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Author Topic: "68 Rear bumper mounting trouble.....hole to hole check dimensions available?  (Read 854 times)
DAVEN1256
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« on: March 28, 2013, 07:35:56 PM »

I had my original '68 rear bumper straightened and re-chromed. I have reproduction 1/4 panels and tail panel. I also have reproduction CHQ bumper brackets with the exception of the center bracket which is the original one to the car.

I am having trouble making the bumper fit right........ I can get it on the car but cannot get the driver side corner bracket hole to line up with the hole in the quarter panel. Also, I haven't tried it yet but it seems it would take a lot of bolt torquing to pull the two brackets that are between the corner brackets and the center bracket tight to the body

I guess the problem could be anywhere.....1/4 panel, tailpanel, brackets or the bumper itself...........Or maybe I am not doing it the right way.

Is there a correct sequence or procedure when mounting the rear bumper?.. ..Maybe a different way would give different results.......Should the brackets go on the bumper first? (how loose or tight?) and then the brackets to the body? Or the brackets on the body first (how loose or tight?) and then the bumper to the brackets? Or a combination of both? What should you tighten first and how hard should you tighten everything?

I also want to make sure the bumper was straightened correctly. The shop that straightened it said they had some sort of guide that they used to make sure everything was right.

Does anyone know of any published "check" dimensions for a '68 rear bumper? To be able to check if all the mounting holes are in correct relation to each other. To be able to prove that the chrome shop did it right.

Thanks.......Dave                                                                     

« Last Edit: March 28, 2013, 07:53:35 PM by DAVEN1256 » Logged
JohnZ
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« Reply #1 on: March 29, 2013, 12:00:30 PM »

Is there a correct sequence or procedure when mounting the rear bumper?.. ..Maybe a different way would give different results.......Should the brackets go on the bumper first? (how loose or tight?) and then the brackets to the body? Or the brackets on the body first (how loose or tight?) and then the bumper to the brackets? Or a combination of both?

In production, the riveted center bracket and the intermediate and corner brackets were attached to the bumper (tight) in an off-line subassembly; that assembly was then taken to the car and installed, with the eight bolts driven from inside the trunk into the brackets on the bumper.
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'69 Z/28
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Stingr69
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« Reply #2 on: March 29, 2013, 01:50:13 PM »

The repro holes can be a nightmare as well as the technique used to fit the panels to the body. I hope your signal light holes are better fit than mine were. They are bad but the body is already painted. Too late for me now. I did fit the bumper first and it did help BUT I assumed the signal lights were going to just go together like original. I was very wrong.  Sad I would advise everyone to fully test fit ALL trim pieces before the car goes in for final bodywork and paint. It is too difficult to fix after the fact.

-Mark.
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vtfb68
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« Reply #3 on: March 29, 2013, 02:08:27 PM »

Dave,
  Simplistic, but have you tried with all mounts and brackets loose? then tighten them in a torquing type sequence till it all comes together. If nothing else its free.
   Good luck,
       Victor
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DAVEN1256
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« Reply #4 on: March 30, 2013, 10:32:38 PM »

In order to pull both intermediate brackets tight to the body, they had to be tightened really hard. Beyond what would seem normal. When they were tight,  the driver side bracket hole center was about a half inch forward of the center of the hole in the 1/4 panel. No way to put a bolt through there.

So I took the bumper off and checked it for straightness by laying straightedeges across the inside edge of the top half. What I found was a subtle kink inwards (towards the body) starting at the driver's side intermediate bracket hole.

Also, with the center bracket in place, if you tighten the just the driver's side intermediate bracket, the passenger side intermediate bracket is a half inch away from the body, and vice versa. That can't be right. To tighten both intermediate brackets tight to the body, you are flexing the body, or the bumper, or both.

Can someone tell me if the bumper should be perfectly straight end to end or if there should be a slight crown in the middle like the trunk lid and top of the tail panel has?

I will be on the phone with the shop who did the work on Monday.





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