Tach filter

[resto75]

My tach on my 75 which is electronic seems to read several hundred rpm higher then what an external tach reads. This also is apparent when you just listen to it run. I have heard of something called a tach filter which is suppose to be a silver looking can type part similar to a condenser. I don't think I have one as my tach wire goes directly from the HEI dist cap thru the dash behind the wiper motor.

Could this cause the tach to read higher than normal and where is this filter located?

 

[silver 80]

I think that the tach filter comes off of your HEI unit and plugs into another wire. There is a thread some where on how to make your own.

the tach filter should be hanging somewhere around your HEI unless it is still mounted to the intake.

 

[mrvette]

the stock tach filter is a black plastic case with white wires on either end...about 5/8 round and 2" long....silver clamp around middle of it is the ground for the device (s) inside the container....

to make a new one requires two resistors and two caps.....and soldering, taping into the harness in series with the present tach hookup wire....

if you can't make one, and solder it up, you will need go to junkyard and find one off another GM car.....will need search a good bit, but they are out there....

GENE

 

[resto75]

Ok well I don't have one that I can find. Do you think this missing filter would make the tach read higher then it should?

 

[VetteAtv]

Did you find out if the missing filter can cause a tach to read high? I have the same issue on my '79.

 

[resto75]

I guess no one knows for sure. If I had a filter I would put it on and see. If I had run across one I would try it. I was over at NCRS event in Old town the other day and asked around but no one knew either.

 

[silver 80]

I would try and unplug mine but I don't want anything to happen to my tach circuit board.
sorry.
If I run across one in my travels I will get it or a couple of them and post.
Has anyone tried to call some of the vette salvage yards.

 

[Copdogcorvettes]

The tach filter is availible from GM and other parts houses. I had to buy a new one for my 80 about 4 years ago. Hold on, The cost was $75. When the 80 was totalled the filter was one of the first things I took off the car and put away for a raining day. The Filter was completely gone when I got the vette and the tach was not working. I replaced the filter first and then found that the board was bad as well. So I can not tell if the filter alone could be cuasing your problem.

Good luck
Gary

 

[silver 80]

I have a drawing for the later model looks like it's just two componets about $1.50 worth of parts. I couldn't tell you if it will work for C3 or not but heck it's just a $1.50
Well it seems to be to big or it just won't upload. if you want the drawing shoot me your e-mail and I'll attach it back at ya.

 

[dbettner]

Ther is a Tachometer filter on Ebay that should fix your problems , you should check it out.

 

[Willis76]

Thought I remebered something on this - try this link:
http://my.execpc.com/~rodney1/corvette/

Good Luck!

 

[bbzdad]

How to make a tach filter

Hello everyone, sorry if this question is redundent but does anyone know how to make a tach filter? I have access to all kinds of electronic components.

 

[silvernblack]

sent you a PM so you can make one for a couple of bucks

or , for like 25 bucks you can try to buy this (call them to see if it will work for you):

Classic Instruments SN2 Tach Filter

and here is the drawing for the tach filter.

 

[bbzdad]

Thanks silvernblack, I'll give it a try. I thought I would try it to prove this is the problem. I replaced the circuit board but the tach runs high and sometimes erratic.