Customs Bench testing gauges?

The gauges in my '41 Buick were cosmetically shot, and I was able to piece together two pretty decent sets to replace them. The '41 gauges (the ivory/copper ones) came from various people (including @McPhail...thanks man) and were all "worked when parked" situations. The '49 gauges (silver/white...shown front and back) came in a trade deal and appear to have been restored, but the guy I got them from didn't know the condition (he also got them in a trade and didn't end up using them).

But back to the question...is there a way to bench test gauges? Running a speedo with a drill? Pressure testing the oil? Obviously there'd be a different trick for each one, but I've searched and haven't found anything definitive, so I thought if someone knows this might be a good place to get all that info in one spot.

 

Good question though I’m no help with an answer I’d be curious as well

 

https://www.jalopyjournal.com/forum...-will-work-with-my-dumb-gauge-thingie.862020/
I made a tester from this thread it works well, with a multimeter you can also determine ohm
range on fuel gauges.
I usually use an air hose to carefully test oil pressure gauges to see if the needle moves,
Remember “carefully “

 

I made resistance boxes with a potentiometer to simulate the sender units.

 

So thoughts from a retired research scientist who built my own equipment frequently. Temperature is easy. Boiling distilled water is essentially 212 degrees, give or take a a bit for ambient pressure. Okay so quite a bit for Denver...

Just drop the bulb in the boiling water and see if it reads correctly. To be a little bit more scientific, borrow your wife's kitchen cooking thermometer (accurate enough for our purposes) and compare. If you have any other way to check the temperature of the water, that will also be useful (and keep you out of the hot water with SWMBO).

Pressure gauges can be checked out using your air compressor and a decent gauged regulator. Just be mindful that you don't over pressure the gauge. I have 2 0.1 psi mirrored gauges 0 to 100 psi, salvaged from older test equipment, that I have used to calibrate both gauges and pressure transducers. However you can probably skip that level of accuracy for oil pressure gauges.

Voltmeters can be checked out against a dvm and a battery, carefully. Just make sure the polarity is correct.

I've done mechanical tachs with a variable speed drill, knowing what the max rpm is supposed to be. I just happen to have a strobe tach, and have used it to verify the rpm.

Never messed with speedometers, we don't need no stinking speedometer! So I have no suggestions there.

I am a mechanical engineer, and therefore don't believe in electricity, square root of negative one..., if you have to ask, talk to an electrical engineer. I have never used an ammeter. Don't trust them. Too many horror stories about them causing fires.

Electrical temperature and pressure gauges can be checked out in the same way. You just have to wire them up like they were in your car. No thoughts on electric tachs or speedometers.

Hope this helps you.

 

Pressure on the oil pressure, don't over range it. I use a pressure regulator with a gauge to test pressure.
Immerse the temperature sender in boiling water for the temperature gauge, 212 F at sea level.
Spinning the speedometer will allow you to see the needle move but I have no idea what speed it will indicate. I have spun them with my fingers just to see if the needle will move.
Observe correct polarity and connect the volt gauge to a battery.
As far as amp or fuel gauges go, I don't have a reasonable suggestion as to how to test them.

Of course, electric sending units are a whole different animal.

I see that I am the slowest typer in the class.

 

Yeah I guess I just assumed you were using mechanical electric would be a whole different process.

Realistically it might be easiest to put a sender on the end and pop it into a motor. Speedo isn’t so simple but on those generally if it spins it works. You just have to calibrate it which generally will depend on what your plugging it into but most of them have a gear on the trans side of things

 

This is all great info. Thanks fellas. I just bought a 12V battery and a potentiometer that will be here tomorrow so I can start testing (or blowing things up, one).

Sorry if this is a dumb question, but can you explain this one (using the DVM to determine ohm range on the fuel gauges)?

 

The OP of the linked thread explains it in the paragraph right after the video. So I don’t screw it up in translation

 

Mr. Google says this:
Common Factory Ohm (Ω) ranges
Empty Full Vehicle Application
0 ohms 30 ohms Most pre-'65 GM
0 ohms 90 ohms Most GM 65-present
16 ohms 158 ohms Most '87-present Fords
73 ohms 8-12 ohms Most Fords before '87 and most Chrysler
240 ohms 33 ohms Use with 3262 sender
10 ohms 70 ohms Ford Bi-Metallic Gauges (pre-1987 F-Series Trucks)
15 ohms 160 ohms Ford Magnetic Gauges (1987 and later F-Series Trucks)

 

Same here!
Just use a potentiometer to simulate the sender unit and get a reading on the gauge.
Then measure the reading across the potentiometer.

You can use this method to "tune" a temp gauge to get the needle in the correct position. [once you measure the value of the sender unit at a particular running temp]
Just add a resistor in series in the sender wire , or Parallel to ground to tune this either way

When testing fuel gauges with a potentiometer , I use a 12v A/C adaptor [from a cordless phone] which has 2 alligator clips on it.[this provides 12v and ground]
Then the potentiometer has 2 alligator clips on it, [from the sender post to the ground wire]

Speedo's are just maths.
Most GM speedos [and Ford] need 1000 revolutions per mile for correct reading
So if your cordless drill turns at eg: 1500 rpm multiply this by 60 [minutes] then divide by 1000 [miles]

1500 x 60 = 90,000
90000 ÷ 1000 = 90 mph

 

Most Fire Dept mechanics have a “ dead weight” tester for gauges. We had to test our test gauges, before we tested our engines. We usually tested water pressure gauges….but the dead weight tester tests pressure, it doesn’t care if it’s water or oil. Might check with your local Fire Dept mechanic for your oil pressure gauge. If you can , it will test the gauge accurately!




Bones

 

I was mulling this over, on and off, all through January, at least as regards speedometers and mechanical tachs. At the same time I'd been clearing out the laundry room, which contained, among a lot of junk, a dead pillar fan. I stripped that down for what I could salvage, most saliently a perfectly good AC motor, expressly to set up a speedometer/tach tester. I even got as far as buying a variable controller for it (all of US$1.65) and was planning to invest in a hand-held optical tach. Not having cash for that just then meant relegating the motor to the Procrastination Box.

OK, one of a whole bunch of Procrastination Boxes. I'm literally surrounded by them.

But the idea was a variable-speed setup which would allow me to check the linearity of the gauge reading, by testing at at least three different speeds and seeing if the correspondence to the input rpm remains constant. On top of that, chances are that I wouldn't always be dealing with a common 1000TPM speedometer. The '60s Austin speedometer sitting on the shelf is marked 1376TPM, for instance. I was hoping to rig a ¼" hex drive, which would allow me to use any of a few sizes of square screwdriver bits, which I've got. It only needs to be close: a speedometer's input torque is too low for a bit of looseness to do any damage.

 

Looks like they came from an Oldsmobile dealership.

 

My 1920 Dyke's Encyclopedia says speedometers read 60mph at 1001(sic) rpm.
We calibrated a friend's speedo with a drill press that had a 1725rpm motor, and did the arithmetic (drive pulley to driven pulley diameter ratio) to figure out the chuck speed in low.
Similar to what Kerrynzl posted above.

 

I have trouble taking my own temperature (no rectal thermometer jokes, please), but I gotta say those are damned fine-looking gauge sets you have there!

 

@Curt Six , I see you have the slow version there

 

Well, since I'm keeping the straight 8 I'd say anything like that speedo you've got would be "aspirational."

That's really cool though, and I haven't seen it. I thought even the bigger Centurys and Roadmasters had the 120mph version. What was that out of?

 

G'day Curt, It,s Euro KPH . I might use it one day. ( famous last words )
Actually 120 MPH is 192 KPH so yours is faster

 

How about using an old contact tach? Seem to run in the 40/50 US $ range.

 

From searching the web, that tester is mentioned in the 1968 Olds 442 shop manual, and maybe other year Olds manuals. If you can find one I would think it should have instructions on how to hook it up.

 

Optical tachs can be had for less than that, but I couldn't spare it.

 

Could you put a dot of white paint marker on the cable and get some software for a smartphone to read the rpm?

 

500 ohm potentiometer and 12v battery showed up this weekend. I’m loaded for bear now.