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Old 06-07-2005, 10:46 PM   #1
PT'S 70 CST
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Tach ?????

I have a tach that has no markings on the backing plate other than 12volt and coil, is there any way to tell what it is 6cyl or 8cyl without the markings on the backing plate.

Thanks PT
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Old 06-07-2005, 11:31 PM   #2
Roberty
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If it's one from our old trucks then I've never seen one without the markings. If it's from something else then it's probably whatever it only came out with - such as on the old Chevelle SS dash with tach is only a V8 since they never made a Chevelle SS with a 6 banger.
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Old 06-08-2005, 12:33 AM   #3
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I asked the same question a few months ago, never really found anything out. If you do let me know, I get that question alot. Lamar.
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Old 06-08-2005, 05:42 AM   #4
PT'S 70 CST
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Yes 67-72 and the backing plate was rusty so the markings were gone. I know that all of them came with markings but if you get one that has been up north around snow and salt the backing plates are a little rusty and you cannot make out some of the markings.


PT
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70 CST SWB
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93 Indy 500 Pace Truck (SOLD)
94 SILVERADO SWB 5/7 drop
2000 Silverado swb
2005 Nissan Altima 3.5 (Surprisingly very fast)
2004 GMC Yukon XL Denali
BATESBURG, SC. 29006
29006
Some of my restorations
http://www.snapfish.com/snapfish/thu...NAME=snapfish/
Restored Tach tins 8 cyl - 6 cyl
http://67-72chevytrucks.com/vboard/s...d.php?t=518185
Contact info(Not my paypal address) DAWGSFAN227@YAHOO.COM

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Old 06-08-2005, 06:45 AM   #5
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Couldn't you test it on a v-8 truck for accuracy? I would like to know as well. Randy
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Old 06-08-2005, 07:41 AM   #6
JimKshortstep4x4
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The tachs are basically the same. They are marked as to whether they are calibrated for a 6 cylinder or an 8 cylinder.

Jim
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Old 06-08-2005, 08:08 AM   #7
Huck
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According to GMC Paul, you can adjust the truck tach's for 6 or 8cyl by turning the potentiometer that is accessed through the hole in the back. In reality, these tachometers were never very accurate. They get worse when you add HEI ignition. I have bought 3-4 tach dashes in the past year that the tach's would move but the readings were so far off that you couldn't get them even close to correct so be aware that when you buy a 30 year old tach dash off e-bay or at a swap meet, get a guarantee that it works or plan on spending another $100. for a repop tach that look similar except the face plate screw holes are horizontal to the pointer shaft and they use phillips screws for mounting the face plate. Also carefully check the rear wiring plastic as you often wind up with a broken ground connection which will cost you another $50. Huck
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