1940 Sending Unit Rebuild

[Chuck Griffin]

I’m aware that “new” sending units are sold, but does anyone sell rebuild kits for sending units? I took the sender out of my 1940 Buick super which wasn’t working and discovered that it comes apart. I figured if I can get parts, it could be repaired. I checked online and couldn’t find anything.

[neil morse]

I don't think anyone make rebuild kits for these units.  I think your choices are either to figure out why it's not working and see if you can repair it, or simply get a replacement.  If you look at the posts from Gary W's thread (that he put up on your earlier fuel gauge discussion), you can see that Gary was able to repair his old sending unit.  I opted for getting a replacement, and the unit I got from Bob's Automobilia has been working great since I put it in about three years ago.

[37_Roadmaster_C]

There are no rebuild kits that I know of. A friend and I had 2 older 36&37 units to repair. My buddy is MUCH more ambitious than I am so he took the lead. He did manage to repair both, mostly connection issues. He even replated the units with zinc for rust prevention. My contribution was to machine new copper sleeve rivets to reassemble the senders like the factory build (I told you he was ambitious!). The units work, but the time and effort were considerable when replacement units are available for a reasonable cost. Thanks Bloo.

[Bloo]

There isn't anything about sending units that lends itself to having a "kit" except maybe the gaskets, and the coated cork floats. Note: Harbor Freight has gasket punches for not much money, and Bob's has coated cork floats.

 

If yours comes apart easily, it must be different that the mid 30s type. Those were riveted with 3 brass hollow rivets. When I did it, 37_Roadmaster_C made the tools to make those rivets and put them back in.

 

In either case, there aren't a bunch of parts to replace. You just have to take the unit apart and fix whatever is wrong. They are a brass brush running on a wirewound resistor. The worst thing you could get possibly get stuck with is having to find and buy appropriate resistance wire and rewind the resistor, which is riveted in place. That is certainly a possibility as the brush could wear through the resistance wire, but I don't recall ever having to do that.

 

All they do is run a wiper across the 30+ ohm (on GM cars) resistor. The wiper is grounded, on the mid 1930s units it grounds through a coiled piece of spring wire. All you have to think about is the circuit from the post, through the resistor (or part of it) through the brush, and to ground. Any questionable connections in that loop need to be soldered. You can't solder to the resistance wire itself, but everything else you can. The resistance must go as close to 0 ohms as practicable (extremely close) with the float hanging down. Remember 30 ohms is all the way to full(!) so it doesn't take much resistance at all to prevent the gauge ever getting down to "E".

 

The mid 30s units have a gear at the bottom that solders on. It sets the clock position of the wiper. There is a little cork washer under a spring down there that acts as a brake, preventing the gauge from waving all over the place when the gas sloshes. Getting that gear soldered in the right position is by far the most difficult part of the whole deal, and only necessary if you change the cork brake washer.

 

Edited May 29, 2021 by Bloo (see edit history)

[Bloo]

7 hours ago, neil morse said:

you can see that Gary was able to repair his old sending unit.

 

Maybe Gary will show up in this thread and clarify, but I believe his unit had been professionally rebuilt beforehand. The rebuilder must have missed ever so slightly soldering the gear back on. That is really easy to do, and I did it a whole bunch of times before I got it right. Gary ground on the stop to fix it, and it worked. I am bringing it up because I think that grinding the stop is extremely unlikely to help on an old corroded up unit that has not just been restored, and would probably do more harm than good.

[buick looks fine for 39]

bloo and 37 roadmaster did a great job explaining the various different aspects involved in repairing your sending unit. If you still want to try repairing your unit let me know what's damaged. I have a 39 unit which has a frozen float arm and I can take my unit apart and see if it has the  serviceable part  you need.

 

                                                                                       Thanks

                                                                                         Leif 

[Gary W]

8 hours ago, Bloo said:

Maybe Gary will show up in this thread and clarify, but I believe his unit had been professionally rebuilt beforehand.

 

That is correct.

I sent my unit out to be professionally rebuilt, and simply installed it when it came back from the shop "as is".

I assumed the unit was checked for proper OHMS range, and I also figured there must be a float arm configuration so the float didn't bottom out.

 

I ran out of gas at just under 1/4 tank showing on the dash.

 

My float was hitting the bottom of the tank , preventing the arm from dropping fully, BUT even on the bench when the arm was allowed to fully drop it never came near 0 OHMS.

 

Luckily, I was able to remove some of the material on the "stop", which allowed the arm to drop a little more, and gave me a reading of .6 OHMS.  

BUT...  The float was still bottoming out in the tank, so I had to bend the float arm, and by trial and error, achieve the tank bottom clearance.

 

I guess my "fix" was unconventional, but it works as it should. 

[Morgan Wright]

Corks are available at the liquor store.

[Bloo]

But you must seal them with something. Something that can resist gasoline that has alcohol in it, so the traditional shellac is straight out.

[Morgan Wright]

Corks are immune to alcohol. Ask me how I know.