Speedometer issue....

[dhallibu325e]

Im hoping somebody can help me out as I have been seriously frustrated for the past 2 weeks trying to figure this out. I just recently purchased a 1987 Bmw 325E - It needs a lot of work, which is to be expected for a 600 dollar car but ever since I bought it the speedo hasn't worked. I went with the simple solutions first. Here is what i tried.

New speed sensor, mounted at diff.
Reflowed solder joints on speedo board.
Checked continuity between harness behind cluser and the plug for the speed sensor at the diff.
Jumped the two wires at the diff to see if the speedo would get a signal.

Everything so far has tested fine. I have come to the conclusion everything in the car for the speedo works.
(Speedo, Wiring, Sensor)

The only thing possible it could be is the previous left something out of the diff when he took it apart, or the diff is not the standard one for my car and it is not passing through the speed sensor. Does anybody have any ideas on how to find out what kind of diff I have and if it is possible that my sensor isnt the right one for the diff?

Thanks to all for your help ahead of time!

[ArtemLepilov]

Did you check the speedometer itself? Do you get the pulse off the sensor?

What do you mean your diff isnt passing through the speed sensor?

[dhallibu325e]

I did test the speedometer.

From the way the speed sensor looks, It seems that there is something inside the differential that spins inside the two posts on the sensor, which then sends a pulse through the wires to the speedometer which then calculates the speed. When feeling inside the hole where the speed sensor goes it seems as if there is nothing in the diff to pass through the speed sensor. Could the previous owner have never put it back in? or do diff swaps cause it to need a different speed sensor... (maybe some longer than others?)

[Ablice]

A speedometer set up correctly should just fine on the entire range of E30 diffs...and there are quite a few of them.

[dhallibu325e]

My final belief is that im missing something inside the diff

[Ablice]

It's all you now

[87'mgodackE30]

Kinda a stupid question, but it happened to me once, did you check your fuses, I had one out once and my entire cluster didnt work.

-Mgodack

[dhallibu325e]

Yes, i tested my fuses, everything has power and is operating correctly. Except there is nothing between the dif and the speed sensor to make the speed sensor pulse. Does anybody have pictures of the inside of the dif?

[luvrocks]

I have a 1987 325 and also had a speedometer that didn't work when I bought it but it ended up being the speedo gears were stripped out. Seems to be a common problem, especially in warmer climates. I had to order and replace all of the factory gears in the speedo with new nylon ones.

[dhallibu325e]

I thought it could be the gears too, but the fact that my odometer doesnt work, and mpg only moves when deaccelerating sort of pushes that idea out - I have come to the realization i am missing the trigger ring inside the diff.... im going to have to put a whole new diff on because i cant just find that part.

[87'mgodackE30]

I've also heard that VDO and Motometer (?) gauge faces are not interchangable...I've also heard that its not true, they are...

check that maybe...but I'm not sure if I'm right, could someone correct me if they are in fact interchangable?

-Mgodack

[hoyabmw]

I've also heard that VDO and Motometer (?) gauge faces are not interchangable...I've also heard that its not true, they are...

check that maybe...but I'm not sure if I'm right, could someone correct me if they are in fact interchangable?

-Mgodack

Well, I swapped a VDO speedo complete into my motometer dash. No problems til I changed the diff (and it hasn't worked since...) It's an autox car that rarely sees other driving, so I guess speed based on the tach.