

Bill.


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## Moosegut

LateralG said:


> Here's what you've got:
> 
> 3-rd gear 3.55 gears at 60 mph 2500 rpm ..... OD 1850 rpm
> 3-rd gear 3.73 gears at 60 mph 2700 rpm ..... OD 2000 rpm
> 3-rd gear 4.10 gears at 60 mph 2900 rpm ..... OD 2150 rpm
> 
> If you go to 4.10 axle, you'll be turning 2150 rpm @ 60 mph in OD. That might be a bit low on the power curve & result in more gear-seeking by the transmission than you'd like. And when it downshifts, you'll be turning 2900 RPM.
> 
> If you stay with 3.55 axle, you'll be turning 1850 rpm @ 60 mph in OD. Definitely too low on the power curve. You'd have to be towing in third gear at 2500 rpm.
> 
> 2500 rpm is a reasonable engine speed.
> 
> With the 3.55 you'll be towing in the more-efficient direct 3-rd gear, and you'll have the full advantage of the OD when not towing. A factor to consider is what % of the vehicle's life will be spent not towing. Another factor is what else you could be doing with the ~$1,000.
> [snapback]91340[/snapback]​


Gary,

I appreciate your answer. Thanks. I understand that my 3:55 will tow at 2500 rpm in third gear. With my current setup - 5.4L with 3:55 - I am down to 45 to 50 MPH on a long, fairly steep grade if I don't get a run at the hill. Will the 4:10 rear allow me to take that same grade with more speed and power? I have had no problems so far because I really have only had one or two hills that slow me down on my way to the site. But I do a lot of my camping in the Adirondack mountains and will be testing out the rig in that environment fairly soon. There are a lot of long steep grades and if I have to slow to 45 every time I hit one, I'd druther not. I can change the gears myself so the cost would be substantially less than $1000. A new TV is not a possibility.

Thanks,

Scott


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## Moosegut

2500Ram said:


> Moosegut said:
> 
> 
> 
> LL,
> 
> If you have the 3:55 and are thinking about changing to 4:10, 4:10 may not fit in your pumpkins.Â You may only be able to go up to 3:73 before you have to swap out the whole pumpkin.Â I was thinking about going up myself and a mechanic friend said it wouldn't be worth the money to just go up to the 3:73 and he didn't think I'd have room for the 4:10.Â I'd like to know what you find out for sure if you research this more.Â If I could change to 4:10 without changing the pumpkins, I'd consider it.
> 
> Scott
> [snapback]91241[/snapback]​
> 
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> 
> Half correct, any gears will fit in the pumpkin/differential but in the 4x4 front Dana 44 you need to change the carrier out after 3:92 about $160 last I checked.
> 
> Bill.
> [snapback]91365[/snapback]​
Click to expand...

Bill, (and LL)

So, if I go with 3:92, I won't have to swap out the front differential? I imagine that 3:92 is a big enough boost to make it worthwhile. Heck, it's only 18 less than 4:10.







I don't understand anything that we've been talkin about. All I know is I know I can change the gears myself. Guide me Landreau.


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## 2500Ram

Moosegut said:


> All I know is I know I can change the gears myself. Guide me Landreau.
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Are you sure, Your pinion preload is very specific, only one shot at this or you start over, your backlash on the ring and pinion gear has to be between .007 and .010. Do you have a shop press, dial indicators bearing pullers/press. It's quite involved the average shade tree mechanic would not touch a differential. That being said it is possible, I did an 8.8 and D44 but it took a month of weekends to get it right and would never do it again. Time is money but this is money well spent for a pro and a warranty.

Bill.


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## LateralG

Here's the latest numbers:

Third gear, 50 MPH:

3.55:1 = 2100 rpm
3.92:1 = 2300 rpm
4.10:1 = 2400 rpm

Does anyone have a HP or torque curve for the 5.4? That would help immensely.

FYI: RPM at any speed, any axle ratio can be calculated from any one known combination. (As long as transmission is in the same gear.)

For example:

1) With 3.55 in third gear at 80 MPH, the engine speed is (80/50) x 2100 = 3360 rpm.
If in OD, then rpm = 3360 x 0.74 = 2486 rpm.

2) At 50 mph in third gear with a 4.55:1 axle, rpm = (4.55/4.10)x2400 = 2663 rpm.


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## LateralG

2500Ram said:


> Moosegut said:
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> All I know is I know I can change the gears myself.Â Guide me Landreau.
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> [snapback]91369[/snapback]​
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> Are you sure, Your pinion preload is very specific, only one shot at this or you start over, your backlash on the ring and pinion gear has to be between .007 and .010. Do you have a shop press, dial indicators bearing pullers/press. It's quite involved the average shade tree mechanic would not touch a differential. That being said it is possible, I did an 8.8 and D44 but it took a month of weekends to get it right and would never do it again. Time is money but this is money well spent for a pro and a warranty.
> 
> Bill.
> [snapback]91370[/snapback]​
Click to expand...

Bill,

I agree with the challenge of properly setting up the assembly.

Also, if the carrier assembly is purchased as an assembly, with ring gear, pinion gear & spider gears installed, then it's pretty much plug-and-play, isn't it?


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## Moosegut

2500Ram said:


> Moosegut said:
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> All I know is I know I can change the gears myself.Â Guide me Landreau.
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> [snapback]91369[/snapback]​
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> Are you sure, Your pinion preload is very specific, only one shot at this or you start over, your backlash on the ring and pinion gear has to be between .007 and .010. Do you have a shop press, dial indicators bearing pullers/press. It's quite involved the average shade tree mechanic would not touch a differential. That being said it is possible, I did an 8.8 and D44 but it took a month of weekends to get it right and would never do it again. Time is money but this is money well spent for a pro and a warranty.
> 
> Bill.
> [snapback]91370[/snapback]​
Click to expand...

Well, you just talked me out of a do-it-myself on that one. I'm getting the feeling I don't just open it up, clean off the old gasket and throw the new gears in.







I'll talk to the brother-in-law (a truck mechanic) and see if he can do it. If not, it'll go in the shop. If it's all worth it.

Thanks,
Scott


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## Moosegut

LateralG said:


> then it's pretty much plug-and-play, isn't it?
> [snapback]91374[/snapback]​


Now plug-and-play is something I understand!!!







So, I guess I CAN do it.


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## larrylisa7176

I had 4.88 gears installed in my jeep wrangler a few months back and watched the mechanic do them. Its no where near plug and play. Requires some specific tools along with a press and knowledge on how to read the ring gear pattern for the correct gear mesh.


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## tdvffjohn

If you have a rear cover on your rear, then it is by no means plug and play. If the entire punpkin assembly comes out as one from the front of the rear, that is what is referred to as plug and play. One unit out and if you have a assembled pumpkin you 'could' replace, but you still have axles to deal with.

Not something you want to learn on and not for someone who is told how to do it. If its a 2 wheel drive truck and you could find a rear with the correct ratio at a junk yard, that would be the easiest. Just swap the rear. Still not cheap.

John


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## 2500Ram

LateralG said:


> Also, if the carrier assembly is purchased as an assembly, with ring gear, pinion gear & spider gears installed, then it's pretty much plug-and-play, isn't it?
> [snapback]91374[/snapback]​


Never seen one sold that way and it would only be possible with a true Pumpkin meaning when you crack the dif the gears and everything come out when you unbolt it to drain the oil. A Dana 44 is that way, a Ford 9" is that way but I'm not sure on the newer equipment. I wouldn't think you would save much money though. Someone still had to set everything up and you'd pay dearly for shipping the pumpkin, it's heavy. It's possible but I didn't see that option when I did mine.

Bill.


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## snsgraham

The sweet spot of the Ford modular engines seems to be right around 3,200-3,400 RPM. My 4.6 was that way as is my buddies 5.4.
Torque wise the modular 6.8 V-10 has something like 85% of the available torque available below 1,900 RPM. On my truck this is about 400+ foot pounds of torque. I would think the torque curve on the smaller modular's would be in a similar spot. All of the ford truck engines have a lot of snap right off the bat.

Scott

Post Script;
I will be most likely adding 4.30 gears to mine eventually. This is a work truck and the MPG's just are not affected as much as the leverage gains of a deeper gear would benefit me.


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## 2500Ram

I just uploaded a few pics to my Gallery of the Ford 8.8 rebuild. This will show you some of what's involved but not everything. The pictures are cover off, Carier with ring gear off, spider gears 2 still inside, New Ring Gear and bearing, old pinion gear in rear housing.

I have more if interested.

Bill.

http://www.outbackers.com/forums/index.php...album&album=169


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## Moosegut

2500Ram said:


> I just uploaded a few pics to my Gallery of the Ford 8.8 rebuild. This will show you some of what's involved but not everything. The pictures are cover off, Carier with ring gear off, spider gears 2 still inside, New Ring Gear and bearing, old pinion gear in rear housing.
> 
> I have more if interested.
> 
> Bill.
> 
> http://www.outbackers.com/forums/index.php...album&album=169
> [snapback]91390[/snapback]​


Fagheddaboudit. Aint no way I'm doin THAT! Oh well. Maybe I'll just start saving my pennies for a new truck.


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