Petrol tank sender

[mike]

Could anyone kindly measure the arm of an original petrol sender unit from centre of pivot point to centre of the float Many thanks Mike

[Rod]

Hello again,
I assume the arm is missing from your sender?
If no-one comes to your rescue, you might have to do it the hard way by measuring the distance from the float arm pivot point and the bottom of the tank and either using trigonometry/scale drawing or a mock up on the work bench to decide what length arm you need? I've had to do this before on industrial machinery. Remember the float shouldn't touch the bottom of the tank on "E" to give you a bit of lee way to get to the petrol station when it reads "E"

[mike]

Great answer Rod, never thought of that, will have to mobilize my brain, maths was my favourite subject both at school and college.The car has a non standard sender fitted, don't now what it's off, so don't know if the readings on the gauge are accurate. Certainly keeping you busy with all these questions. Regards Mike

[Rod]

I'm pretty sure that there are the correct sender unit resistance values published somewhere on one of the Austin sites, Mike. One thing to watch is somewhere along the line with Smiths units, the resistance characteristic changed from low fuel level = high R, high fuel level = low R to the reverse characteristic, but I think that this happened post-war. If you get stuck, an automotive instrument tech can tweak the gauge to suit a sender unit characteristic (provided its near enough) and the resistance unit at the tank end can also be manipulated or changed, and the cost isn't all that scary, here in NZ at least. They will most likely want the gauge unit and sender units out for those jobs, though (in my experience they do).

[peter_christie]

Hi Mike,

Some time ago, Tony Mealing answered a question by describing how to convert a later [Negative Earth] tank Unit to [Positive Earth]. With careful handling, this can be done successfully and it saves a lot of trouble fiddling about with badly worn elderly components. Ask Tony.

Peter C. [6515]

[mike]

Looked everwhere to find Tony's answer for petrol tank sender, but can't fing it. Mike

[peter_winney]

Fact Sheet No 5. Find it in the members area of this site under Technical Documents

[mike]

Cheers Peter, never thought of that, another senior moment, as the years pass they seem to be coming more often. Regards Mike

[stephen_voller]

Just to say that the sender unit is not polarity conscious and resistance is resistance whether the the earth is positive or negative.

[peter_christie]

Hi Steven,

If the resistance coil is wired to the wrong polarity it will register empty on the gauge when the tank is full and vice versa, the later units are Negative earth.

Kind regards,

Peter C. [6515]