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MG TD TF 1500 - TD Fuel Tank Sender Terminal

I have an original sender unit with a cork float & one I bought on Ebay with a tin can type float which unfortunately has a sheared off screw at the wire mounting point. Before I attempt to extract it can anyone confirm this thread? As I'd like to use the one with the can (along with the Abingdon Spares gasket set) I would also like to buy an original terminal post screw to suit that unit if anyone has one lying around in their parts drawer. TYIA. Cheers
Peter TD 5801
P Hehir

Peter - The terminal screw is a 2BA, that I believe is the same as the terminal screw used in the SU fuel pumps. It has a square head on it and uses the same terminal knob as on the SU fuel pumps. If you can't find those items (Burlen Fuel Systems carries both, but the new terminal screw has a hex head on it), e-mail me at SUfuelpumps@donobi.net Cheers - Dave
DW DuBois

Thanks Dave. I've seen screws with Bakelite knurled heads a bit like the shape of a kid's spinning top. Are the originals anything like them? Any chance of a pic showing the original machine screw? Cheers
Peter TD 5801
P Hehir

Peter
Are you looking for a photo of the Bakelite knurled head fastener?
If so, I have one and can take a pic.

Tom
T Norby

Yes Tom that sounds like what I need. A pic would be great & a big help in my search for a replacement. Many thanks. Cheers
Peter TD 5801
P Hehir

Collating the available info it appears the three thread sizes connected with the original sender unit are as follows:

Cover Plate: 4 BA
Tank: 3 BA
Terminal 2 BA

Cheers
Peter TD 5801
P Hehir

Peter
Here is mine. Not certain that it is from 1954, but I suspect it is.

Tom
'54 TF


T Norby

Peter - I have attached a picture of the square headed 2BA terminal screw and the present day knob. The screw pictured is 1 inch long from under the head, which may be longer than the original one, but could be cut down in size as needed. Tom's picture of the knob may be closer to the original knob and it looks like it has a brass threaded insert in it. There were several iterations of the knob over the years. I also have a used knob that looks to be closer to the one Tom shows. I have both the screws and the knobs if you need one. Cheers - Dave


DW DuBois

Thanks Dave. I'll email you direct. Cheers
Peter TD 5801
P Hehir

Yep, mine has a brass threaded insert inside.

Tom
T Norby

Thanks Tom & Dave. Dave you have mail. Looks to be a fiddly operation to replace the machine screw & as fuel can enter the electrical housing I wondered if there is any possibility of a fuel leak there? If so any suggested preventative measures? I'll take care when using the Easyout not to damage any of the threads. Cheers
Peter TD 5801
P Hehir

Read archives, lots in there. Pictures of internals/terminals on Bud's T-talk somewhere I think. George
George Butz

I've reactivated the only thread I could find that has any bearing on my query re fitting the replacement terminal post. Checked T Talk but no info on the sender unit there. I found two pics which I posted on the reactivated thread (one of them was yours George) but I still require a list of the various bits needed, as well as the method, for a successful replacement of my broken post. Cheers
Peter TD 5801
P Hehir

Put the image in the wrong thread. Bud


Bud Krueger

The following pics are of my Ebay acquired sender unit. Though it has the same Patent Number 447499 & overall shape it is a little different to the units pictured above at the terminal. The broken terminal post is clearly evident. Dave is sending me a post & a knob however I still require more info on the remaining post fittings which I've detailed above.

Obviously the post, which has 12V applied constantly, has to be insulated from the body of the switch, (which is at ground potential because it is mechanically connected to the tank via the screws), & the circuit is only made when the contacts are bridged as the float begins to sink. So what is the tiny wire evident in the pics below all about? Cheers
Peter TD 5801


P Hehir

Pic 2


P Hehir

Pic 3


P Hehir

Peter

It is very difficult to make a worthwhile comment on your sender unit without a physical inspection. The wire you are concerned about could be a single strand of a connection wire that arced out to the sender body and welded itself to the case.

I would be moving on, remove the broken screw which should not be threaded into a sleeve that acts to insulate the terminal from the sender body.

On reassembly you need to ensure the internal switch post where it connects to the terminal post is fully insulated from the sender body. This will mean using high density fibre washers and an insulation tube which is inserted into the sender terminal cavity. Fibre washers need to be fitted internally and externally, between the internal washer and the body I would be fitting an 'O' ring to prevent fuel leakage.

Double nut the terminal post the first nut is to clamp the post securely in the sender body and clamp the 'O' ring, the second one (the knob) is to clamp your connection terminal.

I am communicating this process because I had to completely rebuild the crap sender that I purchased in the spare parts market place. Insulation of the terminal post from the sender body was via a piece of heat shrink which was not impervious to fuel and leaked profusely.

Jaycar should be a source for the insulating components.
G Evans

Thanks Graeme. I'd pretty much arrived at the same conclusion & communicated that to Dave. The only thing I've yet to determine is the "insulation tube". I discarded the heatshink idea because I suspected it may not handle fuel. An 'O' ring would also have to be impervious to fuel. The wire is actually free of the case & appears to disappear down beside the post. Seems odd as the post is clearly the conductor so it seems the wire is redundant. I'll pay a visit to Jaycar & take the unit & the bits from Dave with me when they arrive. I can sort out the electrical side but I want to make double sure the bloody thing doesn't leak! I have some insulating paper like material from Element 14 that I use on the rear of ignition switches so that should effectively isolate the post from the body internally. I may even be able to also wrap it around the post. Appreciate your advice. Cheers
Peter TD 5801
P Hehir

Wire emerging. Goes from inside, between case and central terminal insulator, pinched between case and fibre sealing washer (green Abingdon w/Permatex Aviation sealer on it).


George Butz

Wire path inside, it coils/wraps around the pivot/movable contact. This GROUNDS the movable contact. When the float moves, this then touches the fixed which is connected to the terminal/light bulb.


George Butz

Anybody know if Stag or Locktite aviation grade handles fuel? I've made up some cork gaskets but if either of the above is no go, I'll get some Permatex 2. Cheers
Peter TD 5801
P Hehir

The internals of mine are quite different to yours George. I'll take a couple of pics tomorrow before I pull it apart & post them. Cheers
Peter TD 5801
P Hehir

OK, the pictures above are of the original Smiths unit on my TD. I think the principle should be the same?
George Butz

As far as a gasket sealer goes, this is what I use and it works very well, Permatex Ultra Copper. If there is a heat concern, make sure it's the Ultra version. It's about the best I've found. The regular copper version works very well in gas prone areas, just a little less heat resistant than the Ultra. PJ




Paul S Jennings

Yes George it's the same principle as it's the moveable contact that is the earth on mine as well. The pivot of the moveable contact is mechanically & electrically connected to the body of the sender, along with the moveable contact, which is therefore also at earth potential. Mine is also made by Smiths & it seems to be an improved version.

The compatibility with fuel is my major concern with the gasket sealer PJ. I know that Permatex is probably what I should use & the one you've suggested sounds great but as I have both Stag & Locktite, if either will do the job then why not? Cheers
Peter TD 5801
P Hehir

No worries using Stag or an "O" ring with fuel, spend the pennies and get a gasket set from The Frame Up.
G Evans

George these two pics show a couple of positions of the moveable contacts on my unit. In one of the archived threads it was suggested that an earth wire may have originally been fitted under one of the tank or sender housing screw heads & back to the chassis to ensure a good ground. Perhaps it was felt that the Permatex or whatever was used with the gaskets way back when may have prevented the sender from earthing to the tank.

Graeme I have a FTFU gasket set put away for safe keeping somewhere but if I can't find it I'll use the bespoke cork ones I made from a used engine breast plate cover. (Also used it to make a gasket for the oil filler cap) Cheers
Peter TD 5801


P Hehir

Contacts in operation


P Hehir

This is the Moss gasket set I originally purchased but decided against using after reading in the archives that the rubber apparently turns to mush & the tank leaks like a sieve! I did find them useful as templates to make the cork ones. Cheers
Peter TD 5801


P Hehir

Regarding that fine wire--it is there to guarantee a good electrical contact between the pivot and the body of the unit. On my car, it was connected to the pivot at one end and the other end was under the shoulder washer that insulates the connection screw, so it made contact to the body but not to the connection screw. The picture below shows it; sorry, I know it's hard to see, even harder to photograph.

By the way, don't use this as an example of how the unit looked originally; I had to make my own insulating washers from a piece of nylon, as the ones that came with the car had fallen apart.


S Maas

"...Permatex Ultra Copper"
I would not use anything with copper in it around the terminal stud - don't want that stud having any path to ground other than the movable fingers inside the unit. Cheers - Dave
DW DuBois

Thanks SM. My fine wire does make contact with the body as it passes down the outside of the insulation around the terminal post. I can't see it inside the unit but perhaps when the broken terminal has been removed all will be revealed. I'll try not to disturb the internal connection when replacing the terminal. Did you have the external wire mentioned in the archive under one of the screws & connected to the chassis? Noted Dave. Cheers
Peter TD 5801
P Hehir

Hi Peter,
Yours is a slightly different type, When it was used in a car with a fuel gauge the contacts wiped a resistance to give fuel level. When used as a low warning system the resistor was replaced with a plastic rod and a contact. It saved them making two different senders and a few pennies per car.
Ray TF 2884
Ray Lee

Thanks Ray. Managed to find some Permatex 2 here in Sydney @ $6.90 for the 80 ml tube. I'll use that & the cork (if I can't find my AS set), based on the recommendations here & in the archive. Cheers
Peter TD 5801
P Hehir

Fascinating!! It's amazing how many cars you can look at and never see some of these undocumented variations in basic components. I've never seen these variations before. But I've finally seen something relating to the fuel gauge. I'll be darned. I still believe that the soldered tincan is the original version. Bud
Bud Krueger

Just discovered that Pratley high strength steel putty is impervious to fuel. One of its recommended uses is to repair holes in fuel tanks. I'll use a little to ensure the terminal is sealed on the inside of the housing once the post is firmly in place & the locking nut secured. Cheers
Peter TD 5801
P Hehir

The bits arrived from Dave today & I found that my original post is somewhat smaller in diameter than the 4 BA Dave supplied. The original measures about .122" & Dave's about .183". I've dismantled the broken post, contact & insulation which is shown in the attached pic, along with the new post. The issue is the hole in the contact shown top right. From the left the other components are the insulation that was wrapped around the terminal, the two internal insulators, the broken original terminal, the contact & the new terminal post. Not sure how to proceed here. Any advice? Cheers
Peter TD 5801


P Hehir

Typo. That should read "2 BA Dave supplied". The 4 BA is for the cover plate. Cheers
Peter TD 5801
P Hehir

Peter, I don't think I'd open up the holes in your system to match the larger screw. The original is obviously not a 2BA. Can you determine the tpi and diameter of the original screw? Bud
Bud Krueger

Probably from a later production or repro, likely changed design bigger because the tiny originals twisted off.
George Butz

You're right of course Bud as opening up the holes would mean I couldn't use the contact. The insulating L pieces aren't a problem as I have material from Element 14 that I can make new ones from. No idea what the original broken post was but as stated above the diameter is approx .122". I'm keeping it anyway. It isn't 4 BA as I compared it with the cover plate screws. Close though.

Having slept on the problem & noting George's comment, I'm going to make a new contact from some brass sheet, use Dave's 2BA post & nut, pick up 2 fibre washers, 2 more brass 2 BA nuts from Moyles, wrap the terminal in the Element 14 insulating paper & seal it with Permatex. Using the Element 14 I'll also make 2 new internal insulators. Once the post is insulated internally & mechanically secure with the insulated bottom nut, I'll test it with my ohmmeter, fit the lock nut, a star washer, the active feed, another star washer, cut the post down to the correct size & finally fit the black knurled nut. Thanks to all for your input. Cheers
Peter TD 5801
P Hehir

Sorted. Works just like a bought one.

I now know what the second prong, the one on the left when viewed as you peer into the housing, was for. The left prong of the moveable pair of contacts as they rise first makes contact with the very end of the bent fixed contact. This is only in contact for a very short time causing the fuel warning light to blink. As the fuel level falls further this left prong ceases to make contact as it rises above the end of the fixed one & the light goes out. As more fuel is used the right prong subsequently makes contact just below the bend in the fixed contact, the light comes on & remains illuminated until the tank is filled. Cheers
Peter TD 5801
P Hehir

Just fitted the sender to the tank & I can confirm the original screws were definitely 3 BA. Mine were 1/2" steel cheese head slots which I replaced with new 1/2" 3 BA steel round head slots, only because I couldn't find cheese heads. I'll keep the originals & use them temporarily when I again remove the unit prior to using the tank sealing kit. Cheers
Peter TD 5801
P Hehir

I have installed a new fuel tank and fuel level sender unit. The first year 2014, the sender unit worked as it should, that is on and off. This year, when the tank is full, there is a very faint glow in the light and as the fuel level falls, the light gets brighter and brighter. Have I a faulty sender unit or have I been supplied with a resistance style sender as Ray has mentioned? Any thoughts?
Richard
R A B Wilson

Hi Richard,
Disconnect the wire and short to earth, you should get a full bright light. If that is OK then check the terminal resistance to earth. You should have either no resistance or an open circuit. Anything else is wrong and the sender is faulty or resistance type.
If it is a resistance type all you need to do is bend the contact(s) away from the resistor so it will only contact the earth bar.
See Peters photo 21 July this post.
The contacts must not touch the case, it can be done while still in place, but awkward.
Don't forget to drain the tank and disconnect the power. While flooded all is OK but you let air in and bang!
Ray TF 2884
Ray Lee

I'd follow Ray's advice Richard especially about the BANG! What I don't get is that your sender only began to behave like the resistance type after 12 months. That is odd. Cheers
Peter TD 5801
P Hehir

Hi Peter,
if it is a resistor type every time it hits and bounces off the light terminal it will bend the wiper inwards. Eventually it will take a set and make contact with the resistor.
Ray TF 2884
Ray Lee

This thread was discussed between 19/07/2015 and 05/08/2015

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.