Fixed my fuel level sender in a 300SD
 

Thought I'd post this for anyone who might need to do the same job, maybe save them some hassle...

First, take all the crap out of the backseat, instead of trying to work around it (like I did). Then there's a little lever on each side of the seat bottom the release it, then a small screw on either side near the bottom that come out to let you slide the seat back up and off the hooks at the top. Careful pulling it out or the little metal tab the screw was in will scratch the paint (doh!) Keep track of the screws for later!

Second, (Ignore this step if you have the right socket to fit the sender!) unscrew the latches to the compartments in the shelf, then you can work the shelf up and get the compartments out, but you don't need to take out the shelf out all the way. Be careful with how far you bend it or it will crack in the middle (doh! again) You need the drivers side one out to have a hole to reach through to use slipjoint pliers .

Third, pry off the black cap (it's about 4" in diameter, closer to the driver side near the top) and the sender is under that. Unplug the plug. I ended up using slip joint pliers to unscrew it, and it took every ounce of hand strength to do it without slipping and either gouging the sender or gashing my knuckles. If you have the right gigantic socket it will be a lot easier.

Fourth, pull out the sender, and realize that there is a tiny hole near the bottom of it the will be peeing out an invisible stream of fuel while you are holding it there thinking you'll just let a few drops drain off before moving it away from the opening (yet a third doh!). Have something ready to catch drips, and hold it so the last 4" or so are still down it the tank until it all drains.

Fifth, If you don't have the right tool, you'll need to sacrifice a screwdriver and cut a slot in the center of the blade to unscrew the nut at the bottom of the sender. I used a hacksaw, and be patient so you don't over do it. Then the plastic disk at the bottom unscrews by hand, and then the outer tube slides off. BE CAREFUL! The wires in there are hair thin! There are two thin wires the float rides on and a third wire that runs parallel to those. That's what my problem was, the third wire had snapped off where it solders to a tab near the bottom of the unit. Luckily it was still long enough that with a friend to push up on the tab and steady the unit, I was able to grab the wire gently with needlenose pliers and stretch it straight and re-solder it back.

Now the easy part, put it all back together! (minus the one screw you might lose if you don't take all the crap out of the back seat) Now I'll see if it actually works as the fuel drops, but it was encouraging to see the low fuel light go that had been stuck on go out. Wish I had the camera with me...

Good Luck!

Great! Thanks for the write-up and instructions.

? on senderunit repair link/ soydrivermatt
 

Is this the same for a 300D?
Mine works but only when above 1/4 tank....iit seems; and the light stays on all the time....
I will try this if you think it might be a solution...
BTW anyone know the actual size to fit the sender unit bolt???

I think 1 3/4 Inch socket works....I THINK that is the one I used...

sender unit repair
 

If I do get it out, what are the chances that it is repairable???

I am going to make an attempt to fix mine, it only works between half tank and full, and the reserve light never comes on, so I assume a wire is broken and its full of sludge.....occassionally it will read as far as 1/4 tank but never lower than that. I want to run a cable to my trunk so I can manually turn on my reverse lights (whatever works :D) anyways, so I could use the seat removal as a double opportunity.....I need to order a gasket first though.....I've always just gone by the trip odometer, I fill up between 400-450 miles.

From what I remember, that sounds like the same design fuel sender that my 240D had. Mine had the same brokem, hair-like wire that I was able to resolder. I was able to bend the tab to which the wire is soldered to make the wire reach. On W123 chasis the job of getting to the fuel sender is even easier---remove the first aid kit, and the box--the fuel sender is right under it.

Same with the w126 body if you have the right socket :)

thanks a lot for the right up. Exactly what I was searching for. I think the cap for the whole unit is broken as i hear it rattling around in there. Has anyone ever fished this out of there gas tank?

Nope.

I have tried.

I'll get it out when I pull the tank and change the lines. For now, I pretend that its purpose is to stir up the algae and keep it flowing through the lines and strainer.

Fuel sender a breeze to fix
 

I just did mine on my '91 300d. The complete instructions are listed, probably on the diesel forum. The hardest part was once the sending unit is out, getting the black bottom piece off. Like someone else said, sacrifice a tiny flathead screwdriver, cut out a middle piece from it with a hacksaw or Rotozip. You might even be able to use 2 nails, held tightly together in a vice grip. But once loose, the opposite end (the guts of the aluminum sending unit) come out so be ready, just a few inches away from a cushioned surface for it to fall on.

Any advice on how to fix the low fuel light? My fuel gage works OK but the low fuel light doesn't work when tank is almost empty. But every once in a while the low fuel light comes on even when the tank is 1/4 full or more.

P E H

PEH-

Just take the sender out and disassemble it. I think you will find that it is full of mung and the contacts on the low fuel light portion of the sender are coated with the stuff so that they never make contact. I use a pointy set of needle nose pliers to take the funky nut off the bottom of the unit.

Rick

Just got my sender unit out. I went to autozone though and picked up a 1 7/8" socket. I just couldnt deal with wrenching that thing out. Anyways I got the sender out and it had no bottom. Just the three wires and little resistor so there went my repair and drop back in. Anyways does anyone have a fuel sender for a 1983 300SD I could buy off of them. Thanks

Does anyone know what the length of the fuel level sender is??