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280 SE fuel level sender - where to buy

Started by Feather535, 01 October 2022, 09:02 PM

Feather535

So I tested resistance in the fuel level sender in my 280SE and it fails.  There is no continuity regardless of the float position, which explains why the gauge always reads empty.

Does anyone know where to buy a new one?  My usual US parts suppliers don't have them.

Or can it be repaired?  I didn't see an obvious way to open it up when I had it out of the car.

daantjie

Daniel
1977 450 SEL 6.9 - Astralsilber

sutekh


revilla

Hi
Definitely repairable!
Don't get your money stolen from some eBay, and others, speculators.
Don't waste an interesting learning opportunity and the REWARDING feeling to have fixed something in your car.
Throwing parts at it and crossing your fingers that it would work will suck you up into draining money unnecessarily.  No merit.
Here's another thread with a video.
Careful with those wires, they are less than hair thin. But in most cases in the many I have repaired they aren't broken, just not making contact.
Tell us what you find and we'll gladly guide you through the repair process. Each case is different. There are many different failure modes of this little and interesting gadget.

https://forum.w116.org/mechanicals/fuel-gage-repair/msg143496/#msg143496


Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

Feather535

Glad to hear these units can be repaired.  I always prefer to go that way with vintage cars; yesterday I disassembled my washer pump and got it working again. I'll report on how it goes.

Feather535

And hello to revilla in Aix-en-Provence.  I used to live in Lyon!

gurrier

From 15.40 on in this You Tube video gives a good general instruction -a diesel
but seems same unit used.
1973 350SE

Feather535

I removed the sender ad opened the tube.  I didn't look bad--nothing like the ones from diesel cars in the video--but the copper wire that seems to be the return (ground) is broken off at the bottom end.  I don't have any wire that thin, but if this is indeed the ground wire, I'm guessing it might not matter.  So it looks simple enough to remove the old wire and solder a new on in place.  Right?

revilla

Indeed, that's just for the red reserve light (copper like). You can replace it with a similar gage wire. Not the case for the other 2. Those are resistance sensitive for the needle accuracy. Good they aren't broken.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

Feather535

Next episode.  Before taking the trouble to solder in a new copper wire in place of the broken one, I attached the wire with clips at the top and bottom to see if that fixed the problem.  It didn't.  There is still no continuity between the ground terminal and either terminal W or terminal G, regardless of the float position. The temporary replacement wire is on terminal W and the original wires on the other two terminals look intact and connected at both ends.  What's wrong?

revilla

Hi
I'm assuming you have gone through step 1 of the process (check fuses) right?
Please report back with results. We'll get your sender unit back operationally in no time.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]

Feather535

Quote from: revilla on 03 October 2022, 11:56 PMI'm assuming you have gone through step 1 of the process (check fuses) right?

Yes, the sender is out of the car and disassembled, so I'm testing resistance according to page 54-257 of the manual.  With a meter connected to the ground terminal and the gauge terminal (terminal G), I'm looking for resistance to be minimal with the float at the top of the rod and increase as the float goes lower.  But instead the meter indicates an open circuit regardless of where the float is. That seems to explain why the gauge always reads empty with the sender in the car.  I'm guessing something isn't making contact, but the two silver wires are intact and the tiny contacts on the float are touching them. 

rumb

Put your vom probe on one post and move the other along the wire until you find the break in continuity.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

Feather535

Quote from: rumb on 04 October 2022, 10:19 AMPut your vom probe on one post and move the other along the wire until you find the break in continuity.

OK, the wire from the T post, which I believe is the ground (there is no terminal 31) has continuity with the terminal along its entire length.  There is also continuity between that post and the "cap" that everything attaches to.  The copper wire that I installed temporarily on the W terminal also have continuity with the post from top to bottom.  But the G post for the gauge circuit isn't in continuity with any part of the wire or even with the terminal inside the cap that the wire is soldered to.  So it seems like contact must be broken between the post on the outside of the cap and the terminal on the inside.  That sounds hard to repair...

revilla

Ok let's go back to basics here.
You essentially have only 2 wires in the unit (that seems like 3). 1 copper like and 1 thin silver like. The latter starts at W, loops around the bottom base and continues on up until reaching the "cap". Send us a picture on your unit please. The only thing you have to do is making sure there's continuity all along those 2 (yes I wrote 2) wires using the method (sliding probe until continuity is broken) described by rumb.
 What do you get as result?
I think you're measuring continuity in the circuit of red-light-reserve when the floater is NOT in the lowest rest position, which is PERFECTLY NORMAL as it's designed to be. You will obtain around 80 ohms in that circuit but ONLY when the floater is in contact with its bottom base. If you don't, either your red-light wire is broken or the contacts at the base are corroded/dirty. Please report back your observations.
Robert
W116 1977 280SEL & 1979 280SE
[img width=150 height=100][url="http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG"]http://revillagodfroy.com/MB%201977%20280%20SEL/album/thumbs/IMG_0371.JPG[/url][/img]