Traction Avant Petrol Tank Replacement.

Another Reasonably straightforward job.

Ever since we have had the car, when filling the petrol tank there was a strong smell of fuel for some time until the level fell by driving the car so a decision was made to replace the tank.

It is simply held in place under the floor of the car at the rear, under the boot with 2 straps bolted together.

A new one was duly ordered from Fransen's in Belgium along with a new pickup pipe (which proved to be a good idea) as whilst the tanks are the same depth internally, the old pickup pipe was shorter than the new one by 12 cm and was only 17.3cm to the end of the strainer so that means 13.5% of the fuel which = 6.75 litres remained in the tank below the pickup.

With the new pickup there is only 3.75 litres of unusable fuel below the pickup

New Petrol Tank      Old Tank Removed

Once removed it was obvious where the petrol smell was coming from, the joint between the breather and downpipe had failed. There was no way to actually see that with the tank fitted as you can see in the image below as it's right up under the rear seat.

The old tank is quite a bit lighter than the new one and apart from that joint, is in good condition and clean inside and looks to have been galvanised on the outside.

Breather Pipe Joint      New Tank On Car

Potentially I suppose that could be repaired but I don't know how it was originally attached. The new tank has a definite weld where the breather connects with the filler.

The old one may have been soldered or brazed but it's hard to tell. Anyway replacing it meant that the car was only off the road for a couple of hours.

Fuel Gauge woes

Since acquiring my Traction Avant I have always had a problem with the French Fuel Gauge System, basically, it didn't work or had a mind of it's own and the pointer waived back and forth like it was possessed even after I replaced the sender for one I bought in France in 2014.

Having read some old articles from the Traction Owners Club magazine 'Floating Power' on the Jaeger system and how it works I now have an actual working gauge.

Basically the system is 2 opposing coils, 1 in the tank level display and 1 in the sender unit. When the resistance in the sender increases, the needle in the fuel gauge drops down to show less fuel in the tank. Understanding that basic layout helps a lot.

I followed the technical guides and using a multimeter set at 200 oms, found the sender itself was fine at 120 ohms across the 2 terminals for the internal resistance coil.

Next, putting the meter onto 1 terminal and the other to 'earth' (the body of the sender) the resistance also varied correctly as the internal arm 'wiped' across the coil increasing the resistance as the arm moves away from the terminal.

Sender Test 1     Sender test 2     Working Gauge

So it was all working fine on the bench, but would not work when refitted back in the car so could it be the actual gauge or the wiring between the 2?....

I finally realised what I had actually done wrong (eventually) with one of those 'penny dropping' moments.

On the 3 retaining screws securing the sender unit to the tank, I had fitted a fibre washer under the heads to avoid any potential leaks so the earth wire was only touching the screw itself which was going right through the centre of the sender, into the tank top so the earth wire was not actually earthing the sender unit but the tank as the sender is isolated from the tank by the rubber/cork sealing gasket.

I removed the fibre washer under the earth lead and bingo, the gauge works again.

So simple a thing, but ever so frustrating trying to figure out why it wouldn’t work but the old guides got me there eventually.

My fuel gauge sender is a replacement unit running on a 12v conversion car (Slough cars have a different set up). These modern units have only 1 contact arm against the coil internally and not 2 as per the originals described in both articles in case anyone gets confused. Also the one I got from Renel in France has a ‘Q’ and tested label and a date stamped on it and is sold as suitable for 6 or 12v.

The one I also have from CTA has nothing on it (and cost more…..) so as with all after market parts, the quality does vary as does the brain of the car owner.

Last Update: 20th April 2018

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