67 small gauge lens - convex or concave?

67ragtop · 03-26-04, 12:09 AM

As a new member, I would first like to thank the people responsible for putting this forum together and everyone that participates. This is absolutely the best forum for Corvette enthusiasts and has been a tremendous wealth of knowledge for me personally.

I’ve been cleaning up an original 67 convertible I purchased last October. I’m putting the gauge cluster back together and am puzzled at which way the small gauge lens go in. The NCRS technical manual says they have a "concave appearance". To me that means the center portion on the glass dishes in towards the gauge. I’m sure when I took them out, the center area dished out away from the gauge.

Could someone please explain which way these things go in? I would hate to find out down the road that I put them in backwards!

jerrybramlett · 03-26-04, 07:15 AM

The concave shape minimizes reflections so you can read the gauges easier. Chevrolet made the change from convex to concave lenses in the late fifties.

67HEAVEN · 03-26-04, 08:19 AM

67ragtop,

Welcome to

From the perspective of the driver's seat, the lens dish in rather than out.

Glad to have you with us.

67ragtop · 03-26-04, 09:19 AM

Thanks guys. Almost made a huge mistake!

tigernut · 03-26-04, 02:15 PM

Does the same hold true for the speedo and tach lenses?

I'm restoring my cluster as well and all the lenses were dished out.

JohnZ · 03-26-04, 08:27 PM

All are concave (dished in towards the gauge faces) except the tach and speedo on 67's with the U15 Speed Warning Buzzer option; about 10% of '67 production was built with U15, but you very rarely see one - most quit working eventually and were replaced with a standard speedo and lens. Pic below of a '67 U15 cluster - speedo and tach needle centers are different, plus the convex lenses and setting stem and knob that goes through the speedo lens.

tigernut · 03-26-04, 09:01 PM

Thank you John.

Ken Anderson · 03-28-04, 08:33 PM

All Lenses "dish In", Even The Speed Warning Warning. Anything Else Is Not As It Left The Factory. The Speed Warning Uses 63 Plastic Lenses For The The Tach & Speedo (so The Hole Could Be Drilled For The Speed Warning Shaft) And Glass For The Gauges.

JohnZ · 03-29-04, 08:43 PM

From the NCRS '67 Judging Guide: "All the lenses in the cluster are glass, with a concave appearance except the lens over the trip odometer, which is flat plastic. Cars equipped with the speed-warning option, U15, also have a convex plastic lens on the speedometer and tachometer in lieu of glass."

I haven't measured, but it seems like the center of the concave '63 tach/speedo lenses would interfere with the '64-'67 needle hubs, which are closer to the cluster face than the '63 needle hubs.

67HEAVEN · 03-29-04, 09:02 PM

Thanks for the clarification, John. For a moment there, I thought we were about to witness history in the making.

67ragtop · 03-29-04, 10:13 PM

Guys,

I’m no expert here but… My dash is currently sitting on the workbench and I tried installing the lens convex. If I laid the speedometer directly on the lens retaining plate, the speed-warning shaft only sticks through the lens about 1/4”. That is not enough to install the knob. When I secured the speedometer, the situation gets worse as I’m pulling the gauge further away from the lens. Maybe the replacement lens has more of an arc then the originals had? I don’t see how the lens could possibly be installed convex. If anyone has the answer, please let me know. The NCRS website had several (older) postings regarding this. It seemed the consensus there was to install them concave.

JohnZ · 03-31-04, 02:40 PM

Well, I did a little research (if you're not sure, find someone who knows more about it than you do

); I posed the question to Brian Tilles, owner of Corvette Specialties of Maryland, one of the premier C2 cluster/gauge restorers/rebuilders in the hobby, and Brian sent me this note today:

"That is a real easy one. Yes, the lenses were plastic. That means both of the Speedo and tach! They were also curved and installed in the manner that would make them appear concave. They were actually the same that was used in 63. The installation procedure was a little tricky with the lens bumpers installed in a different fashion.
Spacing was critical on the installed lens because of the height difference on the pointers. As you know, the pointer hubs were different and extended further out on this application. Very close to the lens I might add. Also, if the lenses were installed in a convex position, the knob would not install."

Looks like Ken was right on the money, and it also looks like the NCRS TM&JG needs some tweaking! Thanks, Ken

Ken Anderson · 04-01-04, 09:54 AM

You are welcome. Sometimes Noland Adams & the NCRS are little off when it comes to the tech stuff or their memory fades lie mine does over time. This lens issue has been an inside joke with the rebuilders, like Brian, for years.

JohnZ · 04-02-04, 03:13 PM

I submitted the proposal today to revise that portion of the JG - I'm a member of the '67 TM&JG Revision Team.