C3 Headlight Door Adjustment (Read 4622 times)
Mar 18th, 2012 at 7:22pm
Shark76   Ex Member

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 rods) 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 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 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.
IP Logged
Reply #1 - Mar 19th, 2012 at 6:12am

TX 73 gone   Offline
Top Gun Member
My Vette went to a good
Sugar Land, TX

Gender: male
Posts: 2155
Awesome Info. The one I have that will not go down by itself makes the thud so as soon as I get around to adjusting it, I can scratch one more thing off my list. Thanks a lot for all the details,

... ... ...
IP Logged

Copy Rights and Trademarks Disclaimer: The Corvette name is a copyrighted trademark / sales mark of the Chevrolet Motors Division of General Motors. Any use of the Corvette name at this site is used only as a point of reference to their automobiles or automotive products line of the same name. No copyright / trademark / sales mark infringements are intended or implied. This web site is independently operated as a free informational service for the benefit of Corvette Owners and other interested parties. Neither the Chevrolet Motor Division nor any other segment of General Motors or its affiliates or subsidiaries shall bear any responsibility whatsoever for its content.

CorvetteC3.com Privacy Policy: Some or all of our partners, affiliates, advertisers and other associates may collect, serve and/or use computer cookies to enhance user experiences. Cookies are generally not considered "problematic" or harmful. However, please be advised that "cookies and IP related information" are being collected, tracked and used while visiting and using our website. By using and visiting www.corvettec3.com, you agree to be bound by the terms contained herein. Clearing Web Browser Cookies. We use third-party advertising companies to serve ads when you visit our website. These companies may use information (not including your name, address, email address, or telephone number) about your visits to this and other websites in order to provide advertisements about goods and services of interest to you. If you would like more information about this practice and to know your choices about not having this information used by these companies, click here.