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Makes sense. But there's quite a bit of mod to do to add a new pin to the cluster and/or cut traces, etc.

I'm thinking that just putting a resistor on the G1 wire of C200 may be easier. The two circuits appear to be independent (brake test and temp gauge test). But I need to confirm that the schematics match reality on the car itself. I'll cut the G1 wire on one of my cars and see. Let me get these videos done first.

I think 50 ohms will be too low. We may want something like 80 ohms, get us to H but not pegged. I know 80 is a weird-ish value in the resistor world, so later I may recommend something more standard. Stay tuned.
 

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Just checked. 70 ohms gets us into the red without pegging the needle. Anything more than 70 will not be in the red zone. Any less than 60 could slam an undampened needle due to momentum. So I think we should target 60-70 ohms. The location of the resistor is still up for determination and discussion.

I'm also reading about 120ma draw through the 70ohm resistor into the gauge. That's approximately 1W right? We could probably get away with a 1W resistor since it will only be used for a few seconds during cranking (bulb test). But I could also recommend a 2W resistor since engineers like to work in 2x safety factor when possible. Bridges and overpasses usually call for a 4x safety factor IIRC. LOL.
 

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75 ohms are available 82 ohms is a standard value. Two resistors in parallel give a lot of possible values.
I'm thinking that just putting a resistor on the G1 wire of C200 may be easier. The two circuits appear to be independent (brake test and temp gauge test). But I need to confirm that the schematics match reality on the car itself. I'll cut the G1 wire on one of my cars and see.
Comment deleted because I did not read storm9c1's post properly.
 

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I'm also reading about 120ma draw through the 70ohm resistor into the gauge. That's approximately 1W right?
220 ohms is a common value. Three 1/2Watts in parallel would be 73.3ohms 1 1/2Watt. Cheap and easy to get. They take up less space. Pennies versus dollars for 1-5Watt
You could probably get by with 1W but 1/2 Watts are very cheap.
Four 270 ohms in parallel would be 67.5 ohms 2Watt.
 

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Deleted.
 

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As promised, some video to help understand everything I've mentioned recently regarding the temperature gauge and how it works... Part 1 shows a very faulty 9C1 gauge. Part 2 shows a gauge that is working well, but needs a slight calibration adjustment. Hopefully this helps everyone (including the OP of this thread) understand how to move to the next step from checking the sensor to checking (and possibly reclocking or recalibrating) the gauge itself. If it's behaving like the video in part 1, then calibration will be somewhat hopeless without a dampening resistor to prevent violent banging during the bulb test. We are still hashing out the resistor details in this thread. So stay tuned for more of that.

Part 1:

Part 2:

This is my first two public YouTube videos. Quality is not stellar, it's a cell phone, no tripod. This is also a hobby. I'm not a school teacher. I'm not used to presenting to the public. I'm not a videographer. I'm in my mid/late 40s and didn't grow up with a smartphone in my hand. Be gentle on me. LOL. Enjoy.
 

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I think we have a misunderstanding. On page 8A-82-0, the schematic shows G1 in C200 being the bulb test ground signal to splice S212. I'm not touching a hot wire. So I'm unsure where you got S255, etc. Can you please clarify?
Sorry I have delusions that I can multi-task. I miss read your post and the FSM. I have deleted the part that I messed up.

I have miss read the FSM The temperature gauge bulb test switch(key) is C1 C and I thought that the brake warning bulb test used the same switch.
I am wrong the brake warning bulb test uses C1 D.Other cars only have one Bulb test switch and I made a ASSumption.
I thought your solution would set up a "back feed" circuit

OK I am using a 94FSM so 8A-82-0 seems the same for both of us.
The temperature gauge symbol has two terminals at the top and two on the bottom.The top left terminal has what looks like a "left arrow" <-. The right terminal is a power line .These arrows indicate a circuit board connection to some other part of the circuit board but do not indicate where or what. The bottom left terminal supplies ground. The bottom right terminal also has a "right arrow" ->.(just above the C2 A4 and the dotted line.
I just checked Goldsswagon's diagram. It shows the sender circuit going to the "check gauge chip" so no problem.

It is late for me but just adding the resistor into the G1 wire of C200 should work.

I need to take the cover off and have a good look at this area of the cluster circuit board just in case there is something not shown on the diagram.
 

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Sorry I have delusions that I can multi-task. I miss read your post and the FSM. I have deleted the part that I messed up.
Oh trust me, I have the same problem often. I deleted my reply as well.

I will investigate the G1/C200 resistor in the next few days. The 9C1 car (hood) you see in the video was once my racer years ago, now it's retired from that and relegated to a whip. It already has some cut wires in the harness. What's another cut gonna matter. Stay tuned.
 

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With repeated references to "the needle hitting during bulb test" there has been no clear explanation as to what the needle hits.

Motor vehicle Automotive exterior Automotive tire Gas Auto part


The temp, oil and gas gauge are two coil systems without spring return. So when replacing this piece one has to make sure all the needles do not touch the plastic It is easy to just point the three needles straight up.The volt meter is a one coil with a spring so one has to hold the voltmeter needle when replacing this part.

For some theory on the two coil gauges have a look at this thread:


The fuel gauge works opposite to the temperature gauge. In the fuel gauge ground pulls the needle to E(left) whereas ground pulls the temperature needle to H(right)
 

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Right. Good info on the fuel gauge.

I thought it was obvious that the needle hits the plastic stops during the bulb test, I mean you can see it happen in the car. But those pics above are very helpful. Sorry I didn't address that in my video specifically. Maybe I can make a third one. I wanted to address the electrical properties of these gauges first, since that is the most confusing aspect. Perhaps a mechanical explanation video would be useful too... for this series. Let me think about doing one before I clean up the mess I made. Doing videos takes a lot of time, more than you would think.

I knew there was probably a technical term: "two coil system", so thanks for educating me on the proper terminology.

On the old 9C1 forum, one person cut the plastic material and said it fixed the problem. But it looks ugly. And if the dampening fluid is completely gone like the one in my first video, or the shaft is spinning within the armature and the needle too, then removing the stop may not fix the problem at all. If you watch my video, it still bangs hard and comes out of calibration, even without the plastic stops. It's just far more likely to happen WITH the stops.

As for the fuel gauge, that old post is very good. For the record, I already tried to modify a dampened fuel gauge to be a temp gauge. Seems like the fuel gauges retain their dampening (more reliably) so it made sense. But then I realized it moved the wrong direction. LOL. At first glance, one would think all 4 gauges are the same. But they aren't. All four are different. And by the time I completely disassembled a fuel gauge to reverse the direction, not necessarily having the patience and equipment to deal with hair-thick windings, I compromised the dampening fluid on the armature and it wasn't any better off anyways. I wish we had a way just to restore the dampening fluid. I tried some fluids that I had in stock, including very thick and sticky STP oil additive, epoxy resin without the hardener, and perhaps a few other fluids. Organic fluids like honey or sugars eventually dry up solid. Nothing worked like stock. But if we had a source of the real fluid, then we could just restore the mechanical function. Perhaps doing both a mechanical and resistor mod would be a permanent fix.

This is an excellent thread. Thanks for your input.
 

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Awesome tech info here guys - Really appreciate the time/effort to dive into this.

For the damping fluid, maybe try glycerin that's used in bourdon tube pressure gauges to damp the needle movement?
 

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200804

Glycerine usually works by dampening all the gears, levers, and the actual needle. Like water resists a boat paddle.
It might work short term but in a unsealed environment it will dry out or evaporate.
 

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Glycerine
Good suggestion... might try that... I've seen many sealed gauges filled with that stuff. Fuel pressure gauges, for example. Still sold today as "oil filled" or "oil dampened". But I am skeptical that it's not thick enough or sticky enough for our use case. The stock fluid in these gauges are literally just a few drops on the armature at the plastic bushing/friction points. That's why I tried a few drops of epoxy resin (without the hardener). It was the stickiest goo that I could find in my shop. Nope. Then again, I didn't fully disassemble the armature either.

Another option that crossed my mind is the same "sticky grease" that was on 80s and 90s tape decks, you know, the kind that when the deck door opens, it moves slowly and gently. When taking those old decks apart, the door hinges and gears had that type of really thick and sticky paste on them. It looked like Vaseline but definitely was not slippery like grease. I have no idea what it's called. I tried some Google searching for that substance... but nada. Probably because I'm not searching for the correct terminology.

Either way, if the only way to get it onto both ends of the gauge shaft is full disassembly of the armature, that could present a challenge too. It's worth a try but not for your average DIY car guy.
 

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Either way, if the only way to get it onto both ends of the gauge shaft is full disassembly of the armature, that could present a challenge too. It's worth a try but not for your average DIY car guy.
This would be a separate topic.
In the fuel gauge thread I noted one gauge was not dampened. With the fuel sensor you might see some movement. Under test bench conditions it moved very quickly and would hammer into the stop when powered up.

If we limit the gauge check swing a properly working temperature gauge circuit is slow moving and even a undampened gauge should be servicable.

Another option that crossed my mind is the same "sticky grease" that was on 80s and 90s tape decks,
Usually I use lithium (white grease). Depending on application: Lubriplate, di-electric (silicon), and Grote ultra seal are things I use.
 

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Anything above 1.5K ohms (including infinity, open circuit) will just read "C".
a 1K resistor to ground results in an approximately 1/16" deflection to the right.
55 ohms reads slightly past H.
Resistance temperature sensors usually have a logarithmic output.
To clarify this the temperature gauge shows a different amount of movement per degree temperature at the C end and the H end. 70degF(at C) to 200degF(middle)is 130 degrees. Middle to H is just 60 deggrees. Have a look at this generic gauge with temperatures added.
200831
 

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Discussion Starter · #57 ·
Great info & research here.

storm9C1, great videos

So, after watching the videos, my takeaway is this...

When I turn my key to run, my temp gauge moves below cold, (see video https://photos.app.goo.gl/o8jPzvvJRoNFQiX29) so, my temp gauge does work, but the needle has spun on the shaft and now the cold (normal key on position) thinks it's somewhere below cold (the gauge is right, but the needle is wrong). When I ground it out, it moves to full hot (as expected). If I hooked up a pot, I should be able to add some degree of resistance (or subtract? less ohms anyhow, but more than 1 ohm) and the needle would eventually move. (as it does when grounding out).

FYI, I'm running a 160 thermostat & a tune, so I rarely see even 200 degrees.

I still plan on swapping to a spare gauge soon, but I guess it wouldn't hurt to try & reclock the needle, if this gauge is messed up anyhow, but how would I get the needle to stay put & not simply spin on the shaft again?

Thanks!

sod
 

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When I turn my key to run, my temp gauge moves below cold, (see video New video by Robin Schmalzbauer) so, my temp gauge does work, but the needle has spun on the shaft and now the cold (normal key on position) thinks it's somewhere below cold (the gauge is right, but the needle is wrong).
Correct. When you turned the key on, your needle pulls hard to the left stop, far below C, which definitely means it's out of calibration.

Normal operation is that it should pull hard to the "C" position and no further.

When I ground it out, it moves to full hot (as expected).
Yep. So it's working.

f I hooked up a pot, I should be able to add some degree of resistance (or subtract? less ohms anyhow, but more than 1 ohm) and the needle would eventually move. (as it does when grounding out).
Yep. Your understanding is correct. Either use a pot (make sure it can handle 1 watt) or even just a 55-ish ohm resistor. Since 55 ohms should read "H" on a properly calibrated gauge. My guess is that 55 ohms is going to read much below "H" in your case.

FYI, I'm running a 160 thermostat & a tune, so I rarely see even 200 degrees.
Right. This will make matters worse. Even with a properly calibrated gauge, 160 degrees is still on the cold side. Maybe about 1/4 on a normal gauge. Whereas 190 is about half way (just a guess, it's been a while since I scientifically mapped the gauge position with the sensor readings).

Furthermore, you are now taking readings from the water pump, correct? Because you swapped to a 3-wire WP sensor, correct? The WP runs cooler than the head. So I'm also not sure how this may affect the range of the stock gauge.

FWIW, I hope you had a tune done after swapping to the 160 degree the stat. Otherwise you will be running rich. And I hope you don't have frequent short trips, otherwise the engine will never get hot enough to boil out moisture with a 160 degree stat. I run a 180 degree stat in all of my cars. I used the 160 when I used to race, where every little bit helps.

how would I get the needle to stay put & not simply spin on the shaft again?
I don't have a solution YET for making the needle stay put. I've tried several solutions over the years. Later determining that the needle spins on the shaft AND the shaft spins on the armature. So there's two points of slippage to contend with. You can try to reclock it and it may work for a while but it's almost not worth the effort until I test the resistor mod. Because the first bulb test will bang the needle hard to hot, and throw it back out of calibration. I hope to test adding a resistor to the bulb test circuit, that is your only hope (after reclocking).

Is your spare gauge cluster marked "Certified" (ie: 9C1)? And does it also have high miles? You can do the finger test as I show in my videos and see if that gauge has any dampening left. If it does, I'd just swap the temp/volt gauge pod. If you don't want to disassemble the whole thing, then just swap the entire cluster for testing. The legality of running the car for any length of miles with the swapped cluster (odometer) won't be discussed here.
 

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Update: I haven't forgotten about this thread. In fact, I am working with an electrical engineer, and we have a prototype solution to electronically dampen the gauge during the bulb test to protect the needle. Will keep everyone posted as I get closer to the final solution.
 

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Time for another followup here...

And this is a long one! So grab a coffee, pop, or other favorite liquid snack, take a drink... and read up.

After working with my EE friend and trying various solutions, I've determined that an electronic solution is going to be too complex for a DIY. I (we) tried various simple resistor and capacitor circuits with some success at dampening, but those caused other side effects. The end result would need to be a custom module with specialized electronics that would go between the car inputs (temp sensor + bulb test circuit) and the dash cluster.

Completely disabling the bulb test circuit (cutting a wire) can help a little... but I don't recommend it. I have other findings I'd like to share as an alternative.

There's additional information that I learned that caused me to completely shift gears.

A friend brought his '95 9C1 Caprice down for a visit over the weekend. He got this car years ago directly from auction. He drives it rarely. Mainly to car shows. It's completely unmolested. "Customer states" that he thought his temperature gauge was acting up (of course). So I expected the same problem. But nope! His temperature gauge was working great. And during the bulb test, it was properly dampened. It did not peg violently to the right. Instead, it gently moves like it should. And reads cold and warm like it should. End of story right?

Turns out that since he rarely drives the car, he got confused as to which gauge was broken. His volt gauge turned out to be the faulty one instead. LOL.

So this confirms that 9C1 cars do come with the damping fluid in the temp gauges. I think it just wears out over time.

Back to the volt gauge... the symptom is that on his car, it always reads high. At or above the 18V mark.

After testing the voltage at the battery and various test points on the car, everything is normal. 13.X VDC with the engine running. 12.X VDC with the engine off.

This lead me to checking other 9C1 cars (and spare clusters) in my collection. And sure enough, some of my 9C1 cars have lost the damping in the volt gauge. Their volt meter pegs violently to the left (below 8V) when the car shuts off. It makes an audible "click" as the needle pegs down. Additionally, the bulb test during start also pegs it to the left (not because the bulb test circuit is hooked up to it, but instead power is briefly removed from the cluster, causing it to peg down). Again if the damping material is shot, the gauge will peg down violently enough to spin on the shaft.

Ergo, I determined via calibration procedures that his volt gauge did indeed spin on the shaft and now reads too high. Since the gauge pegs to the low end (left), the hammering action has the opposite effect than the temperature gauge (which pegs to the right). So while the temp gauge reads low when this damage happens, the volt gauge reads high. This also explains why one of my own cars reads a little high and I never bothered to figure out why since alternator readings are all normal. So I solved two mysteries at once.

Everything is consistent with my findings on these gauges. The damping (dampening?) fluid eventually wears out or evaporates. The gauges become twitchy (ever see your oil pressure gauge dancing around too?), and eventually come out of calibration due to hammering action.

So........onto my next hypothetical solution. Instead of electrical dampening, we need to restore the mechanical dampening. I thought this would be nearly impossible due to the gauge design. But it's the only option left now.

I've learned quite a bit over the past few weeks on this subject. I've learned the name of the fluid that GM used is called "damping fluid". It was obviously injected into the gauge bushing/shaft interface during the manufacturing process.

I had no idea what type of fluid until I ran into a company named "Nye" who makes lots of these greases and oils for the industry.


The fluid we want is called a "motion control grease". For audio applications, these are also available in oils that can be applied via syringe.

There are so many ranges of oils and greases from super slippery to super tacky. In order to indicate the tackiness, the "kinematic viscosity" measurement is in a unit called "centistokes" (cSt).

Light reading:

Notice that honey is 3500 cSt. This is closer to what we need. In fact, I suspect we need something over 50,000 cSt. For example, I've tried epoxy without the hardener since I found it to be super tacky. It still was not enough. Like honey, it's not a grease or oil, so it does not work long term. Just using it for reference. Back when I tried this years ago, I gave up on the project before finding a suitable fluid and/or finding a way to "inject" it into an existing gauge. Keep in mind that 20 years ago, I did not have the online resources that are available now and I basically forgot about all of this until this thread.

Long story short (longer? LOL), I ordered a small syringe of 500,000 cSt damping oil. That is as sticky as I could get knowing that the gauges are tiny and have little surface area to work with. This particular tacky oil is also used for tone arms on turntables which is a delicate application and works well there, according to what I read.

This is all theory. I'm hoping that the type of syringe I bought should allow me to "inject" some of the fluid down into the shaft/bushing area of the gauge itself to restore the damping effect.

This may work. Or it may not. I can order lower cSt fluids if needed until I find the right one. Assuming the injection process even works.

Gimme a few more weeks. Will continue to keep yinz all posted.
 
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