Electrical Mustang factory tach calibration

Mustang5L5 · Jan 24, 2010

Apparently Ford did allow for adjustibility of the stock Tach. They just either didn't do it well, or chose to leave it off in the upper RPM's.

On the backside of the tach, there are pots that allow you to adjust. 87-88 have 1 pot, while 89+ have two pots....high range and low range.

Basically you need a frequency generator that can generate in the 33.3hz to 466.6hz frequency range. Many people do not have this peice of equipment, but some in technical feilds may.

If you have it, you can generate a signal and then use the pots to adjust your tach. You can actually get it accurate enough where there is no need for an autometer tach.

Guess i'll start tracking down an 89+ tach (greater adjustability) and find the equipment needed to calibrate it and swap it in! I HATE the 5" autometer tachs, and have a small shift light i want to hide in a vent...but an accurate tach would be nice.

There is a good thread on this on corral.net if you want to look for it. I can't really link it, but the info is too good to not pass on to some here.

giddyup306 · Jan 24, 2010

That's pretty interesting. Too bad I tossed out my stock gauge cluster a few years ago. Oh well I like my Auto Meter tach up higher (makes it easier to see out the window).

Shaolin Crane · Jan 24, 2010

im going with a florida 5.0 cluster anyhow but nice find Mike

stang&2Birds · Jan 24, 2010

Mustang5L5 said:
There is a good thread on this on corral.net if you want to look for it. I can't really link it, but the info is too good to not pass on to some here.

People can check out the results from the following Google Search:
How accurate is your stock fox tach - Google Search

The corral thread should be among the first selections.

I'll suggest that the nch software is a good option for most people to generate test signals:
Tone Generator Software - Audio Test Tone Generator Download

Mustang5L5 · Jan 24, 2010

Shaolin Crane said:
im going with a florida 5.0 cluster anyhow but nice find Mike

Well you know me. I'm all about the stock look. If i can get the stock tach to be accurate at 5500 RPM, then I'm all for that

Chrome_Rust · Jan 24, 2010

I used the output from my Mallory Ignition to check the 95 GT cluster in my 93. The Stock tach and an autometer sport comp were dead nuts on...

Mustang5L5 · Nov 16, 2010

Bump...because this is good to know. Got a shift light, but would be nice if my tach was accurate at 5500 RPM

RatStang · Nov 16, 2010

The information for calibrating these would be a sweet addition to the technical thread index!

NIKwoaC · Nov 16, 2010

I was actually surprised to find that mine is within 100 RPM or so, even at 5500 RPM. I know some people's can be damn near 1K off at high RPM.

Mustang5L5 · Nov 16, 2010

Mine is way off. Shift light set at 5400 RPM...stock tach reads up near 7K.

Need to see if we have a frequency generator @ work before I go pulling my tach out to try this.

From info i've gathered on the net, the 89+ tach features a high and low rpm adjustment. The pre-89 tach only has one adjustment...so you can either set it to be accurate low, or accurate high.

NIKwoaC · Nov 16, 2010

SO I was following some links on that google search, and I stumbled across a post where someone said that the 79-86 tachs are more accurate than the later tachs. Is there any truth in this? I've never heard anything like this.

DucatiRdr · Nov 16, 2010

Mike,

Where are the adjustment pots? I happen to have a cluster from a 1989/140 MPH speedo and the reverse side of the cluster has the lighting, circuit and a resister or two, but no pots.

jrichker · Nov 16, 2010

I have a Hickok frequency counter, Hickok function generator (sine, square & triangle wave) & Tektronics 5400 series oscilloscope.

Setting in my garage is a full 89 5.0 Mustang instrument cluster pulled from my 89 GT that got totaled by a hit and run driver.

I have stuff to work with and stuff to work on. If you would be so kind to send me the diagram & tech notes, I will be all set

Mustang5L5 · Nov 16, 2010

PM sent

torch93 · Nov 22, 2010

Shaolin Crane said:
im going with a florida 5.0 cluster anyhow but nice find Mike

yo new at this.... but what the difference between from the florida cluster and others ? m mustang is from Missouri?? cuz my tach i believe is a lil off

Chuckman · Nov 23, 2010

torch93 said:
yo new at this.... but what the difference between from the florida cluster and others ? m mustang is from Missouri?? cuz my tach i believe is a lil off

sounds like you're thinking its a state-to-state difference, its not. Florida5.0 is an aftermarket company, they make abs gauge housings and stuff them with autometer gauges. see Florida 5.0

torch93 · Nov 24, 2010

Ohhhh lol ok I thought it was state to state.. Ok cool cool.. Hey what about the 160mph cluster? Is that from the 93 cobra?

aar0s · Nov 24, 2010

yep, this needs a sticky.

Mustang5L5 · Nov 24, 2010

I was considering it...but until we get some positive feedback on how to perform this, I don't think i can.

A post with some links and a "here, figure it out" from me really isn't tech.

But if anyone has the equipment to do this, I'd like tom hear it so we can put something together for future reference

Maryland Stang · Nov 25, 2010

Here is the info borrowed from 89ragtopgt at corral.net. All credit goes to that person...

89ragtopgt said:
Here are the numbers for those of you who want to check your own tach for a V8. V6 and 4 cylinder will be different by a percentage because of the number of cylinders.

Just connect power(12V) and ground to back of tach, they are marked. Attach a frequency generator to the signal input, it is marked as well (sig)
then gererate the frequencys below and the tach shoud read that rpm. i used a scope to check the output of the generator to make sure it was the same.
The chip that controls the meter is a LM1819 Air-Core Meter Driver. You can download the data sheet and by a resistor /cap R/C CCT change you can make it adapt to a 6 or 4 cylinder motor as well

data sheet here:
http://www.ortodoxism.ro/datasheets/...r/DS005263.PDF

RPM Frequency(~Hz)

500 33.3
1000 66.6
1500 99.9
2000 133.3
2500 166.6
3000 200.0
3500 233.3
4000 266.6
4500 299.6
5000 333.3
5500 366.3
6000 400.0
6500 433.3
7000 466.6
you can play with the 2 pot's to tune it up. One will adjust the low end at 1000rpm(small adjustment) and the other the high at 6000 or 7000rpm(large adjustment). One can find a good balance so it is much more accurate. I bet over 15 years the calibration just goes out.

Apparently you can use tone generation software that you can download onto your PC or laptop. Install the software and use a 1/8" plug on your sound output connected to wires that are connected to the
signal input on the back of the tach.

Electrical Mustang factory tach calibration

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