No speedometer issue after diff replacement

[8920vt]

so i replaced the diff on an 88 e325, put a m3 4.11 diff and corosponding pinion in the E housing. all went smooth and when i went to go test drive it the speedo didnt work.

i replaced the diff speed sensor, nothing, pulled the cluster apart and checked everything, grounds and soldered joints, still nothing

any ideas? this thing is driving me crazy

thanks
ian

[graphikg]

Reviving--- did you get this figured out? Sounds like my problem after replacing my cars rear end components. Cleaned the speedomter wire connections and still nothing.

[DaveSmed]

Checking the speed sensor is pretty straightforward.

Jack up the back of the car, drop the brake and put it in neutral.

Get your meter and set it to either continuity check or resistance.

Unplug the diff sensor and connect your meter to it.

Depending on your diff (LSD vs open) when you spin one of your wheels, the other might spin in the opposite direction. If that happens, chock that wheel so it can't turn. If they both spin in the same direction, you are OK.

Watch the meter, it should alternate between open circuit and continuity as you slowly spin the wheel. (or open lead, and very low resistance.)

[wakeboardr42393]

Checking the speed sensor is pretty straightforward.

Jack up the back of the car, drop the brake and put it in neutral.

Get your meter and set it to either continuity check or resistance.

Unplug the diff sensor and connect your meter to it.

Depending on your diff (LSD vs open) when you spin one of your wheels, the other might spin in the opposite direction. If that happens, chock that wheel so it can't turn. If they both spin in the same direction, you are OK.

Watch the meter, it should alternate between open circuit and continuity as you slowly spin the wheel. (or open lead, and very low resistance.)

why would the resistance change? do the two sides actually connect? i've seen the sensor before and just thought it was a magnet thing that generated pulses of low voltage. I'm interested as to how this works. My speedo and nothing else related (odo, avg speed, etc) are working. and I don't have any ac when axles are spinning in gear on jacks

[jlevie]

The sensor is a reluctance type that generates a pulse train when the sector wheel in the differential is moving. A bad sensor, the wrong sensor for the differential, or a wiring fault are possibilities in this case.

[wakeboardr42393]

By ac i meant ac generated by the sensor- i read in another post that the sensor should generate ac while diff is spinning (such as in-gear), but i'm not sure how accurate this is, either. you seem knowledgable on this subject.

I tried the above posted method, by setting my multimeter to continuity, and had someone rotate the hub by hand while the car was in neutral, and i got short pulses of continuity from the sensor.

next to check is the same test, wherever the 2 wires come up near the instrument panel, to see if the signal is getting that far. I'll have to take the dash apart i'm assuming. there is a more detailed description of how do do this elsewhere.

thanks for the reply! any help is appriciated. i'm not particularly keen to working on electric systems of a car. I have a basic knowledge but the stuff is just very fussy from my experience.

:)

[Doughnut]

Check continuity from the wires in the plug (at the diff) too earth on the body of the car, could be that they were squashed during installation of new diff?

Did you use the same sensor pick up wheel when you swapped internals?

[Cletonius]

Did you use the same sensor pick up wheel when you swapped internals?

This was going to be my question. Did you reinstall the giant toothed ring? That's what passes through the pickups on the speed sensor.

[DaveSmed]

The sensor is a reluctance type that generates a pulse train when the sector wheel in the differential is moving. A bad sensor, the wrong sensor for the differential, or a wiring fault are possibilities in this case.

Holy crap, this is rare. Jim slipped up.

You're thinking of the ABS sensors. The differential sensor is a reed switch and a magnet, very simple pulsed open-closed output.

[FLG]

Holy crap, this is rare. Jim slipped up.

You're thinking of the ABS sensors. The differential sensor is a reed switch and a magnet, very simple pulsed open-closed output.

Jim is correct, it is a reluctance type sensor which sends voltage to the speedometer. It is not a reed switch.

Edit... Maybe you are correct. I have no idea anymore.

Someone Wana clarify?

When I calibrated my speedo I needed a/c voltage in varying wave forms to correspond to a certain speed. Thus I beleive Jims correct.

Sent from my Galaxy Nexus using Tapatalk 2

[Wanganstyle]

Are you sure the speed sensor installed matches the car and the toothed wheel also? \

***** original statement of OP is confusing:******

If the donor of internals and gear is a e30M unit then why was it installed into an eta housing?
the entire E30M unit will just bolt in.

The housings are identical and one has no reason to Interchange unless the iron case was somehow damaged.
*****


There are 2 different diameter steel toothed wheels and 3 different styles of magnetic pickup;

the wrong combination=no speedo reading.

E30 6 cyl and e30m have large diamter tooth wheels
E36 and e34 have smaller diameter tooth wheels and also different magnetic sensors

Sent from my GT-N7100 using Tapatalk 2

[DaveSmed]

Jim is correct, it is a reluctance type sensor which sends voltage to the speedometer. It is not a reed switch.

Edit... Maybe you are correct. I have no idea anymore.

Someone Wana clarify?

When I calibrated my speedo I needed a/c voltage in varying wave forms to correspond to a certain speed. Thus I beleive Jims correct.

Sent from my Galaxy Nexus using Tapatalk 2

Speedometer sensor:




ABS Wheel speed sensor:




Granted I will say that typically, disagreeing with Jim on E30 matters is usually a good indication you are the one that's wrong. Your doubt was warranted.