I have a couple a body Rally Dash 67 through 71 tachometers. How would I go about bench testing them to see if they work? Thanks!!
Bench test factory Mopar tachometer
- Thread starter Surprise67GT
- Start date
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Not sure but, Most are not compatible with any of the modern ignitions. IE anything but factory points!
I rebuilt mine "69" with a newer board from RTE and there a jumpers and such to verify on bench test!
I rebuilt mine "69" with a newer board from RTE and there a jumpers and such to verify on bench test!
Last edited:
It would need a power wire, a ground and a signal wire from the coil's negative side ( w/ points).
You think maybe you could supply some wire colors? Maybe even some pictures? I mean really, the subscription for my new crystal ball just ran out.
I can tell you this. Normally, tach wiring is......
Red=power
Black=ground
Blue or green=negative side of coil.
Since we don't have a color scheme or pictures, we don't know.
My next best guess is blue and two thirds.
I can tell you this. Normally, tach wiring is......
Red=power
Black=ground
Blue or green=negative side of coil.
Since we don't have a color scheme or pictures, we don't know.
My next best guess is blue and two thirds.
Halifaxhops would know how to do this if anyone here can. Calling Haliifaxhops, do you copy? Over......
@halifaxhops Ray, you any help here, buddy?
I have a bench calibrator that simulates the signals. Do it on a car to simulate it prob the easiest, Or a friend that has a 12V power supply and a signal generator ossibly?
Get an old points distributer, and put it in your vice. Use a drill motor to spin it.
Hook up the tach lead to the wire that would connect to the coil.
Ground the dust to the negitave side of a battery, hook the tach plus and minus to battery plus and minus. Be sure the rotation is correct and crank away.
The speed of the drill should be enough to get 2 readings fast and slow.
You can not calibrate the tach but you can see if it functions. And if you know the drill rated rpm you can see if you're even in the ball park
Hook up the tach lead to the wire that would connect to the coil.
Ground the dust to the negitave side of a battery, hook the tach plus and minus to battery plus and minus. Be sure the rotation is correct and crank away.
The speed of the drill should be enough to get 2 readings fast and slow.
You can not calibrate the tach but you can see if it functions. And if you know the drill rated rpm you can see if you're even in the ball park
pishta
I know I'm right....
spinning a distributor with a drill would be the easiest, a 555 timer and a few components on a breadboard could make a crude stimulator with accuracy testing. @KitCarlson you could probably whip one up out of memory. Turn 1M potentiometer to change duty cycle.
67Dart273
Well-Known Member
The thing about a distributor is that unless you have some way of measuring it's speed, you don't know if the tach under test is accurate
I once checked my Autometer by downloading a few audio tone files off the internet. These are easy to find in the music world. I took an old "wall wort" and the easy way is if you find one that is AC output. This means it's a low voltage output direct from a transformer, with 120V at the other end. You connect the low V side to your sound card output and connect the HV side to the tach trigger. There was a thread long ago about this.
Then you multiply the tone frequency to find out the equivalent (whatever) 4, 6, 8 cylinder trigger freq.
I once checked my Autometer by downloading a few audio tone files off the internet. These are easy to find in the music world. I took an old "wall wort" and the easy way is if you find one that is AC output. This means it's a low voltage output direct from a transformer, with 120V at the other end. You connect the low V side to your sound card output and connect the HV side to the tach trigger. There was a thread long ago about this.
Then you multiply the tone frequency to find out the equivalent (whatever) 4, 6, 8 cylinder trigger freq.
67Dart273
Well-Known Member
How to test a factory tach??
OK, Steve, here's what I came up with, and IT WORKS
You need
1 A laptop or even any computer with a sound card and analog output. Mine is pretty low level from my laptop (phones, not speaker) and it worked. Obviously you need basic software, which most computers come with to play sound files through the system.
2 A transformer to step up the voltage, some clip leads, and a cable to "get" the sound out of your computer
3 Some sound files which I easily found and downloaded. I easily found some that worked fine right here:
EDIT DEAD LINK YOU WILL HAVE TO FIND ANOTHER
http://www.ronelmm.com/tones/
I also looked around and found a 440hz tone on the www
The tones translate thus:
That is, 100hz x 60 to get hz per minute, and divide by 4 to convert to V8 tach reading (V8's fire 4 times every crank rev)
100hz is 1500RPM
150hz is 2250RPM
250hz is 3750RPM
440hz is 6600RPM
500hz is 7500RPM
4 A small amount of math to convert the sound file frequency to V8 tach readings
In the top photo, I started out buying a Radio Shack audio transformer, not ideal, and the only one they had in stock. Part no 273-1380.
I also experimented with a "wall wort" you want one that is AC output, NOT DC output, and better the LOWEST voltage output if you have a choice. This one, second and third photos, is a relic from the thrift stores
The third photo shows all that there is for the wall wort. Once again, it MUST have AC not DC output. You hook the analog output of the sound card to the low voltage leads of the soundcard, in this case the USB dongle
The 120V AC plug is then hooked one lead to ground on the car, the other lead to the tach trigger wire, which MUST be unhooked from the coil/ ignition
Photo 4 shows the hookup for the RadShack audio transformer
The black and yellow clips at top, hooked to transformer white and red, come from the sound card.
The black lead of the transformer is the center tap, unused
Ground one secondary lead, and hook the other to the tach trigger (For this transformer, green and blue)
Then, just power up the tach, fire up a sound file, and crank up the volume. Turns out my tach reads "a little low" up above 3750RPM
By the way, that's not an ammeter you are looking at, but a voltmeter!!
NOTE the file download link is DEAD you will have to find another..........source
OK, Steve, here's what I came up with, and IT WORKS
You need
1 A laptop or even any computer with a sound card and analog output. Mine is pretty low level from my laptop (phones, not speaker) and it worked. Obviously you need basic software, which most computers come with to play sound files through the system.
2 A transformer to step up the voltage, some clip leads, and a cable to "get" the sound out of your computer
3 Some sound files which I easily found and downloaded. I easily found some that worked fine right here:
EDIT DEAD LINK YOU WILL HAVE TO FIND ANOTHER
http://www.ronelmm.com/tones/
I also looked around and found a 440hz tone on the www
The tones translate thus:
That is, 100hz x 60 to get hz per minute, and divide by 4 to convert to V8 tach reading (V8's fire 4 times every crank rev)
100hz is 1500RPM
150hz is 2250RPM
250hz is 3750RPM
440hz is 6600RPM
500hz is 7500RPM
4 A small amount of math to convert the sound file frequency to V8 tach readings
In the top photo, I started out buying a Radio Shack audio transformer, not ideal, and the only one they had in stock. Part no 273-1380.
I also experimented with a "wall wort" you want one that is AC output, NOT DC output, and better the LOWEST voltage output if you have a choice. This one, second and third photos, is a relic from the thrift stores
The third photo shows all that there is for the wall wort. Once again, it MUST have AC not DC output. You hook the analog output of the sound card to the low voltage leads of the soundcard, in this case the USB dongle
The 120V AC plug is then hooked one lead to ground on the car, the other lead to the tach trigger wire, which MUST be unhooked from the coil/ ignition
Photo 4 shows the hookup for the RadShack audio transformer
The black and yellow clips at top, hooked to transformer white and red, come from the sound card.
The black lead of the transformer is the center tap, unused
Ground one secondary lead, and hook the other to the tach trigger (For this transformer, green and blue)
Then, just power up the tach, fire up a sound file, and crank up the volume. Turns out my tach reads "a little low" up above 3750RPM
By the way, that's not an ammeter you are looking at, but a voltmeter!!
NOTE the file download link is DEAD you will have to find another..........source
pishta
I know I'm right....
I was thinking about the sound out of a phone/laptop myself. I have a waveform generator I could rig up. I believe its a 5V output.
Heck, even my uber cheap component tester has a frequency/PWM generator/counter.....you could probe your tach input with this and measure the frequency by dividing by 8 and comparing what your tach says.
Heck, even my uber cheap component tester has a frequency/PWM generator/counter.....you could probe your tach input with this and measure the frequency by dividing by 8 and comparing what your tach says.
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