New tach board needed?
09-15-2017, 11:04 PM
#1
Burning Brakes
Thread Starter
New tach board needed?
Pulled into the driveway this afternoon with the 80 and just happened to notice the tach needle pin to the right. It didn't return and I shut down the engine, but the needle stayed pinned to the max rpm.
I was going to try resetting the needle thinking it may have slipped on the shaft? Willcox - is this wishful thinking?
I was going to try resetting the needle thinking it may have slipped on the shaft? Willcox - is this wishful thinking?
09-16-2017, 12:03 PM
#2
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St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Pulled into the driveway this afternoon with the 80 and just happened to notice the tach needle pin to the right. It didn't return and I shut down the engine, but the needle stayed pinned to the max rpm.
I was going to try resetting the needle thinking it may have slipped on the shaft? Willcox - is this wishful thinking?
I was going to try resetting the needle thinking it may have slipped on the shaft? Willcox - is this wishful thinking?
When the board functions, the sine pushes and the co-sine pulls until the board reaches approximately 2500 rpms.... then they flip and the sine pulls and the co-sine pushes... but if one nut is not making good contact or if one side of the board is dead, then it will only read the other side when the ignition switch is turned on and thus the board will either go below zero or it will peg out depending on which nut is the issue.
It would be highly unlikely that the needle would slip...
Willcox
09-16-2017, 01:26 PM
#3
Burning Brakes
Thread Starter
Update - possible cursed driveway
Probably so... when the needle pins to one side or the other it is usually an indication that one side of the board isn't working. The tach board uses sine and co-sign to push and pull. When one side is dead on one side the other other takes over. If this is an original board then I'd look at the board. If this is a new or newer board, I'd take a look at the nuts holding the board to the movement.
When the board functions, the sine pushes and the co-sine pulls until the board reaches approximately 2500 rpms.... then they flip and the sine pulls and the co-sine pushes... but if one nut is not making good contact or if one side of the board is dead, then it will only read the other side when the ignition switch is turned on and thus the board will either go below zero or it will peg out depending on which nut is the issue.
It would be highly unlikely that the needle would slip...
Willcox
When the board functions, the sine pushes and the co-sine pulls until the board reaches approximately 2500 rpms.... then they flip and the sine pulls and the co-sine pushes... but if one nut is not making good contact or if one side of the board is dead, then it will only read the other side when the ignition switch is turned on and thus the board will either go below zero or it will peg out depending on which nut is the issue.
It would be highly unlikely that the needle would slip...
Willcox
09-16-2017, 06:13 PM
#4
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This morning I started the 80 up - tach still pinned to right. Backed down the driveway, put it in first and started moving, so did the tach, it popped back down to normal rpm. Tach worked fine until I came back home and as soon as I pulled into the driveway, the tach pinned to the right. OK, my driveway is cursed!!!
See if your tach filter is loose where it's bolted to the manifold.
09-17-2017, 03:46 PM
#6
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St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
09-17-2017, 08:54 PM
#7
Burning Brakes
Thread Starter
09-18-2017, 09:41 PM
#9
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St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
That is a very good questions...
When the wire breaks and the tach is powered up (key on), without signal it will go to zero... (if it's a factory tach).... This is exactly what you are doing when you do the zero set for the needle position when installing a new board. You power it up with no signal, remove the needle and re-set it.
The factory tach boards (and ours) will also remember it's last reading when shut off, this was something I insisted on when we built the new boards years ago.. The idea was to have the tach board function just like the originals.
Willcox
When the wire breaks and the tach is powered up (key on), without signal it will go to zero... (if it's a factory tach).... This is exactly what you are doing when you do the zero set for the needle position when installing a new board. You power it up with no signal, remove the needle and re-set it.
The factory tach boards (and ours) will also remember it's last reading when shut off, this was something I insisted on when we built the new boards years ago.. The idea was to have the tach board function just like the originals.
Willcox