HELP!! FRONT DIFFERENTIAL Blown 4.8is

[nitrogass2000]

Hello, its that time again with my lovely BMW.

BLOWN FRONT DIFF 2004 4.8IS.

I bought a whole parts car 2005 3.0L

Would it be ok to use that diff in my 4.8is (I know the ratio is different) but would it interfere with the transmission/transfer case somehow?

[Ricky Bobby]

3.0L diffs are 4.10 ratios and the ratios are definitely not the same in 4.8iS

[nitrogass2000]

Or maybe i can slap the two together have a shop swap the correct gear into the 3.0, i think my spider gear or what ever is gone.

[nitrogass2000]

Originally Posted by Ricky Bobby

3.0L diffs are 4.10 ratios and the ratios are definitely not the same in 4.8iS

I do understand that part..... It will just burn more fuel and kick ass from starts (not that it already doesn't kick ass) My question is will it not mess with electronics/transmission/transfer case... ?

[TiAgX5]

Why not look into swapping both front and rear diffs with the 4:10 gears into the 4.8?

[David.X5]

Not addressing whether it is a good idea, but you would have to change the gears in both diffs (front and rear) or else it will tear up something - probably the transfer case. The DSC would also not like that. People do change the ratios by swapping front and rear diffs with other models of X5, but they seem to go the other way.

Given the amount of work, why not get another used diff and the sell the diff you have with the wrong gear ratio?

[Omerta]

Do not run the front diff with a different ratio than the rear(stock). You will have destructive xfer case and DSC problems.

[lo_jack]

These numbers are just for example, but I think demonstrate the problem:

If you have a 32" tire and a 4.10 gear (3.0i), at engine speed 3000 RPM, The wheel is trying to make the car go 69.58 MPH, assuming transmission gear is 1.0 (again, just for example..removes variables). For a diff gear of 3.95 and all else the same, speed is 72.303 MPH.

So I would think that, as there are speed sensors in every wheel, they would get confused and probably create DSC and ABS faults. Turning and cornering might be odd as well, if it did not break something mechanically.

I swapped a rear 3.0i auto diff into my 3.0i manual. I hear the front is harder. Look for threads about this; there have been a few lately.

You could put both diffs in (since you have a whole parts car), but you will zoom through the transmission gears and lower your top speed, plus burn a lot of gas. Your highway cruise RPM will be higher at normal vehicle speeds.

But if you wanted to put really big all terrains on it and change the overall diameter of your tires by a good deal to match the 4.10s and your transmission gears, that would be awesome.

[TiAgX5]

The 4.8 does not have a speed limiter, provided the top speed is not redline in final drive gear, top speed would not be lost (engine will spin to a higher rpm with 4:10 gearing, due to lower gear vs unchanged aero drag).

A vehicle with a speed limiter would have a lower top speed.

The 4.8 will launch harder and accelerate faster with the lower gearing (better 0 to 60, 0 to 100 and 1/4 mile times).

The sensors in the BMW monitor trans input & output shaft relative speed, the wheel sensors measure wheel to wheel relative speed and the TC transfer torque front/rear.

The sensors do not monitor trans & TC speed relative to wheel speed.

Lower gearing WILL work in the application.

[lo_jack]

If the wheel sensors measure wheel relative speed, do they do so only across the same differential or also front to back? If it is the later, you would have issues.