car tech heads help bmw dif

[jabba]

I know its a bike site blah blah.

Anyway got an axle on a trike belived to be off a bmw 3 series question is there is a sensor on the rhs of the diff houseing anyone know what this is?
It is wired up with a permanent live for some reason the axle is mated to a p5 rover v8 and auto tranny.
Dont beleive the sensor is connected to the autobox though.

[SammoJim]

According to my Paynes Manual, and by looking under the `rsend of my `91 318 Touring, it do be the speedo sensor

[Jenna]

could also be for traction control/abs. is it a two wire or three wire sensor?

[jabba]

now you got me 2 I think.
sammojim speedo eh will pass it on if your manual says so must be it.

[Hagrid]

could also be for traction control/abs. is it a two wire or three wire sensor?

I agree with Jenna...

Not cus I've got a bl**dy clue what your whittling on about Jab, but cus shes usually right... (OK OK and I frightened of looking in my mirrors one day and seeing her behind me driving her truck )

[btbloke]

According to my Paynes Manual, and by looking under the `rsend of my `91 318 Touring, it do be the speedo sensor

would agree, was the same under my 88 318i and 84 318i

[SammoJim]

Can`t see how it would be ABS or Traction Control.
ECU needs to read independant wheel speed.
Could be done from the diff, but would need two sensors to read speed of each driveshaft.

[Jenna]

the sensor in the diff is used as the 'divided guide' eg. if either of the wheel speed sensors (normally an abs pick up ring) does not match the one in the diff then the ecu knows that a wheel is spinning and can then apply abs pressure to either directly slow or even stop that offending wheel... cheaper systems just use each of the four wheel sensors but obviously this system is greatly floored if the vehicle is in fact going round a bend and and the wheels should in fact actually be all travelling at different speeds ( Ackerman theory).

At the end of the day it depends on the age of the diff, if fits fairly old its unlikely to be off an abs/TC car in the first place, plus normally the sensors that are the norm in abs/tc uses are three wire as this gives a feed, ground and proportional out put (0-5v or 3v depending on ecu type).. on the flip side a speed sensor is is just a magnetic switch which is just open and closed giving a set number of pulses per revolution, this obviously only requires two wires, one a feed and the other a return to the ecu or dash module where the pulses are represented as a figure on a speedo.

simple huuuu!, bet you wished you never asked now ...

[SammoJim]

the sensor in the diff is used as the 'divided guide' eg. if either of the wheel speed sensors (normally an abs pick up ring) does not match the one in the diff then the ecu knows that a wheel is spinning and can then apply abs pressure to either directly slow or even stop that offending wheel... cheaper systems just use each of the four wheel sensors but obviously this system is greatly floored if the vehicle is in fact going round a bend and and the wheels should in fact actually be all travelling at different speeds ( Ackerman theory).

At the end of the day it depends on the age of the diff, if fits fairly old its unlikely to be off an abs/TC car in the first place, plus normally the sensors that are the norm in abs/tc uses are three wire as this gives a feed, ground and proportional out put (0-5v or 3v depending on ecu type).. on the flip side a speed sensor is is just a magnetic switch which is just open and closed giving a set number of pulses per revolution, this obviously only requires two wires, one a feed and the other a return to the ecu or dash module where the pulses are represented as a figure on a speedo.

simple huuuu!, bet you wished you never asked now ...

NOW I remember why I hate cars and bought a bike!


Then another



And then another

[jabba]

Cant beat a debate its an odd looking diff to be not that I would know its covered in cooling fins.