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914World.com _ 914World Garage _ Best way to fit the mounting brackets to fiberglass bumpers?
Posted by: john77 Jan 20 2021, 03:54 PM
Finally got the front flares welded on, metal finished, and covered with a couple of coats of epoxy primer.
Before I move on to welding up the rears I want to fit the fiberglass front bumper.
What's the best way to fit the brackets to the bumper...
1. Mount the brackets to the car, and then epoxy the bumper to the brackets and just hold in place with tape until the epoxy sets?
2. Test mount the bumper, mark where the brackets should be, and then attach them to the bumper off the car? (Not sure if there's even clearance behind to do this.)
3. Some obvious way I'm too stupid to think of?
I'm assuming two-part epoxy is the best way to attach the brackets to the bumper... although, after losing other car parts on I-405 I figure I should double check.
Posted by: dhuckabay Jan 20 2021, 04:03 PM
Finally got the front flares welded on, metal finished, and covered with a couple of coats of epoxy primer.
Before I move on to welding up the rears I want to fit the fiberglass front bumper.
What's the best way to fit the brackets to the bumper...
1. Mount the brackets to the car, and then epoxy the bumper to the brackets and just hold in place with tape until the epoxy sets?
2. Test mount the bumper, mark where the brackets should be, and then attach them to the bumper off the car? (Not sure if there's even clearance behind to do this.)
3. Some obvious way I'm too stupid to think of?
I'm assuming two-part epoxy is the best way to attach the brackets to the bumper... although, after losing other car parts on I-405 I figure I should double check.
No clue what the brackets are. If metal epoxy sticks poorly. If FRP then no problem. If they are metal you are going to need to do it with bolts. Have had to fiberglass an angle to the main part and then run bolts through the leg out.
Nice looking job on the fender.
Posted by: john77 Jan 20 2021, 04:16 PM
[/quote]
No clue what the brackets are. If metal epoxy sticks poorly. If FRP then no problem. If they are metal you are going to need to do it with bolts. Have had to fiberglass an angle to the main part and then run bolts through the leg out.
Nice looking job on the fender.
[/quote]
Thanks man. They're basically u-shaped fiberglass brackets that you have to attach to the back of the bumper and then bolt into the stock bumper mount holes.
Which reminds me, anyone know if I also need to use the rubber bone shaped piece that the stock steel bumpers mount through?
Posted by: Rleog Jan 20 2021, 04:45 PM
I bolted the brackets on, using the donuts. Then held the bumper in position for test fit. If there is a large gap between bumper and body, the donuts can be shaved.
When I was satisfied with positioning, I mixed a small amount of body filler and covered the ends of the brackets, then pressed the bumper in position until the body filler set. You’re not trying to permanently cement the bumper onto the bracket here, only trying to accurately mark bracket positions on the bumper.
Next remove the brackets and bumper and securely fix the brackets to the well marked locations on the bumper with whatever fixation material you choose.
Someone else may have a better procedure, but this worked for me.
Posted by: wysri9 Jan 20 2021, 04:47 PM
My fibreglass bumpers came with studs glasses in. I made up 2 part brackets that allowed adjustment to fit (on the basis that getting a single bracket measured up and made was too ambitious) and then used the conventional mounting bolts and dog bones. I’ll take some pics tomorrow of the finished set up.
Posted by: Krieger Jan 20 2021, 10:21 PM
Finally got the front flares welded on, metal finished, and covered with a couple of coats of epoxy primer.
Before I move on to welding up the rears I want to fit the fiberglass front bumper.
What's the best way to fit the brackets to the bumper...
1. Mount the brackets to the car, and then epoxy the bumper to the brackets and just hold in place with tape until the epoxy sets?
2. Test mount the bumper, mark where the brackets should be, and then attach them to the bumper off the car? (Not sure if there's even clearance behind to do this.)
3. Some obvious way I'm too stupid to think of?
I'm assuming two-part epoxy is the best way to attach the brackets to the bumper... although, after losing other car parts on I-405 I figure I should double check.
Do #1 then remove the bumper after the epoxy sets and put a few layers of fiberglass on the backside of the bumper and brackets. It doesn't have to be pretty.
Posted by: Retroracer Jan 20 2021, 10:32 PM
Nice looking build!
Yes, my bumpers (QRS I think?) came with fiberglass brackets glassed on. The depth was such that I didn't need to use the dog bones, but I did have to shim one side slightly to get the shut lines side-to-side somewhere near matching....
FWIW, I believe the original factory fiberglass GT bumpers had metal brackets attached.
- Tony
Posted by: wysri9 Jan 21 2021, 06:31 AM
Here are pics of the brackets I made up. By tightening the adjustment bolt to the point where the two halves would just slide, I could mount the bumpers, move the bumper around to get best fit and then remove the bumper prior to locking the adjustment bolt. Worked for me 
The outer bracket needed relieving as shown to allow the range of adjustment, and I used Rivnuts on the inner bracket to allow easy installation once the full bracket was finally adjusted and fixed to the bumper.
Posted by: john77 Jan 21 2021, 12:03 PM
Here are pics of the brackets I made up. By tightening the adjustment bolt to the point where the two halves would just slide, I could mount the bumpers, move the bumper around to get best fit and then remove the bumper prior to locking the adjustment bolt. Worked for me
The outer bracket needed relieving as shown to allow the range of adjustment, and I used Rivnuts on the inner bracket to allow easy installation once the full bracket was finally adjusted and fixed to the bumper.
Damn, that's the kind of over-engineering I can get behind. Great job!
Posted by: mepstein Jan 21 2021, 12:11 PM
Here are pics of the brackets I made up. By tightening the adjustment bolt to the point where the two halves would just slide, I could mount the bumpers, move the bumper around to get best fit and then remove the bumper prior to locking the adjustment bolt. Worked for me
The outer bracket needed relieving as shown to allow the range of adjustment, and I used Rivnuts on the inner bracket to allow easy installation once the full bracket was finally adjusted and fixed to the bumper.
Best solution I’ve ever seen.
Posted by: porschetub Jan 21 2021, 01:08 PM
Crude but effective for my speedster replica I shaped blocks of wood to fit the inside profile ,glued them on then glassed over them then added a steel plate with studs ,glassed them in.
Polyester resin will stick well to steel if you sandblast it or grind it will a very course sanding disk,been doing this for years and never had an issue.
Seen many fiberglass parts with poorly made fastening points...seems to be industry standard 
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