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31pontiac's 1959 Bonneville

2019 December
of the Month

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Last Indian

Exterior panel stabilization

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Exterior panel stabilization, securing & attachment improvements that will help quiet them. If you own a Pontiac from the early 1990s through 2009, then you may have noticed that because of how a lot of the panels were made and attached, there can be that creak or crack when you push on a panel like a front bumper cover or rear cover, etc., but these improvements will also help to improve driving characteristics; yes really! The old cars were not and are not like that! Why? Because they bolted together solid, panel to panel, not with plastic push pins that go in a hole almost half again as big as the pin O.D… Well you can have that same solid non noisy panel setup as the old Skool classics have and had. Why would this improve driving characteristics? Well when panels aren’t stable they negatively impact air movement aka air foil characteristics. This may seem irrelevant at 35mph, but not at 50mph! There is a reason NASCAR as well as well as some of the car industry spends millions of dollars on aerodynamic research, wind tunnels and the like!

 

Still for me, when you build a car, you build a car! You build as a a complete assembly, too be as perfect as you can make it, for every instance and every situation! I may be anal, ok I am, but if I was paying to have a car built, this is what I would want, so why should I not do it for myself?! Really! A very simple example is the vertical edge in the engine compartment where the outer and inner fender are spot welded together (see pic)! While there is no value other than aesthetics in this case this is just a case of a little effort to make an improvement and remove an edge that can get beat up easily and inflict some damage to knuckles or the like.

 

So to the details, again I will use my 2000 Grand Prix for example purposes. First the front end. I’ll start with the bumper support, this piece attaches to the lower hood latch and supports the upper area of the bumper cover with two push pins and one small screw/washer, but also attaches to the steel brace/bracket that the headlights attach. This where I make an adjustment to effect the height of the bumper cover height gap to the hood. I do this by retapping the hole from 6mm x 1.25mm to ¼ x 20 thd… and then placing stainless steel washers between the bumper support and the steel headlight bracket with a SS ¼-20 buttonhead screw through the middle of the washers. This piece also has the ability to be adjusted to some degree at the bumper cover attachment area itself. This includes the fact that it interfaces with the two air ducts for radiator cooling that locate it vertically on molded post of those ducts. These could be shortened or raised by the addition of a spacer if need be. This will in turn changes the gap between the upper lip of the cover and the hood. Likewise the two headlight brackets need to be fixed, as they are not attach properly as a support structure. They allow for to much movement and vibration as they come from the OEM. There are two places I will show to attach these brackets to the core support to make them solid like they should be. This structure with its long span between the factory attachment points at each end of the bracket needs to be made ridged. The two outer holes of the bumper support that interface with the bumper cover will not use the push pin fasteners. Instead it will change to SS ¼-20 buttonhead screws with a SS washer and nut on the underside. This now holds the upper bumper cover tight to the support so there is no movement or flex. 
 

 

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the two pictures above show the vertical edge fix.

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this top portion area fix is the easy part! The bottom side gets much more involved, that will be the next segment.

Edited by Last Indian
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Great info as always, thankz for sharing......And Happy Birthday.

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1 hour ago, JUSTA6 said:

Great info as always, thankz for sharing......And Happy Birthday.

Thanks buddy! One step closer to that 70 1/2 mark so Uncle Sam can start getting his tax money back 😬

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At the bottom area of the front cover there is a lot of work to be done. Other than the 6 push pin fasteners on the top side of the lower air inlets, there are no other retaining fasteners except at the inner fenders. Since there is really no convenient way to use any other type of hardware in place of those 6 push pins, due to the hole size in both the cover and the lower air dam, I decided to go an other way. I also feel that this choice works better in helping to tie the entire front nose area together better, this includes, reinforcing the lower air dam, a bit of a modification to the Inner fenders and front cover! So what I did was this; first I cut an 1/8” piece of aluminum to fit the back part of the lower air dam to take the warpage out of it that occurs over time due to a poor design, heat and the thickness of the plastic. I contour the ends of the aluminum plate to match the air dam and attach it using 3/16 aluminum pop rivets. 

 

This is a picture from a new front cover I’m working on for an other project, but you can see how large the push pin holes are and the holes in the lower air dam that mates to it are just as large.

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Below is a picture of the lower air dam that has been reinforced with the aluminum plate. This stiffens and straightens the defector portion of the lower air dam making it more effective at its function.

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I will update with more info soon.

Edited by Last Indian
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I buy #8 SS Phillips modified truss head lathe screws! These screws work well in plastic and have a large flat head to give good support for clamping. Lay on your back, if you don’t have a lift, and look at the bottom side of the front cover where it interfaces with the lower air dam. This is where you will drill 6 holes 1/8” in diameter through the cover and lower air dam to attach them to each other with the #8 SS Phillips modified truss head lathe screws. Once this is done and the cover is attached to the inner fender the front cover will be quite ridged. Additionally in the front an other part that is prone too vibration are the headlights! This issue I handled by adding stabilizing spacer/shelf below the headlight and attached it to the impact bumper. This, like the front cover, makes the headlights ridged like cars of the past. One additional thing you can do to stiffen things just a little further is a single #6 SS sheet metal screw mid way up and mid way inboard at the front of the front inside fender. Drill a appropriate hole through the plastic inside fender and through the steel inside fender and install the SS screw. This single attachment stiffens the inside fender substantially. All of this will really change the entire quality of the car! How it feels, how it reacts, how it sounds over the road!


The picture below Depicts the attachment of the cover to the lower air damm

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below is showing the stabilizing block arrangement for the headlight assembly. This consists of a shock absorbing lower block, ( like you use to isolate equipment vibration )with an upper soft dense foam pad, ( like you kneel on ). The lower block is bonded to the impact bar and the pad is bonded to the block.

FCE08114-725B-48F7-9B28-802C4863DCCC.jpeg

Edited by Last Indian
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