I recently completed a new project so I thought I’d share some of the development information - a stand-alone Ford Tachometer Tester. Over the next few months I will be developing several new tester products. I’d like to share the development information with the Cougar Community because some of this knowledge doesn’t seem to be readily available.
'60s Cougar (and other Ford) tachometers are wired differently than the typical 3 wire tachometers.These tachometers are connected in series between the ignition switch and the “pink” resistance wire. They measure the current pulses created by the periodic charging and discharging of the ignition coil and convert them to an analog signal used to drive a current meter inside the tachometer for display. A similar system is used on Smiths tachometers found in English sports cars.
The more typical tachometer, as found on GM cars, uses a sense wire connected to the “-” side of the coil to pickup the voltage pulses from the discharge of the coil.
This unique connection means that it is difficult to test your Ford tachometer: you must either install it in a running car or use a distributor machine to connect a coil and distributor to drive the tachometer. After a literature and web search, I didn’t find any commercial products currently available to perform this task.
The tachometer manufacturers obviously had testers for their products but apparently there was insufficient demand to offer them for aftermarket repair usage. The Smiths RVI Impulse tachometer repair manual has a picture of their Ignition Pulse Simulator for testing but that part is no longer available. A similar aftermarket part is available from accutach.com but requires a PC (or Android) with a sound card, 12V power supply, and digital waveform generator software.
Also, during my search, I discovered that Ford used two suppliers for their tachometers: Bendix and Faria. No doubt this was to ensure a constant delivery source throughout production. The Faria manufactured tachometers can be identified by the presence of a post used to keep the needle from falling below zero.
I was asked to develop a standalone tester that could be used to bench test these tachometers to identify parts that needed to be repaired. The requirements were:
simple stand-alone operation (does not require a distributor machine)
ability to test both 6000 and 8000 RPM tachometers
ability to test both Bendix (no post) and Faria (with stop post) manufactured tachometers
built-in reference tachometer
reasonable cost
My approach was to develop an ignition emulator that would produce the correct signal needed to drive a tachometer over the required RPM range. In order to emulate the ignition system closely, it would include:
ignition coil
coil driver with adjustable RPM
spark gap
power supply
In my next post I will address some of the issues I discovered.
The Faria tachs came out in late 69 and have several visual cues that they are Faria, not Bendix:
As Vic mentioned, they have a stop pin at zero (as do my converted tachs).
Faria tachs have three small Phillips head screws that attach the dial to the case, Bendix used three small rivets to attach to the mounting plate.
The Faria pointer is plastic, not painted and turns orange with age. Bendix used stamped aluminum pointers and painted them white.
The Faria case is plastic, Bendix is metal.
Faria tach wires come out of the top / rear of the case and have no grommet. Bendix tach wires come out of the bottom / rear and use a rubber plug type grommet.
Oh yeah, Faria’s plastic cases have molded FARIA into them.
Internally they are worlds apart.
The Faria movement is epoxied plates with a plastic pivot assembly. The Bendix movement used a one piece outer with brass pivot and jewel assembly, like a clock.
The electrical portion is similar, transformer, diodes, cap, resistors… Faria used a plastic ‘board’, Bendix used pressed fiberboard.
-Faria epoxied their movement to the mounting plate and screwed the circuit to the case, Bendix used brass hardware with standoffs and the case only serves as a dust cover.
Both tachs suffer the same electrical failures - components wear out, dry out, etc. But Faria has the added plus of the movement falling apart when the epoxy dries up.
Faria movement on left, Bendix assembly with circuit board on right
The Bendix unit are far superior, but pennies are the name of the game and Faria found a way to be lowest bidder. Chances of finding a good working Bendix tach are much higher than a working Faria, but considering they only had to last 2 years or so any working tach is a miracle.
The Faria tachs were used into the 80s, Bendix stopped in 1970. You might find a replacement tach in a '69, but most had Bendix. There were no Faria tachs in 67 or 68 Cougars or Mustangs, but the 65-66 Mustang Rally-pacs had Faria tachs.
Is the pin at zero visible from the face plate on Faria models? The 69 we have was built 11/19/68 in San Jose and I see no pin so I assume it is a Bendix. Still working fine too.
About ten years ago I had several '68 XR-7 tachs and could not remember which one was good or bad. So I hooked up three of them in series with the coil wire using alligator jumpers and laid them on a towel on the fender of one of my Cougars. I then started the car and not only did the tach inside the car work fine, all of the ones on the fender did too. I had connected a MATCO Tach / DWELL / VOM to the coil as well. All the instruments were within 100 RPM of each other. Scientific? No. Got the job done? Yes. I picked the one that looked the best.
The most annoying feature of original Cougar tachs is that they can fail, and when they fail the car won’t run.
That’s how I recommend folks to test their tachs.
However, there are two modes of tach failures. The first is when the input/output transformer blows, and that’s when the car won’t start because current can’t pass through a blown transformer. The second failure is when the meter guts itself fails, but the car can still continue to run.
Mine must have the latter disease, as the car runs fine, but every so often the gauge will read only half the actual RPM. A smart rap on the dash usually restores it to the correct reading.
It will test both Ford style ( 2-wire) and aftermarket (3-wire) tachometers.
West Coast Classic Cougars uses this unit to test their used tachometers before resale.
