7,8 or 955 Tach Replacement?

Mine is opposite.
Tach works but hour meter quit.

JD still sells them...Not cheap.

One guy here was successfull at fixing His....perhaps He'll chime in and provide some answers.

Its cable driven off the back of injector pump on a 955.

No clue how an electric would work with no ignition...What I have done is mount a reflective part on front pulley?flywheel in my case and have the reader somewhere near it. They do make some aftermarket kits like this........Mounted one on a goofy Suzuki powered jet boat I had when trying to milk as much speed possible by jetting carb and trying different impellers in the pump. That unit is long gone as it was nowhere near fast enough and was never gonna be.

Tractors are kinda dusty dirty under the hood so not sure how reliable something like that would be.

I think it is beyond repair! For a while it would read really high then settle in but finally the needle started spinning like a wacko thing all over the place.
It broke the needle in half then the center part also fell off!!

I had a Perkins 4cyl powered wood chipper that had an electronic tach, it ran off a signal generated by the alternator. The original (Japanese) alternator was replaced by a previous owner with a GM/Delco 1 wire that didn't have the tach terminal installed. I had to put a kit in it, very simple.
Maybe the original JD alternator has a tach terminal? Could have 1 added? Swap out for a GM 1 wire?

svobronco said:

I had a Perkins 4cyl powered wood chipper that had an electronic tach, it ran off a signal generated by the alternator. The original (Japanese) alternator was replaced by a previous owner with a GM/Delco 1 wire that didn't have the tach terminal installed. I had to put a kit in it, very simple.
Maybe the original JD alternator has a tach terminal? Could have 1 added? Swap out for a GM 1 wire?

Click to expand...

I'll look at that. Thanks.

From what I've found online, I think the original Denso alternator should have a provision for a tach signal. I sent a message to DB Electric and asked them that question. I'll post up when they get back to me.

If it has a tach terminal it will be under the sheet metal cover on the back. I'd take mine off and look but it's 3 1/2 hrs away.

I'll see if I can take a look tomorrow.
Thing is, how am I going to calibrate an electric tach? Looks like it would mean buying equipment.
I'm just wondering if the total costs to get an electric working correctly that will hold up to the hot, dirty environment will be significantly less than getting a Deere replacement?

iirc...the factory one is right about 300$....Its been a while since I checked and its such a pita to even change a lightbulb in the dash of mine...I was not looking forward to installing it so I passed. Hour meter has been out since the day we got it apparently.

I think they average about $250 now depending where you look.
Still researching on which way to go.

IF an aftermarket electric tach is adjustable say via a potentiometer. You can use a cell phone tach app to find your RPM to then set the tach. I did this when I added a tach to my 345. The apps are pretty dang accurate.

The videos I have watched do show them adjusting an electric tach based on a meter which takes a reading from a crank pully mark.
I'll look into the phone apps. Had no idea!
Still got to get the back off the alternator first to see if there is a tach output.

DB Electric got back to me and said the Denso doesn't have a tach terminal.

I appreciate the insight. Thanks for the effort.
It's looking like an original is the only real recourse. Oh well. Not the end of the world.