Tach help needed
Thread Starter
Racer
Joined: Aug 2005
Posts: 435
Likes: 2
From: Boise Idaho
Tach help needed
On my 77 Vette I just replaced the circuit board and the tachfilter.
The needle just sits over on 5000 or so with the key off and engine off. When I turn the key on it slowly rotates to 6000 and stays there.
Did I miss something when I put the board back on? Could the new board be bad?
The needle just sits over on 5000 or so with the key off and engine off. When I turn the key on it slowly rotates to 6000 and stays there.
Did I miss something when I put the board back on? Could the new board be bad?
Last edited by supercalvin; Apr 19, 2006 at 11:34 PM.
Burning Brakes
Joined: Jun 2005
Posts: 764
Likes: 2
From: THE OLDER I GET THE BETTER I WAS! NORTHERN ONTARIO
When I turn the key on it slowly rotates to 6000 and stays there.
Did I miss something when I put the board back on? Could the new board be bad?[/QUOTE]
Make sure all the connections are good under the hood...I have seen new boards that are bad but it sounds like a ground issue...check all your connections again. Just for fun try running it without the tach filter before you change anything around again
Did I miss something when I put the board back on? Could the new board be bad?[/QUOTE]
Make sure all the connections are good under the hood...I have seen new boards that are bad but it sounds like a ground issue...check all your connections again. Just for fun try running it without the tach filter before you change anything around again
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
So, tell us .. where did ya get the board? I got mine from Ecklers' and it sucks too 
I replaced the filter, still had no tach. Then I went into the dash to reseal the A.C. system and figured I'd pull the speedo/tach cluster out at the same time and fix it. The instructions said to make sure that my tach read 0 RPM when 12V was applied to it. I did, and it does.
But when I start her up, it shows about 650 higher than actual idle speed, and by the time I'm at freeway speed, it's over 1500RPM off.
When I get on it, my shift points are 5000-5250RPM but by that time, the tach is way the heck down past the redline, it's at the 6:30 position!!
Funny that we should be writing about this: I got my new summit catalog in the mail yesterday and the book is on my desk right now, open to page 96 where the Autometer Tachs are displayed.
I replaced the filter, still had no tach. Then I went into the dash to reseal the A.C. system and figured I'd pull the speedo/tach cluster out at the same time and fix it. The instructions said to make sure that my tach read 0 RPM when 12V was applied to it. I did, and it does.
But when I start her up, it shows about 650 higher than actual idle speed, and by the time I'm at freeway speed, it's over 1500RPM off.
When I get on it, my shift points are 5000-5250RPM but by that time, the tach is way the heck down past the redline, it's at the 6:30 position!!Funny that we should be writing about this: I got my new summit catalog in the mail yesterday and the book is on my desk right now, open to page 96 where the Autometer Tachs are displayed.
Last edited by SanDiegoPaul; Apr 20, 2006 at 02:28 PM.
Thread Starter
Racer
Joined: Aug 2005
Posts: 435
Likes: 2
From: Boise Idaho
Thanks for the replies
Kona...Yep same thing
Which really makes me beleive that G Dad is right with the ground issue.
I didn't even think to check those wires while I had the dash off.
First I will test without the filter. (I just had to crimp those wires didn't I) D'oh
SanDiegoPaul. Actually it was a Mid America Motorworks, but the filter was Ecklers. I also had to take the dremel to the some of the plastic in there to get to board to set in.
If it wasn't for the turn signal and brake lamp in there I might have looked harder at the autometer sets. I really don't want to rewire them.
Thanks for the help guys.
Kona...Yep same thing
Which really makes me beleive that G Dad is right with the ground issue.
I didn't even think to check those wires while I had the dash off.
First I will test without the filter. (I just had to crimp those wires didn't I) D'oh
SanDiegoPaul. Actually it was a Mid America Motorworks, but the filter was Ecklers. I also had to take the dremel to the some of the plastic in there to get to board to set in.
If it wasn't for the turn signal and brake lamp in there I might have looked harder at the autometer sets. I really don't want to rewire them.
Thanks for the help guys.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 179
From: S.W. Ohio. . . . . . NRA Life Member
buy boards from John Gardner. They are a quality board and don't require the nylon insulating washers.
contact via email: jtandjudyg@aol.com
contact via email: jtandjudyg@aol.com
Last edited by Mike Mercury; Apr 28, 2006 at 09:09 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Melting Slicks
Joined: Apr 1999
Posts: 2,010
Likes: 3
From: Moon Twp. PA USA
Got my board from Dr. Rebuild. Works fine. There was also a slip of paper, in with the board, that said if the new board did not fix the tach problem, you could send the tach and new board to this 3rd party for a guaranteed repair. The cost for this service was about $25.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 179
From: S.W. Ohio. . . . . . NRA Life Member
Originally Posted by glen242
Got my board from Dr. Rebuild. Works fine. There was also a slip of paper, in with the board, that said if the new board did not fix the tach problem, you could send the tach and new board to this 3rd party for a guaranteed repair. The cost for this service was about $25.
Doc Rebuild sells the Gardner board
Heel & Toe
Joined: Feb 2006
Posts: 21
Likes: 0
Do not check tach without filter. The filter is a capacitor. If you do by pass filter you may burn board up. We have seen this many times in our shop. Pull dash & connect 12 volt tach to tach signal wire & read after market tach. This will check wiring to tach itself.Connect wire to conector which conect to back of dash. Best of luck.
Thread Starter
Racer
Joined: Aug 2005
Posts: 435
Likes: 2
From: Boise Idaho
Good info thank you
BUT
I just purchased another one on EBAY for $30
If this doesn't work I will give Dr Rebuild a ring.
Those Autometer gauges look better each time I check out their website.
BUT
I just purchased another one on EBAY for $30
If this doesn't work I will give Dr Rebuild a ring.
Those Autometer gauges look better each time I check out their website.
Racer
Joined: Jul 2005
Posts: 499
Likes: 1
From: Winnipeg Manitoba
Those burnt parts are resistors. It looks like R3 is the one that got hot. The bands have faded on R3, but they still look pretty good on R4. R4 got hot just by being next to R3.
In reality, this is not the problem. This is just a symptom of a problem someplace else in the circuit. If you follow D1, you will probably find that the end with the bar goes to R3. What has probably happened is that the other end of the R3 has been shorted to ground. This could happen if assembly into the car shorted the trace to ground, or if D2 (1N5243 zener) shorted out. I would replace D3 with a 1N5245 or 46 before I put it back in a car.
Those resistors are pretty robust components and I wouldn't be surprised if they still work. That circuit board is probably salvageable.
Of course, now that the cars back together, it's a mute point.
(Note: I use lots of Probably's which is the best I can do based on a photo of a circuit)
In reality, this is not the problem. This is just a symptom of a problem someplace else in the circuit. If you follow D1, you will probably find that the end with the bar goes to R3. What has probably happened is that the other end of the R3 has been shorted to ground. This could happen if assembly into the car shorted the trace to ground, or if D2 (1N5243 zener) shorted out. I would replace D3 with a 1N5245 or 46 before I put it back in a car.
Those resistors are pretty robust components and I wouldn't be surprised if they still work. That circuit board is probably salvageable.
Of course, now that the cars back together, it's a mute point.
(Note: I use lots of Probably's which is the best I can do based on a photo of a circuit)
Last edited by Kilroy1024; May 6, 2006 at 04:12 PM.