Gas Tank Leak Woes...(dun dun duuuuun)

[MadMax]

In crawling about, I discovered a leak in the gas tank where it mounts to the bumper of my C303. It was not hit. The leak was caused through ignorance and negligence, so I wanted to share this is the hopes of preventing it happening ever again. Bad repair jobs are everyones problem!

The tank mounts to the bumper and sides of the frame with 4 bolts; these pass through corresponding flanges on the tank and frames, one facing up and the other mating to it from above. These flanges form a sort of U-channel pocket for strength. Normally, water would get all over these, air would get to them, they would dry and last a long time.

The previous owner filled those pockets with some kind of rubber and smoothed it over, in an attempt to prevent water getting in there. The result is the exact opposite: water has been trapped in there and completely rotted it out, causing (eventually) failure of the metal at the flange weld and a leak.

Here is the flange assembly (the tank is on the right, the dark coloration is gasoline):


From above looking down you can see the rubber he filled in the flange "pocket" with, covering the bolt heads. Its clearly rotting away and as it contracted the edges peeled back, letting water in and keeping it there. All the metal surfaces that were covered have serious cancer oxide.


Once the rubber has been removed and the pocket cleaned and wired out, you can see the remains of the bolt heads, now solidly fuzed to the bumper bracket.


This is the same bolts from underneath (covered in corrosionX). Notice the condition of the exposed nut and washer, threads vs. the "protected" rubber covered bolt heads in the previous pic. These can be worked with.


So, aside from causing a leak in the gas tank, it has taken me 2 and a half days to drop the tank BEFORE I can get to even soldering the damage. He even put these filler pockets on the front mounting flanges as well, which I can only assume was done from above when the bed was replaced, as it would be almost impossible from below. Please dont do this to your trucks! Let the water get to them. Let the air get to them to dry the water. Repeat.

On a positive note, I'm going to have a nice restored tank, and Im running my own copper fuel lines in place of the old metal and rubber frankenstein mess thats on there, back where the OEM lines are supposed to be and adding another fuel filter at the tank.

Good times.

[Jimm391730]

I've used cold galvanizing compound, both in spray and brush on form. Never seen any rust until many years later when the zinc has dissipated and then another coat solves it again. Total rust removal is not necessary, it stops iron oxidation, period, even a short distance away from the application meaning scratches or pinholes do not rust, either. https://www.rustoleum.com/product-catal ... ound-spray

[stiffler4444]

I've used cold galvanizing compound, both in spray and brush on form. Never seen any rust until many years later when the zinc has dissipated and then another coat solves it again. Total rust removal is not necessary, it stops iron oxidation, period, even a short distance away from the application meaning scratches or pinholes do not rust, either. https://www.rustoleum.com/product-catal ... ound-spray

Nice product, I'll be getting some of that!

[audiocontr]

I thought this message was specifically for David

[David Dunn]

Lucky he can't spell... it's the same as saying Beetlejuice 3 times

[MadMax]

You know, hey, if you can banish the demons from my truck, that would be great.

[MadMax]

Today I finally got the last of those rusted tank bolts cut off and dropped the tank. I managed to save the adjustment springs in the bolt assembly, which are very good steel like mini coil springs but had to finally make my own saw blade for a small jigsaw that would fit in the limited space I had to cut the bolts. Bolt cutters, handsaws, wrenches, ratchets, air wrench, chisel and 5lb. hammer...nothing was working, and I could not use a grinder or flame because there was still gas and fumes in the tank.

The saw finally worked after I cut down a sawzall blade to about 2", notched it to fit the skil jigsaw and was able to cut through with that using about a 1.5" stroke. No fun on my back in the dirt!

But YAY gas tank is out. *whew*

[NEWFISHER]

Will be nice to see it on the road again.

[MadMax]

Wanted to post some pics of the progress on the gas tank leak. I had mentioned the rubber the previous owner had put in the mounting brackets; Below you can see the rubber (top left) and the damage it caused to the brackets. The areas where no rubber was applied were fine, hardware came off without a problem. Where he put the rubber it has taken me days already to fix, with more to do.



To take the gas tank off, I thought it would be easier to remove the mud flap to get it out of the way. In removing it, I noticed another brilliant move by previous owner guy: He extended the rubber of the flap up above the mounting point, so it would sortof curve up into the wheel well, I guess to "catch more mud." The effect it had was to trap any water coming from above or behind the truck down between the bumper and the flap, rusting it out. Genius!



Here is the rear of the tank where the leak was above the mounting bracket; The damage seems to be from a bad earlier repair. You can see from the inside (bottom right) there is no rust inside, so thats good at least.



The fuel filler can assembly also had to come off to remove the tank. In cleaning it up, I discovered yet another brilliant repair job. Knucklehead pushed JB weld up inside the lid of the filler can to hide the rust and simply painted over the top with undercoating. The can lid and gasket/spring assembly are completely shot.



I've decided to fabricate a new housing for the fuel filler neck/cap. I am making a box for the small recess in the body where the old filler can used to sit. I will mount a new neck to this at about a 45 degree angle, connect to a rubber elbow and run the line through the underside of the body and into the tank along the old route.



This is a bit more than I wanted to take on sitting in the dirt next to my driveway, but it needs to be fixed before winter.

QUESTION: On top of my leaf springs in back is a metal cup which appears to impact the rubber bumper when the suspension moves up high enough; On one side, the metal cup is there, on the other, it is missing. Any idea what that is called and where to get one (or a reasonable fascimile)?

[one2many]

That's the perch for your bump stop that's missing, its job is exactly as you described. From the photo it looks like it might have completely rusted away but that's a bit hard to believe. If you don't want to fabricate something to do the job, (you have the other side to go from) you could contact coatexab@hotmail.com in Sweden, I'm pretty sure Joacim will have something for you there as he's been wrecking and dealing in the C30xx series for years.

On a side note. Are the U bolts around your spring packs badly rusted or are they just covered in crud and or the waxy corrosion inhibitor that gets sprayed all over the under carriage of many Volvos? Its hard to tell from the photos but if that is rust/pitting I see then I would think about changing those as well. They have massive load/strain on them and it could be pretty nasty if one snapped while you driving. Not to mention the cost of a far from home recovery. Any decent spring works that works with trucks would be able to make them pretty easily or Joacim may have a good used set.

All the best

[MadMax]

Finished the repairs to the tank and filler cap, its ready to re-install finally!


2 coats of primer and very heavy application of 3M undercoating applied


New fuel-safe hoses and constant-tension monster hose clamps.


restored the sending unit, gas cap lid and assembly, cut out some new gaskets.


This is the main leak repair near the mounting bracket. Tap & Die to thread out the holes a bit larger, then tinned the threads on small brass screws and put them into the holes. I used 2 different solders, one with a slightly lower melting point, so I could tin as much of the area as possible, then build up the thickness in the areas where it needed it most. After doing the initial layer, I let it cool down and then switched to the other solder so it would apply and fuze in thicker amounts without melting the layers below it completely. It was a delicate dance of the propane torch. I crooned the charms and made the magic.

It is not a pretty sight, no sirs. However, it is never going to leak again there, and its almost completely OEM.

[Jimm391730]

Nice job. Not to take anything away from your work, but I would have brazed the area closed - "soft" solder does crack at times, depending on mechanical stresses. The bronze in brazing rod is much stronger than solder in comparison; since you were working with a torch the higher heat needed would not have been difficult or a problem. I've successfully use brazing to fix some deteriorated exhaust systems (with additional steel sheet metal patches) because the bronze, like the solder, won't ever rust. If I have to use solder (due to heat concerns) a good 3-4% silver solder is twice as strong, mechanically, as soft solder and is just as easy to work with. Regardless, it looks like you do very good work and I don't think you'll have any issues with that tank. Did you use the cold galvanizing primer under the black finish coat?

[MadMax]

I completely agree with you. I went back and forth about brazing it, as I had the materials and tools. However, the heat required for a proper braze would have required redoing the inside of the tank as well with some kind of paint or liner. There was no rust stain or rust at all inside where the pinholes were and the rest of the interior was actually in fantastic condition. Soldering the brass screws into the threaded holes and layering the solder to add thickness to the exterior wall did not require as much heat, so when it was finished there was no damage or discoloration at all inside. In the end though, the final decision was mostly due to my lack of experience with brazing, whereas I am familiar with soldering. I did not want to botch things up, which is distinct possibility in all things.

I did not use cold-galvanizing primer specifically. I did use 2 coats of good primer, then 2 coats of flat black, then 3 coats of undercoating, with 24hrs between all coats and 48 hours between types. I used both a old spool of 50/50 lead solder and a silver solder.

[Jimm391730]

Ah, the interior liner. I hadn't thought of that. Although we all talk about the Pinz's "Red Death" of the liner, for some reason I always just expect a bare steel tank. Sounds like you chose the correct repair. Again, a great job.

[MadMax]

Here are some additional images of the fill/layering work with solder to fix the damaged areas of the filler can lid assembly:



I used brass sheet to form the two halves of the top of the lid and formed the edges to make a cap for each side of the strap. I tinned the brass bits on the underside and the top of the lid, then flipped it over and heated it from underneath to melt the tinned bits together. After that I began to just fill all the holes to make sortof plugs that were larger than the holes. It was really ugly but solid and would be underneath the spring gasket so not seen, but it is much stronger than it was and sealed. The thin plate which held the gasket assembly had lots of paper-thin areas and a large hole as well, so I did the same process with a copper disk I cut out and soldered in place to add strength and seal the hole.



The filler neck, can and mounting bracket were all in really good shape, but all the rest of the components needed work


This is the final assembly before primer, the new rubber gasket is not in yet but you can see the copper disk inside the lid. I did not want to replace the piece with just a flat metal disk, as the original piece had a lip pressed up in the middle so that the rubber gasket had a seat when it was fastened to hold it in place. I also liked being able to use as much or the original as possible.