DIY page. Introduction to Removing Fuel Sender.
 

Isn't that just so annoying when you get on the bottom half of your tank and the needle keeps jumping around? How about when the fluid level takes forever to change or moves instantly in turns, while some of these are more annoying than other problems but the root problem is all the same, the fuel level sending unit. You will find how to clean or replace that pesky unit here. The only things to really point out about the task is that if the tank isn't near empty it will probably be a bit messy to take it out as the fuel slowly enters and leaves the unit, also a 42mm socket is needed to make the task incredibly simple. I made due with some huge channel locks I have, but I also had the trunk divider out at the same time.
http://boostnbenz.1baddsm.com/DIY/Sender/thumb/2.jpg


This DIY can be found in the DIY Wiki HERE.

Any tips for a TD?

Sorry, I'm not very familiar with the 300TDs.

its a pain removing the fuel sending unit on a TD.. i still have yet to find me a socket that can remove that darn size....it is deeply set and has only a small opening unlike in sedans where the size is as much as the first aid kit.

Where exactly is the fuel sending unit on a 300td? Would the nut also be a 42mm like in the 300d?

It's not a 42mm. It's 46mm

That is the same size socket as for a VW flywheel. It's available from Sears for around $15, and from some of the better sandrail shops that work on those engines. I got mine from Sears.

I was at my mechanics shop and he let me try out his assortment of massive SAE sockets. I remember measuring the one that did not fit and it measured out to 45.6 mm. Luckily he had the next size up stashed somewhere

I'm trying to get the sending unit out of my '85 300SD. A 42mm socket is too small, and I ordered it so I could do the job.

Does anyone know what size socket to use for this job? I tried just using some channel locks, but the body of the car raises up around the top of the unit making it impossible to get locks in there and grip it. The only opening I have to access the unit it behind the back seat through an opening in the body.

Any feedback anyone has would be awesome! I've had the backseat of my car in my living room for a week now waiting on the 42mm socket to arrive in the mail, and to my surprise, it doesn't fit.

I couldn't find a thread that shows any steps or socket sizes for removing the fuel sending unit from a w126.

Thanks!

You need an adjustable toilet wrench available at the hardware store for about $10. I've got some posts and a picture on here somewhere. They look like a giant adjustable wrench with a locking wing nut. You set it to the size of the hex nut, put it vertically down on the nut and use an extension thru the hole in the handle to turn it.

FYI, I just did this on my 86 300SDL. It's a 46mm nut. I tried using the toilet wrench but couldn't get her to fit enough because I couldn't wedge it in under the back metal dash and nor thru the hole behind the back seat. Luckily a buddy of mine has a 46mm socket.

My solution to the 46mm nut on my 300TD was to clamp vise grips on vertically (handle sticking straight up), then use a screwdriver in between the jaws as a lever to turn it. It's not super tight, it just gets stuck to the rubber O-ring over time. If you use a little Sil-Glyde on the O-ring when you reinstall, next time will be easier.

The resistance range on the Mercedes sender, at least on the wagon, is the same as a GM sender but reversed; GM is 90 ohms full/0 empty, the Mercedes one is 0/90. If you're fed up with the fine wires on the Mercedes sender breaking, you can use the Equus #9982 universal GM sender by flipping the float pivot assembly upside-down to reverse the resistance range. You will need to drill holes in the top of the tank to screw the mounting flange down. A little fiddling with the float arm length gave me very good accuracy. This renders the low fuel light non-functional, though.