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nickg112

1931 Desoto fuel tank sending unit

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I have a 1931 Desoto 8 cylinder sedan. I removed the gas tank and the fuel sending unit. I checked it and it is not working. I looked for a replacement but cannot locate one. Has anyone ever repaired one of these sending units? If so, please give me some advice. Also, I was thinking about buying a common 6 volt unit and modifying it fit my car. I am not certain of the ohm range that is needed for the new unit. I will need the same ohm range for the dash gauge to work properly. Any advice is appreciated. I have included a couple of photos of my fuel sending unit. Thanks

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I'm in the same boat, the sender from my '29 needs to be rebuilt. I'm going to try to find a place to rebuild mine as it still works electrically, the gears are what need to be replaced. I was going to get a replacement from Atwater Kent, but their website is not working anymore. atwaterkentmfg.com Anyone know what happened to them?

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Let me know if you have any luck. Keep checking this post. I will also let you know if I have any success. Thanks

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I have a 30 Desoto roadster which has what appears to be the same gas tank sender unit. New ones are available for early Chrysler cars with modern electronic moving parts at the arm area and I've installed as replacements in several early Chrysler cars. I may still have a new unit which went unused in one project.

You might drill out the cap rivets on your unit which has steel gears which are probably good. Sometimes cleaning the resistance board surface will bring back good operation.

On the unit with bad gears (probably made of potmetal) new gears might fix it but only if the resistance board is still good. Better check the board and shoes inside before investing in new gears. I have the gears depending on the size in brass as I did replace my gears years ago. The unit is still working 20 years later.

Martin Lum

30 Desoto

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I'm in the same boat, the sender from my '29 needs to be rebuilt. I'm going to try to find a place to rebuild mine as it still works electrically, the gears are what need to be replaced. I was going to get a replacement from Atwater Kent, but their website is not working anymore. atwaterkentmfg.com Anyone know what happened to them?

I wasn't pleased with the Atwater-Kent sender for my car, but your luck might vary. Their new web address appears to be KM Lifestyle Mfg. (508) 792-9500 New Antique Automotive Parts, Aircraft, Agriculture, Marine, Military, Motorcycle, MP3 Radios

I suspect that Chrysler used the same setup across the various makes. If so, then it is very likely that the '31 DeSoto does not use a resistance range that matches any of the modern "universal" style sending units. Since my original was long since missing and I wasn't happy with the Atwater Kent, I modified a modern one to work reasonably, but not perfectly. See: Plymouth: First Decade - Early 1930s Fuel Sending Unit

If I had the original sender in the condition shown by the original poster's photos, I'd give a try at repairing it. As noted by MartyLum it might just be a matter of cleaning the resistance board. For other makes with hard to find parts some people have figured out how to put new resistance wire in. See, for example, Fuel Sender Repair I don't know what the inside of the original sender looks like but if it can be opened up maybe the resistance wire can be replace.

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I am not sure how helpful it is, but a gentleman in our car club used a VW beetle sender or part there of when he fixed up his DeSoto 8.

Cheers

Stewart

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I appreciate all of the information. It has been very helpful. I am going to try two things. One is to take it apart and clean it. My backup is a unit that I am going to purchase at JC Whitney. This is the part number R257060B. It looks like a perfect fit and it comes up as a part that will fit in a 31 Chrysler. It is only $35 and worth a shot. It may be awhile before I get to this. I am making a new harness and will also be out of town for a couple of weeks. When I am done, I will post back and let everyone know. I have attached a photo.

Does anyone know what the resistance should measure on the original unit?post-79353-143139228533_thumb.jpg

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There are some good posts in this thread.

@ Marty: Are you able to tell me where you purchased the new senders or the new gears? You are correct, the gears were pot metal and have crumbled to almost nothing, along with the the cork float. I think some of this is due to ethanol.

@ Ply33: You have a great site there, thank you for sharing what you have learned. One question, did you consider bending the float arm to get the resistance to stay in range? In your opinion would it be possible verse modifying the resistance? It's too bad about the piece from the former Atwater Kent, I had high hopes for it.

@ Nick: I am out of town until Friday. I might be able to pull my sender this weekend to get the resistance readings. When I initially pulled it out, I was able to get correct readings by manually turning the shaft. I'll let you know what I find. I may try that JC Whitney piece too.

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@ Ply33: You have a great site there, thank you for sharing what you have learned. One question, did you consider bending the float arm to get the resistance to stay in range? In your opinion would it be possible verse modifying the resistance? It's too bad about the piece from the former Atwater Kent, I had high hopes for it.

I guess it might be possible to modify the float arm to make things work but I wasn't able to figure out a way that worked well enough for me. I think you'd need a sender that had a full reading about right with an empty reading with too high a resistance and then adjust the float arm so that the float could get all the way up for the full reading and so that when sitting on the bottom of the tank with the correct resistance to read empty. The senders for a VDO dash unit with a 10 Ohm to 180 Ohm range would be your closest match and you won't be reading full even with the tank topped up. And since you wouldn't be using the full range of the sender you will probably have some interesting step changes showing up on the dash unit at some fill levels. I did try using a sender with that range with a fixed resistor in parallel to bring the resistance range closer to what the dash unit wanted and wasn't happy with the results.

With respect to the Atwater Kent, I got a model that pivoted at the top which restricted the range of motion. You can see that in one of the photos that I took with my oval tank mock up. If one got the gear driven one with the pivot centered in the tank and also replaced the shellac coated cork float with something that modern gasoline additives wouldn't eat it might be okay. But it was expensive enough that I thought I could experiment with the much less expensive modern universal style senders.

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I called Atwater Kent for a replacement sender for my '32 Plymouth. They said they could rebuild mine for less, and they did. Good service.

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Rich-You asked about the sender gears. I bought extra gear sets when i repaired mine. I also have a new complete sender which would be a screw on item. Contact me via e-mail for specifics and measure your gears as to diameter and # of teeth before contacting me.

Martin Lum

marty@oldercar.com

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I finally got a chance to work on my sender. My gears have been replaced in the past with what look like a model car ring and pinion. I need to find, or more likely make a set of original style gears to make this sender useful. I managed to find a sender from a '31 or 32' DeSoto(seller wasn't sure. I was told that it was in working condition, however when I checking on the bench it was not. At this point I had nothing to lose so I decided to take apart my new non-working sender to see if I could get it working. I'll do my best to explain the process, next time I'll take pictures for a proper how-to.

The sender is a very simple unit. It consists of an upper body and a lower baseplate. They are held together by five brass rivets, with a gasket in-between. I used a small punch and drove the rivets out. I did this so that I might be able to re-use them. Once the rivets were out, I was able to gently lift the upper body off of the base plate.

At this point I was able to see the inner workings, which consist of a rotating contact arm and the resister wire winding. As I have said these units are very simple, and there is very little that can go wrong inside. I found that after many years of use that there was just enough gunk built up to prevent good contact. I used a little carb cleaner and fine sand paper to clean all of the contact areas. There are three areas of brass that must clean for the sender to work. The first two are obvious, the end of the rotating arm and the resister wire. The other very important area is the contact arm that is attached to the base plate and is spring loaded under the rotating arm.

After cleaning the brass parts, it's time to clean the upper body and the base plate. There are two raised areas on the base plate that make contact with the upper body. There are two holes in the gasket for this purpose so if you replace this gasket be sure to make two holes for these contact points. I used sandpaper to remove the little bit of rust and corrosion I found in this area.

At this point carefully placed the upper body back on the base plate taking care to not bend the rotating arm. I used a very small hobby style c-clamp to hold the unit together. I attached my multi-meter leads and checked the resistance while moving the float arm. I had a range from 0 to 80 ohms from a full position to empty. I checked my reading several times and decided to reassemble the now working unit.

I put a little electrical grease on all of the contact areas and used two small nuts and bolts to hold the body together. I then sandblasted the unit. I reset the brass rivets using a punch that was slightly larger than the rivets diameter. I then painted and installed the sender. I haven't had the car out to fully check the range of the sender but I had a half tank when I started and the gauge is currently showing half.

In hind site, I would use some spray electrical parts/contact cleaner to clean the insides. It's probably much easier, faster and safer for the delicate parts. If I come across another non-working unit, I will not hesitate to purchase it and use this process to restore it. As for my original unit, I am going to get some brass sheet and cut new gears for it and restore it. I will take lots of pictures when I do and update this post to show the process.

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I am going to try the above next week. Your procedure really has some great detail. I will let you know how it works out. I will take some photos. My gears are actually in good shape so i do not think that is a problem. I do seem to have some play in the shaft but that may be an issue with the contact points in the inner workings. Thanks

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The sending unit in my 31 SA is completely different than the pictured unit. It has a variable wire wound resistor at the base of the unit. The wiper is exposed and actuated by a brass float. It looks factory but maybe someone modified the unit before I got the car. I am the second owner. The configuration has the wire wound resistor submerged in fuel until the tank is half empty. It works OK but the wire gauge of the windings is about 12 or 14 so the needle jumps around a little. As a result of the large wire gauge problem, I could never get the unit accurately zeroed. It gives me a close approximation..............FYI there are 4 or 5 vendors in Hemmings that offer rebuild services. One says "starting at $75" so it might get pricey.

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I just wanted to let everyone know that I followed Richasco's instructions and my unit now works perfectly. I found it a little harder to pry the top off and I had to drill the rivets out. The unit was full of rust. I cleaned it and sprayed with electrical cleaner. The brass armature on the end of the rotating unit had to be bent to get an accurate OHM reading. Thanks again for the instructions.

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I'm so glad this worked for you. What did you use to replace the rivets?

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I had a few old rivets that worked fine. You should be able to find some at various old auto parts suppliers. If you cannot find any, I would consider using the old ones with a little adhesive on the rivet such as JB Weld. Remember that when you drill the part that has been smashed at assembly. Just remove enough material to remove the rivet and top of the unit.

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