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I did this over the summer & never got around to posting, so hopefully I haven't forgotten too much. There are several different sending unit designs. This is for a 1990.
The last time my fuel gauge needle started jumping around, my garage said they tightened the grounding nut behind the gauge to fix it. That was about 3 or 4 yrs ago. This time the grounding nut was still tight, & after a few days of erratic behavior it finally died with the "low fuel" light constantly lit. I called around for a new sending unit, but the best site-sponsor price I could find was just under $100. I called the local Saab boneyard & the guy told me he had a few used units at $30 each. It's such an easy job to R&R, I figgerd a used unit at 1/3 the cost of new would be a good gamble. When I got there, he had 3 different C900 models & none of them fit my '90's connectors! Oh well. I decided to try I fix it myself.
I carefully pulled the loose parts out of the tank. On my '90, the sender has a wire-wrapped aluminum center post press-fit into the plastic top cap. This wire captures a flat metal strip at the top of the post, which is soldered on the other end to one of the connector plug contacts. When the tube came out of the cap, it must've dangled by this flat strip until it finally tore the metal & killed my gauge.
The plastic bottom cap is held onto the bottom of the aluminum tube by a press-on "star washer". When you pry this washer off, it jumps! Wear glasses & keep one hand over washer to thwart its escape. This washer also captures the housing between the two end caps. The float slides over the wire-wrapped tube & has a slinky-like coiled wire (ground?) soldered to another connector plug contact. This thin wire was the only thing connecting the top to the bottom, so be careful when pulling the unit out of the tank.
There was another aluminum tube captured in between the two end caps, with a plastic tip on its lower end & two wires exiting the top. This made up the last of the three connector plug contacts. I'm guessing this is the "low fuel" measuring portion of the unit. The float has a guide slot that fits around this tube & keeps it from twisting & winding up (& breaking) the coiled wire.
The first fix I tried was a 2-part epoxy to hold the aluminum tube into the plastic top cap. It held for about a week before the "oxygenated fuel" we have here softened it up enough to let go. *sigh* I needed a mechanical fix, but I didn't want to worry about screws loosening up & backing themselves out. I decided to use a (very) small cotter pin.
The "low fuel" tube & the coiled wire were still attached, so that added another dimension of fun to the project. I cleaned out the softened epoxy & pressed the tube into the cap. It's easy to tell how it aligns 'cuz the two torn ends of the metal strip fit together. The drill was too large to get a straight shot across the press fit section, so I had to drill thru one side & then the opposite side at slight downward angles. I fed the cotter pin thru with a small needle nose plier & bent the tines over. Then I soldered the ends of the torn metal strip together, lined up all the parts, & pressed the star washer back over the center tube.
I must've pressed the center tube in farther than it was originally, 'cuz now there wasn't enough length on it to allow the washer to grip the bottom end. The "low fuel" tube, which is captured between the two end caps, was preventing the caps from fitting close enough together. This was easily fixed by shaving the top end of the "low fuel" tube down by 1/16". The aluminum was soft enough that a utility knife worked just fine for both cutting & chamfering the tube. Everything went back together beautifully.
posted by 146.82.1...
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