Since the early 70’s D & M Restoration has rebuilt many speed warning clusters. We are frequently asked questions from customers who try to install a ’67 speed warning speedometer and encounter several problems. We hope this article will clear some of this up.
In 1967, the Corvette offered an optional speed-warning speedometer. The idea was that the driver would set the small, pale yellow needle on the speedometer to the speed that he didn’t want to exceed. When the main speedometer needle reached the place where the small needle was set, a little hairspring on the large needle would make contact with a peg on the small needle, completing a path to ground. That in turn would set off an external speed-warning buzzer. In order for this to happen, the metal faceplate had to be insulated from making contact with the speedometer main frame and the front of the cluster. This was accomplished by the installation of two fiber washers and two plastic screws, which mounted the faceplate to the speedometer main frame. A piece of electrical tape was also placed on the outer edge of the odometer frame so that any short would be prevented should the frame and face touch.
The face plate also had a flat brass strap that went to the left side of the speedometer frame (looking from the back). It made a 90 degree contact on the speedo/tach mount plate. Note: This 90 degree bend was on the strap and had to be kept from contacting the frame by using electrical tape. When the speedometer was mounted to the backplate, it had to make contact with the plate in order to achieve a good ground. But this was not possible due to the rubber pad and two rubber grommets on the mounting screws. So a brass tab with teeth on it was attached to one of the mounting screws. It then made contact with the frame when the brass teeth on the tab went over the grommet and made contact with the mounting plate.
The needle used on this speedometer was totally different from the stock needles. Because of this, the same style needle was used on the tachometer, minus the hairspring. These needles were almost ¼ inch taller than the stock needles.
In l967, the cluster remained unchanged except for the tachometer and speedometer lenses which were changed to plastic ones (like 1963). The small gauge lenses (4) were glass. They were all still concave but because of the longer needle shaft length on the speedo and tach, if not modified, the needles would make contact with the lenses. In order to prevent this when installing the lenses into the cluster, the small glass lenses were installed normally with the rubber pads first, then the lenses. But on the speedo/tachs, the lens was installed first, then the rubber pads were installed on the backside of the two plastic lenses. Then the lens holding plate was installed. This gave just enough clearance for the needles.
The following is a tip for those of you who are doing their own restorations on ‘64/67 Corvette dash clusters:
When installing glass lenses back into your cluster after you restore it, make sure you have clearance on all sides of glass lenses. Make sure the lenses are not touching the side(s) of the cluster anywhere. Then you can install your plate that holds all 6 lenses in place. If you do not do this, it’s very likely that when a temperature change occurs (i.e., going from your garage to outside or the cooling off in the evening), the glass lenses will crack across the lenses if they are touching the cluster. This would make for a bad situation causing you to have to take the whole cluster out.