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FCP Euro Service Kits

FCP Euro Kits

As the original components on our classics age, a repair or replacement will be par for the
course until each system and component has been sorted out. Yes, some systems will continue
to perform excellently for decades, but eventually all good things must come to an end.

With my 1975 Mercedes 450SL up and running, with the new subframe giving me the ride of a
life time, other components are now beckoning for attention. Such is the case with the fuel
sender unit. After sitting for at least five years with fuel that had turned the color and consistency
of maple syrup, it is no surprise that the fuel sender unit is not functioning properly. I did hope
however that by having fresh fuel in the tank it would eventually begin to dissolve and resolve
the erratic readings at the gauge. Alas, no.

Should your fuel sender on your 450SL or other older model Mercedes, i.e., W123*, W116, W/
R107, etc., not work, it is worth taking the unit out and disassembling it for a potential cleaning.
Understand, it may not always work out to your satisfaction, but if it is cleanable you will save
yourself about $200 at least in the short run.

This article will specifically cover the removal, disassembly and replacement of the fuel sender
unit on a 1975 450SL. Most models are very similar, but check the owners workshop manual for
details on your specific model.

If your model is fitted with a hardtop, it must be removed in order to access the fuel sender unit.
Specific instructions are provided in the owners manual on hardtop removal. If there are any
questions on hard or soft top removal or functionality, let me know and I will gladly do an article
on that.

Next, the soft top will need to be raised as shown. With the soft top in position, the soft top deck
will be visible, along with the plug that covers the fuel sender unit.

Gently remove the plastic cover (plug). Remember, these parts are very brittle and are subject
to cracking. The part does appear to still be available from Mercedes-Benz for $5.00. I’d call
ahead however if you plan on needing a new one.

With the plug removed, the top of the sender will be visible. A 46mm socket will be required to
remove the metal retaining “cap”. It is not advised to attempt the removal with pliers or other
tools that can slip off and damage the top. It is also advisable to avoid any nicks and scratches
of the soft top decking as this area might get damp and begin to rust. Prior to removing the
retaining cap, simply unplug the wiring socket by gently pulling straight up. A very slight wiggle
might be needed to initially loosen the plug. Again, this too is old plastic and most likely brittle. If
there is dirt around the sender, blow or vacuum the area to avoid contaminating the fuel in your
tank.

Once the metal retaining “cap” has been removed, the sender unit is now ready to be removed
by lifting it straight up. It will be helpful to know roughly how much fuel is in the tank as it will
determine how long it will take to drain the sender unit. WARNING: when removing the sender,
do not pull it all the way out at first as gas will be draining from a pin hole on the lower side of
the unit. The draining should be audible and once all is quiet remove the unit fully.

The sender is now ready to be inspected for a potential cleaning. To open the unit, a spanner
drive will be required. This can either easily be made from an old screwdriver or driver bit or
purchased at a home improvement store. With dozens of extra bits floating around, I made mine
and it will only take about 2 min. to do with a Dremel metal cutting disk.

Remove the nut using the spanner drive and VERY gently pull top of sender to remove float
from aluminum housing. If you are fortunate it will not self destruct as mine did. If things do
come unhinged, it will be time for a new unit. Fixing it will most likely result in doing the job again
in very short order.

Here is my 45 year old fuel sender.

A closer look at what time and five year old fuel will do.
If all stays together however, throughly clean with brake cleaner and avoid bumping the
resistance wires. Make sure the center post is very, very clean as any rough spots could cause
the float to hang up and give a false reading.

With everything clean, reassemble in the reverse order and reinstall.

If however a new fuel sender is required, you are able to purchase that through FCP Euro and
that will be a simple plug and play event in the reverse order of removal.

When reinstalling, be sure to have a new gasket, ordered separately and when refitting the
sender, note the unit will only fit in the tank one way by means of a notch on the sender unit just
under the top lip as shown.

If the tank is full hold the sender down with your hand, allowing it to fill with fuel. If you let go, it
will pop up and out of the tank. Once filled with fuel it will sit in place allowing you to easily seat
and fit the metal retaining cap. Do not over tighten, but be sure it is snug and you are done!
The Mercedes W123 sender unit is under the medical kit box on the back parcel ledge.

HELPFUL PARTS

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Written by :
West Kenyon

West Kenyon is a Multi-Media Design Consultant and automotive enthusiast. Cars in his collection include a 1956 Austin FX3-D, better known as a London Taxi, a 1965 Rolls-Royce Phantom V, and a 1975 450SL and 1981 240D by none other than Mercedes-Benz. West said, “owning one or a number of vintage cars is often an expensive proposition", which is why he does the majority of mechanical and interior work/restoration himself. West added, “not only does it save a significant amount of money to do the work yourself, it also provides full opportunity to know the job is being done with excellence and allows for an unprecedented appreciation and knowledge of the car.” For FCPEuro, West will focus on providing in-depth information on both the Mercedes-Benz R107, 450SL, D-Jetronic version and the W123, 240D. Glücklich Autofahren! (Happy Motoring)


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