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Hi, I'm trying to help out a friend who's '79 tach seems to be faulty. Seems to read correctly at idle but at 60 mph its reading something like 4k rpm. Checked the diff ratio it checked out at just a little past 3:1 so assume its 3.33 (car is an L82). Checked the speedometer against GPS and its accurate to within 3 mph at 60mph. I don't have a timing light with inbuilt rpm to verify the tach reading. Did a search of the forums and so far haven't found anyone with exactly the same issue.
I'm picking its likely that the tach board will need changed so looking for these instructions if anyone has a copy? Tried Willcox site but seems its closed.
I have and 81 and just pulled the speedo this morning. Assuming yours is similar and takes about 10 minutes. Remove screws holding clear plastic lens over tach and speedo. 6 upper and 1 each side- phillips. Remove 6 allen screws holding gauge cover on and remove. Tach and speedo with be right there held in with 1/4" hex screws.
Well the 79 tach is very easy to remove. Just screws on trim and the tach screws out it comes.
power the tach with 12 and make sure zero.
board is probably bad.
skip to post 140 for my fix https://www.corvetteforum.com/forums...uestion-8.html
Well the 79 tach is very easy to remove. Just screws on trim and the tach screws out it comes.
power the tach with 12 and make sure zero.
board is probably bad.
skip to post 140 for my fix https://www.corvetteforum.com/forums...uestion-8.html
Thanks, I will pass the info to the owner, we have a 180 mile run on this weekend coming, he often lags behind because he's worried the engine is over-revving so it will be good to sort this problem.
'79 Vette tach removal instructions
