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Hi Gang. Had my car repainted 3 years ago. Paint on the bumpers cracked near corners and letters. It's been redone already, so I have no faith in this Painter to fix. Seems to lift the primer right off the urethane bumper too (I can see the black plastic). Happened on the front bumper too and during our extreme change in temperature (I'm in Toronto Canada). I know "I get what I paid for" but this is a shame after restoring the car. The paint is fresh enough that new painter can match.
Can any Canadian members recommend a reasonable shop to fix this job? I've already spent way more than I probably should have, but my family loves this car. Thanks.
Definitely an adhesion problem,wrong product or careless application.My paint on the bumpers does get minor cracks after a while,but the primer and paint never lift like that.
Your 1st and 3rd pictures appear to be showing an actual crack in the bumper. Is that in fact a crack in the urethane bumper? Is the bumper original to the car? Is the paint original or has it be repainted?
Good luck... GUSTO
Opps... reread your post and see it has had a recent repaint.
Hi Gusto, They may look like cracks in the bumper, but they are not. That's only the paint (and some places with primer) cracked and lifted off the urethane bumper. The Painter I used blamed it on the original painter (unknown from maybe 10-20 years ago) for not using the right primer. Painter I used also said it was impossible to sand the paint right down to the bumper, because it would just eat into the urethane 'cause it is so soft.
Hi Gusto, They may look like cracks in the bumper, but they are not. That's only the paint (and some places with primer) cracked and lifted off the urethane bumper. The Painter I used blamed it on the original painter (unknown from maybe 10-20 years ago) for not using the right primer. Painter I used also said it was impossible to sand the paint right down to the bumper, because it would just eat into the urethane 'cause it is so soft.
Thanks.
That my be true, but I do know we have soda-blasted urethane bumpers through layers of paint and had no difficulty, either damaging the bumper or getting good adhesion.
Considering how urethane does age over time from exposure to UV as well as the solvents involved every time they get painted, it may just be time to consider starting with new bumpers, urethane or otherwise. The original front bumper on my '73 was gone by the early 90's. It literally had the consistency of a chocolate bar. You could pull chunks off as you would a chocolate bar.
I have heard more than one professional body guy comment that the new base/clear paints may not be compatible with the old urethane bumpers. Either the paint doesn't stick, or, the bumper becomes very brittle due to the chemicals in it.
That is a `75 bumper made of the black urethane rubber. They get very brittle with age, and that one is toast. The only way you are ever going to fix the problem is to replace the bumper.
Oh boy - this was not the advice I was hoping for. Is it normal to replace the bumpers during a 30+ year old restoration? If I must replace the bumpers and paint them, do I get plastic or fibreglass?
Oh boy - this was not the advice I was hoping for. Is it normal to replace the bumpers during a 30+ year old restoration? If I must replace the bumpers and paint them, do I get plastic or fibreglass?
That's a tough call and one you'll probably angst over.
Urethane bumpers, especially factory ones generally fit well and can often be painted off the car and very likely match the paint well, especially fresh paint. They also do provide some measure of protection and can take moderate bumps without showing damage. Unfortunately they do eventually become somewhat wavy. I still have the originals on my '85 and they look terrific. Of course they've never been repainted and the car has spent the vast majority of its life in the garage with a cover over it.
Fiberglass on the other hand looks terrific for a very long time... once they are fitted. They almost always require a good deal of fitting to get them to fit properly. Unfortunately they do not accept even moderate bumps with out being damaged. If you feel lucky and can deal with the fitting process they can provide the best long term solution.
That is a `75 bumper made of the black urethane rubber. They get very brittle with age, and that one is toast. The only way you are ever going to fix the problem is to replace the bumper.
I have to agree here, my 74 rear bumper looked similar and it was extremely brittle and the only real cure was to replace it. I chose fibreglass and did both front and rear.
That is a `75 bumper made of the black urethane rubber. They get very brittle with age, and that one is toast. The only way you are ever going to fix the problem is to replace the bumper.
The 73-75 urethane bumpers, are known to become brittle with age and crack, split and break apart. If that's an original 75 bumper, it's lived a lot longer than most of them! The first and third pictures, sure look like an original urethane bumper, that's starting to split and break.
The shot of the paint around the letters, does look like a paint issue though. It reminds me of how old lacquer paint jobs looked, when the paint was put on too heavy. You said that the painter didn't want to strip the bumper, so this could be what's going on there.
Normally a flex agent was used, when painting urethane parts. This allowed the paint to give a little, when the urethane panel "flexed". If the flex agent was left out, and someone pushed on the bumper, in the area of the rear letters, it may have caused the cracking.
No matter what the issue with the paint is, I suspect your problems go deeper. If that is a crack in the urethane, above the tail lamp, then it's time for a new bumper.
As to your question of if it's normal to replace the bumpers, on a 30 year old restoration, it is if you have a 73, 74 or 75 Corvette. The 76 and up, yellow urethane bumpers, seem to last indefinitely, but not the 73-75 black urethane.
The 75 rear bumper, is unique to the 75. It's no longer available in urethane, so your only choices are rigid or flexible fiberglass. Personally, I prefer the flexible glass. It gives the illusion of being urethane, but will never get wavy like urethane does. Both the rigid and flexible glass bumpers, will crack if bumped against something.
Unfortunately the early bumper covers were not very stable, and they get very brittle with age. I have had customers buy NOS covers and try to install them and they crack while installing them. I tried to install a NOS 74 bumper cover about 3 months ago. We had to throw it away. You could not sand it without cracking it. He bought it 15 years ago. A $1600 lesson for him. So for those purest out there that think they may find an NOS one, think again.
I am surprised that one has lasted anywhere close to this long in Canada. You might want to look under there and see if it is, in fact, an original. I know you say it is paint lifting and not a crack, and I will let you determine that for sure, but it is in the most common place for a rubber crack.
My original 73 bumper is still flexable but has some paint crazing at the tip.But it has lived in Canada all it's life. Colder temperature and less UV.
I don't think it's the UV since the paint would protect it. It's mostly the outgassing of the lighter compounds which give the bumper flexability.
All plastics, rubbers and foams deteriorate over time. Look at plastic lawn furniture. I've seen people try to repair cracked 10 yr old chairs only to get more cracks.
I must be the only one that claims that an original 73 bumper is still flexible. It's off the car at this time for a car restoration. So I've flexed it quite a bit. But I did by a replacement GM a few yrs back just in case.
I've read that the GM replacements have better forumulations but they are very pricey.
The paint for the flexible bumpers needs to be more flexible than normal body paint. I'm no paint expert, but I'm sure the factory used a different type paint...or added flex modifiers...for the flex bumpers.
If the same paint was used for body and bumpers on your car, it's not a surprise that the flexing bumper (heat, vibration, etc) has caused that [more brittle] paint to crack. And, as mentioned above, proper preparation of the flex bumper surfaces and proper priming are required to get good adhesion for whatever paint you are using.
The paint for the flexible bumpers needs to be more flexible than normal body paint. I'm no paint expert, but I'm sure the factory used a different type paint...or added flex modifiers...for the flex bumpers.
If the same paint was used for body and bumpers on your car, it's not a surprise that the flexing bumper (heat, vibration, etc) has caused that [more brittle] paint to crack. And, as mentioned above, proper preparation of the flex bumper surfaces and proper priming are required to get good adhesion for whatever paint you are using.
From what I've been told this used to be true years ago but now that just about all cars have flexible bumpers made of materials like plastic or urethane. modern automotive paints and primers already have the flex agents in them. This is what I was told when purchasing paint for my last corvette.
Last edited by augiedoggy; Sep 17, 2014 at 05:21 PM.
I must be the only one that claims that an original 73 bumper is still flexible.
You may be the only one that hasn't had to replace their original cover! My original Canadian, 45,000 mile bumper cover was swept up in little pieces off of the body shop floor this spring. It was the 2 coats of paint holding it together!
You may be the only one that hasn't had to replace their original cover! My original Canadian, 45,000 mile bumper cover was swept up in little pieces off of the body shop floor this spring. It was the 2 coats of paint holding it together!
My car spent a good part of it's life in Winnipeg where the winter temperatures rarely get over -10*C. That must have been it's salvation. The plastizizers were probably frozen solid
Replaced both the front and rear bumpers of my 75 over the past year. I went with Flexiglass bumper covers from Willcox and got a good fit on both ends - and I'm very much a novice in this field. Rattle canned the front myself and paid $600 for the back. You can tell the difference but both work for me as I'll need a complete paint at some point down the road. With the exception of the metal retainers, I easily peeled the old bumper covers off by hand. If I had to do it all again, I'd do it the same way. VV
Last edited by Valley Vette; Sep 17, 2014 at 08:48 PM.
Thanks for all the feedback guys. The bumper is not cracked (I know it looks as though it is). That's just the paint split and lifting off the bumper (no adhesion). I guess no one's recommending one more repaint at a better or more experienced shop?
75 Canadian Bumper Paint Keeps Cracking
The 73-75 urethane bumpers, are known to become brittle with age and crack, split and break apart. If that's an original 75 bumper, it's lived a lot longer than most of them! The first and third pictures, sure look like an original urethane bumper, that's starting to split and break. 
