A quick note. There are 3 holes that allow the fuel level inside the tube to rise and fall. The channel in the maze, 2 small holes in the maze end cap, and a small hole near the bottom of the tube. There is also a hole near the top of the tube to allow air in or out as the fuel level drops or rises. It's pretty easy to see that if there is dirt/contamination in the fuel, the maze and 2 holes will become plugged not allowing the fuel level to drop as designed. If the hole near the bottom of the tube is restricted as well, there is nowhere for fuel to enter the tube (when filling) or exit the tube (while being consumed).

 

Nice wrench - that's a $233 part!

 

Cool thanks, I'll be doing that job when I have the seats out now I see how works. I'm sure we'll all either end up having to do this one day or another. You used an acid to clean the thing, I'll have my pops bring home some nitric acid, good stuff for cleaning aqueous stuff minerals and other water based stuff.

Those really are some thin wires I'll have to be on my best behavior. I guess if I get sick of the car in the process of doing the job I'm just a rag away from getting rid of the thing. I just hate to think about gassing myself inside the coupe.

 

Thanks..I'm down to the plastic end cap. The nut came off easy. Just don't want to force the plastic cap. I was surprised at the cost of these units..

 

r107 fueling

Thanks for all the prompt responses. I removed the old sender, it clicked back and forth when turning end up then end down. Then while doing so it would not click until I shook it a few times. This would indicate that the sending unit was probably sticking. I replaced with a new sender, went down to the gas station with gauge needle on reserve. Put in sixteen gallons and gauge shows full. I am thinking that the reserve means you've got about 2 to 3 gallons left in the tank. With the sixteen gallons I added one would think I've got about 18 to 19 gallons in the tank. Still short by 3 to 4 gallons. I replaced the gas tank valve as well.

Anymore thoughts guys?

 

Thanks for all the prompt responses. I removed the old sender, it clicked back and forth when turning end up then end down. Then while doing so it would not click until I shook it a few times. This would indicate that the sending unit was probably sticking. I replaced with a new sender, went down to the gas station with gauge needle on reserve. Put in sixteen gallons and gauge shows full. I am thinking that the reserve means you've got about 2 to 3 gallons left in the tank. With the sixteen gallons I added one would think I've got about 18 to 19 gallons in the tank. Still short by 3 to 4 gallons. I replaced the gas tank valve as well.

Anymore thoughts guys?

Prompt responses Last post here was in January.
What year and model do you have? What is the gas tank valve?
Tank level is a bit relative. Did you drain the tank?

My thought? Drive it and keep it above 1/4 tank.

 

Just did this today

It took me less than 20 minutes to fix an expensive part!
Thanks!!!

 

Another option to Kaboom
A can of spray , Break Clean or Carb Clean & an old toothbrush .
But I will give the boom a try too
This is an on going problem in this day of corn

 

Couple of notes on the sender, which I just cleaned and tested.

The resistance of the sender, measured between terminal "T" (which connects to the #3 socket on the plug) and ground should be about 3 Ohms with the float at the top, as it would be if the tank is full. (Turn the sender upside down.)

With the float on the bottom, resistance should be about 69 Ohms. Also, when the float's at the bottom, the reserve contacts from terminal "W" and ground should be 0 Ohms--it's just a simple on/off switch.

The resistance between socket terminal 3, which runs to the fuel gauge, and ground should measure 0 Ohms.

I got about 10 Ohms doing this measurement, so either there's something fouled up in the instrument cluster or in the wiring from the socket to the cluster.

 

Added 07/02/2013

 

Happy new year drivers...
Found this thread while shopping for a 1980 450sl fuel sender.
The fuel gauge on my 1980 450 was erratic at best then stopped working altogether then I finally decided to investigate. Looks like my sender was replaced by the previous owner as the bottom of it was compressed like an accordian and I think this replacement was adapted to fit as it seems longer than the origional. I am looking for a 2nd hand replacement if anyone could offer any leads or has one for sale.. Thank you in advance.

 

.


Welcome to the board.

There are several contributors out there with cars in various stages of being parted out, they'll be along...

 

I have one for a '79..Came from a parts supplier when I was fighting fuel system problems. I had already bought a new sender..and this one came in a replacement tank I bought. It was guaranteed and looks fine..Jerry ...870-847-5771..anytime..

 

I took mine out this weekend and found that the thin wire was broken. I replaced the wire with a copper wire, but now when you insert the unit in the tank it reads full all the time. I am guessing the thin wire was some type of material that it did not had continuity when inmersed in fluid. Any one has an idea of what will be a proper repair for a broken thin wire?

 

Hello...I'm going to try to repair the fuel sending unit in my 1981 380 SLC...The copper wire and thin wires are broken. Did you find the proper nicrome wire guage for thin wire? Copper wire gauge? Thank you.

 

After some reasearch the resistor wires needs to be Nichrome. Does anyone know the proper gauge of the O.E.M. resistor wire, I can not find the broken piece. 36AWG, 38 AWG, 40AWG?

 

That wire is made of an alloy that has a certain amount of resistance. The float grounds that wire, so it's essentially working to make the wire "longer" and therefore increasing the resistance. It's the same kind of wire used in, say, a toaster because it gets hot when you put voltage into it.

On my 560SL the resistance measures from 3 Ohms when full and 69 Ohms when it reaches the reserve fuel amount. (Which is helpful to know when trying to diagnose a fault in the gauge cluster.) The copper wire you replaced it with has almost zero resistance, which is why the gauge reads full.

You can find such wire on eBay, and the data you need is the Ohms per foot, and the exact length of the wire needed. Resistance Heating Wire | eBay Note that the "40 gauge Kanthal D resistance wire–Resistance- 84 ohm/ft 275 ohms/m" sounds about right, but you'll have to do the algebra to get it exactly right. If you have an industrial wire shop where you live, they might be more helpful in finding the right type of wire.

I'm not an electrical engineer, but my best guess is that you'll find it easier just to buy a new sender, but if you successfully pursue just replacing the wire, it would help folks if you let us know which kind of wire worked correctly.

 

Got it, when the float is up, the distance from contact points is short, therefore the 3 Ohms, When the float is on the bottom I need to measure the amount of cable between the contact points
and determine the proper resistor cable gauge and Ohm/ft that matches the 69 Ohms reading when the float is at the bottom. I don't feel like spending $200+ dollars for a new sending unit
If I can solder a $5.00 piece of wire to solve the problem, I enjoy the work and the challenge!!

 

My sentiments exactly.

Now that I think further about it, 3 Ohms at full is probably just a measurement error, because the way the gauge works in relation to vehicle ground ideally it would be 0 Ohms when full. But any fuel gauge is going to be a rough approximation anyways, otherwise they'd put little numbers on the gauge so we could know the exact amount.

There's got to be interesting ways to use the leftover 49 feet of wire.

 

Just an fyi...while many parts are interchangeable with the W126 models (560SEL/C etc) the fuel sender is not one of them. The 126 unit is about two inches longer...IIRC.

 

How hard is it to get at the sender and get it out to repair it?

 

Access is under that big plastic plug in your soft top stowage compartment.

 

Once you remove the plastic cap, unscrew the sending unit and you are done. It takes about 3-5 minutes.

 

Not necessarily true on the early models. On them there are several 8MM? nuts to remove. It is not the 46MM screw on.

 

Seems like we had a post a couple of years ago where the 46mm socket wouldn't fit because the gas tank was mounted a little off and the sender was not centered in the access hole. Searched but couldn't find it. IIRC the op had to grind off some of the metal on the outside of the socket to make it seat.

 

I think that was the tank screen.

 

I took the sending unit out and measured the lenght of the resistor cable from the contact points when the float is all the way down. The distance is about 15" of cable. Based on a target reading at that position of 69 Ohms. We will need a cable with a resistance of about 55.20Ohms/ft. Looking at the ones available I will say a 38 awg cable has a resistance of 53.60 Ohms/ft, that is close enough for me. I will order the cable. And I will post the results once installed.

 

Update, I got the 38 AWG resistor wire, all 100ft. I proceeded to weld the wire to the fuel sending unit and....... it works. I got a functional fuel sending unit!!.

The only note that I have is that the reading from testing the sending unit outside the tank do not move the needle 100% to the Full or Empty positions. The needle stays goes 90% of the way to full and it stays 10% short of Empty. I guess there still some different gauge cable that will take it all the way to Full or Empty.

But still a 90% accurate sending unit for $6.00 and I can live with that!

 

hi what if the smaller wires are broken

 

I have cleaned my fuel tank and fuel sender. After cleaning I now have a working fuel sender unit showing exact amount of fuel in the tank but the fuel empty light is on all the time. The fuel tank and sender were very clean concerning the age of the car I expected a lot of dirt and sludge. I have opened and checked again all contacts/wires in fuel sender and looks fine except that when checked it sends electrical signal from bottom contacts and top contacts as well, like there is no ground contact in the fuel sender unit. Any experience or opinion on the mater, since it is to annoying watching fuel empty lamp lightning all the time. Fuel level as I said is working fine and precise.