68 Blower motor housing has gap to firewall
 

I've got a 68 convert and I removed the inner heater box and opposite side blower housing to paint the firewall. When I removed it (long, long ago), the blower housing had some kind of black sealant surrounding it in addition to the usual plumbers dope type sealant on the flange of the blower housing. I've heard all sorts of conjecture on which cars got the extra sealant from the factory and which didn't, with no clear answers. It makes the heater box install look sloppy. I have no reason to believe it was done by anything other than the factory.

Having rebuilt the heater box and repainted everything, I attempted to do a trial fit of the heater box and blower housing (without using the caulking for the test fit). After everything is mounted and fasteners are tightened, I have about an eighth inch gap between the blower housing and firewall along the top edge of the blower housing, but only for a few inches. It appears to be close to where the firewall and supporting inner structure were spot welded, so I can't just tap the firewall and bend it flush to the fan housing. I'm wondering if anyone else has had a problem like this and if this is why GM used the extra sealant on the edges of the fan box for some cars. The gap can easily be filled by the strip caulking, but it is kind of odd. I appreciate any input you have.

Thanks
Joe

P.S. I think my car was spot welded by someone that was having a bad day as one of the quarter panels had all of the spot welds missing where it attaches to an inner structure piece. That was an easy fix...............

Just wanted to add a note to this. I have two blower housings. One of them is original to the car and the other is a used GM housing and both of them are perfectly clean with nothing on the flange face that mates with the firewall. I found that when I place them face down on a table, there is a small gap between the flange face and the table in the same location as when they are on the car, though the gap is only about 1/16" vs 1/8" when on the car

So your box is out 1/16”
And your firewall the same 1/16” it would seem.

If you cant pound an outward bow into the firewall then you might take the time to make a thick iron bar stock reinforcement bar to span that gap area when the box is bolted on .

A 2” long length of 1/8” thick bar stock would be quite stiff.

Kinda the same idea as a valve cover load spreader bar.

It would not look stock if that might matter to you, but it might get you 1/16” closer to having no gap on top.

That's an interesting idea, but you are right, it wouldn't look stock. The gap is also in an area that is between the top left most mounting stud and the mounting screw above the fan so it would take a long support piece to make it work. I think what I'm going to try first is to take one of the blower housings and bend the flange so it would be flat when laid against the table. That will take up half of the gap and the remainder I will just let the rope caulk fill. I might even put some masking tape along the firewall and on the flange of the housing and then run a small bead of SEM black seam sealer in that area. I can remove the tape and it should be pretty much invisible. If nothing else, it will look cleaner than what GM did.