C3 Horn & Tach

[don justham]

1. I have two horns, a 235 and 243. Are either of these the correct horn for my 1970 corvette? If not what are the correct horn numbers? Can a horn be fixed if it is not working & how?

2. My tachometer on my 1970 is not working. Hooked a drill to the dist. side and the tach worked. Do I need to replace the gear inside the dist? Is this difficult to do and how do you do it?

Thanks in advance.

[Jim T.]

Re: C3 Horn & Tach

Sounds like the gears are stripped/broken on the tack gear and the distributor shaft that drives the tack gear. Remove the connector that your tack cable connects to and pull out your tack gear and examine it. You should be able to tell if it looks like a gear is damaged. To examine the distributor shaft gearing cuts you will have to remove the distributor from the engine and then disassemble the distributor. Its is not difficult if you are going to be doing this yourself. Your distributor should also recieve servicing of the upper lubrication cavity of the distributor when you have it out. Do you have a 70 service manual?

[Joe L.]

Re: C3 Horn & Tach

Don-----

1) I agree with Jim on the tach; the distributor gears are the most likely problem given that you've pretty much determined that the tachometer instrument and drive cable are ok;

2) I believe that the correct horns for a 70 Corvette were "245" and "246"

[Harmon C.]

Re: C3 Horn & Tach

To add to the other posts I have found the square end of the cable to be too short either broken or worn off at the distributor end.

[Jack H.]

Yes, broken horns can be restored....

look in the services section of your copy of NCRS Driveline magazine and you'll find several folks offering this service. Dennis Portka from New York State probably has the most experience but there are others.

Also, the specific part numbers used by the factory for your horn are listed in the AIM (Assembly Instruction Manual) and should be called out in the Judging Guide too.

On the tach, don't rule out it's a simple matter of replacing the internal drive cable in the sheath. The end that inserts into the distributor should be square with sharp corners. If prior owners/mechanics mis-installed the cable (failed to insert fully and/or failed to fully tighten the attaching ring), the drive cable could now be rounded off and slipping.

Of course 'chomping' down on the drive end of the cable with drill's chuck, doesn't help matters either, but you DID verify gross functionality of the tach itself. If this is your problem, you can repair by replacing the tach cable altogether (you'll fight getting the replacement through the firewall grommet and routing it properly under the dash) or you can disconnect both ends, remove the original drive cable and install a replacement using the generic speedo cable repair kits (assortment of lengths that you cut to match) available at any auto parts store.

Done correctly, the generic repair kit DOES work! Plus, it's dirt cheap when compared to a replacement tach cable. If you go this route, be sure to buy some cable lube at the parts store and lay down a fresh coat for the internal walls of your existing cable sheath.