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Weld Bonding a 55-59 Chevy Truck Roof
You hear a lot about the metal adhesives being used in body shops and restoration shops. The process of weld bonding boasts quicker panel replacement, less clean up, and a more professional looking finished job. There is also a lot of resistance in using new technologies in old car and trucks. But I have to tell you I'm a convert to weld bonding and will be using it more often where it can be used. For the task force truck it will add structural integrity to the parts replaced, like roof skins. Door skins, Corners and any part that does not carry load or support the main structure of the cab.
We have the 55-59 big window in the shop we've been slowly repairing and when it came to the roof we decided to replace rather than fix the problems it had. The old roof was rotted around the rain lip, dented and dinged all over the top and was just to flexible when you pushed on it. Each time we tried to patch it up it buckled badly.
A new roof was needed but we couldn't see scalping a good truck for a roof so we ordered one from Dynacorn. It arrived in good shape and had a nice fit out of the box with only minor tweaking to the cab in the front around the windshield area and the pillars. We took off the old roof, cleaned up the channels and glued and spot welded the new one on. It was almost that easy. It took more time to plan than it did to actually apply the adhesive and spot weld the panel. The pre fitting and cleaning was the major part of the task, It had to be bare metal in the rain lip, the roof lip top and bottom and the under side of the rain lip so the adhesive would stick and the spot weld could be done.
We used Lord Fusor brand 108B metal bonding adhesive which is a medium drying time product taking about 45 - 50 minutes to setup and 8 hrs to a full cure. It can be spot welded wet or dry, We welded wet. Below are some pictures of the process.
We cut all the way around the roof edges to get better access to the rain lip. We wanted to just pop off the spots and not mangle up the edges to much. At this point we treated the inner roof with rust converter to add a little protection for the next 50 years.
Once the major portion of roof was off we worked on the pillar area and windshield area. We patched up the radio speaker hole and starightened the lip.
This is where they used lead as body filler. It comes out easily with a torch but there is always a thin layer of lead remaining which must be removed and if you use lead filler to replace it remember that it can't be lead free body solder. Lead Free has a higher melting temp than the base lead you have on the cab.
With the roof skin fitted and test fitted we tried putting the roof on with a "one drop its on" kind of technique. Reason being that once you apply the glue you can't lift it back up to make adjustments, once its down its down so the test fits are important. The rear was going into the rain channel first and then the front would be lowered and slid into the pillars, clamped around the windshield edge and then around to the back. With all that figured out we laid down a 1/2" bead of the Fusor 108B and set the top in place. From this point you have about 40 minutes to clamp up the roof skin at 70 degrees, hotter temps take less time.
There are tiny glass beads in the adhesive mixture that keep the correct bond thickness. You could over clamp so use just enough pressure to displace the glue and hold the skin firmly in place but not so much as to dent the metal or crush the beads. Your not pulling panels into place with the clamps the roof should fit nicely with no big gaps or twists before you glue it so clamp pressure should not be an issue. Once we got all clamped up and wiped the excess adhesive off we started spot welding at the windshield lip.
The recommended minimum spot weld distance is no less than 4 inches apart. Try not to go over old spot welds or welded up drill holes. You want to spot on clean flat metal. Any closer than 4 " you run the risk of burning out the adhesive between the spots and severely weakening the bond.
We did need to bend out the rain lip a little to get the spot welder electrodes on the channel.
All that's left is to weld the roof to the dog leg part of the front pillar and fill the area with Allmetal and apply seal sealer in the rain channel.
The spot welder we used was an HTP QuickSpot II. A very nice welder for the price of $595. It has several settings for metal thickness up to what they call 2+2 mm for a total of 4 millimeters, two 14 ga pieces, heavy enough the spot floor panels if you buy the longer electrodes. It has a pulse setting for burning through adhesives and primers, and an adjustable timer that automatically shuts the welder off at the correct weld duration. No trying to hold the tongs closed and flip the switch to start and stop the weld. It will weld 180 spots per hour on 20 gage.