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1941 Buick Limited Limousine


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Matt,

When I dropped the gas tank on my '40LTD, I had to build new straps out of flat stock, as they were almost rusted thru.

I used wash machine drain hose (split open and trimmed) as my top and bottom cushions .

 

Also, back to your clutch / brake pedal issue, the next time you have her up on the lift, check the 2 holes in the 'clutch equalizer" (bell crank).

Mine was almost "blown out' where the rod from the clutch pedal hooks in.

I tig welded it up and re-drilled the hole just a bit back, so there is plenty of stock for the next guy.

 

Mike in Colorado

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39 minutes ago, Bloo said:

If you really want to know, make sure it goes 0-30 ohms. Measure the sender outside the tank and find out how low it goes (closer to zero ohms the better). Put the sender in the tank and make sure that it still all the way down (in ohms) where it was. This assures the float does not hit bottom. Hitting bottom is not only bad for the float, it prevents the gauge going all the way to "E".

 

Then, flip the tank upside down and make sure the sender goes to 30 ohms (or more). If not it will never get to full. Also, the float should get real close to the top but not hit.

 

Third test: (optional, but a good idea if you do not like pulling gas tanks out). Put some gas in the tank with it sitting level on the ground, and then suck it out through the pickup with a hand pump. Do not attempt to use an electric one. The squeeze bulb or bellows type are easiest (and the plunger pump at harbor freight is useless).

 

Suck the gas out, wiggling the tank a little, until the sender reads zero ohms (or as low as it went when it was out of the tank). Now move the discharge hose to another can and keep sucking until you suck air. The second can is your reserve, and you can see how big it is.

 

If the pump sucks air before the sender gets all the way down (in ohms), you will run out of gas before the gauge gets to "E". IMHO it pays to figure this out while the tank is out on the ground and you can re-bend the float arm easily.

 

If there's no sock filter on the pickup, put one on. Have fun!

 

I've used water instead of gas.  Then leave the tank open in the hot sun till it dries out.  I like your procedure for determine reserve - gotta do that one.

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Took the tank to my friend at the radiator shop and when he saw it in the back of my truck he said, "Jeez, how old is that thing?" Then I had him look inside and he was shocked. He'd never seen such a contrast. Neither of us could think of a single reason why or how that tank should look so good inside and so ancient on the outside. He poked around and agreed that whatever that wrap is on the filler neck has to go and we should investigate and repair whatever is underneath. He also spotted an area on the bottom of the tank that he thought might have been repaired once before, although if there is a patch it is not visible from the inside. He thought maybe a pinhole leak that they just smeared goop on until it stopped. They'll boil it out and clean it and pressure test it to see what's going on and fix anything that needs fixing.

 

He did note that they don't have their large immersion tank any longer so he won't be able to completely clean the outside of the tank. I'm not going to worry much about it, the underside of my car is plenty crusty, so I'll figure out how to make it look reasonable when it comes back. It may just be as easy as giving it a quick dusting of undercoating to just even it out, or maybe I'll be dumb enough to spend the time with some kind of solvent slowly scraping all that goop off. We'll see how it looks when they're done.

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Posted (edited)

One, my gas tank is finished already. Either they're not very busy or it didn't need any work. Good news. I'll pick it up in the morning.

 

I also have a question that's completely unrelated to gas tanks, but something became shockingly clear to me today. I bought this handsome 1942 Packard 160 formal sedan with a divider window just to have some new inventory. The price was right, I've known the car for decades, it's an all-original 38,000-mile survivor (just how I like my cars), and I think it will make a nice tour car for someone (not me, don't worry). Anyway, I took it for a drive this morning and realized that the Packard rides much better than the Limited. Not a little, but A LOT. There's almost no impact harshness on bumps, but Packard just oozes over them and you barely feel them. My Buick, even with an all-new front end, new shocks, and radial tires, still kind of crashes over bumps. It's not even close. I can't imagine that the Buick did not feel as good as the Packard when they were new, so what am I missing on my car? Why does my car still send a significant shudder through the entire body every time it hits a bump? Why does the Packard feel like it's made from one chunk of iron while the Buick feels almost fragile?

 

I should also point out that I had this same impression when I owned both the Limited and a '41 Cadillac 60 Special--the Cadillac ignored bumps that would upset the Buick. Both of those cars had virtually identical suspensions. What gives?

 

Could it be the tires? The Packard is sitting on Lester wide whitewall bias-plys. The Limited currently has Hercules 10-ply truck radials from Diamondback. I did notice a bit more impact harshness when I first installed them, but they were not A LOT worse than the old Firestone bias-plys that were on the car when I got it and since then I've rebuilt the front suspension and shocks. I run them at 32-35 PSI (they're rated to 60 PSI since they're truck tires), which I figure is a good compromise between heat, ride quality, and tire life. Should I run less tire pressure? 25 PSI like it says in the manual? Go back to bias-ply tires? Try the new Diamondback Auburn radial that isn't a truck tire?

 

I also thought that maybe I should replace my body mount bushings, which are original and probably hard as rocks. That surely transmits a lot of NVH through the body structure on bumps, no? What else is there? The front shocks are rebuilt, the bushings are new, and everything is tight. What am I missing? There's no way a Buick limousine should be notably worse than a garden-variety Packard sedan in that department.

 

I could push it to the back of my mind because I'm so happy with the car otherwise, but now that this Packard has reminded me that it could be better, I'm not sure what I should do to fix it. Any suggestions?

 

Thanks!

 

By the way, here's the Packard:

 

Packard2.thumb.jpg.83da5463babd71bf0f9cfae5a7b387cb.jpg  Packard4.thumb.jpg.6a234cf7b3389a3f48a858867ce87c60.jpg  Packard5.thumb.jpg.ef97ede149c404f5fb5757e28afd1613.jpg

 

Edited by Matt Harwood (see edit history)
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It is the build construction quality and weight - my 41 60 Special was superior car to my 1941 Buick super (very tin-y car) - when it came time to sell one the Buick was first out the door (mainly because tin-y, hated closed driveshaft, and ...)  All said though, the Buick was I thought a zippier car (it could run circles around the Cadillac) and easier to keep running.  Then, I switched to Auburn's and probably will not do any prewar Cadillac's or Buick's unless they are just passing through. 

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Posted (edited)

Matt,

1, Take the STP out of your shocks.

2. Get some "Lesters"" with the 4 1/2 white walls.

 

You really would not want to buy my "Martin's". Ed would have a fit.

The "BABY" rides smooth as silk since I put hydraulic jack oil in the shocks.

 

Mike in Colorado

100_1235.jpg

Edited by FLYER15015 (see edit history)
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2 hours ago, FLYER15015 said:

Matt,

1, Take the STP out of your shocks.

2. Get some "Lesters"" with the 4 1/2 white walls.

 

You really would not want to buy my "Martin's". Ed would have a fit.

The "BABY" rides smooth as silk since I put hydraulic jack oil in the shocks.

 

Mike in Colorado

 

 

The shocks are rebuilt and have the ISO 32 hydraulic oil in them, which is the thinnest available (about 10W), but I'll take your advice. I ordered some 5W motorcycle fork oil and I'll put that in there to see if things improve. Anyone have any ideas for how to get the oil out of there with the shocks still on the car? Turkey baster?

 

But first things first--I still have to put the fuel system back together. Today I figured I'd test the wiring and run a new wire to the back of the car for the sending unit. Before I dug in, however, I though it would be a good idea to test the gauge and new sending unit. So I connected a test lead to the wire at the rear of the car and to the terminal on the sending unit. Then I attached a second wire from the body of the sending unit to good ground. Turn on the ignition, move the sending unit arm, and the gauge should...

 

...What the? Oh goddamn it. Of course it doesn't work.

 

With the sending unit connected, turning on the ignition makes the needle twitch to just above the EMPTY line. Move the sending unit to full (top of travel) and the needle moves to full empty, completely bottomed out. It does not move towards the FULL end of the scale. Only about 1/16" from just above EMPTY in the empty position to just below EMPTY at the full position. 

 

In the past five years, I've probably purchased seven or eight sending units for this car, always intending to get the fuel gauge working. Along the way, we have installed those sending units in other cars in an attempt to get their fuel gauges working. Two or three Cadillacs, a Chevy, a Packard, and another '41 Buick. In every case, simply swapping out the sending unit made the gas gauge work properly. And in every case I can find on this very message board where someone had an inop gauge, changing the sending unit fixed it. 


For me, however, it is always uphill both ways. It couldn't possibly be a simple fix on my car. 

 

So I checked my wires. Good continuity from the back of the car to the gauge. Just in case it was shorting out somewhere, I bypassed the wire inside the car and connected my test lead directly to the back of the gauge and to the sending unit. Same result. 

 

Then I tried connecting the sending unit terminal wire to the other terminal on the gauge--nothing at all happened, so at least it's [probably] wired correctly. 

 

I have two theories. One, the gauge is just broken. I have another one, but I don't much relish the idea of going into the dash to pull the old one out and put the new one in. The fact that it twitches a bit in response to the sending unit's motion suggests it may be operable, but I'm not sure. 

 

Theory number two is based on the wiring diagram:

203481393_n_131942BuickShopManual-ElectricalSystem-053-053.thumb.jpg.ece9135489873e9578d0a9ac15dd5222.jpg

I've highlighted the fuel gauge circuit, and you'll note that it draws power from the ignition switch, runs through the gauge, then back to the sending unit where it is grounded. The sending unit is a variable resistor attached to ground. That's how the gauge works, by indicating the resistance in the circuit. Simple enough.

 

But you will also note there is a SECOND wire going from that same terminal that gets power from the ignition. That wire goes to the accelerator starter switch on the carburetor, then to the starter solenoid. Hmmm. Do I have it backwards? Is the gauge powered by the ignition or is the entire ignition system powered THROUGH THE GAS GAUGE?  If the latter is the case, why does the ignition switch turn the gauge on and off?  Shouldn't the gauge be awake all the time if it's getting +6V from the solenoid THEN feeding it to the ignition switch? There's something I'm not understanding here.

 

To make it relevant to my situation, my car does not use the accelerator switch and there's no wiring in place for it. It has been bypassed in favor of a pushbutton under the dash. I reconnected the starter switch when I first bought the car, but that made it much harder to start, so I went back to the button and I'm happy with it that way. My theory is that somewhere in the bungled wiring that the previous owner installed, that wire from the fuel gauge to the accelerator switch is just hanging loose or is maybe even connected to the wrong terminal somewhere. Could it be grounding out somewhere and causing this problem? And if I simply disconnect that wire at the gauge, will the gauge work properly without whatever that wire is? Or will it kill the entire ignition system? Can I just run a separate 6V power wire to the gauge from, say, that bus bar I plan to install? What is that wire's job and is it necessary for the proper operation of the fuel gauge and/or ignition system?

 

I don't know. I have to figure it out. If I'm doing all this work and spending all this money just to continue to have a broken gas gauge and a car that runs exactly the way it did before, I'm going to be pretty unhappy.

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I don't know if I can help on the gas gauge. I bought one from "Bob's" and just threw it in. Got lucky I guess.

But I did note that she being a stock 6 volt system, the wire going to the gauge seemed quite big, so there must have been a resistance calculation back then.

I used the same gauge wire for my ground on the frame and tried to keep it as short as possible.

 

Shocks = you can siphon them out with a coke bottle and some 1/8" model airplane fuel line (soft silicone).

However it tastes terrible...........

 

Mike in Colorado

 

 

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I suspect your main culprit in the harsh ride is your tires. I know that you don't like a particular source for bias ply tires, but I think that you will find that the original size bias ply tires will ride softer than the nice heavy duty 10 ply truck radials you currently have. As a compromise, you might try lowering the tire pressure to the original specification and see how that changes the ride.  

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Posted (edited)

The gauge is powered from the ignition switch. it also powers the other stuff you highlighted (part of the autostart system).

 

Test the sending unit with an ohmmeter (DMM). 0 ohms empty, 30 ohms full.

 

Then, Ignition on, wire hanging loose at the back of the car, gauge should be pegged. Short wire at back of car to ground, gauge should go to zero. (I gather you have done some of that). Until it will do that, nothing else will help.

 

2 hours ago, Matt Harwood said:

But you will also note there is a SECOND wire going from that same terminal that gets power from the ignition. That wire goes to the accelerator starter switch on the carburetor, then to the starter solenoid. Hmmm. Do I have it backwards? Is the gauge powered by the ignition or is the entire ignition system powered THROUGH THE GAS GAUGE?  If the latter is the case, why does the ignition switch turn the gauge on and off?  Shouldn't the gauge be awake all the time if it's getting +6V from the solenoid THEN feeding it to the ignition switch? There's something I'm not understanding here.

 

It is not how it looks. The gauge is powered by the ignition switch. The wire to the solenoid does not REALLY go to the solenoid, just the little relay on the solenoid that kicks the solenoid. It gets power from the ignition switch like the gauge, but via the accelerator switch. That relay coil floats. It gets its ground from the voltage regulator. There is no power on that little relay coil to feed back to the gauge.

 

2 hours ago, Matt Harwood said:

To make it relevant to my situation, my car does not use the accelerator switch and there's no wiring in place for it. It has been bypassed in favor of a pushbutton under the dash.

 

So it isn't relevant to your car. All you need is switched (ignition) power to the gauge, a good ground on the gauge, and a nice insulated wire to the back. That's it.

 

Is it possible the get the wires reversed on a 41 gauge? Maybe the guy who did the harness butchering got that wrong.

 

 

 

 

Edited by Bloo (see edit history)
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Thanks, Bloo.

 

The sending unit checks out in terms of resistance. That was my first thought. We haven't had a bad one yet, but that only means I'm due.

 

I have a new theory that the wire running through the car is shorted to ground. My gauge has always read empty. I'm going to disconnect that wire from the gauge and see if it goes to FULL. That's one variable to eliminate. 

 

Looking at the wiring diagram, where does the ignition switch get power? There are three wires, one to the fuel gauge, one to the coil, and one to the cigar lighter. But only one of those is connected to the battery/starter/solenoid via the accelerator switch. Where is the ignition getting power if not from that wire off the fuel gauge?

 

I'll also check to see if the wires might be reversed. They're correct according to the diagram but that doesn't mean they're right. The previous owner really hacked up the wiring so there's a lot to sort out.

 

I have a few more things to check and maybe we'll make some progress. Thank you!

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11 hours ago, Bloo said:

The gauge is powered from the ignition switch. it also powers the other stuff you highlighted (part of the autostart system).

 

 

Thanks Bloo, great dissertation - i'm keeping this.

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13 hours ago, Matt Harwood said:

 

Looking at the wiring diagram, where does the ignition switch get power? There are three wires, one to the fuel gauge, one to the coil, and one to the cigar lighter. But only one of those is connected to the battery/starter/solenoid via the accelerator switch. Where is the ignition getting power if not from that wire off the fuel gauge?

 

It's the cigar lighter wire. The diagram is a bit pixelated, but if you squint just right, there is a tie point where it crosses the "10BRC" wire (Voltage Regulator, Ammeter, Light Switch).

 

The "BAT" terminal on the voltage regulator is the "hottest" point in the system when the generator is charging and keeping up. It is really the best place to power accessories, and that is what Buick has done here.

 

If you power a light or accessory from the starter post or solenoid instead, all the current it draws will register as "charge" on the ammeter, and you probably don't want that.

 

If you draw accessory and lighting power from the "BAT" terminal of the voltage regulator, as Buick has done here, current flows to the accessories and lighting without going through the ammeter. Only current that is actually charging the battery flows through the ammeter. Also, when the generator does not charge, power for the accessories flows from the battery through the ammeter backwards, showing a discharge.

 

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8 minutes ago, Bloo said:

 

It's the cigar lighter wire. The diagram is a bit pixelated, but if you squint just right, there is a tie point where it crosses the "10BRC" wire (Voltage Regulator, Ammeter, Light Switch).

 

The "BAT" terminal on the voltage regulator is the "hottest" point in the system when the generator is charging and keeping up. It is really the best place to power accessories, and that is what Buick has done here.

 

If you power a light or accessory from the starter post or solenoid instead, all the current it draws will register as "charge" on the ammeter, and you probably don't want that.

 

If you draw accessory and lighting power from the "BAT" terminal of the voltage regulator, as Buick has done here, current flows to the accessories and lighting without going through the ammeter. Only current that is actually charging the battery flows through the ammeter. Also, when the generator does not charge, power for the accessories flows from the battery through the ammeter backwards, showing a discharge.

 

 

I see it now. Good call. I couldn't sleep last night thinking about where the power was coming from. Thank you!

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Well, no dice on the wiring. Disconnecting the wire from the sending unit changed nothing. Gauge is still broken, although whatever I did made the needle stop moving altogether--not even a twitch. Of course, now that I've been jamming my hands behind the dash and jostling everything, my turn signals no longer work, either. And since there's no gas tank in it, I can't even test whether it still runs--I have doubts now simply because of how truly farked up the wiring is on this car. In the past I've spent a few nights in jail for beating people with my fists--I think I'd do happily do another one if I could find the guy who hacked up the wiring in this car.

 

Guess it's time for a new wiring harness. I wasn't going to drive the car this summer anyway.

 

What a good idea this was. Just a simple job, right? Easy.

 

I'm such a fool.

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Don't despair, Matt.  It's all pretty simple under there.  I would be very surprised if you dislodged anything that's going to make your car not run.  Let it sit for a while and then take a deep breath and try to see what's going on with the wires.  I know it's hard to see under there -- if you have one of those LED flashlights with a magnetic swivel mount, that can make a big difference. 

 

And if you DO end up putting in a new harness and need any advice, I'm your man.

 

Neil

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Posted (edited)
2 hours ago, Matt Harwood said:

Well, no dice on the wiring. Disconnecting the wire from the sending unit changed nothing. Gauge is still broken, although whatever I did made the needle stop moving altogether--not even a twitch. Of course, now that I've been jamming my hands behind the dash and jostling everything, my turn signals no longer work, either. And since there's no gas tank in it, I can't even test whether it still runs--I have doubts now simply because of how truly farked up the wiring is on this car. In the past I've spent a few nights in jail for beating people with my fists--I think I'd do happily do another one if I could find the guy who hacked up the wiring in this car.

 

Guess it's time for a new wiring harness. I wasn't going to drive the car this summer anyway.

 

What a good idea this was. Just a simple job, right? Easy.

 

I'm such a fool.

 

 

 

Stand in line........I have a car apart today I though I could finish in three days for the entire job......it's going to go 8 to 10 full days, with a helper. The last two projects did the exact same thing. I have been at this well over 40 years, and I still have issues like this all the time. Just think, in another 20 years, you will be numb or dumb.....just like me. 😭

Edited by edinmass (see edit history)
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Posted (edited)

Sounds like me with my dome light.  Every time I did anything to the lights or under the dash, it quit working.  I finally found the loose connection.  I thought I had it fixed several times and was very frustrated.  You are infinitely smarter than I when it comes to this stuff, so I have confidence you will get it done.

 

p.s. My fresh water pump install is dripping.  Let’s get together for a drink! 

Edited by 39BuickEight (see edit history)
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Posted (edited)
48 minutes ago, Matt Harwood said:

Well, no dice on the wiring. Disconnecting the wire from the sending unit changed nothing. Gauge is still broken, although whatever I did made the needle stop moving altogether--not even a twitch. Of course, now that I've been jamming my hands behind the dash and jostling everything, my turn signals no longer work, either. And since there's no gas tank in it, I can't even test whether it still runs--I have doubts now simply because of how truly farked up the wiring is on this car. In the past I've spent a few nights in jail for beating people with my fists--I think I'd do happily do another one if I could find the guy who hacked up the wiring in this car.

 

Guess it's time for a new wiring harness. I wasn't going to drive the car this summer anyway.

 

What a good idea this was. Just a simple job, right? Easy.

 

I'm such a fool.

 

First of all - I hear you on prior "mechanics" and "handymen"! I currently have two on my list I would consider treating the same way - the first is whatever troglodyte welded the king pin pin retaining pin on my Packard, and the second is the guy who used 3" construction screws in every electrical box I've opened up in my house!

 

I'm sure you'll get it figured out soon. Maybe you could run wires from your new sending unit to under the dash, drive the car, and fix the gauge when snow flies again?

I decided to do a few small projects 8 weeks ago - king pins and replace intake manifold. Going on waiting six weeks for the machinist that promised less than a week! Anyway, keep your chin up, and good luck with your car. A lot of us are learning from your experiences, good and bad!

Edited by Ken_P (see edit history)
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Posted (edited)

Awesome. Decided to get the tank ready to go back in the car so I can start it and get it off the lift and shove it in a corner and forget about it for a while. Got my freshly cleaned tank and found a small hole in the filler neck overflow where someone got too aggressive with a grinding wheel. Welded that up. Then filled the tank with water to test it because now I don't trust the radiator shop, and water started seeping out from under all the undercoating goop.

 

Guess I'll add a new gas tank to the list of things that I didn't have to buy two days ago. Oh, and nobody reproduces a Limited tank, which is 22 gallons, so I'll have to settle for a 17 gallon tank. Hope it fits.

 

Hours of my time and hundreds of dollars just to have a car that is worse off than it was when I started. How awesome am I?

 

 

Edited by Matt Harwood (see edit history)
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Matt...... Next time I’m in Northeastern Ohio, I’m taking you out drinking...........on me. I think we both need it. Hope you like Crown Royal! 
 

There is nothing so rewarding and frustrating than a pre war car. Love them one day, hate them the next. 

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Matt,

 

Is there a Gas Tank Renu franchise anywhere near you? I have never done business with them, but I hear good things about them. Other than that, you might want to try a different radiator shop. I have to drive about an hour to get to an old fashioned radiator shop but they do good fast and reasonably priced work. There are still shops out there that can and will fix your gas tank. That would probably be better than trying to switch to a smaller tank that might not fit correctly. Other than that, hang in there. You will get it all fixed and the Limited will again be your favorite car to drive.

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+1 on gas tank renu.  A leak on fill-up was a loose rivit on my sender unit. It was fixed with 2 part epoxy and has been fine since 2003.

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I have used Gas Tank Renu many times, including on the '35 Lincoln and '29 Cadillac. I'm a fan. I'll be taking the tank there later today. It's just that I didn't feel like spending the $450 to clean a tank that was already clean and usable. Well, usable before I paid someone $180 to clean it.

 

This stupid side project is going to cost like $800 and 25 hours of my time before it's all said and done, and the result will be a gas tank that's no cleaner than it was before, a car that runs no differently than it did before, a gas gauge that still doesn't work, and broken turn signals that worked right up until I started this project. Money well spent? You decide.

 

When will I learn to just leave stuff alone and live with crappiness like everyone else seems to?

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21 hours ago, Matt Harwood said:

 

I see it now. Good call. I couldn't sleep last night thinking about where the power was coming from. Thank you!

Actually Matt, I'm glad to see you blazing the trail here.  These are problems I will be facing with essentially the same car.  I've copied a number of your exploits with results and commentary from others.  Great thread here!

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Posted (edited)

Tank is on its way to Gas Tank Renu. They say it may be up to 30 days before I get it back. They're apparently very busy right now. Maybe I'll buy a new tank just so I can drive the car. I can't believe I was so stupid as to take the gas tank out during prime driving season. What kind of idiot does that? I honestly thought I could replace the sending unit and run new fuel lines in a day or two after work. LOL, what a dumbass!

 

I went through my pile of parts and found this:

 

440757862_20200521_1036171.thumb.jpg.bb732a95ef77aad4ea030d3dff3f4af2.jpg

 

How to test it before I tear the dashboard apart? Just connect it to +6V, to the sending unit, and ground the sending unit? Does the gauge housing need to be grounded as well?

 

 

Edited by Matt Harwood (see edit history)
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1 hour ago, Matt Harwood said:

When will I learn to just leave stuff alone and live with crappiness like everyone else seems to?

 

This is a good question.  My FIL ( rest his soul)  used to leave everything broken.  If it didn't work he just didn't need it.  My one son fixes every little thing as soon as it breaks.  For my part I assess the loss of convenience before taking on a major repair project.   When we got Dad's Cadillac I replaced the power window motors where-as he beat on the door panel to stimulate the action.  When my '56's horn didn't work right I lived with it for several years while other, more important,  projects were attended to.  All three of us are (were) happy in our approach.  

I can only say I am impressed each time I have a ride in any of my cars.  Somethings will break. It is the nature of parts that are twenty+ years old.  But most things stay together and work great!  I am always amazed at how well all the cars are put together such that they have attained their individual age. Even in junkyards it is amazing that things are still together and yet can come apart when needed.  

And I can certainly endorse taking a break from the hobby when it is overwhelming.  

 

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If I recall correctly, the gauge housing does not need to be grounded.  My memory is that the contacts on the gauge are insulated from the housing.  I agree with Ken -- this is all good stuff you are doing (although you may have chosen an awkward time to do it). 😜

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OK boys, please check my math.

 

I wanted to bench test that NOS gauge, so I connected as shown in the wiring diagram below. That should replicate how it's connected in the car, right? Power to gauge, wire to sending unit, sending unit grounded. I used test leads, not in-car wiring, and connected directly to the terminals on the battery, which should be full +6V power and a good ground. 

 

1529600070_GaugeDiagram.thumb.jpg.f77e18feb32e985f8389ff5eb4033521.jpg

 

I connect it and guess what? It does EXACTLY THE SAME THING AS THE GAUGE IN THE CAR. Sending unit at the top position (full tank) gauge shows EMPTY, totally bottomed-out on the scale. Moving the sending unit to the bottom position (empty tank) and the needle on the gauge moves slightly towards FULL, about 1/16". That is EXACTLY how the gauge in the car was acting. I even switched the wires on the gauge and it didn't move at all, so I know it was connected correctly as shown above.

 

Than I re-checked the sending unit, which still shows 0 ohms at the top position and ~28 ohms at the bottom position--close enough to 30 to be usable.

 

Is it now reasonable to assume that this sending unit is defective? Is there something other than resistance that's a factor in its operation? Am I missing something? I suppose both gauges could be bad, but if they were both bad, would they fail in the exact same way? What other variable remains beyond the sending unit?


I'm going to be seriously unhappy if it's this new sending unit that sent me down this path (remember what I said about being due for a bad one a few posts back?).

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I am guessing since I don't know if the 1941 gas gauge works the same as the 1937 and 1938 gas gauges. If they are the same, I think your gas gauge ground is probably bad due to corrosion and your test of the other one did not have it grounded. The 1938 Service Manual has two conditions in which the gauge shows empty under all conditions... 1. wires reversed on the gauge and 2. dash unit not grounded.

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Posted (edited)

0-28 ohms is enough to get good swing on the gauge (but to get all the way from E to F you are gonna need all 30 of them).

 

It is either a bad gauge, or it is connected incorrectly. The gauge must be grounded. These GM gas gauges are all the same electrically from the mid 30s (or earlier) through sometime in the mid 60s.

 

Here's how it works. There are two coils inside pulling opposite directions on a pole piece. The pole piece is attached to the needle.

 

One coil is grounded and runs on 6 volts all the time. The other one is grounded through the sending unit resistor. How hard it pulls is variable, depending on how much resistance the sending unit provides.

 

The coils are in a constant tug-of-war to move the pole piece. Since variation in the battery voltage affects both coils, it doesn't screw up the accuracy much.

 

 

Edited by Bloo (see edit history)
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Okay, I looked back at the wiring diagram and it indicates that Bloo is correct (no surprise) -- the gauge unit is grounded through the housing.  (A little hard to see on this image.)

 

wiring_diagram3_LI.thumb.jpg.7ec236d591705508b7c080b91d5b5852.jpg

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Posted (edited)
1 hour ago, JohnD1956 said:

@Matt Harwood  A photo of the back of that NOS gauge would be helpful.  

 

Here it is.
 

20200522_135444.thumb.jpg.4f94d447e641996876565104890e3df7.jpg  20200522_135453.thumb.jpg.b7c93baa6af7e6e9c4c0bb4b4d86df41.jpg

 

I tried adding a ground wire to the body of the gauge (the brass area under the terminals), but that generated a giant spark when I connected the power wire to its post, which melted the hair-like wire going to one of the coils, so this gauge is fried. The gauge must ground somewhere other than the body, but I can't see where that might be. Grounding the terminal that goes to the sending unit is shorting it (so it will always read EMPTY) and grounding the other one is grounding +6V power, so that's obviously a mistake. How is it mounted in the dash housing? I would have assumed the two posts also hold it in place in the gauge somehow. Either way, additional bench testing is irrelevant.

 

EDIT: I see where I screwed up. Now that I examined the gauge, the brass plate on the phenolic block on the back of the gauge is where it grounds to the dash. I grounded it to the body underneath, which is why it shorted out. Operator error.

 

Do I buy another gauge or another sending unit or both? I haven't eliminated either of them as a variable, but either of both of them could be borked. Shoveling money into the fire is how I usually solve problems--do I just keep going? $800 or $1000 to solve this "minor" problem, what difference does it make now?

 

Or do I just keep putting gas in it every 200 miles like I always have and live without a gas gauge and simply swallow my frustration, chalking up all that wasted money to the cost of being an idiot?

 

 

Edited by Matt Harwood (see edit history)
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Matt, I would buy another dash unit and continue.  Since your test of the dash unit (until it got fried) showed that it was behaving exactly as the one in the car when it wasn't grounded, maybe there's a problem with the ground on the one that's in the car?  That could be an easy fix (maybe that brass plate on the phenolic block is badly corroded or something).  But getting the old unit out of the dash is not easy (trust me).  NOS or used dash units come up pretty often on eBay, so I think it's worth getting another one so you can diagnose the problem and know where you stand.

 

In fact, I just did a quick check and found this '41 Olds unit for $9.00 that I'm sure has the same guts as the Buick one and could probably be adapted fairly easily to fit the gauge face from your fried unit.

 

https://www.ebay.com/itm/NOS-FUEL-GAUGE-FOR-1941-OLDSMOBILE-CARS-NEW-OEM-DASHBOARD-METER-OLDS-GAS/373019578574?epid=24014418199&hash=item56d9b310ce:g:xGEAAOSw4ApegSgt

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