C3 headlight door Adjustment
Le Mans Master
Joined: May 2003
Posts: 8,876
Likes: 3,556
From: Fernandina Beach FL
2023 Restomod of the Year finalist
2020 C3 of the Year Winner - Modified
Here you go-
https://www.corvetteforum.com/forums...alignment.html
"Sharing the fruits of my hard labor. I've seen a number of incomplete and/or erroneous posts on this subject, so I reasoned out the process and tested it on my 76. Here are the steps in the correct order. Do this with the engine not running and no vacuum in the reservoir, or you could get pinched fingers (or worse). Remove the grill (5 screws) so you can reach the mechanism from the front as well as from underneath.
1. If a new installation, center the headlight door in the opening by adjusting the pivot points and the collars (on the hinge posts) at the upper rear corners of the assembly. Hold the door in the closed position and adjust the pivot points until the corners of the door are aligned with the corners of the opening. Don't worry about the final open/closeed height at this point - just be sure the door is centered and on the same plane as the surrounding bodywork when held in the closed position. Tighten the pivot point mounting bolts and verify the alignment is still correct in the closed position.
2. Loosen the 3 bolts on the bracket in front of the vacuum actuator (NOT the ones on the vacuum actuator itself) - the ones that locate the bracket holding the linkage with the springs and the clevis (remove the clevis to get at the center bolt). To remove the clevis, first remove the 2 springs that attach to the clevis pin, then the cotter pin and the clevis pin itself. The other 2 springs can stay attached.
3. Adjust the full open height with the adjusting bolt - the one on the arm that contacts the headlight frame when full open. Out is lower, in is higher. Use a long socket extension and a universal joint to reach the adjusting bolt through the grill opening. Make the bottom of the bezel flush with the front edge of the opening.
4. Actuate the mechanism by hand so you can feel the "over center" condition when the door is fully open and the linkage fully extended forward. Move the bracket until you get a slight interference fit - the linkage gently, but firmly, "snaps" forward into the over center position when you actuate it manually. Tighten the 3 bolts loosened in step 2.
5. Adjust the clevis by turning it on its shaft until the clevis pin (the rod that goes through the clevis, and where the springs mount) is all the way to the front of the curved slot it rides in. Remove the clevis pin and turn the clevis 1 to 1 1/2 turns counterclockwise to give a slight interference fit at the end of its travel in the open position. The clevis must extend enough to push the linkage into the over center position, which is what locks the door in the open position. The interference fit ensures this locking, and prevents rattles too.
6. Last step - adjust the closed position with the small hex bolt - this is in the center of the linkage, and points down at the ground when the door is closed. The hex is small - the same size as the diameter of the bolt itself. Adjust so the front edge of the door is about 1/32" inch lower than the front edge of the opening. This will minimize wind noise and water entry.
7. Test. The door should snap into full open firmly, with a click, but not a thud. If it makes a loud thud or a bang, re-do step 4. The thud means the over center position is too tight, and this will put too much strain on the linkage, damaging it over time.
Note: It goes without saying, but just in case, you should use a good lubricant on all pivot points and moving parts in the linkage."
https://www.corvetteforum.com/forums...alignment.html
"Sharing the fruits of my hard labor. I've seen a number of incomplete and/or erroneous posts on this subject, so I reasoned out the process and tested it on my 76. Here are the steps in the correct order. Do this with the engine not running and no vacuum in the reservoir, or you could get pinched fingers (or worse). Remove the grill (5 screws) so you can reach the mechanism from the front as well as from underneath.
1. If a new installation, center the headlight door in the opening by adjusting the pivot points and the collars (on the hinge posts) at the upper rear corners of the assembly. Hold the door in the closed position and adjust the pivot points until the corners of the door are aligned with the corners of the opening. Don't worry about the final open/closeed height at this point - just be sure the door is centered and on the same plane as the surrounding bodywork when held in the closed position. Tighten the pivot point mounting bolts and verify the alignment is still correct in the closed position.
2. Loosen the 3 bolts on the bracket in front of the vacuum actuator (NOT the ones on the vacuum actuator itself) - the ones that locate the bracket holding the linkage with the springs and the clevis (remove the clevis to get at the center bolt). To remove the clevis, first remove the 2 springs that attach to the clevis pin, then the cotter pin and the clevis pin itself. The other 2 springs can stay attached.
3. Adjust the full open height with the adjusting bolt - the one on the arm that contacts the headlight frame when full open. Out is lower, in is higher. Use a long socket extension and a universal joint to reach the adjusting bolt through the grill opening. Make the bottom of the bezel flush with the front edge of the opening.
4. Actuate the mechanism by hand so you can feel the "over center" condition when the door is fully open and the linkage fully extended forward. Move the bracket until you get a slight interference fit - the linkage gently, but firmly, "snaps" forward into the over center position when you actuate it manually. Tighten the 3 bolts loosened in step 2.
5. Adjust the clevis by turning it on its shaft until the clevis pin (the rod that goes through the clevis, and where the springs mount) is all the way to the front of the curved slot it rides in. Remove the clevis pin and turn the clevis 1 to 1 1/2 turns counterclockwise to give a slight interference fit at the end of its travel in the open position. The clevis must extend enough to push the linkage into the over center position, which is what locks the door in the open position. The interference fit ensures this locking, and prevents rattles too.
6. Last step - adjust the closed position with the small hex bolt - this is in the center of the linkage, and points down at the ground when the door is closed. The hex is small - the same size as the diameter of the bolt itself. Adjust so the front edge of the door is about 1/32" inch lower than the front edge of the opening. This will minimize wind noise and water entry.
7. Test. The door should snap into full open firmly, with a click, but not a thud. If it makes a loud thud or a bang, re-do step 4. The thud means the over center position is too tight, and this will put too much strain on the linkage, damaging it over time.
Note: It goes without saying, but just in case, you should use a good lubricant on all pivot points and moving parts in the linkage."
Safety Car
Joined: Nov 2005
Posts: 3,532
Likes: 1,185
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Thanks for the info. I was just looking at the 82 AIM and it looks identical to the 74 in the pics, but it does not show screw 10 down stop or 5 up stop. Does anyone know if they are the same screws on the 82, but GM conveniently left them out of the diagram?
