Topic: GAS GAUGE SENDER ACCESS HOLE


shoebox    -- 10-04-2020 @ 8:48 AM
  The trunk mat in my 39 Merc is all there, however so brittle that if lifted or removed it will become just pieces. That being said, I need to replace the gas gauge sender and am wondering if there is an access panel/hole in the trunk floor to get at the sender? Also, I have not checked the usual sources yet, but is the sender same as Ford? Thanks !


nelsb01    -- 10-04-2020 @ 12:00 PM
  There should be a small "trap door" (access) in the middle of your trunk.
It is a single screw and will allow access to the gas tank sending unit.


shoebox    -- 10-04-2020 @ 3:28 PM
  nelsbo1, Thanks for the info, I thought I could feel the panel you speak of through the mat, just wanted to make sure. Has anyone a recomendation for a source for a sender? I'm aware of the usual sources/catalogs however sometimes one place has a better product than others. Thanks again.

Scott


nelsb01    -- 10-04-2020 @ 8:20 PM
  First, dont give up on your sender until you test it out. Sometimes it is just the float that needs repair.
You can test the dash gauge by disconnecting the wire from the screw on top of the sending unit and then with ignition switch on, touch the wire to the chassis. Do this with a helper sitting in the drivers seat. When they tell you that the gauge is moving stop holding the wire to the chassis. If the dash gauge moves, then the problem is with the sending unit in the tank.
To test the sending unit you will have to remove it from the tank. Make sure that the battery is disconnected so that there is no chance of spark.
Once the sending unit is out of the tank you will be able to tell if the float has a leak. There are people that can repair original sending units. You will have to ask for names, as I do not know of anyone personally.
There are original replacement senders out in the market place. Reproduction ones have not been reviewed with alot of satisfaction. All Ford/Mercury 6v senders are the same except for the length of the rod to the float. You will notice that there is a clip that connects the float rod to the sender. If you can find a NOS or used sender that works, you can open the clip and use the float rod that is on your bad unit. The challenge will be finding another sending unit. They show up for sale every now and then.
Hope this helps.



carcrazy    -- 10-04-2020 @ 8:50 PM
  If you don't want to disturb the trunk floor mat but you want to access the sending unit, you can always remove fuel tank from the bottom of the car. This entails some work but will preserve your floor mat.


TomO    -- 10-05-2020 @ 8:21 AM
  I love your 39 Mercury. It looks like it is in great condition.

In addition to Bruce's comments:

To check the float, remove it from the sending unit and submerse it in a pan of water that was raised to the boiling point and then removed from the flame. If it has a leak, you will see a stream of bubbles coming from the float.

If the float is good and the sending unit does not register correctly on the dash gauge, the problem may be the contact points inside the unit. The top of the unit can be pried off and the contacts cleaned by spraying the contacts with tuner cleaner and operating the arm many times. Be careful of the fine hair like wires inside the unit. If you break one, it will have to be silver soldered.

The arm on the 39-40 Mercury is the same as the 41-48 Ford and Mercury. The P/N for these sending units is 99A-9275.

I don't know if the sending unit wire is long enough to allow you access to it if you drop the tank before disconnecting it. I have always disconnected the wire before dropping the tank.

I had an original 1965 Cutlass with a rubber trunk mat that was hard and brittle. I managed to remove it and lay it upside down on a piece of hardboard. Then I used Gorilla Tape to tape it together and to reinforce it. It saved the mat, but you could still see the cracks.


Tom


Rockfla    -- 10-16-2020 @ 9:50 AM
  Shoebox
I have the same issue with the front floor mat for my 39 Mercury........IF your mat is good enough you think you want to save it, get a piece of canvas OR some thin Neoprene sheet and some contact cement and cut it to the same size and use it to glue your mat too and stabilize it!!!!


shoebox    -- 12-24-2020 @ 10:10 AM
  I always want to express gratitude promptly when someone responds to a question I ask on a forum such as this. However with all that has gone on this year well, I missed the boat on this one. THANK YOU to all who provided input on both my gas gauge and trunk mat issues. I will be sliding something under the trunk mat and attempt to lift and remove and flip, then do the Gorilla tape to perhaps save it. I will be accessing the gauge sender from the top and diagnose as has been suggested. Thanks again and MERRY CHRISTMAS to all.


TomO    -- 12-25-2020 @ 7:30 AM
  You can determine if the problem is the gauge or the sending unit by disconnecting the sending unit wire to the gauge, clip a test lead to the gauge post and ground, then turn on the ignition switch. If the gauge is good the needle will move towards full.

I like Rockfla's idea of gluing a piece of canvas to the back of the mat better than my solution of using Gorilla tape. It will do a better job of stabilizing the mat as it will not be just small areas reinforced as with the tape.

Clean the back of the mat with soap and water, then clean with denatured alcohol. Use 3M Rubber and Vinyl #80 Spray adhesive to attach the canvas to the rubber.

Tom


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