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MG TD TF 1500 - Fuel Sending unit interesting find

I set about today to clean my fuel sending unit and get it mounted in the fuel tank (Center unit in the pictues). I found I have three fuel sending units. My original and two others I have picked up over the years.

I noted that all three have different lengths and bends to the flote lever, so they are probably from different cars.

Two, my original and another, have a threaded post to mount the electrical wire to the unit. The third has a spade terminal.

Two are marked Smiths Motor Accessories. My original has no name on it, just a symbol.

All three have patent 447499.

The metal housing is near identical on all three. Two have 6 round metal posts on the outside of the center section.

The metal cover that is attached by 4 shrews, all show signs that they originally had a blued finish.

The knurled bakelite knob and the small nut that holds the isolator in is size 8 BA

Here is the interesting part. My TD has two brass fingers that rotate up and down with the float rod. One of these fingers makes contact with a brass rod that attaches to the electrical wire. It is this contact that turns on the fuel light in the TD.

Why there are two fingers and only one contact caught my attention.

I opened up the other two and to my surprise, there is a tightly wound wire rheostat that sits between the two fingers. The fingers run up and down the rheostat.

This indicates that these units came from cars with standard fuel gauges. As the fingers move up or down the coil, it would vary the voltage to the guage.

So, if we figure out what cars these were from, we have a perfect way of adding a regular fuel gauge to a TD. It should be easy to change the float rod to the correct one for the TD.

I can't say how far up and down the float goes, so it could stay on full for some time, but it should still give a reasonable estimate of what's in the tank.





Bruce Cunha

Here is a picture of the outside of one of the other units with one of the rheostats.

The second Picture is of the other unit




Bruce Cunha

Here is mine cleaned. Be careful when you clean out the unit. There is a fine wire that runs from the terminal to the swivel where the float rod is. You don't want to break this.

I did not disassemble the float rod assembly. A little penetrating fluid got the float rod moving up and down with almost no effort.

It is not showing up well in the pictures, but the cover has a definitely bluing tint to it. This is from the inside of the cover.

I also noted that the metal of the edge where the bolts go into the tank was warped in the areas of the holes. This indicates it was overtightened. I assume to keep it from leaking.

I did a little bodywork on the edge to get it flat and then used a file to smooth the lip to assure it was flat.

I will post a finished picture of the unit tomorrow.





Bruce Cunha

Bruce
I have a 4 seat PB from 1934, the first MG I believe which was fitted with a fuel gauge (as well as a main/reserve fuel tap control). Signs of the issues from meeting changing demands of buyers.

The fuel gauge uses a float and has both an on/off switch which lights a low fuel level bulb in the fuel gauge as well as a rheostat which operated the full/empty needle in the gauge.

I suspect the basic design remained unchanged providing a range of fitting options for a variety of car makes and types.
Ian Bowers

I concur that the plate was blued. I of course had to polish my housing. :-)
Christopher Couper

Ian. That appears to be the case. The patent never changed on these, even though the housing changed a little (the 6 round posts on the center of the case, and the rheostat).

It would appear that parts are interchangeable. I believe I could add the rheostat to the TD.

But as stated. The float would still not go all the way to the top for a TD tank.
Bruce Cunha

Bruce,

When you reinstall the sender, you may consider replacing the gasket with an improved version which works well in preventing leaks, here is the link.

https://www.mg-parts.co.uk/index.php?route=product/product&product_id=213

John
J Scragg

This thread was discussed on 28/01/2022

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