Tachometer question

[brn2rde]

Just installed a new Tach cable on my daughters 69, and the reading is obviously and highly innacurate. Stock gauges, stock cable, EI distributor.
Anyone want to take a stab at what is happening? I lubed the cable prior to installation with a bit of 00 grease, and cable spins freely. Also, I 'think' I can hear the tach when the engine is running...

Thanks for you assistance....

[Mackn367]

Is it showing too high or low?

[brn2rde]

Too high. A quick throttle blip shows a huge rpm jump that is clearly not near accurate, and the needle appears to have alot of 'float' to it.
Thanks for respoding. Hoping for a simple resolution.

[Mackn367]

I actually fully disassembled my tachometer and posted pictures on my member's garage page but I just realized you are asking about a '68 and I have a '67.5... I'm not sure how much different they are... but what it sounds like to me is the internal spring that creates resistance is loose or just lost its springiness haha.

On mine the spring actually was completely off and the needle would just spin round and round - also it actually broke my needle and I had to re-glue it back together.

[spyder]

Go electric!

viewtopic.php?f=3&t=15556&hilit=tach&start=15#p123126

[brn2rde]

Thanks. Does anyone have pics of the internals of the tach before and during dissamebly? I believe that spyder is on to something wtih the broken or slack spring, but never having had one apart, I am not sure what that looks like.

Not looking forward to taking this out of the dash. Guess I am glad I put off the windshield install for a few weeks so I can move the dash out a bit. Going backward to go forward is not my favorite direction.

[Mackn367]

Thanks. Does anyone have pics of the internals of the tach before and during dissamebly? I believe that spyder is on to something wtih the broken or slack spring, but never having had one apart, I am not sure what that looks like.

Not looking forward to taking this out of the dash. Guess I am glad I put off the windshield install for a few weeks so I can move the dash out a bit. Going backward to go forward is not my favorite direction.

If you go to my members garage I have pics

[brn2rde]

Pulled my tach yesterday and dissasembled. I cannot see anything visually wrong with it. Spring and needle look good. Actually entire tach looks pristine. Am wondering if the drive itself in the back of the tach is the problem. I will put a couple drops of lube in there and test again. Weird....

[AustinEngy]

My 66 has a very similar problem, at idle I usually get a reading between 2000 and 3000 RPM and at highway speeds I can push it well past 7000 RPM according to my tach. Did lubricating your tach solve the problem? It's a very strange problem.

[nismou20]

Spyder, How is the calibration done when indexing Datsun needle onto Autometer? Eyeballing would be inaccurate. Any alternative than to purchase a signal generator? I’m liking how you integrated these two items. Indexing is easier on mechanical old tach as there is a 0-stop. Electronic doesn’t.

[spyder]

The electric gauge has no stops. When I turn the key off the tach freezes where ever it is. When the key is turned on it goes to zero. Two coil phasing.

Edit. PM me for faster reply's. I tend to drift off for days these days.

[brn2rde]

My 66 has a very similar problem, at idle I usually get a reading between 2000 and 3000 RPM and at highway speeds I can push it well past 7000 RPM according to my tach. Did lubricating your tach solve the problem? It's a very strange problem.

Yes, and no. I lubed the cable but still had the issue. Then, while fooling with cable routing problem ceased. My take is the cable housing is compromised somewhere and is binding/releasing, causing the tach to be wildly off. Right now, no problems so we are leaving it alone.

[baxtersit]

I have a 66 and always thought my tach was reading way too high and with the 5 speed that is in it now, 66 mph reads over 5000 on the tach. The previous 4 speed also seemed to be about the same. I decided last week to check it and ordered a laser photo tachometer off of Amazon and checked it yesterday. 3000 on my tach reads 1650ish on the laser meter which seems closer to me. So are there two different sets of gears available in the distributor drive that would account for the error? The tach itself seems very smooth in operation and the cable is well lubed.