tach
Pro
Joined: Nov 2004
Posts: 659
Likes: 0
From: Flower Mound Texas
Most tach problems on this year model are caused by the tach circuit board. It is a common failure point. It's located right behind the tach gauge. There is a plethora of threads on this forum about this problem and some very good advice for how to troubleshoot and some recommendations on which boards to avoid. If only I had read them before I had the tach problems on my 75.
When you say you hooked up a tach and verified it's getting a signal, where did you connect it to to verify this?
When you say you hooked up a tach and verified it's getting a signal, where did you connect it to to verify this?
Drifting
Joined: Nov 2005
Posts: 1,795
Likes: 1
there should be a filter for the tach right near the distributor.
did you check for signal at the filter or at the distributor?
if at the distributor try unplugging the tach from the filter and
and plug it directly in to the distributor if it works you need a new filter, do not run this way or it will damage the tach circuit board
if it still does not work then it sounds like the circuit board itself.
there is a member of the forum here in NJ ----ACECO (George)
he recently repaired my board for me and can probably fix yours also.
i suggest contacting him rather than buy the replacement board from one of the vendors as a number of people here on the forum have had
bad luck with the aftermarket boards.
good luck with it
did you check for signal at the filter or at the distributor?
if at the distributor try unplugging the tach from the filter and
and plug it directly in to the distributor if it works you need a new filter, do not run this way or it will damage the tach circuit board
if it still does not work then it sounds like the circuit board itself.
there is a member of the forum here in NJ ----ACECO (George)
he recently repaired my board for me and can probably fix yours also.
i suggest contacting him rather than buy the replacement board from one of the vendors as a number of people here on the forum have had
bad luck with the aftermarket boards.
good luck with it
Thread Starter
Racer
Joined: Dec 2004
Posts: 336
Likes: 0
From: crystal lake Il.
I connected at the distributor. I can`t find a tach filter at all. The brown wire goes directly from the dist. thru the firewall. I looked under the dash and nothing. I had the motor replaced about 1200 miles ago. If the filter was left off would that fry the circuit board? Do I need a new filter and board? wheres the best place to get them? Thanks
Drifting
Joined: Nov 2005
Posts: 1,795
Likes: 1
Originally Posted by painterman52
If the filter was left off would that fry the circuit board? Do I need a new filter and board? wheres the best place to get them? Thanks
this is how mine was connected. they had bypassed the filter
and when i pulled my tach my board had a catastrophic failure
board
back of tach
inner housing
Aceco ( george ) was able to repair this and my tach works perfect now.
he also builds breadboard tach filters, while not original in appearance it
gets the job done.
send him a PM and see if he can help you out.
Drifting
Joined: Nov 2003
Posts: 1,634
Likes: 4
From: Northern NJ
St. Jude Donor '04 & '05
Greetings,
You should not eliminate the tach filter for any length of time as it helps protect the tach circuit board from electrical spikes. Many here will tell you it is not needed as it works fine w/o the filter. It will work w/o the filter but for how long is the question. Some probably for a long time. Others, well, GM put the filter there for a reason. So this may, or may not, be the reason your board failed.
You can get a replacement tach board for $65-75. However many here have had issues with the replacements not working right, providing incorrect RPM readings. Your original board can often be repaired for approx half the cost of a replacement. I can provide additional information on this if you PM me or e-mail me at aceco@optonline.net
As for the filter I've seen repro replacements for approx $65. The filter only has 4 inexpensive electronic parts in it and can be reproduced for much less than this if originality is not a concern. Again contact me if I can provide more info.
Lots of luck!
You should not eliminate the tach filter for any length of time as it helps protect the tach circuit board from electrical spikes. Many here will tell you it is not needed as it works fine w/o the filter. It will work w/o the filter but for how long is the question. Some probably for a long time. Others, well, GM put the filter there for a reason. So this may, or may not, be the reason your board failed.
You can get a replacement tach board for $65-75. However many here have had issues with the replacements not working right, providing incorrect RPM readings. Your original board can often be repaired for approx half the cost of a replacement. I can provide additional information on this if you PM me or e-mail me at aceco@optonline.net
As for the filter I've seen repro replacements for approx $65. The filter only has 4 inexpensive electronic parts in it and can be reproduced for much less than this if originality is not a concern. Again contact me if I can provide more info.
Lots of luck!
Last edited by ACECO; Jul 30, 2006 at 12:50 AM.
Racer
Joined: Sep 2005
Posts: 260
Likes: 0
From: Wheaton Illinois
The tach in my 76 died last fall. I had a short in the instrument circuit and it burned up the board. After a lot of research here on the CF I decided on a replacement board. Apperently the early GM electric tach board had some design problems. There is a guy who has redesigned the circuit and makes new boards. The CF members who know about electronics (I don't) think highly of his product. His name is J Garder. I know Dr. Rebuild carries his boards and for a while he was selling them direct on E-Bay. I found an old thread about tach boards that may help, http://forums.corvetteforum.com/show....php?t=1277602
The board is very easy to install. Getting the tack out is not very easy.
The board is very easy to install. Getting the tack out is not very easy.
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Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
The blown parts on 1Z87L8's tach board are on the power supply input,
NOT the tach signal input.
A missing tach filter has nothing to do with this failure.
The Tach PCB itself has plenty of filtering to protect it against spikes.
The filter stops RF noise from entering the cab on the tach signal line and interfering with the radio.
NOT the tach signal input.
A missing tach filter has nothing to do with this failure.
The Tach PCB itself has plenty of filtering to protect it against spikes.
The filter stops RF noise from entering the cab on the tach signal line and interfering with the radio.
