Community Forums

idoxlr8 · 08-06-2017, 10:27 PM

Trying to troubleshoot a problem with my tachometer in 98' American Dream with a C8.3 and MD3060 Trans. I've verified the tach does work, and I've replaced the belhousing sensor, but still not working.

Best I can tell after digging around looking at MD3060 wiring diagrams is the engine RPM sensor on the bellhousing goes to the transmission controller, then it disappears. I'm not sure if it feeds into a Vehicle Interface Module which then outputs to tach or if the sensor is "shared" with the controller somewhere.

Does anyone know?

dbarton291 · 08-07-2017, 12:26 PM

The engine tachometer normally isn't shared between the engine ECM and the Transmission controller.
The tachometer that is in the dash is usually an output from the engine controller.
I would start from the wiring at the tach itself and work backwards. Just a suggestion.

Piker · 08-07-2017, 06:27 PM

Most people will tell you that your tach signal comes from the alternator.

I've questioned this on our rig, since I've actually driven our rig WITHOUT an alternator, and the tach still worked just fine. Same MD3060 as you. I see no reference to the tach signal in the allison wiring diagram, so there must be another sensor somewhere... I'm just not sure where. It's not on the engine, as I've had the engine out completely for a rebuild.

Maybe there's another sensor on the tranny bell housing that I haven't seen somehow.

-cheers

Bob_C · 08-07-2017, 07:06 PM

Google tack sensor for your setup....

idoxlr8 · 08-08-2017, 07:55 AM

I've found a lot of different posts about people trying to fix these things, but not much about what they found to resolve it. Lots of guessing and not very good wiring diagrams to go off of.

I have been assuming the sensor is a two wire crank trigger/flywheel type sensor since there are two wires on the tachometer to the sensor, but I suppose there's a chance it is driven by the alternator and they just ran an extra ground for some reason.

Last night I reached around the back of the alternator and I can feel two main power cables and three small wires, two of those wires run to a connector, and the third is standalone going into the harness. Guess I'll do some more research into what those go to.

Palazzoteam · 08-09-2017, 10:04 AM

Quote:

Originally Posted by idoxlr8

Trying to troubleshoot a problem with my tachometer in 98' American Dream with a C8.3 and MD3060 Trans. I've verified the tach does work, and I've replaced the belhousing sensor, but still not working.

Best I can tell after digging around looking at MD3060 wiring diagrams is the engine RPM sensor on the bellhousing goes to the transmission controller, then it disappears. I'm not sure if it feeds into a Vehicle Interface Module which then outputs to tach or if the sensor is "shared" with the controller somewhere.

Does anyone know?

M..q+

idoxlr8 · 08-09-2017, 03:43 PM

Quote:

Originally Posted by Palazzoteam

M..q+

???? Lost me on that one.

I did get a better look at my alternator wiring, none of the three wires hook to the field posts like others I've seen for tachometer outputs.

Mr_D · 08-09-2017, 03:46 PM

Quote:

Originally Posted by bob caldwell

Google tack sensor for your setup....

Try "tach" or "tachometer" rather than "tack" which will get you horse riding items.

idoxlr8 · 08-14-2017, 10:13 AM

I believe I've located the RPM Sensor finally, opened up the hatch under the bed and finally spied this critter - sure looks like a RPM sensor to me, it's not shown on the Allison wiring diagram as it's in the bellhousing, I assume it's detecting flywheel teeth.

dbarton291 · 08-14-2017, 10:22 AM

It won't be shown on the Allison wiring diagram. The transmission doesn't drive the engine tachometer.

idoxlr8 · 08-14-2017, 04:17 PM

Quote:

Originally Posted by dbarton291

It won't be shown on the Allison wiring diagram. The transmission doesn't drive the engine tachometer.

Right, but the transmission does have an RPM sensor, which is the sensor I thought was acting up to start with. It's a continual learning experience haha.

dbarton291 · 08-14-2017, 05:14 PM

Yes it does. The 3060 has three speed sensors. One on the output, one internal to the trans that measures torque converter turbine speed and an engine speed sensor in the converter housing of the transmission that is externally accessible.
If you've found a speed sensor in the engine flywheel housing, that may be the one that provides the signal used for the engine tachometer.

idoxlr8 · 08-14-2017, 10:14 PM

Verified that is indeed the tachometer sensor tonight, I used my MSD Signal generator on the wires there at the sensor and it did run the tach. So good news, wires are ok, tach's ok, just need a sensor. Glad to finally have tracked it down.

idoxlr8 · 08-16-2017, 11:10 AM

Called Spartan and ordered a replacement for this sensor. PN# was 5MT2005B which is a replacement that is 690 ohms 3/4-16 thread, but it's not the original pn which spartan said wasn't available anymore. This appears to be a Midtronics Brand, and I'm guessing Spartan marks these up quite a bit if anyone else is shopping around for one you could probably save some $$$ if you bought it someplace else.

I'm going to try and find the original PN when I remove the old sensor.