TheSamba.com :: View topic - Sender units keep breaking, any ideas why?

Tue May 06, 2008 8:39 am

I have just fitted another fuel sender unit into the tank on my 412 and it worked after a good clean up of the connections.

Went for a drive this morning, it showed over full as the tank is full but after about 5 minutes it stopped working.

When I got home I popped the unit out and as I suspected the resistance wire that runs through the inside of the cylinder has snapped.

This is the third unit this has happened on and I'm either very unlucky or there is another problem that I am missing somewhere that is breaking the wire. Spoke to someone earlier today and he suggested that it might be something to do with the little box behind the gauge, can't remember what he called it :?

Anyone know what might be the problem? Could it be a short circuit in the fuel gauge to sender wiring that is using the resistance wire as fuse or is that impossible? I'm stumped...

Sun Jun 01, 2008 10:37 pm

What year is your 412? I'm going to guess early '73 if you have the bolt-in (screws to mount it) sending unit in the tank. My late '73 has had problems with the gauges failing, and I learned that the early-style gauge wouldn't work.

If you can pull your clock unit out of the dash (you'll curse doing this task, I know I did), see if there's a little tin box with wires going to/coming from it before the gauge. I've heard people refer to this as the vibrator block, and some as the voltage stablizer. The latter sounds more likely. If it does, this is the type of gauge that goes with the late-style sending unit, which was a twist-lock mount into the tank, and also has the float attached to a swinging arm instead of within a cylinder.

Also, a good indicator of what kind of gauge you have (early or late) is that the early clock gauges had two indicator lights for the turn signals (and matches up with the cylindrical sender), and the late '73 ones had a single indicator light for turn signals (which matches to the arm/float style sender).

Try this: disconnect the wires at the sender, as well as the gauge. Take a multimeter and test the wires for continuity. If you have the option, set the meter on the audible setting (so that it beeps when you touch the pos. & neg. leads together). Put the leads on each end of each wire to make sure they are not broken (should beep). Then try puting one lead on the end of the wire, and one end to the body of the car (a good ground).......only one of these should 'beep' or show continuity. If both do, then it's possible that your power wire is grounding/shorting out along the way.

Travis

Mon Jun 02, 2008 4:47 am

wshan,, we have geeve many information for that on ,,stf,, the little small box ,, on the guage is ,,,voltage regulator ,, or vibrator is the samething ,, and the fuel sender work in sérial with the litle box ( samething chrismas light ) and if you d,t have the good model for the sender, the résistance inside of this sender can burn,, first look if you have the original guadge on your car,, ( they are the same for70-71-72 and différent for the 73-74 ) plus look for the sender , they are différent too,, for the same year,, you can buy on the market , many différent tube fuel sender ,,( example for type1 and 2 and 3 ) look if you have the good model for your car,, witch the good résistance inside the sender ,,bb412

Mon Jun 02, 2008 6:05 am

Firstly my 412 was registered in Oct 72 and is UK spec (RHD).

I have checked behind the gauge and there is indeed a little tin box fitted there, ( the metal box with the orange back on it?)

as for the sender unit itself my tank seems to have only the fitting for the tube one with the part number 411919049.

I have managed to source another sender unit and will check out the wiring before I fit it this time, although it has been suggested to me to attach another wire from one of the sender unit screws to the bodywork on the car in case the tank itself is not earthing properly? ie hit a bump and it shorts out??

Is there a way to test the stabiliser at all or does anyone know if it is the same as fitted to another Type so I can change that as well if I need to?

Tue Jun 03, 2008 6:53 am

Looks like you have a '74 gauge with voltage stabilizer connected to a '73 and earlier sender. I'm not sure if they are compatible and could be source of problem... Has the gauge been replaced?

PS - Travis, I've been emailing you...

Tue Jun 03, 2008 7:04 am

I don't know Bill is the short answer.

Trying to get to the bottom of it though.

Beginning to look like either the tank or gauge has been swapped though :?

Tue Jun 03, 2008 7:22 am

The '74 tank wont fit in an earlier car unless the sender access hole in the sheet metal is moved. So, most likely the clock has been swapped.

Tue Jun 03, 2008 7:35 am

Well then, as the access panel for the sender unit is central and lines up with the sender, looks like the guage may indeed be the culprit.

Can the guage just be swapped for an earlier one without having to change the clock on the dash? and would it need to be from another 412 or would a guage from another car such as a Beetle or bus fit?