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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > N20, N26, B46, B48 Turbo Engine / Drivetrain / Exhaust Modifications > Differential ratios?
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      09-13-2019, 08:53 PM   #1
Tantibus
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Differential ratios?

Hi guys!

I have a question in relation to the differential ratios on the f32 models.

Iíve blown my rear differential and was wanting to source another one, but the ratios are different.

Thereís a 3.15 and a 2.81 ratio. I was wondering if thereís a way to find which one can be used without looking at the diff under the car and what each of them are for?

Itís a 2015 420i, auto gearbox and n20 engine.

If someone can help, it would be a huge help!
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      09-14-2019, 12:21 PM   #2
rjd_F30
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How did you blow your differential?

I would go to realoem.com and look up the part number for your differential and then go from there.
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      09-15-2019, 05:24 PM   #3
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Thanks for the reply!

Iím honestly not too sure, itís likely because Iím putting down too much power, but I was sure that the bottom end would be able to handle the power gains.

I did check out realoem.com, wasnít lucky enough to find the part I needed.

Thanks so much for your help though!
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      09-15-2019, 08:48 PM   #4
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Hi that model came with a 3.15 differential if it is an automatic you can check. https://www.automobile-catalog.com/auta_details1.php
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      09-15-2019, 09:01 PM   #5
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Quote:
Originally Posted by Tantibus View Post
Thanks for the reply!

Iím honestly not too sure, itís likely because Iím putting down too much power, but I was sure that the bottom end would be able to handle the power gains.

I did check out realoem.com, wasnít lucky enough to find the part I needed.

Thanks so much for your help though!
Hmmm, I think this should be the page for your car. https://www.realoem.com/bmw/enUS/sho...diagId=33_2122

This is the differential for an October 2014 build, right hand drive, rear wheel drive 420i with an automatic transmission. If that info is correct (less the build date, I just guessed yours) then it looks like you should have a 3.15 final drive ratio. Hope that helps! If any of that info is wrong, post the exact details of your car and I can take another look.
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      09-15-2019, 10:12 PM   #6
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Quote:
Originally Posted by Tantibus View Post
Hi guys!

I have a question in relation to the differential ratios on the f32 models.

I’ve blown my rear differential and was wanting to source another one, but the ratios are different.

There’s a 3.15 and a 2.81 ratio. I was wondering if there’s a way to find which one can be used without looking at the diff under the car and what each of them are for?

It’s a 2015 420i, auto gearbox and n20 engine.

If someone can help, it would be a huge help!
Getbmwparts is a good source for correct part numbers too
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