Fuel Tank Repair
928 gas tanks often develop a crack, on the bottom, just off to the side of the metal cradle that supports them. I've had 2 with just such a problem...but I've repaired both. This is the way I repaired them (and that makes it the *right* way! ;-)
Jack the car up and clean the tank bottom. Inspect it well and find exactly where the crack is leaking.
Run the car almost completely out of gas.
Jack the rear of the car up VERY high. 2 foot up at the jack points. You'll need it to be this high to be able to slide the cradle out once it has been unbolted.
Remove the right rear wheel. Just for more room and more lighting.
There is a metal strap that supports the tank neck. LEAVE IT ALONE! You don't need to drop the tank to fix the crack and this strap will become the only main thing supporting the tank further into my procedure.
Drop the fuel tank outlet shield from the bottom rear of the tank cradle.
Get a BIG, portable gas can. I use a plastic, 5 gallon, motorcycle gas can with a 2 foot long, one inch diameter, flexible, clear neck.
Lay the can down on its side behind the gas tank so as to be able to reach the filler hose of the can up to the fuel tank outlet hose.
With a couple of pieces of wood as "pads", pinch/clamp the fuel supply (from the bottom of the gas tank) hose with a set of vise grips so that remaining gas in the tank is cut off.
Remove the hose clamp from the fuel filter. My cars have filters in this location, so I remove the clamp at the filter, leaving the short ~8 inch long section of rubber fuel line attached to the outlet of the tank.
Plug the now free black rubber outlet hose into the motorcycle gas can neck.
Release the vise grips, allowing the remaining fuel to drain from the tank into the can.
Put your floor jack under the tank, right in the middle of the cradle and set the jack's height so that it just touches the cradle. Don't worry...the tank is plastic, it's empty and it's light.
Unbolt all four corners of the cradle and slide the floor jack out of the way, off to the side.
Drop the metal cradle, push it out from under the car, slide the floor jack back under the middle of the tank and let the tank drop that 1/2 of an inch untill the jack supports it.
You already know where the crack is. It's most likely on the edge of one of the molded "guide" recesses that the cradle snugs into. Scrub the crack with a wire brush and some gnarley sandpaper so as to get a fresh layer of plastic exposed all over and around the crack. Take a piece of tire innertube (VERY IMPORTANT!) and cut a section large enough to cover the crack PLUS about a one inch buffer around the crack.
Get out the J.B. Weld.
With your rubber patch sized and ready, mix the JB Weld and "glop" it all over the crack and out to about a 1/2 inch buffer zone around the crack.
Lay the rubber patch over the JB Weld. It'll stick there pretty well as the JB Weld begins to cure.
*****Very quickly, reinstall the gas tank cradle BEFORE the JB fully cures.*****
The rubber patch serves one main purpose and that is to keep the JB Weld from gluing the cradle to the tank.
The REASON that I say do this as described above is that the JB Weld is not flexible and the clamp that holds the tank is definately applying pressure which flexes the tank. (That's why it cracks in the first place!!!!)...sooooo, we want to fix the crack under installed torque. If you were to completely remove the tank and fix the crack off of the car, your "fix" would itself split as soon as you torqued the cradle back into place.
Eh? Yeah? Hmmmm? Yeah! Pretty smart! [huffing on my finger nails as I buff them on my sweater tied around my neck in fraternity BMOC style!]
How tough is it to remove the gas tank? In the 928OC tips, there is a post to raise the car 2-3 feet. Not an easy task. When removing the tank, have you found it necessary to raise the car this high?
78 5 speed
My jack stands are only about 18" and I had no problem. More tedious than hard. The trickiest part is to get the vent hose between the upper half of the tank and the fill section out without breaking off the connections. Tight!
79 US 5 speed.
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