Are all reproduction tachs the same?

[davepl]

Mine reads 2150 with the key on and engine not running. 4500 at idle. Talked to Pertronix, hooked my scope up to it, did a bunch of troubleshooting, found nothing. So I completely disconnected the distributor and it still does it. So it's got to be the tach. I see 12.24V at both connections and it has a good ground.

Anyhow, mine came from (I think) LMC, and I'm wondering if everyone out there is selling the same tach with the same movement or if a board vendor has a better one, etc.

If I have to go through removing the cluster and column again I might as well put one in that I'm confident about.

[TBONE1964]

Originally Posted by davepl

Mine reads 2150 with the key on and engine not running. 4500 at idle. Talked to Pertronix, hooked my scope up to it, did a bunch of troubleshooting, found nothing. So I completely disconnected the distributor and it still does it. So it's got to be the tach. I see 12.24V at both connections and it has a good ground.

Anyhow, mine came from (I think) LMC, and I'm wondering if everyone out there is selling the same tach with the same movement or if a board vendor has a better one, etc.

If I have to go through removing the cluster and column again I might as well put one in that I'm confident about.

Dave,

Sounds like it is shorted out or may have been wired incorrectly at one time. Did you by this from LMC?


I have one here that is an aftermarket I can sell you. I can test it first to make sure it is OK. I did not buy it new but I know it has never been used. I also have nice restored original GM tachs as well as some NOS tachs.

You can PM me if you are interested. I got you covered.

[John H.]

Dave,

Left a pm. I have oem and repro available to test your issue. Repro from classic industries, but who knows what Chinese province it came from....

['68OrangeSunshine]

Dave, Do you have a Pertronix Ignitor III, by chance? I have a P II, and no problems with tach. but I heard the III has Tach issues because its a multi-spark system.

[davepl]

I do have a III. I have a II in my 2+2 with a repro hood tach that works fine.

Unless the III killed the tach or I somehow fried it, it reads 2150 with the distributor disconnected now, so its not causing it at this moment.

['68OrangeSunshine]

I don't have a III, but a buddy of mine has one on the 429 in his '72 F250. He said he emailed the company about his tach issues and they told him to put a II in.
Check with Pertronix.

[davepl]

Pertronix actually let me talk to one of their engineers. My tach appears cooked but here were his suggestions in case anyone else runs into this. No idea if they solve it, but sounds plausible.

1) Try a 0.01uF cap in series on the coil-tach line. This would block the DC voltage but allow tach pulses to get through

2) If that alone doesn't work, at 10K resistor (1/2W)

I'd put a II in it but hate to pay $125 for the privilege of downgrading.

[TBONE1964]

Originally Posted by davepl

Pertronix actually let me talk to one of their engineers. My tach appears cooked but here were his suggestions in case anyone else runs into this. No idea if they solve it, but sounds plausible.

1) Try a 0.01uF cap in series on the coil-tach line. This would block the DC voltage but allow tach pulses to get through

2) If that alone doesn't work, at 10K resistor (1/2W)

I'd put a II in it but hate to pay $125 for the privilege of downgrading.

That is good information Dave. So the staff at Pertronix would tell you that hooking a tach up to the III will smoke it (unless you modify like stated) but Ok with a II.

Thank you for sharing this.

Take care,
Tom