Guitar Tuner Speedometer

I got one for y’all: now before you laugh me right off the message board, please consider the feasibility of this idea.

I have a 1994 Jeep Cherokee Sport: 4.0L: Straight 6. About two years ago my instrument cluster went out and along with it went the gas gauge, speedometer, and tachometer. By “went out” I mean that it melted…it cannot be replaced without a major rebuild of the cluster/wiring harness. One would think that this would represent major obstacle… what’s the old adage…poverty is the necessity of invention?

So here it is: the rear end of my jeep makes a whirring sound. This sound, deemed harmless to the gearbox by my mechanic, starts at about 40 miles an hour and increases until about 70 and then dissipates. You can imagine it like this: oooooooooooo00000000OOOOOOeeeeeeeeewwwwwHHHHHHHHEEEEWWWWWWW00000000OOOOOOoooooo. Got it?

I can generally guess how fast I am going by the level and pitch of noise. I haven’t gotten pulled over yet so I suppose I am doing something right…I have a solution though. I want to get a guitar tuner and record the tone of the noise and correlate it with the speed. (With a car driving beside - passengers relaying speed and tone data.)

So for instance:
40 Mph would be a C♭
50 Mph would be a C♯
60 Mph would be a F♭
70 Mph would be a G♯

Do you think it would work? I’m racking my brain and I don’t see why it wouldn’t work, unless road noise may interfere…it certainly won’t be the stereo…that burned out too.

I can see it now: Officer: “Son, do you know how fast you were going?” Rob: “Well officer, I think it was about a F♭”


I can’t stop laughing as I type this. One problem I see is that if you’re driving into a 10 or 20 MPH headwind or tailwind it’ll throw you off by quite a bit. My chuckle of the day!

Time for a gps for speed, a mechanic to replace fluids at least. Guy is waiting for the failure for a boat payment?

Ha! SheeshL I never thought about that (The Tail/Headwind). That’s true. But I’m looking to see more if the theory itself is sound. That’s a good thought.

I went under the car with him and we replaced fluid and looked for wear. The gears looked like they were shiney but there was no evidence of metal shavings. He said it “was an old Jeep thing.”

The guitar tuner is unorthrodox but I’d certainly never laugh at doing this. Sounds like an aggravation though and my preference would be a used cluster from eBay as they can be had for 25 bucks.

There can be problems with the differential (wheel bearings, pinion bearings, backlash, etc, etc) that are not visible to the eyeballs and which will not leave any metal shavings.

It’s not just an old Jeep thing; it applies to anything with a ring and pinion gear.

The band Psychostick has a ditty called H♭…
That must be pedal to the metal… :slight_smile:

It might work… but you could also use the GPS on your smart phone (if you have one) I used to do that with my GF’s old car, as the speedometer worked when it felt like it and we often had to drive past several speed cameras. I don’t know about Apple, but for Android phones there is a free app called “GPS Essentials” which does the trick. I’m sure there’s something comparable for an iPhone, though maybe not free. If you get a dash mount for your phone, you could even make it somewhat convenient. There are also apps like “Torque” that will do this and give you a slew of other very useful info about your vehicle, but Torque only works with OBDII vehicles and with a 1994, yours is probably OBDI. (and you also need the bluetooth tranceiver to plug into the diagnostic port on your car) There are probably dedicated speedometer apps too, though I haven’t looked for them.

This is likely going to be much more accurate than your plan (though maybe not as fun and certainly not as inventive)

you can tuna guitar but you can t tuna jeep?

I am looking for a used Cherokee tho…

This is not that far fetched. In the past before cops did traffic control, they had to calibrate their radar with a tunning fork at 55 mph. I forget what the tone was, but it was accepted in a court of law. Now, an old cop might understand but if you were really speeding, it just means they would smile while they wrote your summons when they heard your response.

But, you are sure rationalizing keeping a POS car.

This might just work!! Love it

You might want to sell your idea to Hyundai for its Sonata model. The low trimline would be the Sonata F, the mid trim line could be the Sonata B-flat and the highest trim line the Sonata C.

My Dad said that when I ran over his foot once.

Don’t we all rely on our ears to judge our speed and Engine RPM.

When you goof up and put the shifter into 2nd instead of Drive, I know I never get over 30mph and realize my mistake.

I doubt that an E-bay cluster will help, @OK4450. It sounds like the harness is roasted.

This thing can’t have too many more miles left in it, so I’d go with the GPS idea. By the time you work all this out with the guitar tuner, and just get used to it…the engine or Tranny will give out.


Except that there is no C or F flat, that I remember those I believe would be B and E.

I got a cheap (free?) speedometer app, nice big dial, works fine.

@Pvt_Public‌ except that there IS a c-flat and a f-flat. It is a major scale.

@Yosemite‌ you’re exactly correct. The wiring harness melted. We have spoken to dealers etc. It would need a new harness, cluster and all and that just not worth it. The jeep had 185,000 when the odometer went out 2 years ago so there’s no telling the amount of miles it now has.

@texases‌ I downloaded the app before but it just feels cheap: like the easy way out; and it does not work when you can’t get reception. And it is in those very towns, with no reception, that seem to be most strict with speed…need to boost revenues somehow I suppose.
There is part of me that wants to do this to contribute to whole of human knowledge. Haha or just headed towards my next dope slap.

Well, C flat = B, and F flat = E, right?

Thanks for the laughter.

It’s only viable if you can definitively correlate the notes with the speed in a meaningful manner.
Here’s a thought: pick up an audio-based tuner (not a headstock tuner), and a speed radar system, and have a friend drive on a remote road while you attempt to correlate the notes with the actual speed. If you can manage to do so, and the readings repeat, then you can stick a tuner to your dashboard and know your speed.

@"the same mountainbike"‌ ha that’s pretty much what I was thinking but I hadn’t thought of the radar gun. Where might I come across one of those? Borrow it from the local baseball coach?

If C corresponded to 60mph then C# would be 63.6mph.
Each half step is a factor of ~1.059: 12th root of two on the even tempered scale.
Just sayin’…

@circuitsmith‌ fair enough: I was just giving a “for instance.” Those pitch ranges I selected were arbitrary and haven’t been tested yet.