Smith's Tach Replacing A SW Tach?

REDSC400 · #1 (**permalink**) 11-18-2003, 11:48 AM

Gents:
I currently have a SW 8,000K tach which has been less than accurate and is suspect. I am thinking about replacing it with a new Smith's Cobra tach from Nisonger.

Has anyone done this conversion? Are there any things I need to know before commiting to this change? Nisonger states, that they can test and modify their Smith's Tach to work with the MSD-6AL multi-spark unit. If you have had Nisonger do this work, I would love to hear from you and what the outcome was.

Also, Nisonger tells me the SW is a 3 3/8" tach while theirs needs a larger 4 1/4" hole. Perchance, does anyone have a good suggestion as to how to cleanly make the dash hole larger by 7/8" without buggering it up? I suppose a drill mounted hole saw would be the best alternative?

Background:

428FE with MSD-6AL and Mallory Unilite breakerless (optical) distributor. Mallory active power module. Mallory ballast resistor. MSD tachometer adaptor #8910.

Current SW tach readout "bobbles" and "floats", especially when the engine is cold and when warm, the readout is just erratic and just seems to drive me crazy.

I just do not want to go from the frying pan into the fire, as it were.

mr0077 · #2 (**permalink**) 11-18-2003, 12:05 PM

Art, are you sure you should be running a ballast resistor? I have almost the same setup as yours, SW gages and an MSD setup. Per ERA and MSD instructions, I used no ballast resistor...I also had a problem with erratic tach readings just like you describe. I bought a tach adaptor, hooked it up, made it worse. I went back through my wiring and found out I had the "rong" wires hooked up to the tach. Disconnected the tach adaptor, hooked the tach up per wiring diagram and no problemo since then...anyone want to buy a tach adaptor?
Good luck, let us know how it comes out.

REDSC400 · #3 (**permalink**) 11-18-2003, 12:24 PM

Hi MR0077:
I am glad you got your wiring problem sorted out! Can you remember exactly which wires were connected wrong? Were these wires that were connected wrong those on the back of the tach or elsewhere?

Now, as far as the ballast resistor is concerned, it was recently added. The "floating" was present both before and after. I added the ballast resistor after frying my 605 when testing the kill switch. You may be just be lucky, so far, in not using the ballast resistor with your Unilite distributor. Here is a link to the ERA website for a Unilite and MSD wire diagram. Also, in talking to the Mallory techs, they advise the use of the ballast resistor and power module to protect the 605 unit in the distributor.

My advice...

without a ballast resistor:

do not jump start your car

do not use the kill power cockpit switch with the engine running.

Either of these actions could send an impulse or voltage surge into your system and without the ballast resistor, the typical item to fry is the 605. (the 605 is the little electric eye sensor inside the Unilite). ((I now carry a spare 605, rotor and cap with me just to be safe... sigh))

http://www.erareplicas.com/427man/wiring/msd.htm

mr0077 · #4 (**permalink**) 11-18-2003, 01:35 PM

OOPS! I didn't note you were using a Unilite...I have the MSD distributor, I guess it would make the difference.
As to the wires, I honestly can't remember, I believe it was the wiring from the MSD to the tach, but all my ERA and MSD "stuff" is at home. Let me look tonight and see if I can figure it out, but it was the same thing, tach would float and wander around, had only a "vague" relation to engine speed, would not follow engine speed at all. All I did was get the MSD diagram and the ERA diagram out while I was upside down under the dash, just traced the wiring, and found the problem.
I'll give a shout when I get my stuff tonight.

REDSC400 · #5 (**permalink**) 11-18-2003, 04:25 PM

Hi Ken:
yah, you are right, the benefit of the MSD distributor is that it does not require the separate ballast resistor. You can forget my warning then, about the jumping and switch. Phewww!

Yah, If you could I would like to know what you fixed. Since you were under the dash, perhaps it could be the connection to the tach itself?

Thanks,

mr0077 · #6 (**permalink**) 11-18-2003, 05:48 PM

Okay, Art,
here is what I'm coming with from the fog of 3 years ago...looks like I had the std ERA wiring hookup, but with the help of ERA, I finally figured out to wire from the MSD box tach output directly to the signal terminal on the back of the tach...of course, this was AFTER I bought and installed the tach adaptor...LOL!!
Anyway, try wiring directly from the tach output on the end of the box away from the big power cables, directly to the back of the tach...worked for me.
Good luck

Len Hurlburt · #7 (**permalink**) 11-18-2003, 06:06 PM

Art - You may want to look into an Autometer #2499 tach as a replacement for your SW. It's the same size and looks similar to the SW, and may be a better match for your SW guages than the Smith's tach. It seems there are a number of us out here with the same problems with their SW tachs. I sent mine back to the SW facility in El Paso for repair. If they can't do something with it, I'll go with the Autometer. Cheers, Len

Roxie_427 · #8 (**permalink**) 11-18-2003, 06:30 PM

Alternatively, look into the AutoMeter Vintage series. They have the black background, white markings AND white needles. I searched around for AutoMeter part numbers, but, with the time I have this evening, I've only found an FFR reference to them.

http://parts.factoryfive.com/roadste.../interior.html

I saw these gauges during a recent visit to Shell Valley Companies. They offer them as an upgrade to their standard VDO gauges. It's really a no-brainer, looks-wise.

Good Luck.