Everybody knows it's possible to convert your vintage 1953-56 Ford F-100 small window pickup cab to a big window pickup cab with relative ease. All you have to do is buy an aftermarket kit and either install it yourself, or have it installed by a capable body shop. However, when it comes to doing the same thing to a classic, Second Series '55-59 Chevrolet or GMC, it's a little more complicated, but not in the least bit impossible.

"The basic principle is pretty much the same with both the Ford F-100 and the mid-'50s GM light duty trucks," commented Cimtex Rods' Darrell Cimbanin. "Both of these cabs feature dual wall construction and are easy to work on. The only difference is that no one out there in the automotive aftermarket offers a big window conversion kit for early Chevrolet or GMC trucks."

So what's a mother to do? The good news is that there are plenty of '55-59 Chevrolet/GMC big window cabs sitting out there in junkyards (especially in the West) that, sadly, may only be good for one thing, their big back windows.

"These '55-59 Chevrolet/GMC cabs usually suffer from seriously rusted floorpans and body rot on the lower quarter panels. The good news is that when it comes to the rear window area, early Chevrolet/GMC trucks seem to exhibit little or no rust damage, and you can usually buy the rear window clip from these old cabs for approximately $250!"

However, Cimbanin cautions would-be big back window conversion specialists that in order to do the job right, it's necessary to make sure you also receive the inner wall substructure as part of your classic Chevrolet/GMC big back window clip.

"You need this piece to strengthen the cab's outer wall," said Darrell. "On small window cabs, the surrounding sheetmetal area provides the cab's rear wall with all the necessary strength it needs. However, with a big back window model, that strength is gone, so it was necessary for the factory to provide an inner wall to shore up and strengthen the back of the cab."

Installing one of these big back windows is pretty straightforward. First, you have to remove the pickup bed in order to gain full access to the back of the cab. Removing the gas tank comes next, as you're going to be working in a "hot" area. And finally, removing the small back window glass and the factory bench seat pretty much clears the way for reconstructive surgery.

First, our installers draw a cut line around the inside circumference of the truck cab's back window area, remembering this is double wall material. Basically, the cut line is drawn along the body and door jamb seam lines using a black felt tip marker.

With that done, the next order of business is drawing a cut line around the outside circumference of the small back window. Darrell draws his cut line just a tad above the stainless steel exterior trim mounting holes on the cab to allow for enough material to lap over.

However, just prior to actually cutting into virgin sheetmetal, the Cimbanins first reinforce the lower inside section of the cab's rear wall with three pieces of steel rod in order to maintain the rear wall's shape during the crucial cutting process. With that done, Tim Cimbanin tackles the cab's interior using a Sears Craftsman electric cutter.

Once the interior cuts have been made, it's time to tackle the outside of the cab. Cimbanin starts from the bottom trim line and works his way around the circumference of the truck cab. Once the cuts are made, the small back window panel can be easily removed.

The next order of business is trimming away the excess material from the outside of the donor clip. First, the Cimbanins draw a second set of cut lines, only this time just below the stainless steel trim mounting tab holes so the sheetmetal overlaps when the two pieces are joined.

With that done, the inner sheetmetal is again trimmed to size following the cut lines drawn and cut using the old panel. Once trimmed to satisfaction, all that remains is to fit the new panel into the opening. Obviously, some minor trimming and fitting may be necessary.

Once satisfied with the overall fit, our installers begin tack welding the new panel in place, working center out. Of course, this is followed with final welding, and then it's time for bodywork and paint.

When the job's completed, you'll have a big back window cab you can be proud of at a cost of around $750, new window glass and weatherstripping included.

Cimtex Rods
P.O. Box 205
TX  76537
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