Tach Filter
Thread Starter
Instructor
Joined: Mar 2006
Posts: 131
Likes: 0
From: San Bernardino California
Tach Filter
Just curious.. I relized there is no tach filter on my 79 .. when i went to hook the tach up .. it works .. but the rpms are off... idle shows 2500 and a slight bit of gas it will rev up and peg ... so will a tach filter solve this ...and .. is there any way to make one myself instead of waiting for shipping and all of that .. thanks
Burning Brakes
Joined: Jun 2005
Posts: 764
Likes: 2
From: THE OLDER I GET THE BETTER I WAS! NORTHERN ONTARIO
Originally Posted by alotaball
but the way my tach is responding .. is that the result of having no tach filter ..
Thread Starter
Instructor
Joined: Mar 2006
Posts: 131
Likes: 0
From: San Bernardino California
i found it ... but i also found a lot of threads were people bypassed it and it still functions... I would still put one for precautionary reasons .. but .. i am wondering if this is going to fix my problem or if it is something beyond that .. that is wrong
Burning Brakes
Joined: Jun 2005
Posts: 764
Likes: 2
From: THE OLDER I GET THE BETTER I WAS! NORTHERN ONTARIO
I would still put one for precautionary reasons
Good idea you should have my e mail address...send me a note I will ship off a diagram of a filter you can build...check all your connections the connector at the distributor can make it's way loose & cause problems..
Good idea you should have my e mail address...send me a note I will ship off a diagram of a filter you can build...check all your connections the connector at the distributor can make it's way loose & cause problems..
Thread Starter
Instructor
Joined: Mar 2006
Posts: 131
Likes: 0
From: San Bernardino California
well when i bought the car ... it was not hooked up .. so i hooked the wire up to the tach .. marked on the hei .. and it came to life ... Just way off.. the idle is smooth as glass .. has to be in the 800 rpm range... and it shows that is at somewhere near 2000..
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Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
Originally Posted by alotaball
i found it ... but i also found a lot of threads were people bypassed it and it still functions... I would still put one for precautionary reasons .. but .. i am wondering if this is going to fix my problem or if it is something beyond that .. that is wrong
The tach itself right has adequate filtering to protect against high voltage transients (D1, R3, C3, R4). Putting the tach filter (R1, R2, C1, C2) in front of the input filter does not provide much additional protection. However, it should do a pretty good job of stripping off any RF noise that could interfere with the radio.
I think its unlikely, but possible the tach filter is the source of your problems. A change of Tach filter has often helped when the tach didn't work at all because the filter was open circuit. I don't recall too many cases of an erratic tach being fixed by a filter change (in the last year that I've been watching). Try putting in a quicky filter with R2=10K and C2=100nF. And yes I mean just the two parts. Its so close to the "real" filter that If that doesn't fix it, a new filter won't either.
Good Luck
EDIT- Looks like Mike beat me to it!
Have to learn to type faster......
Advanced
Joined: Feb 2002
Posts: 97
Likes: 0
From: Sapupla OK
Tach Filter for a 78
I have been looking for a replacement tach filter for my 78 at Autozone, O'Reillys, etc and can't seem to find one. Do they exist or is there a suitable substitute I can use?
The radio whine is fierce and seems to come through even with radio off
Thanks for help (as always)
Ken (molchaser)
The radio whine is fierce and seems to come through even with radio off
Thanks for help (as always)
Ken (molchaser)
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Mine was eratic above 3,000. It would fluctuate all over above that RPM. I bought a new filter from ZIP and it works flawlessly now, smooth as silk. Mine was original and was just an electrolytic capacitor, since then they've been refined as the above schematics show.
Bill
Bill
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
topgunn, would I be able to disconnect the tach wire from the distrubutor and then put the tach filter inline between the tach wire and the distributor without cutting or splicing any wires? In other words, does the wire going to the tach output plug into the filter, then the filter into the distributor? I dont' want to cut any wires to install one inline.
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Originally Posted by C3 4ME
topgunn, would I be able to disconnect the tach wire from the distrubutor and then put the tach filter inline between the tach wire and the distributor without cutting or splicing any wires? In other words, does the wire going to the tach output plug into the filter, then the filter into the distributor? I dont' want to cut any wires to install one inline.
Bill
