well the brand new circut board that i installed fixed the eratic behavior beautifully for about 300-400 miles...
my needle was rock solid and appeared to be very accurate after installing it...
but while cruising this weekend it started its wierd behavior again... :rolleyes:
not sure what im gonna do now but i thought some of you with the same problem would like to be kept up to speed on this...
im gonna call the tach guy today and i will keep yall posted...

 

Sign, what kind of weird behavior?? if the needle is flicking all over the place especially at higher rpm's......it's the tach filter under the hood....

need build a new one....or make sure the clip on the factory one is attached securelyto the engine....

but if the tach is dead totally, you might check a few voltages, on back to see if maybe it's a loose wire, or if not, you may have a bad meter movement...the part that drives the needle....lovely...

GENE

 

Here is a link to a guy who makes tach filters if you're interested!
http://my.execpc.com/~rodney1/corvette/

:auto:

 

I've seen some different views on this, (don't need a filter/do need a filter)but I've now come to the conclusion that although the tach will work without a filter, it will eventually get fried, since the filter's there for a reason.

By the way - mrvette, i didn't know the filter had to be earthed (i assume this is why it has to be screwed to the engine tightly?) mine's been bolted on the heater plenum since i had the car - i thought just assumed this was the way...
:nonod:
How do you go about rebuilding one?

 

TheoUK,
Hi, after I changed my manifold the tach was acting kinda strange. I cleaned up the tab on the filter & clamped it securely to the manifold & the tach has worked fine ever since (apart from once, but I don't really want to talk about that! :bb ).
I've got a circuit diagram for a filter somewhere. If you need it I can email it to you.
:cheers:

 

The filter is two pole, pie network....and yes it should be grounded to electrical ground...engine, or any other....

look on the forum search under tach filter, and the schematic should pop up somewhere.....

Radiio shack parts, or better yet a REAL parts house...

GENE

 

ok...this is kinda strange but my tach worked perfectly today...HHMMM
heres a little history on my tach saga...
last year it was acting a little funny sometimes so while at Carlisle i talked to several people about tach filters...
one was a guy that repairs clocks, speedos, tachs and various gauges for vettes...
i cant remember the name of his business but i DO know that it is a popular one that many here would recognize...
anyway...what he told me was that if it is working at all...the filter is good...
he said that if the filter was bad...the tach wouldnt work at all...
if the tach is sparatic...it is the board OR one of a few other things...
the other guy that i spoke with sold tach filters...
he in no uncertain terms told me that he would be happy to sell me a filter but he felt confident that it would not fix my problem and that he agreed with the other gentleman that i had spoken with...

as it turned out...my problem was a bad module in the distributor...
replaced the module (actually a whole new distributor) and the tach worked fine...(for a year)
then a couple of months ago it started acting funky again...
so a couple of weeks ago i replaced the tach circut board...
perfect again! for about 500 miles or so it has been rock solid and very acurate...
then yesterday i went for about 100 mile ride and boom...back to screwy!
dances all over the place...pins itself to 7k and bounces back to 1k and so on.
well...today i put about 20 miles on it and it behived perfectly all day again...
hhhmmm...wonder how it will be tomorrow? LOL
i DO have a filter on the engine as you can see in the pic below...
i intend on replacing it ASAP wether its good or not and we will see...

 

You want wacky? My tach zeroes at 2500, and then rotates BACKWARDS! Haven't figured that one out yet...

 

:eek: :lolg:

 

mrvette- I've had a look on the forum archives and found plenty of info on the filter. Also found the design drawing for it - looks like it wouldn't be too hard to rebuild one. Thanks for the advice :)

Paul - The drawing you're talking about, is that the same one that's been posted on here a few times, the one that looks like an original schematic? If so, then I've found that, but thanks all the same!
However, the one I've found is linked to in loads of threads, but they all seem to have the last inch or so of the picture missing off the bottom.... Do you have a more complete one?

 

theouk,
Yes, that's the one I've got by the sound of it (a .GIF file?)
:cheers:

 

Yeah that sounds like the one...
Although there's a bit missing off the bottom, the main circuit diagram is still there, so I reckon I could knock that up without too much trouble...
I think I'll see about the possibliity of holding it all in the original case, that would be a nice tidy fix. That'll be a project for when I don't have oil leaks and other mundane BS to deal with!
Thanks for the offer all the same, matey!
:cheers: