I'm replacing the rear body mount brackets on my '79. As is typical for a street driven car that old, the originals were disintegrated. The fiberglass was cracked and distorted. It looks like the body was pulling against the mount nut, which caused the bottom of the mount pillar to bulge downward. After grinding out all the broken material and cracks, I used a heat gun and 2 x 4 to try and flatten the pillar bottom.

After I repaired the pillar, I did a fit check with the new bracket, and here's where my questions come from. The replacement bracket has two vertical and two horizontal tabs. The holes on the vertical tabs don't line up with the holes used on the old bracket, but I can drill new ones. I'm assuming that when I fit check the new bracket, I place the vertical tabs flush against the pillar. Is that correct? There would be one with a single hole against the back of the pillar and one with two holes against the outside of the pillar. With these in place, you can mark where the holes are for the remaining four rivets on the two horizontal tabs.

When I align the vertical tabs as described above, the horizontal ones do not touch the body. I can only assume this is because there is still a slight downward bulge on the pillar bottom. The gap is small, so I'm thinking of just sanding the pillar down on the the bottom until the horizontal tabs touch. However, I also thought about heating the pillar up and putting the bracket over the end and jacking the body up hoping the weight will flatten the pillar bottom even more. I cannot decide which is the better approach, but I'm leaning towards heating it back up.

Finally, with the vertical tabs aligned as described, the bolt hole in the pillar is not perfectly aligned with the bolt hole in the new bracket, but the original probably wasn't either. The entire bolt hole is visible through the bracket hole, so I assume this is OK since the bolt hole isn't blocked and the bracket still provides the structural support.

Am I on the right track with the heating, or would sanding be better? Or is there a third option and I'm about to screw something up. Advice, insight, and experience appreciated. Thanks.

MajD

 

Is this the #4 body mount reinforcement that you are referring to?
I replaced mine a while back. First thing I would do is compare the new reinforcements to the old ones provided that there is enough metal left on the old ones. Check to make sure that the holes are manufactured into the new part in the correct location. Mine had to be wrestled into place a little. I set one rivet on the front first and then slid a punch through one of the holes on the side and put it through the fiberglass hole and used the punch to "jack" it into position. While holding upward pressure on the punch I had my helper put a rivet through the other hole on that side and set the rivet with my air tool. I kept working my way around until everything was held in place with one rivet per side then I went back and finished off the rest of the rivets. If I remember there is only one rivet on the rear of the reinforcement.

 

It is the #4 reinforcment, and there is only one rivet hole in the back. There is nothing left of the original mount for comparison. There were spiderwebs of cracks between the rivet holes, so most of them have been filled in as part of the repair and will have to be redrilled. I put the mount up to the pillar and the two holes in the side vertical tab are actually above the original holes, so I cannot use the punch approach. Here are pictures of the original damage:









Notice the way the pillar was bulged at the bottom. That's what I tried flattening out after removing all the damaged SMC. Here's the pillar after initial repair work. There is still a ground out crack I need to fill, but it's good enough for a fit check.





It seems like there is still a slight bulge on the bottom keeping the reinforcement from seating properly, as I described in my OP. Sorry the pictures are so big. Thanks.

 

I would just do all of the fiberglass repairs, put the new reinforcement in place, mark and drill for new holes, and rivet in in place.

 

Agreed. F/G repair then use new mounts for a template.

 

What are your plans for the cage nut? Before you rivet the reinforcement back on the cage nut gets riveted from in the inside pocket.

 

What are your plans for the cage nut? Before you rivet the reinforcement back on the cage nut gets riveted into place from inside.

 

The caged nut is not required. It was installed that way for ease of assembly. A large flat washer and nut is just as good. I actually make my own flat washer and cut it in a square shape to fit down in the pocket and provide more support. Even more support than if you re-installed the caged nut assembly.


For what it is worth...so people who may look at these two photos and do the same thing. KEEP IN MIND that IF you use pop rivets. And install them as like they are shown here....it would be WISE that you also use a flat washer on the INSIDE to allow the rivet to pull against it......instead of pulling against the fiberglass and the rivet pulling through it.

DUB

 

Yeah, should have mentioned that. 1" body washer on the inside.

 

So just to confirm. You put a washer between the large hole (body mount) and the bracket? I have to do this exact fix soon and need all the advice I can get.

Thanks, Jesse

 

No. The washer is on the inside of the car to give the head of the pop rivit something to grab onto (other than old Fiberglas)

make ke sure the rivit is long enough.

 

Not to be hyper critical...but the large washer in the inside is not for the 'head' of the rivet...but rather the shaft or shank of the rivet to pull against. you can see the head of the rivet in the photo can be seen from the outside.

YES...the 'grip range' of the rivet is also important. Make sure your rivet is not too long.

DUB

 

I plan to use the standard soft aluminum body rivets, but my original question was regarding how the mount sits against the pillar. Your mount looks different than mine. Your tabs have a sharper crease at the bend. Did you make them?

Your mounts are flush against the body at all rivet points. When I align my two vertical tabs against the post, there is still a gap between the body and the horizontal tabs. I've already done the repair work, and my original post offered a couple thoughts on how to decrease the gap. I just wanted some inputs from other folks. Thanks.

MajD

 

I assume you got the correct gusset for your year model. You may have the wrong ones for your year.

Posting a photo would be great also.

If you applied and mat and resin to the very bottom of the body...that can cause it to not seat correctly. Also..if you also made it wider...it can cause it to not seat correctly.

DUB

 

Sorry. No idea. Bought them 6-7 years ago from a forum member. No idea where they came from originally. Sorry

 

Thanks for the info. I double checked and I'm sure I have the correct reinforcement. The picture below shows how the pillar was originally deformed with the bulge at the bottom.




I didn't apply mat and resin (though maybe I should have). After grinding out the cracks and shattered SMC, I used a heat gun set on low to soften up the fiberglass a little bit. I used my hand and pressed a 2 x 4 against the pillar bottom to flatten the bulge. I filled in the gaps with a mixture of epoxy, milled fiberglass, and colloidal silica the consistency of cake frosting. After it dried, I sanded off the excess and this is what I have.




There is still a little work to to do, but I wanted to fit the bracket. When I put the two vertical tabs against the pillar, the horizontal tabs didn't sit quite flush with body. I'll try and get a picture tomorrow, but it's difficult to hold the bracket and the camera phone at the same time. I think there is still some of the bulge left. Thanks.

MajD

 

Put a bolt with large washer on it and put it through the body and gusset and tighten it up and then take the picture.

DUB

 

That's a good idea. Give me a couple days to get out to the car and snap a few pictures. Thanks.