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Maritimer

Rear Bumper Installation questions

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Trying to get my bumper back on and aligned after a rechroming and the contrary to the FSM the thing is a PITA to install. Seems no matter what way I tighten it down or twist brackets the bumper wont go on without hitting the rear valence in some way or chipping paint with it 😧. Is there some magic trick to getting the bumper installed to prevent this? Should there be spacers for the rear brackets to help bring the bumper away from the valence? should the bumper be lined up straight with the bottom of the taillight trim? Should it go into the dip on the rear valence?

 

Any help/pictures of a proper install would  be appreciated.

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I'm up by Burnside.

It's a '72 but there's more than a few 69-70 parts on it so the bumper could be either. Looks like it's a rear curvature issue more than anything but the only bumper work I've done was taking it off the car. I've got a few body shims I can play with to space out the centre bolts but it doesn't seem like a normal thing to do as far as I've seen online. Was hoping I'd just bolted the thing on wrong but the bumper may be out of shape.

I already tried calling blue but couldn't get him on the line.

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Hopefully you're only working with the center section without the ends attached - much easier that way.  Something must have changed the arc of this section if it did not touch prior to rechroming.  Did the chroming shop have to do any repairs to the section?  What about the mounting brackets - any work done on them?  You should expect about 1/8" gap (or more) between the middle of the center section and the rear valance panel.  If you start adding shims or washers you may end up moving the end pieces back to the point their mounting bolts thru the fender won't line up.

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When I adjusted the bumper on my '72, I simply added a SS washer or two between the bumper and bracket.  First, I straightened the bumper mounting tabs and bracket to what I thought seemed correct and best fitting of bumper and bracket.  The holes on the quarter panel were sufficiently oversized as to not cause fitment issues to the best of my recollection.  For my car, one side need the spacer washers, the other side was fine.  Also, I am positive my bumper is not the original bumper and that a small rear end tap had occurred sometime in the past prior to my ownership...so, your mileage will vary.

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Finally got back to it and got some photos, the bumper snapped at me while tightening it and notched my paint a bit. Anyways, ignoring the fingerprints does this shape look right? My car seems to have a bit of a Chrome smile on the back but  I was under the impression that the rear bumper was supposed to be mostly level. I’ve got about 1/4” worth of Chevrolet body spacers in it to get it to this point...

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12 minutes ago, Patcon said:

@240260280

Not to thread jack but how did you make the sniffer? I understand the part I see, what about the ends in the exhaust?

Braze or screw rather than solder... the solder weakens in the heat.

The top pipe is the intake 3/4" copper ~ 2' long. I used a 1/2 to 3/4" coupler at the nose to capture the exhaust correctly.

The bottom pipe is the exhaust. It is ~ 2" shorter than the top tube.  It is 1/2" copper with the end (front most part) capped with a 1/2" copper cap.  There is a 1/4" hole drilled ~ 2" back from the 1/2" cap. This is where a venturi effect sucks the exhaust out of the pipes.

I used an O2 sensor tap (spark plug hole tap) to put a thread on a copper ring that was placed in the junction T (2 X 3/4" and 1 X 1/2").  4 90degree street elbows make the loop and are adjustable to bring the two long pipes tightly together.  It works well on large exhausts.  For small, just use the top part don't double back; just extend a 1/2" pipe a foot behind the T.

 

Edited by 240260280

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The reason for the double back design and long length is to ensure the sensor is sampling undiluted gas at idle.  If an opening in the sniffer tube is exposed to fresh air, or if the openings are close to the tip, it is possible for reversion of fresh air to contaminate measurements at idle. Shorter tubes or a straight tube with inlet in the pipe and outlet behind the car are ok at speed.

Edited by 240260280

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