SprintCarDriver

Is there a Tach filter on the 78 and if so where is it located?

dman535

Parts book quotes the name part number 75-80. It should be attached to the intake manifold, drivers side rear.

From what I have been told its not required.

Paul Borowski

Not at all needed, so this owner thought too...

dgruenke

There should be three wires that plug into the coil on the distributor. The large one is from the battery (gives it juice). There are two smaller ones, side by side, in front of the battery wire. One of those is the tach wire. If you follow that wire, it should have an in-line filter in it. Good Luck.

mrvette

Yes the tach filter or electronic equivalent is required with a stock tach, it smoothes out the pulses from the dist. to the tach doesn't bounce around at various RPM's.....

GENE

dman535

I removed mine from my car and the tach works perfectly. It is impossible that its removal would cause a safety issue. All the filter really is is a capacitor, designed to filter out a range of frequencies on the electromagnetic spectrum.

Here is a schematic of the GM tach filter ( from a Fiero board)

mrvette

The Tach filter is NOT an RFI/EMI thing....it's to integrate out the pulses going into the tach...the HEI or any coil rings quite a bit when points/sending unit opens up the primary circuit....and it's those extra rings that cause sometimes the tach to read rong...this can vary a bit from tach to tach and maybe even the specifics of the HEI....but at any rate the filter cures any problems....

that schematic is not the one I have....I dunno what they did for the 6 cyl engines, but on the vette it's one more pole to the filter, and differant resistor arrangement....

GENE

MIKER

mrvette,
check out this post from the archives. Is the schematic posted by Smokehouse69 the one that you are talking about?
http://forums.corvetteforum.com/zerothread?id=136220