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Rocketman Tachometer Question

Posted: 12 Jun 2019, 09:47
by cj750
I've had a Rocketman 8000 RPM 3-wire tachometer in my '69 Eliminator for several years, and have been very very happy with it. Unfortunately, when I started the car yesterday, the tach needle immediately dropped to a position about 20 degrees below the Zero marking, and stays there regardless of RPM. The car runs fine and all the other gauges behave normally. I did a quick check for blown fuses, obvious loose wires, etc. Everything appears normal at first glance, but I haven't yet done a detailed inspection.
Factory service manuals aren't going to be of any help with this, so I'm curious if anyone has encountered a similar issue and what it turned out to be.
Thanks in advance.

Re: Rocketman Tachometer Question

Posted: 12 Jun 2019, 10:33
by BigCat68
I had very similar problem, I called Rocketman , all I had to do was rev the motor above 3500 rpm. Sure enough it fixed it. He explained what was going on with my issue, but I would call him.

Re: Rocketman Tachometer Question

Posted: 12 Jun 2019, 10:39
by TheRktmn
https://www.rccinnovations.com/index.php?show=support

My new tachometer doesn't work - Prior to S/N 5000:
Some things to check before returning the tach:

Is the tachometer needle on the wrong side of the stop pin?
Symptom: You can rotate the pointer backward (CCW) from 0 to 60 but not from 0 to 10 (CW).
This can happen during shipping or if the tach loses signal or voltage while the needle is beyond it's 'tipping point'. The 'tipping' point is around 3500 RPM on a 6000 tach and 4500-5000 on an 8000 RPM dial.
Caution: DO NOT try to lift the pointer over the stop pin! To correct this you have two choices:
1. Take the tach out and manually rotate the pointer counter-clockwise back to zero or
2. Reconnect the tachometer leads, start the engine and rev it past the tipping point. Once past the tipping point the needle will become active again. Reduce the RPMs to idle and shut down the engine. The needle will rest on the stop correctly.

Re: Rocketman Tachometer Question

Posted: 12 Jun 2019, 10:52
by cj750
Hmmm. None of that sounds like what's going on with my tach. Plus I'm certain I revved it over 4500 as I was driving around after this happened. But I'll give the engine a good twist later on just to be sure.

Jay

Re: Rocketman Tachometer Question

Posted: 12 Jun 2019, 11:12
by bmwhd1
Not sure if this is related but I've noticed my Rocketman clock-to-tach conversion occasionally takes 5-10 seconds to start working after the car is started. The needle doesn't move when the engine first fires but then jumps up to the correct reading and works fine from then on until the car is shut off.

Re: Rocketman Tachometer Question

Posted: 12 Jun 2019, 11:51
by cj750
BTW, I don't actually see a stop pin on the '69 tach. My '70 (Rocketman 6K) tach has one, but none on the '69. Are '69 and '70 tachs different that way? I always thought they were the same, but never really paid attention to stop pins before.

Re: Rocketman Tachometer Question

Posted: 12 Jun 2019, 13:09
by TheRktmn
cj750 wrote:
12 Jun 2019, 09:47
I've had a Rocketman 8000 RPM 3-wire tachometer in my '69 Eliminator for several years, and have been very very happy with it. Unfortunately, when I started the car yesterday, the tach needle immediately dropped to a position about 20 degrees below the Zero marking, and stays there regardless of RPM. The car runs fine and all the other gauges behave normally. I did a quick check for blown fuses, obvious loose wires, etc. Everything appears normal at first glance, but I haven't yet done a detailed inspection.
Factory service manuals aren't going to be of any help with this, so I'm curious if anyone has encountered a similar issue and what it turned out to be.
Thanks in advance.
cj750 wrote:
12 Jun 2019, 10:52
Hmmm. None of that sounds like what's going on with my tach. Plus I'm certain I revved it over 4500 as I was driving around after this happened. But I'll give the engine a good twist later on just to be sure.

Jay
Uh-oh. I misread your first post.
Normally a pointer below 0 jumps up to just under 0 when powered on but cannot go past 0.
If it's not moving at any RPM it's busted and needs to come back.

A Faria built tach it has a stop pin down by the zero.
A Bendix (Beede) movement did not have one and I add one under the center medallion.
My new movements do not require a stop pin at all.