Tachometer Whats UP!!!!
Thread Starter
Pro
Joined: Feb 2007
Posts: 548
Likes: 1
From: Victoria VA
Tachometer Whats UP!!!!
Well I noticed today when I went for a ride I gave the 77 a good run and when the tach got up around 5000 to 5500 it seemed to drop off some, The next time I noticed it even dropped back to 4000 then jumped around. So I was unsure of just what rpms I was running. What could this be and is there a simple quick fix?
Burning Brakes
Joined: Jan 2009
Posts: 1,224
Likes: 1
From: Clarksville Indiana
can you clarify if the engine rpm's are jumping around or just the reading on the tach and the engine is running fine? I cant help ya much either way, but I know it will tell somebody something... lol
Burning Brakes
Joined: Jan 2009
Posts: 1,224
Likes: 1
From: Clarksville Indiana
oh no I am just used to being the middle man between my customers and my techs. asking questions get them to the problem quicker a lot of times. I want to hear the answer myself. my tach in my nova does the same thing intermittantly, some voltage drop or something, the engine speed dosent change just a screwy tach.
Instructor
Joined: Oct 2006
Posts: 219
Likes: 0
From: Jupiter FL
The most likely problem may be the tach board is going. Another thing that causes the needle to act erratically can be if a damping fluid that is in the meter head dries up. Either way, solvable issues.
www.harrisonspeedometer.com
www.harrisonspeedometer.com
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Since your tach is electric [not mechanical like earlier years], the problem is the tach driver board {inside the instrument cluster} or the line filter {engine compartment}. Both are available and both can be replaced or repaired without too much trouble. {What damping fluid?}
Racer
Joined: May 2007
Posts: 370
Likes: 0
From: Cherry Hill N.J.
Tach Whats up?
The filter you are looking for should be located near the base of the distributor...on driver's side......It is a metal cylinder about 1 1/2 inches long with a brown(?) wire at each end. Real easy to access and replace..
Good Luck
Good Luck
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
There are differing opinions as to the purpose of the tach filter, however all seem to agree that you can bypass it for testing purposes. Just unplug the wire from the filter at the distributor and plug the tach wire directly in there. If the tach then functions correctly, then you know the filter was the problem. It's available from some of the Corvette parts suppliers.
If you decide the tach board needs to be replaced, do some research here to find which one works best, some are a waste of money and time.
If you decide the tach board needs to be replaced, do some research here to find which one works best, some are a waste of money and time.
Last edited by '75; Feb 8, 2009 at 12:35 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Do an "Archive" search on tach filter. There have been many posts, and some show the specific circuit and components of that filter. As I recall, it is a resistor [or two] and a capacitor...not a big deal to replace with simple parts you can get at Radio Shack.