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Jeff I indu

49 royal first drive towed home

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Well, it's not all bad. Got tags on Thursday and insurance on friday and decided to take about a 10 mile loop and go up a hill to see how fluid drive transmission would pull in high range and if it would kick down based on stepping on the gas. Half way up the hill it stalled. I am in a rural area so backed it down the hill and tried to start it and acted like it was out of gas. Called the wife and she brought me a few gallons. Unfortunately I dumped it all in the tank and didn't save any to prime the carburator. Once it started turning over slowly called aaa and had it towed home. 20 minutes on a battery charger and a little starting fluid and it started right up fine. Bought this car at auction last fall, put a few gallons of gas on it and it seemed the gas guage did not work as it was buried on empty. A few weeks ago I bought a new sending unit from auto city classics in Minnesota. Easy install and shazam, it said I had a full tank. Should have known better. Today removed it, sticked the tank and have about a inch of gas from from what I put in it last night. I played with the float while grounding the unit and no matter what position the float was in the gas gauge only says full if sending unit is grounded and empty if ungrounded. So i think i have a bum sending unit and will take it up with auto city on monday.

Two questions, my belief is that the gas guage is a slave to whatever amperage the sending unit sends to it. The gas guage seems to work, so what else could it be other than the bum sending unit? No matter what position the float is in the gas guage only says full.

Also, I never did get the chance to go up a hill. Once you start up a hill do you leave the fluid drive in high range and kick it down or do you clutch it and drop it into the lower range?If you drop it into the lower range will it be in the high side of the lower range? Should the lower range only be used from a standstill? I suppose I will find out soon but dont want to shift to the lower range at maybe 25 mph and find out its geared so low it causes the engine to rev up too high. Still learning I guess

Jeff

 

 

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I feel your pain. I had a 49 DeSoto Suburban, way back when, with Fluid Drive. I remember that the car would stall out sometimes between shifts, too. 

Well, it decided to stall out about halfway up on the steepest, busiest hill that led back to the center of town through a traffic light. And to boot, I could never get the vacuum assisted brakes to work properly so when I started to roll backwards towards the traffic light and the center of town, and because the car wouldn't restart when I tried, I was standing on that brake pedal as hard as I could but the car kept picking up speed. (The e-brake was all worn out, too. I tried it. No good!!!) As panic set in I decided the only way out of this situation was to "ground" the big boat by hopping the curb and coming to rest halfway on the road and the sidewalk. 

As far as the fuel gauge is concerned is it a one or two wire unit? I am pretty sure it should be a 2 wire unit. The sending unit, when installed into the tank, gets its ground from the tank to the flange of the sending unit. You need to make sure there is a clean contact surface between the unit and the tank.

Take a look here:

Do you have a downshift button on the end/tip of the shifter arm? I had one on my DeSoto and I could downshift by pushing the button.

 

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Sounds like the guage itself doesn't have a good chassis ground or is bad on the empty side.

The guage moving to full when power is applied and sender is grounded just tells you the full side coil is good and has a complete circuit. Empty side is grounded through the chassis.

 

Measure resistance across the sender and move it looking for corresponding change , it's likely good.

Edited by 50mech

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You shouldn’t need low range to pull a hill unless you’re starting from a stop. Even then high range should be fine. Be careful downshifting into low range. My 52 grinds if I’m going more than 15 mph or so. Of course I have 127,000 miles on my car so who knows. These cars were designed to be driven in high range pretty much all the time. Low was for snow or sand or other low traction conditions. It’s a bulletproof trans so any problems are usually electrical.

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The sending unit is one wire and I believe I have a very good ground at the tank. This is still a 6 volt system. When the sending unit is grounded is when the gas gauge needle jumps to full. I have not checked ground at the gas gauge itself. Will do that today

 

I do not have a downshift button on the shifter arm. The carburator has a wire that controls the kickdown switch. I just haven't stomped the pedal yet. Just not sure when or how is the appropriate time to use the lower range on the fluid drive

Jeff

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Here's a visual of how it works internally.

Two coils, both get power from the SW post. One grounds to the frame, one to the sender post.  Powered up they fight each other, change in resistance at the sender determines the power one of the coils get. If the other gets none because of a broken wire or corrosion at the frame then the one controlled by the sender always wins.

Screenshot_20200726-102726.png

Screenshot_20200726-102757.png

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Okay.

Was the original sending unit a 2 wire type? I cannot remember if it should be a 2 or 1 wire type.

You can ground the sending unit body/flange remotely while it is installed in the tank to be sure you have a good ground.

Also, if I remember correctly, the voltage to the sending unit is a pulse - like a blinker - not a steady voltage.

Anyway, click on the picture I sent you above and there is a ton of info on troubleshooting your issue.

 

As far as using low or high range - I remember my car(s) with fluid drive would automatically downshift in the high range if the car/engine was struggling up a hill. The shift in high range from, let's say 4th to 3rd, should take care of going up hills if the car slows down too much. However, if you shift from high range to the low range position manually you may over rev the engine going from 4th to 2nd unless, as stated before, you are almost stopped or stopped.

You can also, as you stated, use the kickdown switch on the carb.

 

(If I am incorrect with any info I have offered please, anyone, feel free to correct me but be nice about it. I haven't driven a Fluid Drive in over 35 years and I am going by memory only) 

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Single wire unit, blue wire , steady power at ign on from ign switch to gauge , 1 blue wire from gauge to sender.

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Got a analog multimeter and pulled the new sending unit again.  Set it on ohms X1k, grounded the unit so that the fuel gauge reads full. The ohm meter needle moves all the way to the right and reads zero. Moved the float several times and no movement of ohm reading

 Set it to 10 DCV and got a reading of 6 volts at the screw of the sending unit

 Again moved the float and no matter what position I still have 6 volts at the screw of the sending unit. I'm not the best with a analog multimeter but shouldn't either the ohms or voltage change based on the float position?

 

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Just retested with 4 hands to hold things this time. I have between one and two ohms of resistance no matter what position the float is in. Its bouncing a little. Voltage remains at 6 volts regardless of float position

 

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Sounds like your sending unit is not working properly.  The resistance between ground adn the terminal should vary as the arm sweeps thru it's range.

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1 hour ago, Jeff I indu said:

Got a analog multimeter and pulled the new sending unit again.  Set it on ohms X1k, grounded the unit so that the fuel gauge reads full. The ohm meter needle moves all the way to the right and reads zero. Moved the float several times and no movement of ohm reading

 Set it to 10 DCV and got a reading of 6 volts at the screw of the sending unit

 Again moved the float and no matter what position I still have 6 volts at the screw of the sending unit. I'm not the best with a analog multimeter but shouldn't either the ohms or voltage change based on the float position?

 

Not if you make the measurements with the wires hooked up and power on.

 

Have the sender hooked to nothing sitting on a bench.

One lead where the wire goes, one lead on the body of the sender. Then move the arm.

Setting should just be ohms x10....not 1k. Your sender maxes at like 30ohms or 70 can't remember which. Nowhere near thousands of ohms.

 

So the meter should move between zero and 3 or zero and 7.

Edited by 50mech

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How about a pic of the entire meter with leads?

 

Seems something is off.

 

DJ

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Unfortunately that meter isn't going to work for resistance here. I looked up the manual for a gmt 312 and it actually does only measure resistance in thousands of ohms.

When 1 is actually 1000, 30 is going to look like zero.

 

You may be able to see a voltage change if you run the meter in series.

Sender unhooked but grounded, one lead on car wire one on sender terminal.

 

Depending on the operation of this meter it may still not show ( depends if it uses an internal shunt)

 

Edited by 50mech

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This meter is all i have for now. I hooked the sending unit up in series and cant detect a voltage drop at all when moving the float. There is a garage up the road and I will check with them tomorrow to see of they have a better meter. Still need to check the gas gauge for grounding issues up front. Just trying to verify the sending unit first. Thanks for everyone's input. It really helps a ton. Will advise more tomorrow.

Jeff

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I tested the sending unit at the local garage. They had a digital meter but the lowest ohm setting was 200 ohms. But it read from 7 down to 2 while I was moving the float so I will assume it's good. Loosened and retightened the mounting screws and nuts on the back of the gas gauge. Same thing. Only reads full. One other thing. When I turn the key the dial bangs to full hard. Not gradual at all. I think 50mech is correct. If there are two coils that fight each other the one that pulls to the empty side is bad. A new gas gauge is about 35 dollars delivered on Ebay. Will be purchasing it shortly. Thanks for all the advice

Jeff

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Actually sounds like a bad sender if it maxed at 7 ohms. Though if for some reason it was reading in 10x that would be basically dead on correct. A lot of digitals have 10x set by the buttons at top and just show a little indicator on screen.

Looks like 10-73 is the right range so with room for error in rounding 20-70 would be acceptable.

Edited by 50mech

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