Front bumper x 2
 

My '74 T/A is almost finished. The car is a 49k mile car that has been garaged most of it's life. Both the front and rear bumpers were in really good condition compared to most of these. That being said, the front black bumper section keeps getting cracks in it. I believe that the cracks appear after handling, such as when the front bumper was installed. We have repaired and painted it three times now and it has cracks at both ends again. How can we fix this to stop this from happening? I will get a couple of pics and post them up.

Here are the cracks I am talking about.

Same issue here.

Ok, what are you using to fix the crack? Are you just skinning over with bondo or some other patch. Check out the body repair section and get their input. I think you may have to open that area up as a V to get it filled and then paint.

I am pretty sure that is what the shop has done. We understand that the cracks can go deeper than the primer/paint. They sand it down, fill the cracks (not sure with what) and then repaint. As soon as any amount of flexing is done, the cracks come back. If this was a roached bumper, I would understand. This is a low mileage car that has been stored indoors almost it's entire existence.

is it an endura material like the earlier 70-73? if so or even if not, confirm what filler they are using on it & if its not the 3M or SEM flexible bumper/plastic filler thats probably why its cracking. ive used the SEM flexi-weld product on a few different materials from a 72 endura nose to a 78 nose & also 79-81 flexible wheel flares, its held up crack free for 10 years on the 78 & 81 cars & going strong on the 72 nose for 5 years. this is in the midwest where the cars go from 0f to 90+f each year as well as lots of flexing when installed.

another thing guys with endura bumpers do is to use a coat or 2 of epoxy primer, everyone says API is the best but i used a different brand on the 72 nose & it likely helped a lot with avoiding cracks.

& a final thing to try if they arent is a flex agent in the paint/clear on top of a flexible primer, flex agent will cure out but allows the parts to be manhandled during installation without cracking as easy... on my 81 i had some welting left over that was painted with flex agent, could bend it almost 180* & it wouldnt crack, a couple months later it would crack at much less of a bend angle.

hope you can figure it out but need to confirm what material they are using, painting plastic & rubber can be a B!