PROCEDURE: Fixing broken bolts on the fuel tank where the fuel sending unit attaches:

[artguy]

Section 1 of 4:

Quick Summary:

http://www.captive1.com/mrk/1_normal_broken_w.jpg

http://www.captive1.com/mrk/2_bolt_repair_diagram_w.jpg

A: Drill a small pilot hole as straight up and down as possible.
B: Drill a larger hole, the necessary size for the new bolt.
C: Thread the hole from the bottom up.
D: Install the new bolt with rubber washers


Detailed Explanation:

The Problem: You need to remove the sending unit from your fuel tank and you break a bolt while trying to get it off.

In my case, I soaked all eight bolts with penetrating liquid for five days before I tried to loosen them. Six came loose, but two broke loose from the tank at the rivet/weld underneath. The nut and bolt just spun when I turned it. So to get my sending unit off, I needed to break the bolts intentionally…and then repair them afterward.
http://www.captive1.com/mrk/3_rusty_closeup_w.jpg

I had two bolts that needed to be fixed. Note the rivet/weld underneath:
http://www.captive1.com/mrk/4_two_broke_one_good_w.jpg

[artguy]

Section 2 of 4:

I drained the tank, made sure my life insurance was up-to-date, and commenced drilling holes into my gas tank while it was 20ºF outside.

First step, I used duct tape to generally seal the hole. I also wadded up duct tape and stuck it in the tank, under the two bolts, to try and catch as much metal filings as possible when I drilled through.
http://www.captive1.com/mrk/5_preparation_w.jpg

Next I used a hacksaw blade to flatten the broken bolts as much as possible. You could probably do a better job with a Dremel saw or similar device…I didn’t have one.

A flat, level surface, on the broken bolt, is essential for drilling a straight hole.
http://www.captive1.com/mrk/6_using_hacksaw_w.jpg

The existing bolts take a 10mm nut. I wanted to utilize the round collar at the base of the broken bolts, so I chose to go one size smaller for the replacement bolts (8mm nut). You will need a quality metal drill bit and the thread tap for the appropriate bolt size. I also used a smaller metal drill bit to make a pilot hole first. This made the drilling much easier.

Use a metal punch to dent or scribe a dent on the bolt. This will keep the drill bit from wandering. It’s important to drill as straight up and down as possible. Take your time and be patient. If you drill at any kind of an angle, your new bolt may not fit through the sending unit’s hole easily (this happened on one of mine).

Here is the broken bolt after I drilled the new hole through it. Clean up the metal shavings as much, and as often as possible, to minimize what will fall into the tank.
http://www.captive1.com/mrk/7_filings_after_drilling_w.jpg

Once the holes were drilled, it was time to tap the new threads. The round collars on mine were spinning, so I used a vise grip pliers to hold them as I turned the thread tap.

If you’ve never used a thread tap, they are easy to use, but unforgiving. Turn it a couple of turns, back it out, and clean it off. Then do it again a little further. Don’t force it. You should “feel” it cutting the metal somewhat easily. If it gets hard to turn at all, stop and back it out. You can break the cutting teeth easily. I have two taps now to prove it.
http://www.captive1.com/mrk/8_vice_grips_threader_w.jpg

[artguy]

Section 3 of 4:

This shows the tap all the way through and finished:
http://www.captive1.com/mrk/9_tapped_through_w.jpg

Here you can see the new threads:
http://www.captive1.com/mrk/10_finished_threads_w.jpg

You might be wondering, “Why go through tapping new threads? Why not just drill a hole and slide a new bolt through and put a nut on top?”

The problem is that you have no way to hold the bolt in place while you install the sending unit. You need the threads to “hold” the bolt so you can install the sending unit over it, put the nut on, and then tighten it down.

NOTE: Technically, when you put the nut on the new bolt, the motion of tightening the nut will actually turn the bolt back out of the threads. There isn’t much you can do about this, and fortunately it normally won’t be a problem.

The problem happens if the threads on the new bolt become damaged in any way, which then makes it hard to screw the nut on. This happened to me on one of my replacement bolts. I didn’t drill the hole straight up and down enough. When I put the sending unit on, I had to force it over this new bolt and that damaged the threads on the bolt enough that the nut didn’t go on nice and smooth. So I had a hard time tightening this one.

Here I have the new bolt screwed slightly. I put rubber washers on to give it a seal.
http://www.captive1.com/mrk/11_new_bolt_visegrip_w.jpg

Here is the new bolt completely installed and tightened from inside the tank. Note the inset picture. It shows the new bolt (hex head) and an old bolt’s rivet connection:
http://www.captive1.com/mrk/12_new_bolt_w_old_w.jpg

[artguy]

Section 4 of 4:

Here I have both the replacement bolts installed:
http://www.captive1.com/mrk/13_two_bolts_installed_w.jpg

Here is the new gasket installed over all the bolts, included the two new ones:
http://www.captive1.com/mrk/14_gasket_installed_w.jpg

Finally, here is the top of the new sending unit all tightened down. The new bolts are the two at the top, closest to the hoses:
http://www.captive1.com/mrk/15_sender_installed_w.jpg

[Dave M]

Well done and very nice write up. Your handle is meaningfull.

In order to prevent the new 8mm bolt from backing out (other than using a lock-tight or equivalent product and waiting), one could thread an 8mm nut onto the bolt prior to inserting and then use it to lock the bolt in place. Difficult to explain, easy to do ;)

Dave M

[Dave M]

Very nice. But I have never seen so much rust on a car here in Japan in that section, usually zero rust.
Except from cars driven in some islands like Okinawa (subtropical climate) and in the northern part on Hokkaido island close to Siberia where there is a lot of snow for a long period each year.

Or, a nice Canadian sending unit :D

http://img.photobucket.com/albums/v11/dave_macisaac/Bimmer/Fuel%20Pump/DSC00506.jpg

[Ross]

Nice fix.
the dremel isn't a good idea though, sparks and all.

[shogun]

Very nice. But I have never seen so much rust on a car here in Japan in that section, usually zero rust.
Except from cars driven in some islands like Okinawa (subtropical climate) and in the northern part on Hokkaido island close to Siberia where there is a lot of snow for a long period each year.

[2fast]

Man thats rusty! mine is made out of plastic, great write up.

[uscharalph]

Nice job. Hopefully I'll never have to use this writeup. LOL!!!!