C3 79 rear urethane bumper question
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Melting Slicks
Joined: Mar 2002
Posts: 2,164
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From: Beringen
C3 79 rear urethane bumper question
I have bought a new rear bumper fascia for my 79 due to someone rear ending me and the Original bumper ripping.
I got a new Eckler's urethane replacement in and apparently there is a difference. The Original has a small lip on the top edge where the bumper meets the fiberglass. This is meant to conceal the Original metal retainers that sit in between the fascia and the fiberglass. Apparently the bumper creates and opening between the bumper and fiberglas when attached. I didn't have that with the Original due to the presence of that lip on the bumper.
There were also other type of retainers with the bolts already on them. I used those as well but to no avail.
Anyone encounter this and how did they solve it ?
I got a new Eckler's urethane replacement in and apparently there is a difference. The Original has a small lip on the top edge where the bumper meets the fiberglass. This is meant to conceal the Original metal retainers that sit in between the fascia and the fiberglass. Apparently the bumper creates and opening between the bumper and fiberglas when attached. I didn't have that with the Original due to the presence of that lip on the bumper.
There were also other type of retainers with the bolts already on them. I used those as well but to no avail.
Anyone encounter this and how did they solve it ?
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
When ever I install a GM restoration part urethane bumper. Regardless if it front or rear bumper cover. AND the metal retainers that slide onto the top edge of the rear bumper so you can use the sheet metal screws to attach it along the top edge often times are rusted to pieces and can not be re-used. I fabricate a strip of metal that goes along the top edge usually out of stainless steel. I drill holes where required in it so the new screws I use with the spinning washers can be used. Then I will drill 1/8" holes in the bumper and this strip and carefully countersink the urethane a little bit so the "pop-rivets" I use will hold this metal strip in place and the heads of the rivets are flush.
OPTION 2:
I slide on "J-nuts" and install it. I usually do this for fiberglass bumpers because they have enough strength that the metal strip is not required.
The side retainers with the 10-24 threaded studs made into them. I often times will knock them out if the threads are bad or if the studs seem loose. Weld in new ones and then install them in the rear cover and pop rivet them in place also. Sometimes I may not choose to pop rivet in the side ones due to they often times can be installed by hand and held into place when the nuts are being installed and tightened.
Make sure that you use nuts with washer large enough to cover the holes in the sides of your quarter panels. If you sue washers that are too small in diameter...they can easily pull through or damage the fiberglass.
DO NOT tighten the screws and nuts too much. Excessive torque will often times cause for warping of the bumper when it is placed out in the sun. The screws and nuts only have to be tight enough to hold the bumpers position.
On fiberglass and urethane bumpers I will often times use VERY THIN stainless steel washes that I use as shims between the bumper cover and the body. SO when I tighten it up...I can slide a piece of aluminum foil between the body and the bumper. What this does is makes it so when the bumper and body are painted and cleared. That the thickness of clear that I apply to the flanges of the body and the bumper will not "squoosh-out" in time. When I am done you can not see the stainless steel washers and can not tell that there is a gap at all....and the clear will not move due to the edges are not touching at all.
DUB
OPTION 2:
I slide on "J-nuts" and install it. I usually do this for fiberglass bumpers because they have enough strength that the metal strip is not required.
The side retainers with the 10-24 threaded studs made into them. I often times will knock them out if the threads are bad or if the studs seem loose. Weld in new ones and then install them in the rear cover and pop rivet them in place also. Sometimes I may not choose to pop rivet in the side ones due to they often times can be installed by hand and held into place when the nuts are being installed and tightened.
Make sure that you use nuts with washer large enough to cover the holes in the sides of your quarter panels. If you sue washers that are too small in diameter...they can easily pull through or damage the fiberglass.
DO NOT tighten the screws and nuts too much. Excessive torque will often times cause for warping of the bumper when it is placed out in the sun. The screws and nuts only have to be tight enough to hold the bumpers position.
On fiberglass and urethane bumpers I will often times use VERY THIN stainless steel washes that I use as shims between the bumper cover and the body. SO when I tighten it up...I can slide a piece of aluminum foil between the body and the bumper. What this does is makes it so when the bumper and body are painted and cleared. That the thickness of clear that I apply to the flanges of the body and the bumper will not "squoosh-out" in time. When I am done you can not see the stainless steel washers and can not tell that there is a gap at all....and the clear will not move due to the edges are not touching at all.
DUB
Le Mans Master
Joined: Dec 2009
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From: Saskatoon Saskatchewan
Race Director
Joined: Apr 2009
Posts: 19,294
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From: Charlotte NC
No.
Keep reading. I read that paragraph several times and it is correctly written. The next sentence describes WHY I am doing this. The aluminum foil is a gauge...it makes it so you know that you have the bumper and body not touching. So the paint will not "squoosh-out" in time due to compression at the edge. The paragraph mentions thin stainless steel washers being used.
DUB
Keep reading. I read that paragraph several times and it is correctly written. The next sentence describes WHY I am doing this. The aluminum foil is a gauge...it makes it so you know that you have the bumper and body not touching. So the paint will not "squoosh-out" in time due to compression at the edge. The paragraph mentions thin stainless steel washers being used.
DUB
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
DUB
