Dead Tach?....I need help

[RedBarchetta]

Car: SPF #747
Situation: Dead tachometer
History: Tach used to work great. Had to take apart the MSD ignition to troubleshoot ignition woes. Put it all back together and fixed ignition, but tach started to bounce wildly. Then it quit all together after a couple miles.

Installed the MSD tach adapter yesterday. There are two ways to install, depending if your tach is voltage triggered or current triggered. According to the Superformance manual, the wiring diagram shows it's voltage triggered. I wired the tach adapter to the letter. Still didn't work. I then (for grins) re-wired it for current triggered. Still didn't work. I rewired it back to voltage triggered and loomed everything, so at least I can drive it without wires hanging everywhere.

WHAT NEXT?!? Should I pull the tachometer and send it out to a tach specialist? Is there any other way of testing this before I create a big hole in my dash?

Thanks for suggestions!

-Deano

[Ron61]

Deano,

I am no MSD ignition expert by any means but if I understand correctly the tach worked ok until after you took apart the MSD set up to work on it. Then it started bouncing and then quit. That would sound more like a loose connection somewhere or a possible short. I use a Jacobs but I had that happen and the trigger lead connector had gotten loose over the years and it took me a while to find the connector in the loom. I now have a schematic of just where it and all other connectors are located. I am sure that you have already checked all of this but just thought I would give it a shot. Another way I have tested a tach is just take it and run wires from it to one of my other cars.

Ron

[BlueRooster]

Deano,

My tach bounces a lot too. It seemed to happen after the car warmed up. It was at its worst late last year when my coil contacts were loose. I figured this was the problem, so I bought a new coil (MSD) and the problem went away. Now last week I took a nice long 2 hour drive and on the way back home, I got stuck in a rain storm. I hightailed it up the interstate back home but I noticed on the way back that the tach is bouncing again. I am perplexed also. As I have no idea how changing the coil seemed to fix the problem and getting stuck in the rain seemed to bring it back. BTW, I also have the MSD ignition, and it did not seem wet when I got back from the rain storm.

Dane#623

Oddly enough, after I looked my post over, I realized that my avatar looks a lot like my actual tach...If you want a first hand view at what the tach bounce looks like, there it is.

[RedBarchetta]

Dane,

FYI. I'm running an MSD 6AL with new Blaster 2 coil. I also just changed the magnetic pick-up and the cap & rotor (none of which should cause the tach to go haywire or bad all together).

I'll have to check voltage on the MSD box to make sure I'm getting a reading from the tach port. I'll also have to do some kind of continuity check at the tach connections to see if something there has gone astray. At least I have enough miles on the car to know when I'm inching toward 6 grand.

[RedBarchetta]

Anyone here familiar with "Mo-ma's" instrument service out of Albuqurque, New Mexico? I just got off the phone with them and they explained to me the "weak link" (circuit board) on the factory Smith's tachs. Apparently it doesn't take much of a voltage spike to fry these. They say they can insert a German circuit board (higher quality) and repair the tach for $175 (+ $5 shipping).

I don't know these folks from Adam, but I am finding out that all of the local speedo/tach shops don't want to work on this Smiths' gauge.

What are my other options? Who sells new/refurbished 4" Smith's tachs?

[Mike Simard]

Red', I'm not familiar with them but Nisonger charges $125 to upgrade a Smiths for an MSD. For about $195 you can buy a new one from them and not wait several weeks for yours to be returned.

[RedBarchetta]

Mike, thanks for the reference! I found their web site with a Google search.

-Deano

[Fred Hamilton]

I had the same problem, Tach was working fine did some other work, dash lights and switchs. Checked all the new items and they worked fine but the Tach was dead. After hours of looking I to thought I had fried the Tach. I took the tach out and hooked it up to another car, it worked fine. My problem was the MSD capacitor had come undone, re soldered and all was well. Some times we get so deep into something we forget the easy $hit.

[RedBarchetta]

Fred, that would be great......if I was running an MSD capacitor. I'm not, but I guess I'll have to really inspect all the wiring to ensure I don't have some sort of short circuit.

Regards,

-Deano

[hoppy]

If this is considered a hijack, just kick my A-- out.
I have a SW tach and MSD-6. The tach has a tendency to occasionaly stick up in the 4000 range. That is why I though my 3.54's were causing excessive RPM at cruise. A scientificlly applied knuckle rap on the face of the tach knocks it back down to a reaonalble (35-3600 @ indicated 80mph). Do you think it is a tach problem, or do I need to look at the MSD closer (not that I woud know what I'm looking at/for)?

[DonC]

ATerry:
A rap on the tach bringing it back to where it should be indicates a problem with the tach, not the msd. Some airplane and helicopter dash boards are designed to vibrate during flight to do this automatically for the driver.
DonC