Fuel tank sender unit

[roy0147]

My 1959 car has many problems so I was trying to tackle what I thought would be an easy one.
When I first got the car the fuel gauge was working but most of the petrol leaked out from the carb. faulty needle valve and the gauge then showed zero. 
I have now put in about 10 litres but the gauge still shows nothing. I took off the small plate at the front of the tank unit to reveal the pot. and what I assume are the wipers (see photo). A bit of petrol came out when I removed the plate.
I wonder what possible faults I may have and whether I should remove the complete unit or are there other checks I could make.
The cork gasket on the smaller plate looks ok but I assume there is a larger gasket for the main unit and, if so, it does not show in the RMC spares list.

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[canuck]

Hello Roy,
These old sender can offer grief. 

First test I would do is to remove the wire from the sender unit. With the ignition switch in the ON position earth this ring terminal. Your fuel gauge should read full. If so this proves out the wiring between the tank and the dial. 

There is a gasket between the tank and the sender unit,#17 below.




The part number is 2H1082 and should be readily available. I link below a source, shop around if need be.

rimmerbros.com/Item--i-2H1082

You could be wrestling with a sunken float. Of course removing the sender unit from the tank will reveal all.  I would procure the gasket prior to removing the sender unit.  
If you need to drain the tank there is a plug, #2 in the sketch above. Hopefully yours is not frozen. The option is to drive around until you have used up at least 3/4 of the fuel you have to avoid spillage of this liquid gold.

Back to you

Bruce

edit: I just revisited your photo. The 'wipers' appear to be at the top of the coil indicating either a stuck float arm or a sunken float as previously mentioned.  

B

[roy0147]

You always kindly reply to my queries with useful information so thank you very much.
I will get a round gasket as I can see what you are saying that the float is  in the down position. The gauge did work originally before the petrol drained out and that is probably when the float would have gone to it's lowest point.
Is it right that some petrol was in the potentiometer space when I removed the small front cover? I may need to get a new gasket for that plate as well.
The sketch you show is fine but is there one showing the float assembly as well please?
Kind regards,
Roy

[canuck]

Hello Roy,
It has been quite some time since I was last inside one of these units. I do recall my unit being dry, but with age I suppose petrol could find its way into this winding area. I don't think having petrol in there is desirable. Perhaps when you  have the unit on your bench take a look for a way that the fuel gets in there. Could be a seal or grommet or the like ? however I  am guessing on this . 

My float was a brass one and dry so I did not investigate any further. On these brass float the only way fuel could get in there was through a bad solder join. 

Question;
1) There is a number on that winding cover plate, can you see what it reads?  
2) Take a look at the photo below. I don't recall having this bit of metal on the winding pick up wire?  




Not sure what this is or what it does. Maybe some other owner will be along to help us out. 

Another thought? You mention that the gauge was functioning but it stopped readings when the fuel level ran low, yes? Maybe the float arm is simply 'jammed" in down position? Could you carefully try to slide the wipers (careful to not damage the windings)?  down? effectively lifting the arm?
I believe  this will be difficult as access is a bugg*r through the opening in the tank mounting bracket however maybe worth a try?  I am only suggesting this with no experience doing this. 

 
Bruce

[roy0147]

Bruce,
Thanks again and I have disconnected the wire and earthed directly to the battery earth to be sure as I found many places not earthed (even the engine when testing the spark with a plug resting on the block!), turned on the ignition and unfortunately the gauge still remained on zero. I rather hoped the wiring was fine and the problem was in the sender unit.
When I had the cover off I did gently try to move the sliders, they did move a bit and I could see the brass nut on the pivot move a bit but I did not press too hard for fear of breaking it. So it may be stuck. The part number on my unit is Smiths Motor Accessories 12v FT5300/71. I can see on the Smith's site mention of FT5300/73 from a Morris Minor 3-8o ohms but nowhere can I see/71.

To check the wiring I will need to get behind the instruments so do you have to remove each from the dashboard or is it easier to release the dashboard itself?
That takes me to some of my other problems that I wasn't going to burden you with now but none of the panel lights are connected, the main beam dips ok but the blue warning light does not show. I would therefore have to get to the back of all the instruments and somehow make connections to the bulbs.

One other problem is the reverse switch. The bulb is good but I cannot access the gearbox to check the wires and see if the switch closes when reverse is selected. To check if the connection from the fuse unit gets to the gearbox I will need to expose all the wires in the engine bay to trace the correct one I presume. To check the wire from the gearbox to the reverse lamp needs some other magic. If only I could get to the exit point from the gearbox!

One final problem is the windscreen wiper motor. I did various checks with ignition and wiper switch on I got 12.75v between contacts 1 & 2, 2 & earth. The commutator looks ok with clean gaps and the brushes were making good contact. Turning the commutator by hand and the wipers moved freely. With all connections removed the resistance of the windings = 6 ohms. I am not sure of the connection from the base to the gearbox but assume it is to do with the parking arrangement. I don't know what else to check but so far all looks good but it does not run! It is a Lucas DR3.

I apologise for all these minor niggles.

[ozieagle]

Hi Roy,

A useful reference is Barney's MGAGURU site. Here's a link to the fuel sender.

mgaguru.com/mgtech/electric/et214.htm

I actually have a Wolseley 1500, very similar car. For your behind the dash electrical issues, I would remove the dash. Again not overly hard, in the 1500, but I don't know about the Riley. I will attach a photo,. showing where the screws are. A tip, use a piece of thick rag to cover the steering column, where the dash will rest, to stop it being scratched.

Herb

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[canuck]

Roy,
Bummer, not much help from me on the fuel gauge functionality, apologies. 

I am not sure how Smiths number these gauge units. I suspect by car model & fitment. The Riley gauge is a standalone unit while the MM one is incorporated into the speedo dial? This may be the part # difference? perhaps the resistance readings are the same?  Let's hope someone else will be along to steer us right.

However;
From your post my understanding is you are experiencing a wide bit of electrics failures, so let's check the basics first. 
The main fuse box has only 2 fuses. The terminals A3 to A4 fuse does provide power to the circuits/units you mention are acting up. Ensure the fuse is good, do a continuity test as the fuse may look good but not be. Ensure these fuse box connections are 'surgically' clean and sound.  Remember this fuse & circuits is ignition switched so the switch needs to be in the on position.
FWIW the accessories that you are struggling with are all coming from the A4 terminal. This is where I would start the sleuthing. 

NB: disconnect the LT lead at your distributor while doing all this, you don't want to damage the points etc. 

The dash instrument lights are powered from the lighting switch so this is straightforward to investigate. 

If you need to yes dropping the dash may be the easiest for wires access however you will still need to fiddle about behind it to remove it. On my car I needed to unscrew the rev counter cable and the speedometer cable to allow for the dashboard to come far enough out to access behind it.

If the fuse investigation does not put the reversing light right, you may need to drop the rear crossmember of the transmission for easier access to the switch.  The switch is located on the RH side of the  gear lever tower, #122 in te sketch below. 



Support  the car solidly on jack stands before crawling under and use a trolley jack to support the rear of the transmission as you lower it. 

Let us know how you make out.

Bruce


  

[roy0147]

Thank you both for your helpful suggestions. The MGA info. was interesting and so detailed. As a result I have detached the wire and measured a resistance of 55 ohms to the sender body. This looks a bit high as I only have about 10 litres in the tank. The MGA unit is rated at 0 - 60 ohms but it is probably not a FT5300/71. I wonder if anyone does know the range for my unit (some Smiths ones show 0 - 180 ohms).
For the time being I am going to assume that the sender unit is OK (as the gauge did register earlier) and the problem is in the gauge or wiring associated with the A4 terminal.
By the way the worst part of this job was re-fitting the tiny washer and nut to the terminal post with poor access and a small gap to fit my large thumb and forefinger - took nearly an hour of bad language!

I think I will try to remove each instrument rather than the whole dashboard to access the panel lights. I can see (with a mirror) that there are no connections to the bulbs but hopefully I will be able to run new ones via the P switch and a 12v supply - should this come via. A4 or picked up somewhere behind the dash?

I am going to 'chicken out' of dropping the transmission for my reverse lamp - just pretend it is a Wolseley 1500 for the time being!

Can anyone suggest anything for my windscreen motor ills or should I post a new question on the Forum?

As an update I have managed today to fit the new brake cylinders and have bleed all the brakes with the help of my long suffering wife.

Regards, 
Roy
 

[tonyhosk]

Roy

The panel light wiring comes off the lighting switch itself - a red wire to the panel light switch, then red/white to the three panel lights.

Tony

[roy0147]

Thanks Tony - that is really useful. I can see now that to access the switches and the dials it may be easier to remove the dashboard after all.
Cheers,
Roy

[canuck]

Hello Roy,
Yes do check the fuse box and connections carefully. This wouldn't be the first time these old components let an owner down.  Oh BTW I have a T shirt to prove it.  

The parking function of the wiper box is simply a position of the commutator wipe. As to the rest of the motor perhaps another visit to the MGA site will help you out. Link below.

mgaguru.com/mgtech/electric/et217.htm

Onward and upward.

Keep well

Bruce