Sign in to follow this  

Burnt points and fuel gauge malfunctions issues resolved.

Recommended Posts

Thought I would offer up some comments gained over the past two months chasing two perplexing issues. I can't believe it took this much time to figure this out, and got all sorts of help (some good, others not) as to what the issues were. As with so many things, turned out to be some rather simple fixes, but what a challenge in figuring this out. Guess I need to get another 10,000 hours in rebuilding this old stuff.


This is all for a 1937 Dodge MC pickup that is undergoing a full frame off restoration. Literally, every nut, bolt and screw removed, and all parts restored. 


1. Burn points - once I got it started, kept burning out the points. Found an old condenser had been used in the engine rebuild, and replaced that. Cleaned points, but they kept burning to the point that the truck would stall out and not start. Installed a new coil. After speaking with a retired auto-electric guy in the area, he had me check voltage, and wouldn't you know that the rebuilt generator was putting out over 10V. Adjusted the brush and got the output to 7.5, which is within spec. Voltage at the distributor is about 4V. Seems like a fairly straightforward fix, but you have no idea how long I chased this. Took me some time to figure out that the points were the reason the engine was stopping and not start.


2. Fuel gauge - man, this one was a killer. Had a NOS gauge that was blowing fuses. Sent it to Bob's Speedometer and they told me it was not good. Bought another one from them. When power turned on, gauge spiked to full. Didn't know if it was a bad gauge or other wiring issue. Sent the gauge back (twice) and they confirmed that it was OK. Checked all grounds and they were OK (tank). Finally dropped the tank this past weekend and pulled the sending unit (a repo). Using my meter, confirmed that it was working (range is from 0 to 90 ohms). 


Pulled the gauge out of the truck, and using some leads, connected the gauge and sending unit as they would be installed (needed to ground the gauge mounting flange). Attached it to the battery and the needle spiked. Happened to move the float, and noticed that the gauge did work, but was reading full with the float in the low position and empty with the float in the high position (backwards). But this was great progress as I could actually see the needle move. 


Apparently, this is what I was seeing with it installed. With just a few gallons of fuel, the float was in the full down position, and the gauge read full. Switched the wires, but did not change. 


Spoke to Bob's and they mentioned that the gauges are designed to read 0 to 90 or 90 to 0 ohms. My repo sending unit was configured to read full when the shortest distance is achieved in the rheostat. Bob's suggested I try and switch the position of the float, but after some experimentation, discovered that it only fit in one direction. So, I took the plastic rheostat off the sending unit, rotated it 180 degrees and remounted it using a few small brass screws. Now it works exactly as it should. 




While I had my test system in place for the gauge, I tested the original gauge that was all crusty, and it worked fine. 


Can't thanks Bruce and Matt at Bob's enough for troubleshooting this with me, and their patience. In retrospect, I would never install another fuel sending unit/gauge without first testing them for operation. Guess we ought to keep in mind that repo parts are not necessarily identical to the originals, and we just need to confirm operation, etc. 


Attached some pictures to show parts. 





  • Like 2

Share this post

Link to post
Share on other sites

Thanks for sharing. The guy here in CA that did a nut and bolt on his 38 had the same feul gauge problem and Bob's did his also. Was a defective gauge.








Share this post

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this