changing gears in my diffs?
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changing gears in my diffs?
New to the Forum... Thank you all for your information. Not sure how this works or if I am posting this question in the correct place but here goes...
I have an 02 excursion with the 7.3..... rear end needs to be reworked and I am thinking of lowering the gears from 3.73 to 4.30 and adding an ARB. I currently run 315 but may go bigger in the near future. I also am adding armor front and back....I pull some but mainly use off road and as a daily driver...
Thoughts?
I have an 02 excursion with the 7.3..... rear end needs to be reworked and I am thinking of lowering the gears from 3.73 to 4.30 and adding an ARB. I currently run 315 but may go bigger in the near future. I also am adding armor front and back....I pull some but mainly use off road and as a daily driver...
Thoughts?
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
Thoughts... 7.3 tolerates 35’s without a regear ok but the 4.30 sure is more fun to drive.
Other then cost the ARB is great, I have them front and rear.
Armor, meh. I have it but it just lipstick. Suit yourself.
put a tape measure to verify your tire height, my 37’s are just barely over 35. Then compare your rpm to stock using the AOD box
https://www.randysworldwide.com/calculators/rpm/
Other then cost the ARB is great, I have them front and rear.
Armor, meh. I have it but it just lipstick. Suit yourself.
put a tape measure to verify your tire height, my 37’s are just barely over 35. Then compare your rpm to stock using the AOD box
https://www.randysworldwide.com/calculators/rpm/
Logistics Pro
Joined: May 2017
Posts: 3,523
Likes: 483
From: Southern OH
I wouldn't recommend an ARB in the rear of a daily driven vehicle, on the street with it unlocked all you have is a $1000 open differential that does nothing to give you better traction when one wheel is on a loose/slick surface, sure you can lock it if you want to wait for the compressor to build pressure and the locker to engage but with it locked you have a $1000 spool that will chirp tires going around the corners. I think you would be better off putting a Detroit locker or Detroit Truetrac in the rear. For gears I would go with 4.10 if you are keeping the 35s and 4.30 if you are going with bigger tires, however if you do get 4.10 gears and decide to get bigger tires later 4.10 gears and 37s isn't bad on a 7.3. The 7.3 makes its torque low in the rpm band and doesn't need to rev as high as a 6.0 or a gas engine.
Gear calculator Gear Ratio Calculator
Gear calculator Gear Ratio Calculator
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
Stock 31” tire on 3.73 @70mph = 1981 rpm
315-35” tire on 4.10 @70 mph = 1929
315- 35” tire on 4.30 @ 70 mph = 2023
keep in mind though....most tires labeled 35” are not really that tall. My 37”s measure 35.5 tall and turn 2050 rpm at 70mph
but my 40’s are a true 40”
ARB vrs others... about the only time the my arb is less then idea is around the city in the rain. Making a sharp turn at an intersection and needing to accelerate hard results in wheel spin before you can hit the switch, alsmost all other traction needs are well suited to the ARB for me. Especially snowy roads where a locker can be a hinderance. Learn the pros and cons of each and choose.
315-35” tire on 4.10 @70 mph = 1929
315- 35” tire on 4.30 @ 70 mph = 2023
keep in mind though....most tires labeled 35” are not really that tall. My 37”s measure 35.5 tall and turn 2050 rpm at 70mph
but my 40’s are a true 40”
ARB vrs others... about the only time the my arb is less then idea is around the city in the rain. Making a sharp turn at an intersection and needing to accelerate hard results in wheel spin before you can hit the switch, alsmost all other traction needs are well suited to the ARB for me. Especially snowy roads where a locker can be a hinderance. Learn the pros and cons of each and choose.
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
Need a few speciality tools to R&R the diff and set the pinion debth and backlash but DIY is not unheard of.... I have a gear shop do mine.
Ive run both the Detroit no spin locker and the Tru Trac and prefer the Tru track on the street but the Detroit in the dirt the clunking and banging of the Detroit is irritating on the road. I’ll never run anything but an ARB again. Unless it’s a spool. LoL
Ive run both the Detroit no spin locker and the Tru Trac and prefer the Tru track on the street but the Detroit in the dirt the clunking and banging of the Detroit is irritating on the road. I’ll never run anything but an ARB again. Unless it’s a spool. LoL
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Logistics Pro
Joined: May 2017
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From: Southern OH
@00t444e
I like detroits and have run them on my jeep but they can cause issues in the snow on the road
I like detroits and have run them on my jeep but they can cause issues in the snow on the road
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Junior User
Joined: Jul 2006
Posts: 77
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From: Wake Forest, NC
I'm doing it right now - replacing 3.73s with 4.30s.
https://www.ford-trucks.com/forums/1...ion-build.html
The rear will get a Detroit TrueTrac. I'm leaving the front open. I plan on running 35" tires, but I could step up to 37s in the future.
CR
https://www.ford-trucks.com/forums/1...ion-build.html
The rear will get a Detroit TrueTrac. I'm leaving the front open. I plan on running 35" tires, but I could step up to 37s in the future.
CR
Cargo Master
Joined: Mar 2005
Posts: 2,790
Likes: 24
From: Mount Royal, NJ
On 35's, If you are towing or ever will tow, get 4.88 gears. You'll come close to a stock 4.30 gear with OEM tire size performance.
If you never will tow, get the 4.30 gears. They will be closer to stock performance with those tires.
ARB's are expensive. figure about $1000 per axle for the lockers, Then you have them installed for about 600 to 800 bucks each. It starts to run into ouch time. Then there is the wiring, and, if they are ARB's, installing the compressor and lines. Then where do you put the switches? That is why I ended up installing myself. But you better be very mechanically inclined and have the tools to back it up. ARB's are not nearly as easy in total as a standard Diff to change out.
If you never will tow, get the 4.30 gears. They will be closer to stock performance with those tires.
ARB's are expensive. figure about $1000 per axle for the lockers, Then you have them installed for about 600 to 800 bucks each. It starts to run into ouch time. Then there is the wiring, and, if they are ARB's, installing the compressor and lines. Then where do you put the switches? That is why I ended up installing myself. But you better be very mechanically inclined and have the tools to back it up. ARB's are not nearly as easy in total as a standard Diff to change out.
Logistics Pro
Joined: May 2017
Posts: 3,523
Likes: 483
From: Southern OH
For a gas engine that would be right but for a 7.3 Powerstroke you don't want gears that low unless you have even larger tires. The 7.3 has a lower rpm range and makes peak torque at a much lower rpm than the 5.4 or 6.8 gas engine.
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
3.73 @ 70 w stock 31s = 1900
4.88 @ 70 w35’s = 2300
4.30 @ 70 w35’s = 2000
Why do you recommend 2300 rpm for the 7.3 ?
Tuned
Joined: Sep 2010
Posts: 424
Likes: 5
From: Missouri
I did the 4.10’s with a trutrac last year on my 7.3 running 35’s. Honestly didn’t notice much difference,which is ok as I mainly did it in preparation for the travel trailer we plan on getting next year. If everything goes well...should also be getting a BTS trans before we get the trailer.
Ford did the work with OEM rear 4.10’s and Yukon up front with the newer aluminum rear diff cover for $2k
Ford did the work with OEM rear 4.10’s and Yukon up front with the newer aluminum rear diff cover for $2k
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Thank you all for the info and opinions....I decided to go with the ARB in the rear and 4.30's... I am having my mechanic do it ( I wish I had the time ) and it should be done by the middle of next week... due to a shload of little things on the front end that needed some attention it is going to hurt the wallet......I will keep you all posted.