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Garage => Mechanicals => Topic started by: Feather535 on 01 October 2022, 09:02 PM

Title: 280 SE fuel level sender - where to buy
Post by: Feather535 on 01 October 2022, 09:02 PM
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.
Title: Re: 280 SE fuel level sender - where to buy
Post by: daantjie on 01 October 2022, 09:31 PM
Ebay
Title: Re: 280 SE fuel level sender - where to buy
Post by: sutekh on 01 October 2022, 11:16 PM
Quote from: Feather535 on 01 October 2022, 09:02 PMOr can it be repaired?  I didn't see an obvious way to open it up when I had it out of the car.

https://forum.w116.org/mechanicals/1979-300sd-reserve-fuel-light-stays-on/msg153312/#msg153312
Title: Re: 280 SE fuel level sender - where to buy
Post by: revilla on 02 October 2022, 01:15 AM
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


Title: Re: 280 SE fuel level sender - where to buy
Post by: Feather535 on 02 October 2022, 11:16 AM
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.
Title: Re: 280 SE fuel level sender - where to buy
Post by: Feather535 on 02 October 2022, 11:17 AM
And hello to revilla in Aix-en-Provence.  I used to live in Lyon!
Title: Re: 280 SE fuel level sender - where to buy
Post by: gurrier on 02 October 2022, 01:36 PM
From 15.40 on in this You Tube video gives a good general instruction -a diesel
but seems same unit used.
Title: Re: 280 SE fuel level sender - where to buy
Post by: Feather535 on 03 October 2022, 08:47 AM
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?
Title: Re: 280 SE fuel level sender - where to buy
Post by: revilla on 03 October 2022, 09:02 AM
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.
Title: Re: 280 SE fuel level sender - where to buy
Post by: Feather535 on 03 October 2022, 11:47 PM
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?
Title: Re: 280 SE fuel level sender - where to buy
Post by: revilla on 03 October 2022, 11:56 PM
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.
Title: Re: 280 SE fuel level sender - where to buy
Post by: Feather535 on 04 October 2022, 08:13 AM
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. 
Title: Re: 280 SE fuel level sender - where to buy
Post by: rumb on 04 October 2022, 10:19 AM
Put your vom probe on one post and move the other along the wire until you find the break in continuity.
Title: Re: 280 SE fuel level sender - where to buy
Post by: Feather535 on 04 October 2022, 09:35 PM
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...
Title: Re: 280 SE fuel level sender - where to buy
Post by: revilla on 05 October 2022, 12:05 AM
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.
Title: Re: 280 SE fuel level sender - where to buy
Post by: Feather535 on 06 October 2022, 08:19 AM
Quote from: revilla on 05 October 2022, 12:05 AMYou 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"

This is the key!  I see now that the silver wire is a loop.  Before I tested continuity on each leg of the loop relative to a different terminal.  Now measuring only from terminal W, there is continuity all along the wire until it returns to the bottom of the cap, but not between the wire and terminal G. So I think the conclusion is the same: there is a broken connection between the post for terminal G on the outside and the copper terminals on the inside that the wire is soldered to. 

How to repair that is the question.  It looks like it would involve disassembling and reassembling that side of the cap == lots of time.
Title: Re: 280 SE fuel level sender - where to buy
Post by: Feather535 on 06 October 2022, 09:17 PM
Quote from: Feather535 on 06 October 2022, 08:19 AMNow measuring only from terminal W,

Sorry, I wrote this wrong: it's from terminal T that there continuity all the way around.  Terminal W is for the reserve light, and that's a separate story.