JD 70 Diesel Tachometer Quit

ROSchell

Member
I had posted previously about burning out the coils, points and switch on the pony motor of my 1956 John Deere 70 Diesel. In replacing the switch, the dash had to come out, which means the tachometer cable was unplugged from the back of the tach. I finally got the correct coils for the plug wires, got the points in and replaced the switch a few nights ago and am happy to say, the pony motor starts and runs fine now. I don't remember noticing whether or not the tach worked when we started it the other night, but I did start it today, and noticed it is not working. I do remember having a time getting the cable hooked to the back of the tach. Today, I also took it off and eventually got it re-attached and when I started the diesel, the tach needle slowly turned completely around the gauge a few times and stopped. Here is where it sits now and doesn't move.

mvphoto106289.jpg


It's kind of a son-of-a-gun to get the cable screwed onto the back of the tachometer as it is a very stiff cable and not easy to manipulate, and of course, there is limited room to maneuver behind that dash. It seems to be in place, but it just won't grab the threads, like it's possibly not in there far enough. Eventually I can get it to grab and connect. Is there a certain way the cable goes into the tach? Did we possibly do something to it when we took it off the first time as it seemed to come off a little stubbornly. Any help would be appreciated.
 
I guess my question is whether or not there is a specific position the cable needs to be at for it to plug into the back of the tachometer.
 
Cable end is square and must go all
the way in. You might try inserting
a small screwdriver and turning it
a tad if it isn't going all the way
in. On my Ford it was easier to
hook up the tach first and turn the
cable end until it slid in and then
hook up the other side.
 
I hate to tell you this but when the needle winds
around like that it usually means the tach has become
inoperable. Either the tach had not been turned in a
while and when you reinstalled the cable you got it
connected properly then something may have stuck in
the tach and what happened was the result. Or you did
not get the drive cable aligned with the square
receptacle in the tach. Then when the cable nut was
tightened force was placed on the tach internals. Then
when it turned the the needle twisting occurred.
 
(quoted from post at 19:41:34 06/02/23) I hate to tell you this but when the needle winds
around like that it usually means the tach has become
inoperable. Either the tach had not been turned in a
while and when you reinstalled the cable you got it
connected properly then something may have stuck in
the tach and what happened was the result. Or you did
not get the drive cable aligned with the square
receptacle in the tach. Then when the cable nut was
tightened force was placed on the tach internals. Then
when it turned the the needle twisting occurred.

The tach had been working fine until I replaced the switch. We could pull start it to move it around and it was working. If anything, it's probably your latter idea where I didn't get it inserted properly and tightened it down. Although I am able to spin the post on the back of the tach with my finger and get the needle to move????
 

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