Looking through the electrical sections of some of my manuals for some other stuff I came across the "tach filter" in the radio section. It's stated as "Radio Static Suppression". Is that all it's really for? Or does it actually have something to do with protecting the tach like everyone seems to claim?

Ive seen the same thing. Also in some wiring diagrams its shown in line with the pink (hot) wire to the dist, not the tach wire.

The filter, I believe does take out the noise from the radio. It also is supposed to keep the tach from eratic needle bounce. Maybe Joel will offer more on this.

[QUOTE=corvette440hp]Maybe Joel will offer more on this.[/QUOTE]

WHUT???
I can offer an opinion, based on a swag, and info from GM manuals.
The tach filter is supposed to keep noise out of the tach signal, which could cause the electronic tach to bounce, or flutter, or even give a false reading all the time. It's like a suppressor, of sorts...so they say. It also is supposed to keep the signal fairly steady during a miss-fire situation, or voltage fluctuations in the charging system.
As most of us know, electronic stuff really don't like voltage spikes...spikes BAD...let smoke out of 'puter... Voltage spikes from a failing/damaged ignition module could potentially damage the tach...


dam spelchek...Adams' Apple2008-09-02 10:13:39

Joel's opinion is right on.  The tach filter is kind of like a shock absorber for your tach reading.  It smooths out the erratic signal, and helps prevent spikes.

Larry

[QUOTE=VetteSpecialties]Joel's opinion is right on.  The tach filter is kind of like a shock absorber for your tach reading.  It smooths out the erratic signal, and helps prevent spikes.

Larry
[/QUOTE] mkapp78792008-09-02 13:43:56

The electrical noise affects the tach and the radio.  The capaciter on the blower motor, turn signal flasher, etc. do the same thing.  Any electrical spikes or fluctuations will cause a noise in the radio.

[QUOTE=mkapp7879][QUOTE=VetteSpecialties]Joel's opinion is right on.  The tach filter is kind of like a shock absorber for your tach reading.  It smooths out the erratic signal, and helps prevent spikes.

Larry
[/QUOTE] [/QUOTE] I definitely think that it serves both purposes. That's why there are condensers located all over and also all the shielding around the distributor and plug wires. They were used to cancel out interference with the engine running with the radio playing.

Searching through my 78 GM shop manual, which covers ALL 78 Chevrolets, it appears the Corvette is the only one with a tach filter. Don't see it for Camaro or Monte.

The way I understand it is because of the fiberglass firewall. A regular steel cars didn't have the problems needing all the condensers to ground to cancel out the interference.........it was a problem mostly for the vette.