Home page
  Home Page   Contact Us   Our History   Advertise with Us   Sponsor List   Link to Us   Compare Levels   Member Agreement   Privacy Policy   About C3VR
  Community Forums   Active Threads   Forum Search   Top Posters List   Private Messenger   C3VR Email System   C3 Corvette Quiz
  Members Vettes & Pictures   Member Stories   Member Stats   Real Time Member Map   Member Search   Lifetime Member List   Member Calendar Entry Form   Who's Online
  C3 Registry Data   C3 Corvette Statistics   C3 Corvette Tips & Tricks   C3 Corvette How-Tos   Corvette Club Listing   Corvette Event Listing   Mechanic Directory   Corvette VIN Decoder   Save the Wave   Corvette Emblem History   C3 Corvette Birthday Calculator   C3 Corvette Build Dates   Corvette Parts Illustration Catalog   Shark Bytes - Online
  C3 Corvette Parts Auctions on eBay   Corvette Books   C3VR In-Stock Apparel & Accessories   C3VR Member Name Badges   C3VR Custom Apparel & Accessories @ Zazzle   C3VR Window Stickers   C3VR Member Deals & Discounts   C3VR Member Calendars   Shop Amazon.com
☰
SPONSOR AD SPONSOR AD

Topic: SPEEDO/TACH

in Forum: C3 Electrical


Already a Member? Click Here to Login

SPEEDO/TACH

Posted: 9/2/08 6:02pm Message 1 of 5
wayne80
Former Member
Send PM
Canada
Joined: 8/23/2008
Posts: 12
Vette(s): 1980 Dk. Claret T-Top
Just purchased a 1980 L48. While bringing it home the speedo and tach quit at the same time. New Transducer and cable fixed the speedo but can't figure out the tach. Any suggestions where to start?
 
wayne80
gold member



SPONSOR AD:: (Our Sponsors help support C3VR)

SPEEDO/TACH

Posted: 9/2/08 6:17pm Message 2 of 5
Profile Pic
kstyer
Lifetime MemberLifetime Member
Moderator
Send PM
CUYAHOGA FALLS, OH - USA
Joined: 12/2/2003
Posts: 6424
Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!
The tach is a computer board and gauge.  It has a feed from the distributor that goes through a tach filter under the hood, then to the dash unit.  There it connects to a printed circuit, and to the tach board, which the tach mounts to.   There also needs to be a 12 volt lead and ground to the tach board/tach.
 
Start by checking fuses, and the connections under the hood.  Then you get into the dash and look for loose connections.  You can use a dwell meter with the black lead connected to any good ground, and then hook the red lead to various points and you can see where you have the tach signal, and where you lose it.



SPEEDO/TACH

Posted: 9/2/08 8:11pm Message 3 of 5
mkapp7879
Former Member
Send PM
Joined: 10/21/2003
Posts: 1220
Check that the tach wire gets to the distributor and isn't damaged. Then bypass the tach filter to see if that helps.
 
Then, most likely, change the tach board. I've replace two of them in the last three years, including the one on my 25 mile Pace Car. Was told by the guy over on CF who repairs them that the electronics just get old and malfunction.
 
Easy fix for the later C3s, maybe 30 minutes. Get at it from the front of the instrument panel, removing the clear lense and the gauge bezel. Three screws remove the tach. Change the board and put it back together. Might have to reset the needle by pulling it of and setting it to zero.



SPEEDO/TACH

Posted: 9/3/08 8:52am Message 4 of 5
wayne80
Former Member
Send PM
Canada
Joined: 8/23/2008
Posts: 12
Vette(s): 1980 Dk. Claret T-Top

Thanks to both of you. We'll be on it today.




SPEEDO/TACH

Posted: 9/4/08 10:07am Message 5 of 5
VetteSpecialties
Former Member
Send PM
Mounds View, MN - USA
Joined: 5/24/2007
Posts: 1031
Vette(s): 70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe
Since they both quit at the same time, I would concentrate on all the areas in common, like power feed, and grounding.  It would be quite a coincidence if they both had a different problem at the same time.

Larry



in Forum: C3 Electrical


SPONSOR AD: (Our Sponsors help support C3VR)