Can someone help identify my rearend ring?

[mwdsonny]

Everything I see says my rearend is supposed to be a 4.47. But when I installed 35s on my bronco my speedometer was perfect according to both gps and radar signs. I had some funky shifting, something I couldn’t place my finger on, so I decided in my wisdom to update my tire size from 33s to 35s and shifting seems right but speedometer is off 5%. Doing the math 33s with a 4.46 rear end is about dead on to 35s with the 4.7 rear end. So I took and checked my rear end and the housing said 4.46 the same as my door called for. I decided to do a fluid change and check the gear. I found part number MB3Z-4209-FA which only thing I can find says it’s a 4.27 so I’m wondering if ford maybe installed a wrong rear gear.

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[Bigmoose]

Which trim?

 

[mwdsonny]

2021 badlands non sas 2.3L auto.
also to clearify I was not the original owner I bought it in Oct 2024 with 11,400 miles on it.

 

[Ducati1098]

Everything I see says my rearend is supposed to be a 4.47. But when I installed 35s on my bronco my speedometer was perfect according to both gps and radar signs. I had some funky shifting, something I couldn’t place my finger on, so I decided in my wisdom to update my tire size from 33s to 35s and shifting seems right but speedometer is off 5%. Doing the math 33s with a 4.46 rear end is about dead on to 35s with the 4.7 rear end. So I took and checked my rear end and the housing said 4.46 the same as my door called for. I decided to do a fluid change and check the gear. I found part number MB3Z-4209-FA which only thing I can find says it’s a 4.27 so I’m wondering if ford maybe installed a wrong rear gear.

It’s 4.46
That’s an engineering number, not a service part number.
The actual part number is MB3Z-4209-C
Also, it’s not uncommon for factory speedometers to be off by 3-5%

 

[Brian_B]

My immediate thought on seeing this thread pop up

“Why would anyone pierce their rectum?”

 

[mwdsonny]

It’s 4.46
That’s an engineering number, not a service part number.
The actual part number is MB3Z-4209-C
Also, it’s not uncommon for factory speedometers to be off by 3-5%

wouldnt that then make mpg off by 3-5% I would think that would be a huge lawsuit and fines from the epa for falsifying mpg stats.

 

[VAtruck]

If you divide the number of teeth on the ring by the number of teeth on the pinion, it will give you the ratio.

 

[Dadsquatch]

Sounds dirty….

 

[DarthLincoln]

My immediate thought on seeing this thread pop up

“Why would anyone pierce their rectum?”

yeah I busted out laughing when I first read the thread title in the Latest Posts feed.

 

[Ducati1098]

wouldnt that then make mpg off by 3-5% I would think that would be a huge lawsuit and fines from the epa for falsifying mpg stats.

No. It would change your calculated MPG or whatever the instrument cluster shows.
It’s never going to change your actual MPG

Either way you look at it, with tire wear, your speedometer is never going to be perfectly accurate. Which is why 3-5% is just considered normal, for every vehicle.

 

[BigMeatsBronco]

it says it right there 42 ÷ 9 = 4.66 ratio. wait that dont make sense... Usually the manufacturer does list the tooth count in the part number, but apparently not in this case...

 

[BlueWaffle]

My immediate thought on seeing this thread pop up

“Why would anyone pierce their rectum?”

Because instead of a yucky fart noise... Now I can wiggle just right and it'll whistle

 

[SierraBronco]

My immediate thought on seeing this thread pop up

“Why would anyone pierce their rectum?”

You can make shapes! Like play-doh gone wrong. Or right if you’re in to the kind of thing.

 

[mwdsonny]

I guess my title game is weak. .

 

[Keith J.]

Everything I see says my rearend is supposed to be a 4.47. But when I installed 35s on my bronco my speedometer was perfect according to both gps and radar signs. I had some funky shifting, something I couldn’t place my finger on, so I decided in my wisdom to update my tire size from 33s to 35s and shifting seems right but speedometer is off 5%. Doing the math 33s with a 4.46 rear end is about dead on to 35s with the 4.7 rear end. So I took and checked my rear end and the housing said 4.46 the same as my door called for. I decided to do a fluid change and check the gear. I found part number MB3Z-4209-FA which only thing I can find says it’s a 4.27 so I’m wondering if ford maybe installed a wrong rear gear.

I work at the Ford Sterling Axle plant and every ring has the ratio cast into it and every pinion has the ratio stamped into the pinion head. Unfortunately, we lost the bid for the Bronco/Ranger differentials to Dana, not sure if they have identifications like that or not.

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