Reaper19

I have a 1981 corvette and after troubleshooting, disconnecting speedometer cables for a possible ticking sound I found that actually the ticking was coming from the tachometer when I get up to 2000 to 2200 or above while doing speeds of around 50 mph or above. I have searched the Internet and found how to replace the tachometer and circuit board, but can the tach be taken apart and lubed? Or does the whole tach assembly need replacement?

Thanks

0Willcox Corvette

Are you sure it's the tach? I've never seen or heard that before.

If you'd like to be positive, send me the tach I can put it on my tester and see if it ticks.

Willcox

Reaper19

Thank you for the reply. I'm not completely positive, but so far I have tested the speedometer by disconnecting the upper, lower, running with only the bottom cable and no cable and the sound still appears to be coming from the dash. I have eliminated the transducer took it apart and it looks brand new, the previous owner was trying to troubleshoot the cruise. I am als trying to reconnect all the wiring to the cruise and get it working.

My next step is to pull the tach connection at the distributor and test drive. This should keep the tach from spinning and if I still hear ticking, start hunting down another possible source. If no tick then it points to the tach and I will need to have it repaired and send it up.

0Willcox Corvette

You could just pull the tach, hard wire it and use the distributor for signal.. that would be easier than sending it to me.

Instructions are on my site on how to easily pull the tach.. and how to hot wire it.

Run power and ground to here:


Corvette Tachometer Testing, Removal, Board Installation, Video Link 1978-1982

mikem350

I think the clue here is it shows up at 50 mph...

0Willcox Corvette

And one reason I don't think it's the tach.

Possibly another quick check would be to just drive the car in low until it hits 2000-2200 rpms, see if it does it at 35 mph @ 2200.

Willcox

Reaper19

I'm going to try your suggestions after work and let you guys know what happens. If I disconnect the tach from the distributor to stop it from working temporarily and the ticking goes away during the test run, we know the tach is the issue. If the ticking remains then it is coming from someplace else and need to find out what it may be since then speedo and tach will both be eliminated after troubleshooting both.

Thanks

Reaper19

Well, I disconnected the Tach from the Distributor, took the car for a test run and the ticking was still there. This concludes the speedometer, cables, transducer and the Tach are working properly without creating the noise.

I started searching around the car while it was running, revved up the engine a few times and noticed their is a ticking that comes and goes from the engine at a higher RPM. Originally when I bought the car in October it had 99,200 original miles on it and one of the lifters was sticking and ticking at idle. I had my mechanic do a complete go around with me and we replaced exhaust manifold gaskets, intake gaskets, and did a transmission seal job. These were the major items needed and I did some general maintenance as well. He expected since the original oil and top end of the engine looked a little dirty the lifter would stop after a few oil changes. The car was owned by an older couple and they only put 1,000 miles a year on the car since 1988 but took care of the car and it was well maintained. After a few quick oil changes and driving the car around more the lifter stopped ticking at idle.

I guess it is time to start searching around again for the possible ticking sound when I reach 50-55 mph and 2000-2200 RPM. I also noticed when driving down the freeway near the retaining wall I can hear an echo of the ticking sound bounce off the wall, which sounds like it is coming from under the car or under the hood. I am wondering now if the lifter, valve or bearing is slapping around at highway speeds or there could be an exhaust leak causing the ticking and making it sound like it is coming from under dash with the windows up.

The other item I need to address, the PO did not run the spark plug wires between the engine mounts and engine through the spark plug shields (driver side shield is missing need to replace), but chose to run them around the exhaust over the frame and then back up to the distributor, which may be sparking at high speeds causing ticking?

Any ideas you guys might be able to share would be very appreciated. I know with 99,950 original miles on the engine it may also be time to think about a rebuild or crate engine like the GM ZZ4. A couple of guys in our local corvette club have done both and the ones that rebuilt their engines said if they did it again they would do the crate engine, it is much more economical and you get an engine with twice the horse power with a warranty. Then just hold on to the original motor in case you decide to rebuild or sell the car with the original motor.

Reaper19

Just got back from my corvette mechanic this afternoon. He listened to the knocking from the top and bottom of the engine. The knock is coming from the bottom and he said they can pull the oil pan to look for issues, but with 100,000 miles on the car it would probably be more economical and money well spent to do a complete rebuild with an upgraded cam and higher 9.5 to 1 compression pistons.

0Willcox Corvette

Ouch, that's not good.