[wmurrell]

Does anyone have any documentation that would support when the 1965 tachometer was changed from an all green band to a version that was green, changing to red? All I can find is that is was sometime in mid-year. I have found some opinions that it was somewhere around late April or early May. Comments? Thanks!

[Jeff Hamlin]

I just checked the '65 Service Bulletins and saw nothing.

Check with Pete Serio if anyone would have info on it, it would be him.

http://precisionpontiac.net/

[padgett]

68 parts book grp 9.750 shows three tachs for '65 Tempest: six cyl, 8 cyl points, and 8 cyl TI ignition. No mention of different faces. Plain green has 6412412 on the back. Only thing on back of the 5200 red line is a big "15".

[Peter Serio]

There is an electrical part on the circuit board of many of the 65 and 66 factory GTO tachometers which has 4 diodes inside of it. Two Zener diodes and 2 rectifier diodes. Since the 65 and 66 circuit boards were mostly "hand soldered" in order to save time & money GM had a special module custom-made that has those 4 diodes inside of it. So rather than have to solder 4 diodes X 2 leads per for a total of 8 leads to the board the packaged item only has 4. One is a common ground and inside of the module the 2 Zener diodes are joined cathode to cathode so you only have 4 "leads."

This custom made module has a date code stamped in white ink on top if it. It has a month and a year. Two digits for the (year). I have had many 100s of GTO tachometers pass thru my hands & I pay attention to the date stamp on that module. From what I have seen on the '65 factory rally gauge GTO in dash tachometers the cars started out with an all green band on the dial from zero to 8,000 RPM. The new owner of the car was suppose to set the twist pointer (in the clear lens) at 5,000 RPM. In effect that was your "red line." As the model year goes on it is normal for GM to make changes, around the end of the year 1964. (From the circuit boards I have seen) They modified the accent paint stripe on the tach dial and from that point forward it shows a green band from zero to 5,100 RPM and then it changes a red/orange fluorescent color from that point onward to 8,000 RPM. I believe this change was set in place around the re-start of January 2nd of the year 1965. Since instrument clusters were all assembled at AC Delco in Michigan then shipped out to the assembly factory(s), it is very possible that there could have been some overlap of a week or 2 + or "-" to these dates.

[padgett]

Don't have any here but my memory is a bit different. The d'arsonval tachs used in the 60's were either passive (points) or added a transistor front end (Delcotronic).

Back in the day I just added a one transistor add-on board with this front end to a passive tach to make compatible with a Unitized or HEI.

Like this (two pages combined):

[tallrandyb]

Thanks Pete. When my car was restored they put Rally gauges in but it has full green, and mine is a late June/July build 65. I’m going to pull my dash next summer during the Florida heat to fix a few things, can I just buy the correct red-line face and swap them then? If so, do you sell them?

Thanks!

[wmurrell]

Originally Posted by Peter Serio

There is an electrical part on the circuit board of many of the 65 and 66 factory GTO tachometers which has 4 diodes inside of it. Two Zener diodes and 2 rectifier diodes. Since the 65 and 66 circuit boards were mostly "hand soldered" in order to save time & money GM had a special module custom-made that has those 4 diodes inside of it. So rather than have to solder 4 diodes X 2 leads per for a total of 8 leads to the board the packaged item only has 4. One is a common ground and inside of the module the 2 Zener diodes are joined cathode to cathode so you only have 4 "leads."

This custom made module has a date code stamped in white ink on top if it. It has a month and a year. Two digits for the (year). I have had many 100s of GTO tachometers pass thru my hands & I pay attention to the date stamp on that module. From what I have seen on the '65 factory rally gauge GTO in dash tachometers the cars started out with an all green band on the dial from zero to 8,000 RPM. The new owner of the car was suppose to set the twist pointer (in the clear lens) at 5,000 RPM. In effect that was your "red line." As the model year goes on it is normal for GM to make changes, around the end of the year 1964. (From the circuit boards I have seen) They modified the accent paint stripe on the tach dial and from that point forward it shows a green band from zero to 5,100 RPM and then it changes a red/orange fluorescent color from that point onward to 8,000 RPM. I believe this change was set in place around the re-start of January 2nd of the year 1965. Since instrument clusters were all assembled at AC Delco in Michigan then shipped out to the assembly factory(s), it is very possible that there could have been some overlap of a week or 2 + or "-" to these dates.

Thanks for joining the conversation. I am not sure about the January change over date. I have a relatively low mileage original (mostly) that was built in the first week of April and the tach has a green band. I manage the '65 convertible tripower/4 spd registry and we have a few low mileage cars that folks have owned for a long time. There is another car that was built during the fifth week of March and he has owned the car since 1975. The tach in that car also has the green band. Both of the cars I referenced were assembled at the Pontiac plant. There is a lower mileage car in the registry that was built later in May and the tach has the green to red band.
Since the cars were not owned from the beginning, you never know for sure if the gauges have been swapped out at some point. I was hoping that there might be some owners with low mileage cars that could share what type of tach they had.

[tallrandyb]

wmurrell,

The answer to your question would be great to know. My 65 GTO was invoiced in may 65 and with other EUN numbers I have seen, those implied a June/July build for my car according to my EUN on my Protect-o-Plate, I thought. I'll have my dash off next summer so if a green-to-red band tach face is more accurate I could swap one in then.