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I actually have an idea of how I want to approach this, but I thought I would get some collective ideas from the crowd...
I've had this Roadster since 1980 (second owner), but it had to sit outside (tarped) in my back yard for about 3 years. Now retired, I'm ready to spend the time I have restoring it.
Naturally, my first step toward restoration is to replace the body mounts. Most of them are in really good shape, but water has sat in the #2 body mount area and created some rust.
The bolt-through area isn't actually "gone", but it's rusted enough to eat the through-hole to where the edges of the hole are thin.
However, about a 3/4" out from the edge of the hole, the steel is reasonably solid again. The hole itself still exists, it's just not solid around the edges.
I "could" just treat it and leave it, but I don't like the idea that any rust in the future would weaken the mount and allow it to collapse.
Mount #1 is rock solid as is all the rest of the frame, seat belt reinforcements, etc. It's really a clean car to start with except for what outside storage did to this #2 body mount.
Like I said, I think I know how to approach this, but before I go any further, anyone have any thoughts on it?
Knowing that you are going to have the body off the frame. You can do as you thought and sand blast or media blast that area and get the rust out.
Then you can cut a square plate and EITHER weld it to the bottom side of the #2 mount. Knowing that they make 'weld through; coating you can spray on the CLEAN metal...this new square steel plate should not rust for a long, long time.
OR...you can install the same square plate so it fits inside the #2 pocket area and weld it in....Using the same weld through coating.
You can also bond this square plate in using some adhesive from SEM. (Part number 39747) It will work but the metal need to be really roughed up and make sure you completely cover all bare metal with their adhesive due to being epoxy based...it will not allow the metal to rust that is covered with it.
IF you weld or bond the plate on the bottom of the rail....make sure you compensate for the thickness of this added piece of metal and remove the required amount of shims that would equal the thickness of the metal you installed there.
Your can cut the bottom of this area out and fit a new piece in place also and weld that in.
Well, the car is really too clean to do a body off at this point. I'm doing the "lift one side at a time" to change out the mounts.
That means that I have about 4" or so clearance between the frame and the body rail.
I can't (properly) weld a plate on the inside of the well due to clearance issues, and for the same reason, I can't really cut out the bottom and weld in a new piece.
So what I was already leaning toward was your second to the last suggestion. That is, I can cut a solid piece of steel to fit on the bottom, and I thought I would drill holes in it to give me areas where I actually can reach with my MIG and weld it solid to the bottom. Where the plate would reach to the vertical side walls of the post is perfectly solid so I would have restored full load carrying ability to that area.
I know that I can achieve the same end by bonding (the plate underneath) instead of welding, so I think I'll sleep on that a bit before making a final decision.
I don't really want to do it that way because I will have to shim up all the other body mounts by the thickness of this one plate (not really a big deal, though... certainly won't be noticeable if the body is raised 3/32" higher from the frame overall).
What I was hoping was to find that #2 had been shimmed which would allow me to simply let the repair plate replace the shim(s). However, NONE of the mounts on the same side (right) were shimmed from the factory, and I know that because I'm the second owner of the car, I bought it when it was 5 years old (1980), and there isn't a hint of any body work being done on this car anywhere.
I don't yet know if there are any shims at the #2 position on the Left side, but I do know that there are no shims on #'s 1, 3, and 4 positions on the Left side.
Anyway, thanks for confirming my thoughts on the subject.
Since I'm just starting the resto, I wonder if I should start a thread to create a journal for where I'm at going forward.
If it' solid rusted in there then that will change any plans you have now
No, it's all good. All of the mount bolts are out on the right side and all loose or out on the left side. It's the right side at the moment that I have spaced up a good 4" or so off the frame. When I finish that side, I'll drop it and then lift the left side to do the same.
In fact, the #1 and #3 mounts on both sides are perfect and came out easily. Nothing more than the lightest surface red dust rust.
It's the #2 mounts on both sides that caught some water from sitting outside and have medium rust that I need to attend to as described above.
Both of the #4 mount bolts needed to be cut cuz the nuts broke loose from their cages and spun, but that was no biggy. (A slight hassle on a convertible, but still no biggy.)
No other rust in the #4's except the cages themselves, and I'm just going to replace them with a nut and big washer.
UH OH ,if the no.2s caught water , what's going on higher up ?
my 77 had a similar problem , the no. 2 on right side had rust under the rubber , I had the entire car stripped down so I got my little sandblaster in there and cleaned it up ,put a smallish plate in and welded it up, some nice tack welds will hold it , it wont go anywhere ! .I just cleaned up underneath and put rust sealer stuff on it , as the rust wasn't as bad underneath . .
the sill plate runs underneath and has a matching hole that lines up (obviously ! ) so there's two layers of steel down there
Here's a pic of my 77 without the windscreen , I cleaned up the dried up old (now) useless sealer from all over the area and scraped it out of the firewall join and put some fresh stuff over the join . Then repainted it black , I was lucky , rust free , but it was weeping a bit of water in the rain .
you can see the firewall join edge ,where that white (sealer) stuff is . But with the glass out I took off all of the surround trim just to check it ,thankfully it was like new up top.
I don't seem to have an after pic !
Where the yellow arrows are pointing is where the fiberglass firewall section is riveted to the birdcage and this area is where the sealant from GM can crack and allow water to come inside the car. BUT..it does not cause for the #2 area in the post to fill up with water.
As typically happens, virtually all of the flowable black sealer along and inside the cowl is dried and cracking, and I'm pretty sure that water came through the rivets under the bonding strip. That's the only place that makes any sense considering what I see.
The birdcage is very nice throughout along the top behind the cowl, so the leak was pretty local being that only the base of the #2 Mount shows corrosion.
I've been away from the trade for almost 25 years and I'm finding that there are some newer products available to do some of this stuff, so what product are we using these days as the best option to redo the flowable black sealer? I'm going to do the entire area to restore it's integrity.
09-13-2018, 10:41 AM
75' Vette Body Mount #2
