Fuel sending unit/ clean or not to clean

[rb6667]

Hello All, I have my sending unit out of the tank to replace the cork gasket.   My needle jumps around at times, and I'm tempted to take it apart and clean it.  However, I see after searching for other posts, that these things can easily be damaged while taking them apart.  I never have seen the reserve light come on for all the years that I owned it.  The inside of the tank looks very good from what I can see looking through the sending unit hole.  I drained the entire tank, and will replace the screen at the bottom of the tank with a new one.

SO........the 64 thousand dollar question:   Take the sender apart or not?       This is a 68 280SL. Has the later sending unit.

Advise appreciated very much,
 

RB6667

[ja17]

Hello,

Is yours the lever type or the cylindrical type?

[Larry & Norma]

Mine is the cylinder type, it is possible with care to take it apart.
Gently clean the crud off the fine wire and the float contacts.
This should fix the problem.

[rb6667]

Hi Joe, This is the later cylinder type of sending unit.  I'm concerned that once that nylon nut on the bottom is taken off, it may not hold once put back together.  I saw one of your earlier posts where you advise that rubbing alcohol does a great job of cleaning gasoline residue/gunk.

My needle seems to hang up at times showing empty, and then when the car moves, it will work correctly.  Needle also jump around sometimes. 

I have soaked the nut with PB Blaster overnight, so I'm ready to go if I have good chance of not tearing anything up.  A new one is over $250.00.

Thanks very much,

RB6667   

[ja17]

I never had any issues with the nut coming back off after the plastic seal has been borken. These units were also used on many sedans of the era. A good inexpensive used one should not be hard to come by in case yours is scrap. I have noticed that there are three types, the early lever type, the early cylinder type with three internal  contact  wires,  and the latescylindrical type with  two internal contact wires.  By" internal contact wires" , I am refering to the contact guide wires that the float contacts. These contact guide wires stretch from the top to bottom of the float.

[Leadfoot]

I had the same problem with my fuel gauge.

Started with the sending unit, everything was good.

the problem was the connections in the gauge panel, the back of the gauge panel has copper tabs that conduct the electricity to the gauge, they become "tired" and don't make a good connection. gently pry them to make a good connection and you should be good to go.

[stickandrudderman]

The cylindrical senders can indeed be stripped and repaired. I have about a 50/50 success rate.

[scoot]

Bouncing around - I would guess this is a bad contact, possibly at the plug itself.   No low-fuel light - Make sure of this - the light is really dim.

Attached is a little diagram that tells you how to test your sender (out of the car).   You need an ohm meter.  Pins 2 and 3 in my diagram should ground when the tank is empty.  If they don't, that is why your low fuel light is not coming on.  But keep in mind that the low fuel light is EXTREMELY dim.

[rb6667]

I should have followed up on this post earlier since it has been a year ago that my question first came up.  Pleased to say that a good soaking in rubbing alcohol solved the dancing needle problem. 

 I simply covered the small hole on the side with some aluminum tape, and filled the canister up with alcohol and let it soak overnight.  The problem was the float was hanging up on some grunge on the shaft that the float rides up and down on.   

Kudos to Joe for his alcohol trick, and Scoot for the diagram.  I've saved that diagram for future usage.

 

[ja17]

Now if we only knew what version scoots sender was?  The specs are different for at least one of the others.

[scoot]

Now if we only knew what version scoots sender was?  The specs are different for at least one of the others.

My diagram is for the tube-style sender, not the float-style sender.  They are completely different.  I don't have specs for the float-style sender.   I think I also have a little diagram for the fan potentiometer somewhere...