trunk floor replacement

[roadtrp204]

I came across some trouble today trying to fit my replacement truck floor. I have only seen one replacement part offered and it does not fit the '75-76 strut bumper models. My original floor bends up on the ends to clear the mounts for the bumper struts, while the replacement is the same level all the way across.

This is just a word of caution for those of you late model owners who are thinking about replacing a rusted trunk floor. The replacement can still be done but it would require cutting the center out of the replacement and sectioning it in to the original end humps that go over the bumper strut mounts (if they are not completely rusted away).

The good news is I am using a early style fiberglass bumper so I just cut off the bumper strut mounts and all is good.

[Dave Bell]

Replacing the entire floor... I like it!.. Frankenstein patches are the methods of us cheap guys... Note bar stock re-inforcements of various places as well

- Dave

[Will98D]

I bought my replacement trunk panel from Restoration Design; maybe PP sells the exact same part, but RD is not far from me in MI. Anyhow, the part was really well made, with galvanized steel, and all the correct dimples and impressions in the stamping. For $175, it saves a lot of dinking around with patches and looks pretty original once installed. However, I'm sure the caution about the later bumpered cars still applies, because this one was straight across the back.

BTW, Dave Bell: looks like you did prety well with the MIG avoiding blow-through on the thin sheetmetal. Did you use a backer to help with this (like a big copper or aluminum bar)? I used a small Lincoln with solid wire and C25 gas, and it still was touchy when it came to dropouts. Parts of it look beautiful, like a row of dimes, but in other areas I really could have used that bar.

[74914]

I'd also be interested in any tricks you use to aviod blow-through. I use my Hobart 135 set on the lowest power and almost lowest feed and need to be real careful and weld just in short increments.
Thanks
Ed

[Will98D]

get a big (3/8 - 1/2" x 2" x 6") copper bar (or aluminum) and put it in contact with the metal behind the area where you are going to weld; support it well. when you weld, the copper will pull heat out of the area and also hold the molten puddle in place so that it solidifies as you move away. obviously this is most effective for horizontal position welds. I think an old buss bar might serve this purpose well. Also, you will do better with 0.024" solid wire and C25 (25% CO2, 75% Argon) than with a flux-core wire. I'm no master welder, but I got these tips from one and they are effective. Good luck.

[Dave Bell]

I used to blow lots of holes in sheet metal... but mostly via trial and error I have discovered some techniques and gained experience so that I rarely blow holes in good sheet metal and can now weld badly rust damaged metal, (read thinned out by rust but cleaned up with a wire brush), only blowing an occasional hole.

First, I am no expert, but my experience shows me that blown holes come from areas where the excess heat cannot escape fast enough through the metal and it blows through.

Tricks..
If welding thick to thin, start the arc and build the initial weld pool on the thick metal and with the gun/arc, drag the melted metal down to the thin piece... spending less time with the arc on the thin piece than on the thick piece.

If welding thin to thin

1) If one piece is fresh metal, e.g. patch, and one piece is damaged/thinned... treat the new piece as the "thick piece" as it will take more heat

2) If the situation is tough... no heat sink for excess heat... or some of the metal you are welding to has really been thinned out, then turn down the heat and wire speed and sputter a small bead of metal onto the difficult area... the sputtered "weld" will be crappy but then you can go over it again with normal higher heat and wire speed and the metal you sputtered on will melt in with the new material while acting as a heat sink or buffer.

3) Turn down your Inert gas pressure a little... too much will tend to encourage blow through on tender areas.

4) Don't point the gun/arc directly down toward the metal, point it back toward the already formed bead and weld pool that is naturally thicker than the metal you are joining... Treat the bead as the "Thicker piece of metal" as decribed above and drag metal down over the thinner pieces you are joining. I one piece is newer or thicker metal, point the gun/arc toward that piece as it will take more heat and "pull" metal down to the more tender area.

Normally I use .030 wire even on the sheet metal stuff ... too lazy to change out to a smaller size.. This is what I used on the welds you saw in the photo.... but it does help to switch to a smaller .023 wire size that does not produce as much heat and the weld bead will also be narrower. I keep a couple small rolls of the .023 handy for more difficult areas

I have not used a backing plate for an initial weld, although I hear they can help.... I have used a backing piece of copper a few times to help me fill a hole more rapidly and cleanly.

Now welders who have been trained and really know what they are doing should chime in and correct my amateur techniques and wramblings. I would like to learn more about welding sheet metal myself.

- Dave

[roadtrp204]

The replacement was from Restoration Designs. My friend owns a body shop and the stuff I have recieved from RD is superior to any aftermarket replacement panel I have seen and the fit is as good as OEM.

Dave, sounds like we took the same course in 914 welding. All the techniques you described are the same things I learned along the way. I must be getting better each piece looks better than the last and I am usually the one called upon by my friend to do rear quarter replacements, floor sections, and welds that will remain visible to the customers.

There are three welders at the shop, mine is the smallest and most prefered by myself for the 914 and others for sheet metal. Its a Lincoln weld pack 100 with the gas kit. When I got it I practiced with the flux core wire for about an hour and then went and got the gas kit. I run .023 wire and 25/75 CO2/Ar mix, this seems to work great on the various conditions of 914 metal. If the metal is thick enough (rust) to support a weld I can get it to stick and hold.

To date I have welded:

• passenger seat floor
• R/L logitude overlays due to side jack point rotted away
• patch sections at lower R/L front quarters
• filled in front running lights
• rear trunk floor
• R rear jack poit triangle
• R sail panel
• R rear quarter panel
• battery tray