Preserving Original Dash Gauges

[MercMontMars]

Hi there, I had some questions in regards to preserving my 52’ Pontiac’s original dash gauges. What I am wanting to do is preserve the original appearance as much as possible but restoring accurate functionality.
 

Each gauge (fuel, oil pressure, temp) gives a reading when run on 6v, none of them are accurate. Fuel gauge shoots to Full when it receives power and stays there, temp gauge quickly rises to 250 but the motor runs very cool (verified with temp gun) and I haven’t tested the accuracy of the oil pressure gauge but let’s just assume it’s not working. 
 

Anyone out there familiar with these old gauges and how to get them reading properly again without too much alteration? And if I were to change the car’s electric system to 12v, is there a way I can keep them as they are without frying them?

 

Just trying to gather as much info on them as I can before I open anything up. Thank you for any help!

[Terry Harper]

Why change to 12 volt? 

[TerryB]

Older thread but might help.  Seems the gauges might develop issues over time.  The temp gauge works off the variable resistance of the sender unit.  The resistance changes as the engine temp changes. Looking at eBay the temp sender units are pricey.

 

[Bloo]

1 hour ago, MercMontMars said:

Fuel gauge shoots to Full when it receives power and stays there,

That sounds like a problem with the fuel sender, wire to the back, or tank ground.

 

1 hour ago, MercMontMars said:

Temp gauge quickly rises to 250 but the motor runs very cool (verified with temp gun)

I don't know about this one. Is it an electrical gauge for sure? If so, grounding the sending unit wire should send the gauge to one end of it's travel, and disconnecting it should sent it to the other. Without my books handy at the moment, I don't know which is which.

 

The gauges (except ammeters) have grounds even though it isn't obvious. If the gauges were not well grounded to the cluster, or if the cluster was not well grounded to the car there would be undesirable behavior from the gauges. If you are in there looking around, look closely because the gauge grounds (to the cluster) are usually not obvious, it might be the sharp edge of a piece of brass or something like that.

 

The traditional way to "convert" gauges is to run them on a resistor. The trouble is resistors wont just drop 12v to 6v, what voltage you get is load dependent. The gauges are designed to be insensitive to voltage variations to some extent, but they do not draw constant current, so the supply voltage is going to swing all over the place. You could look into something called a "Runtz" that is probably a linear regulator. That is a better solution, but in my opinion likely to run hot because it is a linear regulator. Maybe not. A gauge doesn't draw much current. The problem with resistors or linear regulators is that you have to waste as heat exactly as much power (Watts) as the 6V device is using. There are DC-DC converters available all over the place (ebay, amazon) now that would solve that problem, but the extremely dirty electrical systems of old cars tends to be really hard on solid state electronics. I predict there are going to be failures. Also, DC-DC converters make gobs of radio noise, so if you have an AM radio, it might knock reception out with a bunch of static. DC-DC converters are probably the future of conversions, but I'll let others work the bugs out.

 

GM gauges were the same basic construction for decades, so it is probably possible to rivet the face of an earlier gauge to a later 12V one. Gauges changed to 12V but gas tank senders stayed the same. I'm not sure if the temp sender changed. I expect not, but if it did there is probably a later sender for a GM gauge that would fit.

 

 

1 hour ago, MercMontMars said:

oil pressure

Isn't this a mechanical gauge? No problem if so.

 

Most conversions have an aftermarket gauge panel under the dash.

 

As you have probably guessed I wouldn't do any of this. In my professional life, I was often asked to sort out 12V conversions after the fact. It was a lot of work nobody wanted to pay for and the previous work was always of really bad quality, making the situation worse than it needed to be. "But it worked before" is something I used to hear a lot. To this day I have never seen a conversion that had 100% of the factory equipment working. For those reasons I consider 12V conversions to be godawful messes (perhaps unfairly in some cases, but there it is). Some people need to do it if there is a 12V accessory they can't live without. That doesn't get them out of the trying to make everything work again, it just means they have to do it all instead of just fixing the car and going out for a drive. I'd rather just go for a drive LOL. When I was younger, I drove a 6 volt Nash for 3 winters, and the only trouble I had was some of my friends complaining I couldn't give their 12V cars jump starts anymore.

 

Best of luck whatever you do.

 

Edited August 2, 2023 by Bloo (see edit history)

[DFeeney]

Both the temperature gauge and amp gauge can be repaired   buy a shop.   These repairs are beyond the average person.  Pay the money, put the part in a box,  send it out and when it returns it will work.  10 years from now when you look at the price you will say,  "What a Deal"

[Rata Road]

I just put a 12v battery in the boot and run my gadgets off that. Charge it once a week or so.

Car stays original, replacement parts are easy to find and work and car value doesn't drop. 

[MercMontMars]

@Rata Road That is actually an amazing idea.. so simple but I’ve never thought of that before! I will be stealing that. 😉

Edited August 2, 2023 by MercMontMars (see edit history)

[MercMontMars]

@Bloo Thanks for the reply Bloo! I’m not too sure on what the temp gauge is, I haven’t disassembled anything yet as I’m scared to see the mess the previous owner has created. They’ve made a very finicky taped-up mess of the wiring, no clue what they were trying to do. I agree with you on the 12 conversion problems, it’s only been an idea of mine because I know a new wiring harness is in my near future. Don’t feel too safe with 70+ yr old wiring along with previous owners handling it as destructively as possible..(??) once everything is sorted out and I have a not-so-tired starter motor I probably will keep the car 6v. I’ll be using your advice as I check all my grounds and such soon. 
 

You mentioned radios, and that’s another thing I’m trying to figure out. I have the original Chieftain radio, it seems to all be there but I can’t get any life out of it. I’ve tried it with a 6v battery in and I don’t get any lights or hum, almost as if it’s simply been disconnected. Before I get into any serious disassembly with it, what should I check for? If I’m not wrong, don’t these use vacuum tubes?
 

 

[Bloo]

3 hours ago, MercMontMars said:

 

You mentioned radios, and that’s another thing I’m trying to figure out. I have the original Chieftain radio, it seems to all be there but I can’t get any life out of it. I’ve tried it with a 6v battery in and I don’t get any lights or hum, almost as if it’s simply been disconnected. Before I get into any serious disassembly with it, what should I check for? If I’m not wrong, don’t these use vacuum tubes?

If you don't have any electronic experience (especially soldering) you might have to send it to someone. Do you know how to solder? Do you have a multimeter? They do use tubes, but the tubes are the least problematic thing really (except for the OZ4 if it has one, those had a shorter life than regular tubes). At the top of the list for trouble are paper capacitors, with electrolytic capacitors in second place. I mean you could have bad tubes, but basically no one does, and they go buy new tubes on ebay, and nothing changes.

 

The very first thing that needs to be changed is the buffer capacitor. It is a paper capacitor, and if it is bad, it screws up the vibrator. Generally speaking it is a soldered in part. Back in the day if you didn't change it when you put a new vibrator in, it voided your warranty. Buffer capacitors were a big problem back then. They aren't making any new vibrators, so it is a good thing not to screw up the one you have if it happens to be good. Sometimes bad ones that just have dirty points can be revived. They do make solid state replacements. They are controversial for reasons that go way beyond this post, and that isn't a fight i want to get into 😛 . At the bare minimun change the buffer. The paper capacitors will need changing too at some point, maybe even to get it going. If it hums loudly, the electrolytic capacitors are bad. I don't mean mechanical hum. These radios make a mechanical hum. It's part of the charm. If the glass tubes light and the vibrator hums, and still nothing from the speaker, there's a good chance the OZ4 might be bad. It's probably metal, if it is glass, you probably won't see light in it even if it is good. Maybe a blue/purple/pink glow but don't count on it.

 

A pro will want to replace all the paper and electrolytic capacitors right off the bat, and with good reason. While some radios still sort of work with original parts, ALL paper capacitors are technically bad. They rotted internally from the acid used to make the paper, and they cause most of the trouble seen in tube-based equipment today. Paper capacitors are replaced with film capacitors in 2023, and while they can fail too, they hardly ever do, and there is no acid rot problem.  Most electrolytic capacitors are bad by now as well. They are moist inside when new and fail from drying out. The seals last about as well as the gaskets elsewhere in an old car. They were more problematic than paper capacitors back in the day, but today have a better chance of still sort of working than the paper ones do.

 

P.S. I'd go read the "Sonomatic" thread over in the Buick area. That is a way more complicated radio, yours will be easier, but the basic technology is similar and you might find it interesting. He has a synchronous vibrator which is tougher to troubleshoot than the asynchronous vibrator and OZ4 that you probably have. It is also a multiband radio, which means he will probably have alignment to do once he gets the radio restored. If only the usual sort of parts are replaced yours won't need alignment, unless someone already screwed with the adjustments.

 

https://forums.aaca.org/topic/399991-super-sonomatic-super-project/

 

 

Edited August 3, 2023 by Bloo (see edit history)

[Rusty_OToole]

Gas gauge on full usually means a shorted out wire between the gauge and tank. If the gauge stays on 0 it usually means a faulty sender.

[JACK M]

15 hours ago, Rusty_OToole said:

Gas gauge on full usually means a shorted out wire between the gauge and tank. If the gauge stays on 0 it usually means a faulty sender.

Same if electric temp gauge.

What you describe sounds like you have bad senders.

The test is to ground the sender wires (disconnected) with the key on. If you get different gauge action from grounded and ungrounded you can bet on bad sender.

[Bloo]

16 hours ago, Rusty_OToole said:

Gas gauge on full usually means a shorted out wire between the gauge and tank. If the gauge stays on 0 it usually means a faulty sender.

Except for one tiny nit I have to pick. On this car (and a lot of other GM cars of the period) the gauge works backward from what you would expect. A wire shorted to ground gets you "E" and a broken wire or an open sender gets you "FULL".

[Rata Road]

We have a guy over here that changes the old valve radio internals to modern.

You get FM etc but retain the old look.

Personally I dont bother with sound.

[28 Chrysler]

I agree with Bloo 99% I  call the buffer capacitor a filter capacitor. Keep the old glass tubes unless they have a white film inside.

 

[Bloo]

I didn't mean the filter, or at least I didn't mean what I think most US based antique radio hobbyists would call the filter, though the filter is of very high importance and deserves mention too.

 

The buffer i was talking about is a little paper capacitor of about .0015uF with about a 1700 volt (preferably even more voltage) rating that keeps the points from burning up in the vibrator. An original probably looks about like any other paper capacitor. maybe about like this one:

 

 

It's job is kind of similar to the condenser in a points-and-condenser ignition. Like the condenser in a car, it's uF value is fairly critical to prevent the points from burning up, and it has to deal with high voltage spikes, so the higher the voltage rating is the better.

 

The guy in this link calls it a "timing capacitor", which I have never heard before, but it is a fairly accurate description I think.

 

https://www.cool386.com/vib_life/vib_life.html

 

Here's one marked .0015 MF at the left. MF and uF were interchangeable terms in the US at the time and both meant microfarads. That relay-looking thing at the left with it's "starting coil" marked is the vibrator.

 

[Bloo]

2 hours ago, Rata Road said:

We have a guy over here that changes the old valve radio internals to modern.

You get FM etc but retain the old look.

Personally I dont bother with sound.

 

I'm not crazy about that idea as it means gutting or partially gutting a radio in favor of some little board that is not serviceable and probably won't last decades. Then what do you have when it breaks? Maybe you can get something else new, or if the hobby continues declining maybe nothing. On the other side of that coin I have a 70 mercury with AM-FM-Stereo, and the 1969-1970 Ford/Bendix solid-state radios are a horrible design that never really worked right, sounded bad, and failed constantly. They are a very strong contender for the worst car radio of all time. I'd be lying if I said I didn't consider converting it.

 

There are little boxes available that plug inline in your antenna cable and can take an audio cable or bluetooth. I think maybe there's FM too. It rebroadcasts the music on some AM channel that you tune into. If you are using bluetooth it would be completely invisible. The conversion would be less noticeable in my Mercury, but in a 1952 model Pontiac, or any 1952 model really, that's tubes and a vibrator. It makes that BWOmmp! noise when you turn it on, and produces a very soft mechanical hum while the sound comes up slowly over a few seconds as the tubes warm. That is all part of the experience in my opinion. Something would really be missing without it.

 

The downside is of course that you cant leave it running for very long at all with the car parked and the engine off, or you will risk a dead battery just like your grandparents would have. Tube radios do draw a lot of current.

 

Edited August 3, 2023 by Bloo (see edit history)

[Guest]

I switched my 38 over to 12v rewiring the car in the process.  Single wire alternator on a bracket and I have had years of nice trouble free operation.   I did pick up a set of mechanical gauges to check the electrical ones when I was done.  Readings were all spot on.  The only item hard to find that I had to order was the points, everything else napa or advance had and I could compare price.  The coil required replacement and after spending $$ sending it to the expert to rebuild only to have it die 6 months later I fabbed my own system which has been working perfect since.  I'll see what I did with the gauges tomorrow.  

 

If your gauges/sending units aren't working right then they would need to be replaced/repaired regardless of voltage choice.

 

PS I tried to get gauge answers for a good while but never found them in response or archives.

[PhilAndrews]

Ooh. I remember doing my gauges.

That was from necessity- previous owners had burned the coils up.

If yours is an electrical gauge, there's a couple issues it may have but the most likely is the temperature sender thermistor has gone "soft". That is, it drops to a lower resistance than it should with the heat of the engine.

Obviously the fix is a replacement sender but back in the fifties semiconductor technology was very much in its nascence and the "cold" resistance versus the "hot" was rather narrow compared to today's counterparts. The temperature versus resistance curve is "off" compared to what the gauge requires. 

I rewound my gauges to accept the temperature sender resistance curve for a '65 C10 pickup, the senders for which fit physically and have a moderately similar curve. They're also readily available at most parts stores for cheap.

What you might be able to do is add a resistance in line to bring the 250 to read 180. That's only a band-aid though. You might be able to adjust the coils to read a C10 sensor but it's tricky to get right. 

 

As for the radios- the Delco units are really very good. Nice sensitive radio with a quality final output stage. I made a Frankenstein by conglomerating the 12V parts from a late 50's Buick radio to turn mine 12V natively but they work fine at 6. 

It'll just need a rebuild. It's not a task for a beginner, though. I added a Bluetooth reciever to mine; it has a passthrough which means the radio works as factory with nothing connected, but I can send music to it from my phone on the move, which is great. Looks and sounds just right. 

 

If you're planning on gutting it for something modern let me know and I can probably rebuild it instead of that. I'm with the guys that say it's a good radio, don't trash it if it's able to be rebuilt. 

The only real caveat is the tuning coil frame is made from pot metal and can suffer from zinc pest, rendering it almost impossible to tune, but there's fixes for that.

Cost me about $45 in parts to rebuild mine factory fresh. Food for thought.

 

Phil