Re: fuel tank sending unit

Posted by HH56 On 2022/7/25 15:43:39

The senders on 48-50 models are completely different from the straight resistance type senders used before and after those years. Fords used a similar setup but as far as I know NOS Packard senders are almost extinct and no resistance type sender has been found that works satisfactorily. Ford units are almost as hard to come by. The only option I have heard of so far is to have your sender repaired if possible or, as some have done, change to a modern gauge setup and fit that unit in the old cluster.

The sender used in 22-23 series is a type sender that has no changing resistance but rather a bimetal arm working an ordinary on/off contact. The heater resistance in the sender can be measured but is a fixed value and depending on if the contact is opened or closed as the float is moved can be 0 ohms or some number. The sender heater is in series with another heater in the gauge portion and between the two the bimetal in the sender is made to move to open or close the contact to ground. The float puts more or less pressure on the bimetal strip attachment point depending on fuel level so length of time heater action needs to work on the bimetal is changed depending on what it takes to make the bimetal move and close the contact. Because the heater cools and heats as the contact opens or closes, the actual signal out to the gauge is just a series of pulses where the supply voltage going thru the gauge and sender is connected to ground for a period of time. The frequency and length of the pulses or connection to ground is determined by the changing pressure on the bimetal caused by the float.