Tachometer Help
Thread Starter
Intermediate
Joined: Feb 2012
Posts: 42
Likes: 0
Tachometer Help
The tachometer on my 1977 L82 is not working correctly and I need some assistance before purchasing parts. I accomplished the test as indicated on the forum.....it shows 1000-1500 PRMS with power off and 0 RPMS with just the ignition on. Seems to work fine in the driveway, but when driving, does not indicate over 3000 RPMS with increased throttle application. Do I just need to replace the filter?
Sorry if this is a repeat. I was unable to locate my exact problem in the Forum. Any help would be greatly appreciated.
Jerry
Sorry if this is a repeat. I was unable to locate my exact problem in the Forum. Any help would be greatly appreciated.
Jerry
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
It is possible that the filter is gone...common problem. That isn't very expensive. If you have the dash apart check the condition of the circuit board for the tach. If it is really bad or corroded then that may be the problem.
Those are good places to start since they are cheaper than a tach.
Those are good places to start since they are cheaper than a tach.
Le Mans Master
Joined: Sep 2002
Posts: 5,235
Likes: 898
From: Myrtle Beach SC
Jerry
I'm of the view that 90% of tach problems are the tach board but, as 86 coupe suggests, replacing the filter is the least expensive and easiest place to start.
The challenge for 77 owners is that you have to pull the dash apart to get to the tach board unlike us 78-82 owners who can simply pull the tach/speedo console out and than access the tach board. If you pull the dash apart to inspect, than I would suggest you replace the board. Its 35 years old and its not uncommon to have the circuit path burn or delaminate...I doubt you would want to inspect, leave the original board in place and than reassemble the dash...no easy task.
If you read previous forum discussion threads, you'll have across some pretty good information and probably repetitive. Wilcox does a nice job of hosting videos and instructions for 75-77 owners and you may have already checked those out.
If you decide to pick up a board, this link is to an article and what to look for or ask about before picking one up. Keep us posted on your progress.
Tach Boards
I'm of the view that 90% of tach problems are the tach board but, as 86 coupe suggests, replacing the filter is the least expensive and easiest place to start.
The challenge for 77 owners is that you have to pull the dash apart to get to the tach board unlike us 78-82 owners who can simply pull the tach/speedo console out and than access the tach board. If you pull the dash apart to inspect, than I would suggest you replace the board. Its 35 years old and its not uncommon to have the circuit path burn or delaminate...I doubt you would want to inspect, leave the original board in place and than reassemble the dash...no easy task.
If you read previous forum discussion threads, you'll have across some pretty good information and probably repetitive. Wilcox does a nice job of hosting videos and instructions for 75-77 owners and you may have already checked those out.
If you decide to pick up a board, this link is to an article and what to look for or ask about before picking one up. Keep us posted on your progress.
Tach Boards
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Tom is correct.. most of the time it is the board. There is a bunch of info on our site to help you as well.
The fact that the board is going to zero tells me you do have power and ground to the tach. So for testing, remove the tach filter and plug the tach up directly to the distributor. See if your tach still works in the same fashion. The picture below will show you how.
I don't think it's necessary but below is a picture of how the board works and what you should expect on each terminal. But with you having power and ground the only thing it could be is either a filter issue or a board issue.
Oh.. Our boards were made after Tom wrote his article.
Our boards don't use washers and are made right here in Indiana...
The fact that the board is going to zero tells me you do have power and ground to the tach. So for testing, remove the tach filter and plug the tach up directly to the distributor. See if your tach still works in the same fashion. The picture below will show you how.
I don't think it's necessary but below is a picture of how the board works and what you should expect on each terminal. But with you having power and ground the only thing it could be is either a filter issue or a board issue.
Oh.. Our boards were made after Tom wrote his article.
Our boards don't use washers and are made right here in Indiana...
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