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10-11-2009, 12:53 AM
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#1 |
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Mad Scientist
Join Date: Jul 2005
Location: Enola Arkansas
Posts: 380
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78 tach reading double
78 factory tach, 454 swb truck
Tach reads really hight...like double. Any ideas. Everything seems to be in place, even some type of thingy in the wire leading to dizzy cap.
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 Everythang relates to Beer!86 1/2ton on tons! sbc/465/208/D60/14/35's 81 Postal....with 468 bbc 97 Merc Marq comuter 07 Suburban 02 Danger Ranger |
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10-11-2009, 12:56 AM
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#2 |
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Mad Scientist
Join Date: Jul 2005
Location: Enola Arkansas
Posts: 380
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Re: 78 tach reading double
Also...T400 is missing the electric hookup...any pics or idea what goes to it? Carb switch maybe?
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Everythang relates to Beer!86 1/2ton on tons! sbc/465/208/D60/14/35's 81 Postal....with 468 bbc 97 Merc Marq comuter 07 Suburban 02 Danger Ranger |
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10-11-2009, 08:55 AM
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#3 |
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Registered User
Join Date: Jul 2007
Location: Ontario Canada
Posts: 1,006
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Re: 78 tach reading double
Cant help you on the tach but the gas pedal has a switch on it for the 400 unless it did not come from factory with the 400.Found this thread ,should help you out some http://67-72chevytrucks.com/vboard/s...d.php?t=313083
Last edited by ont_guy_38; 10-11-2009 at 09:03 AM. Reason: added more info |
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10-11-2009, 10:35 AM
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#4 |
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Mad Scientist
Join Date: Jul 2005
Location: Enola Arkansas
Posts: 380
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Re: 78 tach reading double
thanks for answering the switch question and link! Tach issue anyone?
__________________
Everythang relates to Beer!86 1/2ton on tons! sbc/465/208/D60/14/35's 81 Postal....with 468 bbc 97 Merc Marq comuter 07 Suburban 02 Danger Ranger |
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10-11-2009, 12:40 PM
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#5 |
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Registered User
Join Date: Oct 2006
Location: In the Indiana Corn
Posts: 449
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Re: 78 tach reading double
Some tachs have a switch on the back to switch between 4, 6, or 8 cylinders. If it's not set right, the tach will read wrong.
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1988 R2500 Crew Cab Immediate plans- get it running! Future plans- Rear disc swap & Hydroboost Dually conversion with shackle flip-n-switch 4x4 conversion with 52" springs Maybe some new body panels  Who needs a car when they make crew cab trucks? |
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10-11-2009, 01:13 PM
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#6 | |
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Moderator
 
Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,977
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Re: 78 tach reading double
Quote:
If it worked once upon a time then your tach drive circuit is dying. If it's a transplant you may have a 6 cylinder tach. Read the backside of the gauge face... I have yet to see a tach that didn't say 8 cyl or 6 cyl on the blue backside of the metal face but YMMV. Crossy 73-87 Factory Tachometer Information Several people have built replacement meter drive circuits using modern parts. Google found this guy. http://www.instrumentsrus.com/gm.htm Last edited by hatzie; 10-11-2009 at 01:14 PM. |
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10-11-2009, 05:21 PM
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#7 |
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Mad Scientist
Join Date: Jul 2005
Location: Enola Arkansas
Posts: 380
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Re: 78 tach reading double
It's a factory tach truck. it has a resistor or something between the brown tack wire and cap...seems factory installed.
__________________
Everythang relates to Beer!86 1/2ton on tons! sbc/465/208/D60/14/35's 81 Postal....with 468 bbc 97 Merc Marq comuter 07 Suburban 02 Danger Ranger |
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10-11-2009, 05:25 PM
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#8 |
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Mad Scientist
Join Date: Jul 2005
Location: Enola Arkansas
Posts: 380
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Re: 78 tach reading double
Thanks hatzie! I think that's the radio thingy I have in the wiring. guess my tach is just going bad.
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Everythang relates to Beer!86 1/2ton on tons! sbc/465/208/D60/14/35's 81 Postal....with 468 bbc 97 Merc Marq comuter 07 Suburban 02 Danger Ranger Last edited by hiway; 10-11-2009 at 05:26 PM. |
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