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CORRECT: diff info (archive)

[ Follow Ups ] [ 5-series (E28) Message Board ] [ Msg. Board FAQ ]

Posted by Rob Anderson on January 29, 2001 at 18:10:40:

In Reply to: Re: 3.73 diff specs? posted by RonW on January 29, 2001 at 14:04:50:

The speed sensor on every E28 is in the diff. It reads the signal off of the ring gear. What it really is, is a pulse generator. If you remove the speed sensor you will see it has a U shape that sticks into the diff. There is an extra plate that is in the diff which is attached to the ring gear. What happens is that this plate has a number of tabs that come off of it that when the diff rotates they pass through the center of the U of the sensor. Depending on the number of tabs to pass through the sensor in a given time tells you the speed. The reason you do not need to use the sensor out of the diff you removed is because all of the extra plates are the same. They are all the same diameter and all are calabrated to how fast the rear wheels are spinning. Don't worry about it. Use the best sensor and throw it in the car. The only change you will see is at a given speed you will be turning higher RPM. You can calculate how much higher using the equations on my technical articles page which I have a link to on another post of mine to this thread.

Lastly, please do not post wrong information, I understand that we are all hear to help each other, but I have found it confusing numerous times just trying to figure out what is correct and what is incorrect.

Older BMWs such as E12s, E9s, E3s, and others use a mechanical speedo drive which is run off the output shaft of the tranny. THIS IS DIFFERENT FROM the E28s and later cars. Only on these older cars do you have recalibrate the speedo if you change the diff ratio. On the E28s and newer cars you do not have to.

M535i SIG Chief Technical Advisor

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