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Installing a RIGID fiberglass front bumper cover for a 1975 Corvette
To start this off...PLEASE read this so you can better understand what is explained in future posts
I am installing a rigid ( NOT flex-glass) front bumper on a 1975 Corvette. I am also doing the rear bumper as well but that will be in a another thread.
PLEASE keep in mind that I have installed the rigid fiberglass bumpers since 1985. And I do not do the flex type because ...I just do not like them. To me...they are too thin and feel cheap...and ...keep in mind....I got used to the really heavy thick fiberglass bumpers from a long time ago.
So...use what you want. If you have installed flex bumpers and are happy...GREAT. I am only posting this so those who want the rigid design can possibly employ this and get there bumpers to fit like a glove.
AND...as you will see in this thread....that REGARDLESS if it is a RIGID or 'flex' type. What I ran into on this car still required bumper modification due to a very poor previous body repair. So their are NO GUARANTEES that gettign a 'flex' bumper is going to completely solve all fitting issues.
Hopefully some of what I do will help others or possibly 'explain' why the fiberglass bumper they installed has problems in the surface across the top edge where the bumper meets the body. And that goes for BOTH design...rigid or 'flex'.
LASTLY....also keep in mind that these hand laid bumpers are made by people. And the 'human factor' does come into play. And I know this and have experienced it for decades. Complaining about it often times falls on deaf ears when I express what I find. And getting another part due to the one I have was faulty...well... the one they send may actually be worse and I loose time waiting on parts to arrive. So I typically fix what I have unless it is a compete disaster of a part. And knowing where to 'check' the part for possible air pockets and potential failure is something I am accustomed to doing. SO...honestly...I do not loose any sleep over it or get upset. it is all a part of doing this job and making sure that the bumper is solid and will not come back with issues when they are outside and get hot. SO much of this depends on who is laminating the part. So...that means...NOT all companies who make these rigid bumpers have the same problems. But it is still possible and checking them should be done so you do not have any surprises when it is on and painted.
The Corvette came in and the owner had already removed the front bumper cover.
This photo is showing the masking tape that I applied VERY CAREFULLY to the painted surface to protect it.
After the tape is applied. I take a pencil and mark the oval slots where the studs go through the front flange so the bumper can be secured to the body. I mark the width of the oval slot in the metal retainer behind the fiberglass...and NOT the lager oval slot in the fiberglass itself. So you may need to get down and look carefully.
Then I applied a layer of my mold release wax and allowed it to dry.
Now I apply a piece of tape across the top edge of the bumper being installed. I go and install the bumper on the car. The bumper basically centers itself...and I transfer the pencil lines I made on the front clip to the tape I applied on the new bumper.
Then I measure how far down from the top edge of the car the hole is..and measure down the same amount and route out the hole so the metal retainer can be installed.
I then prep the flat surface where just put the oval slotted holes for the retainers.
I then take a handle from a plastic screwdriver and I lightly tap on the sharp edge of the bumper where it meets the panel. This sharp edge CAN have air pockets in it and NOW is when I want to know if they are in there or not. I preform this test on ANY sharp 90 degree bend in the panel. I also check the 'bumperettes'.
The test did provide some areas where the gelcoat popped off the bumper covers edge and exposed air pockets.
I take the factory retainers an weld the stud to the retainer so it can not spin.
When that is competed. I then install these retainers....and while clamping them in place. I drill a 1/8" hole. Countersink the hole a bit so the head of my 1/8" rivet is flush or slightly under the surface of the flange.
A rather good one...you can see on the right side that the air pocket was just below the thickness of the gelcoat at the corner. NO WORRIES..as I wrote before....I am going to fix this stuff.
Here I ground down the fiberglass and got the air pocket to be level so I can fill it in. NO big sweat.
The same goes for the side that had the really good air pocket. I just ground it out.
NOW the fun begins. Getting the front bumper set in place. The gap on the left side is really bad DUE TO previous bad body work. The bumper is sticking out so far due to the radius of the body being wrong.
This car is NOT having the front clip painted...so I have to modify the front bumper cover to correct that very bad gap.
Close up view on how far away the bumper is. The bumper is touching at the top corner...but the gap in front of the headlight needs to be corrected..and I will show you how I did it.
Body is masked off...and waxed up the tape...and now with the bumper on and clamped/nutted in place and all prep grinding at the top edge completed. I am ready for filling it in.
Notice on the top edge of the bumper how I basically removed all the gelcoat and gettign the air pockets out.
I applied the Vette Panel Adhesive. while it was setting up..I carefully blocked it down somewhat. Much more to go...this is just the first go round.
AS you can see..I also applied some VPA on the cut I made to hold its position. I will laminate it on the underside when I remove the cover. but the VPA is good enough to hold it for now.
AS you notice...I stopped the adhesive at the top corners and did NOT go down the sides at this time..that is coming later.
With a wax interface on the tape and the VPA up against the wax, what do you use to remove the wax(or do you) prior to sanding on the VPA so as to not smear the wax around the exposed glass and VPA?
Another good tutorial session. I will be approaching this phase soon except I was going to be bonding the bumper to the body, may rethink this after seeing some results.
With a wax interface on the tape and the VPA up against the wax, what do you use to remove the wax(or do you) prior to sanding on the VPA so as to not smear the wax around the exposed glass and VPA?
Dave.
The wax is not wet. I let this mold release wax dry...so there is like a crusty coating where it does not come off.
But IF I have a concern... which in 30 years I have not been bit by the wax on that back edge..I wipe it with acetone. Even though the VPA has good 'bite' ....it does not stick and pull any of this wax.
Another good tutorial session. I will be approaching this phase soon except I was going to be bonding the bumper to the body, may rethink this after seeing some results.
Hopefully when you see it when I am done...you DO choose to not mold them in. But if you do mold them in... do hope all goes well for you.
I used to do it a long time ago...but back then the bumpers were really thick. Now-a-days...they are not like that. And I know some people have done it but I would like to see one out in the sun. The ghost line will more than likely appear.
09-11-2016, 06:41 PM
Installing a RIGID fiberglass front bumper cover for a 1975 Corvette
