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MG MGB Technical - Fuel Sending Unit

Looks like I recieved the earlier 76'ish model instead of the later for my 79 B, its a long story, I could tell it if you really want to hear it but the point is that its not going to be sent back and exchanged. I am just wondering if it is compatible with my 79 system. Also why is there a wire running in the sending unit that looks like its going to be submerged in gasoline ? The idea of that never has sounded safe to me.

Thanks,
James

James

if you dissassembel a sending unit you will find that the internal wire wound resistor is submerged in fuel.
John H

I'm using a Very late sender in a '75. I'm doing so because it's got it's own fuel up take, and I can run fuel injection. You need two fuel lines for that.

Works great.
If you have a tank that already has a fuel uptake in it, like mine, you will need to unclip the float and turn it around. Other wise it will catch on the other fuel uptake line. A bit fiddly getting it into it's hole, but not particularly hard.
I also seem to remember adjusting the fuel gauge a little by the simple expedient of bending the needle a tiny bit. However this is not realy necessary, I happen to have the guage apart while I was painting the inside white (to improve the brightnes at night) and I thought I might as well get it perfect. I held the float on half way and adjusted the guage to Half.


Peter

I just reread you post, sorry, I missread and thought you had an earlier car with the later sender, not V.V.
As long as you have some sort of fuel line out of the tank. The very late cars have this incorperated into the sender and no other fuel line.
Peter

Yea, My head has just been cloudy from this last order I made from england. Its the correct sending unit for the tank and the tank should fit my later model car. Ive just been having a little bit of a headache with all of this. For example, spending the money on braided fuel lines and having them be on the shoddy side, with horrible clamps, shipping costs etc...

Im still curious about the wire running in the unit.

Also just to make sure things are clear I bought the tank and sending unit in england for a Rubber Bumper car. I specified 79B but I know there are some differences in US and UK specs.
James

The fuel gauge has to have an electrical connection to the variable resistor (sender) attached to the fuel float.
On mine there is a fuel uptake that sticks into the middle of the tank, and there is a fuel sender about half way along. There is a wire to the sender.
It will be coated in polypropylene or something similiar to what plastic petrol tanks are made of.

On the old, non fuel uptake, version. The sender attached directly to the back of the metal disk/cover with a short peiece of metal, that was insulated from the cover by a short cyliner of hard brown material.
Peter

Adjusting the gauge to read half when the tank is half full might be neat, but surely it is far more important to have it reading acurately at E. The easiest way to calibrate the gauge is at the gauge itself - there are two holes in the back of the case (could be covered with cork plugs) with slotted plates behind. Twist these to calibrate. Make sure you use an implement that fits well, the plates are only thin and can be 'rounded out'. Do F first by filling up, then run it out to do E. I put a gallon back in before calibrating to give me something of a 'reserve'.

For an electrical spark to cause an explosion it has to be in an atmosphere and not liquid fuel, and there has to be a certain amount of oxygen present with the fuel vapours at a ratio of around 14 parts oxygen to 1 part petrol. It's going to be a lot 'richer' than that inside a tank. But at the end of the day, if it were unsafe we would know about it by now.
Paul Hunt 2

Paul, not to hijack this thread, but are you saying that the calibration can be carried out at the gauge regardless of the way the sender is working? The gauge on the 70 B I care for works normally for a bit, and then goes to empty at half a tank... staying there. We tend to go 275 miles and buy fuel, usually putting in between 10 and 11 USgal.

As always, thanks for your contributions to our cars!

dave
Dave Braun

Be gentle with those adjusters, mine have corroded solid and no longer move.
(empty corresponds to the top corner of the E by chance!)
Peter

Dave - if the gauge goes down so far normally then suddenly drops to below E i.e. the same as when the ignition is off for the remainder of the tank, then the sender is faulty and needs to be replaced, no amount of adjustment of gauge or sender will correct that, as you will probably find the resistance wire has broken half way along. However if the sender is a new one and does that from the start you will probably find the resistance wire former is distorted and lifting the wiper off the uninsulated part of the resistance track - BT, DT. You may be able to tweak the wiper to get over that problem, but if there is any roughness in the movement of the wiper over the resistance wire it will probably wear through in a short time - BT, DT also. I had to replace the senders in both my cars relatively close together in time, and both needed significant recalibration of the gauge to get the needle moving from F to E. Both failed again way too soon, but the replacements for those have (so far!) lasted much longer. One of the 2nd replacements didn't need and further recalibration, but the other did.
Paul Hunt 2

thanks Paul!
Dave Braun

This thread was discussed between 12/07/2007 and 16/07/2007

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