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Old 03-12-2018, 10:26 PM   #6
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Join Date: Nov 2010
Location: calgary alberta
Posts: 2,642
Re: Looking at buying a 1955 GMC, common rust spots?

-eyebrow above window, mice like to nest inside truck in that area so their nest contents attracts water and rusts out the area. the new part comes with the roof attached unless a supplier has wised up and is selling the underside part
-area of the roof all the way around cab just above the rain gutter. may look good but check for soft spots especially if there are low spots in the gutter
-area around the rear window. check for soft spots. water stays behind the window rubber and causes rust out
-area around the windshield rubber, usually at the lower rear corners, same scenario as the back window. may have to lift the rubber some to get a good look at the pinch weld
-front side cowls, behind the front fenders. water collects in the cowls from debris collected in the side cowl area. they have drains but the drains plug. the water collects and builds inside the vents until it comes through the kick panel vents and spills out onto the floor. from there it sits and rusts the floor and hinge pillar vents. if the floor looks at all like it is sagging in the area around the pedals, or from the seam in the floor forward, then check the front cab mounts under the floor. open the vents, remove the vent covers, remove the vent door, look inside with a mirror and a flash light. also look up from below to see if the hinge pillars and front fender mount are intact and solid
-front cab mounts, see above
-front hinge pillars, see above. the water comes from the floor and drains into the hinge pillars. there is a panel inside the door that comes off so you can see inside and down. front hinge pillars are several pieces. check the online suppliers for pics
-cab steps and rocker panels. see above. water from the floor collects there as well and rusts things out. these parts are all interconnected so it can make the door hinge pretty unstable
-door rear hinge pillar lower section. stuff, like rags etc, gets dropped into that hole behind the door pillar and then that area rusts out.
-rear cab corners. there is an inner and an outer. pretty common repair that may have been done somewhere along the line before you got the truck. sometimes these corners are not put on very straight and may be full of bondo or fiberglass, steel wool or cement (yup, seen it)
-rear cab mounts. check under the cab where the cab mounting bolts go through. this area is like a sandwich of steel with a through bolt. it is common for the sandwich to become stuffed with dirt and it tends to stay wet for awhile. a common area for rust and poor integrity. mine was basically just layers of rust with a bolt through it
-there is an area under the fuel tank and above the rear cab mounts that has an L shaped brace to connect the floor and the rear cab wall. pretty common area for rust because under the tank is sort of a well area and also collects old gloves, rags etc over the years. the L shaped bracket is a build it yourself deal as I haven't found any in the aftermarket. while there also check the pinch weld for the back wall to the floor.
-the front fenders usually rust out around the headlight buckets and the eyebrow above. also around the rear lower mount area behind the tire. there is a vertical reinforcement part on the backside of the fender for stability and it also has the lower mounting nut caged in it. the area between this and the outer skin of the fender has a tendency to hold debris and rusts the area out. the upper rear bolt, near the cowl, also has some reinforcement behind it and has a tendency to rust there as well.
-the cab relies on the integrity of the front and rear mounts for stability. the long term door fitment can also have a bearing in these mounts because the cab can be allowed to flex, to a degree, if these mounts are not in tip top shape. once the cab and doors are installed and fitted then the rad support would be the next item that needs to also have good mounts because the fenders use this height as a guide. the fender to door gaps are adjusted by installing shims under the front cab mounts or the rad support mounts. it is imperative that these areas are solid if you want to keep the doors adjusted properly and have the door to fender gaps consistent. the other item of importance when talking about door adjustment and gaps is the trans cross member. a lot of these have been removed over the years to accommodate a different engine/trans combo. the trouble comes when a frame stiffener of some sort is not placed near the area of the cab mounts. with no stiffener the frame is allowed to spread apart or come together and this becomes an issue with the cab location. cab location affects door fitment and door to fender fitment.
anyway, check the build threads for the 55-59 trucks and you will likely see what I am talking about. also, an idea is to see what replacement panels are available online and check those areas closely on your truck. the panels are built because those areas commonly need rust replacement panels.

good luck, post up some pics of the project if you end up buying. I suggest to take a few notes of the most common areas and check there for sure, but also take a pair of safety glasses, a clipboard and pencil (they write upside down) and go from one end of the truck to another. write down what you see for problems. if you plan on doing a rebuild to stock also check the front end and steering parts, springs, shock mounts, park brake parts etc etc

keep in mind Orrieg's post about costs compared to a new cab. my cab was really bad, worse than first thought once it was apart. if doing it again I would be better off buying a new cab. they come with doors as well. if you include cutting and welding supplies, zip discs mig wire, anghle grinders, costs for sandblasting, wear and tear on the tools, bodyshop supplies like several different primers, sandpaper , bondo, tools you may need to buy, etc plus add the costs for a set of door hinges and doors that come with, then a new cab may be a better option depending on how bad your truck ends up being. this doesn't take into consideration the wear and tear on the body, especially if you don't have proper respirators etc. it will also get you to a finished truck quicker. there is a company that assembles the cab with jigs so everything is square and true. the doors are adjusted etc. one of the truck mags had a write up on them. classic trucks maybe? you can also sell some of the original parts, like doors, dash panel etc if they are half decent. just a thought and the reason why I advised to get a full and complete list, be honest with yourself, then price it all out. add some for parts you missed etc, and then decide.
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