47-55.1 Welding the top and bottom half of the cab together

[Thadious]

So, after sandblasting my cab with crushed glass grit, I've started to notice little pinholes and more showing up and growing around the corner window and below the center back window. Deciding that I wasn't going to do all this work to have the 'unknown' of that back seam and pinholes haunting me, I sourced a second inside cab section, cut it out, sandblasted and cleaned it up.

So, today I cut out the inside cab of my project, and I'm glad I did!

There were far more pinholes than I expected and the joint half of the two sections was heavily rusted out.

My intention is to brace the cab seam from the outside to prevent any movement, layout and cut a new seam section from 14ga steel, then bit by bit cut out the original seam, weld the top and bottom halves together as close to the outside of the seam as possible and slowly work my way around, completing the weld fully. (This is largely due to the common complaint of the seam rusting over the years and messing up paint jobs and continually corroding.

Once the seam has been fully welded, retrace the weld line onto the new brace, cut and weld the new brace section in then install the "new" inner cab, and finally remove the outer braces and clean up the welds.

Anyone have any thoughts or experiences?

Cheers!
Ted.

[dsraven]

if you're gonna go ahead be very carefull of warpage and distortion from welding heat. it sneaks up on you and before you know it it's too late.
have you looked for another rear cab wall?
what year is the truck? I assume it's an AD version due to a seam in the rar wall.
a few pics would help

[dsraven]

I am assuming your plan is to replace the seam, a small section at a time, with a piece of solid steel sheet formed to look like it has a seam in it. then fab up a new inner stiffener that will replace the horizontal inner section, where the two parts were originally joined on the backside (inside the cab behind the inner panel)?
if thats the plan, try to duplicate the original metal thickness to avoid shrinking/stretching of the two parts at different rates and also try hard not to weld too much at a time because the time you save welding fast is nothing compared to the time it takes to get the panel back straight again after. I find it best to have something else to do when welding stuff like this, so you can do a small spot, go do your other thing for a bit till the WHOLE area cools off, then come back and do another small spot, etc etc.

[dsraven]

will you mig or tig the panels?
as you likely know, mig is possibly easier but is harder to do metalworking on as it becomes brittle when hammer dolly is used. tig is softer and more maleable for doing panel work after.

[Thadious]

My thoughts are to brace it from the outside before any interior work is done. This will involve a square tubing U shape that reaches around the back of the cab and around both sides to the back edge of the door. From there, multiple fingers to attach it to the cab right above the seam line (at the round) and a couple angled supports to hold it.

From there, create a cardboard template of the inside seam, re-cut it from 18ga steel (original sheet metal thickness is about 0.025") and preweld the 2" drop down lip to the inside of the new piece.

Next, clamp what's left of the existing seam together and cut out a 6" section, starting in the middle. After each section is removed, grind it as close to the outside face as possible until it just starts to separate. Make sure the faces are clean of rust (the cab was blasted from the outside, so I'm hoping to get to clean metal), clamp the seam tight and tack it. Wait for it to cool. Slowly work outwards 1" at a time. Mig welded, (min heat, 0.023" wire). Continue to work outward.

To be continued...

[leegreen]

I may not be reading this right, but if you are planning to butt weld 14 gauge to the skin of the cab I'd be worried about how to control warping and how you would work the sheetmetal where thick meets thin to flatten and stretch the welds

A simulated seam is tempting, but having the flanges on the seam would be helpful to shrink in the right horizontal radius to match the cab, either with a shrinker or by bending small tucks into the flange. That horizontal radius along the seam line is probably the hardest part to fix post weld if it goes wrong. I think the flange with many small tucks could be useful after the welding to tune up the seam by playing with the tucks to change the curve. you could flatten a tuck with hammer and dolly or deepen one with a tucking fork

I'd cut some good radius templates of the areas on, above and below the repair and use them frequently while welding. Go slow as dsraven suggests but put the templates on frequently and hammer stretch each weld to keep the cab surface matching the template.

cut and butt method could be useful, especially the long section under window

bracing may get in the way. I'd consider doing the repair in sections so the cab holds it's own shape

[Thadious]

The bracing will be on the outside of the cab, simply to hold the shape.

Inside, both of the top and bottom curve to the inside of the cab and have a flange that's about 1 1/2" wide (and the two are bolted together in 3 places. I'm reducing that 'flange' to about 1/8" (one small section at at time) then clamping them together, and tack welding them, one small section at a time. The outside bracing is to help keep the shape. There are only small tack welds (which will be ground off later) holding the bracing in place.

The 18gauge new flange will be welded in place of where the old flange was, where the tack welds all along the seam are. The reason for the 18ga use is that it's just shy of the 2x 0.025" that the top and bottom of the cab are made from originally.

And yes, VERY slow. Tacks only, no long beads, ground and smoothed.

The desire is to repair the rot (in some cases missing entirely), not trash or have to replace the cab (I've repaired a LOT already and not wanting to do a do-over!) and to seal up that seam that many complain about and can't be rust stabilized most any other way.