Tach ????? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

PT'S 70 CST · 06-07-2005, 10:46 PM

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

Roberty · 06-07-2005, 11:31 PM

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.

lamar · 06-08-2005, 12:33 AM

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.

PT'S 70 CST · 06-08-2005, 05:42 AM

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

byrd · 06-08-2005, 06:45 AM

Couldn't you test it on a v-8 truck for accuracy? I would like to know as well. Randy

JimKshortstep4x4 · 06-08-2005, 07:41 AM

The tachs are basically the same. They are marked as to whether they are calibrated for a 6 cylinder or an 8 cylinder.

Jim

Huck · 06-08-2005, 08:08 AM

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

06-07-2005, 10:46 PM	#1
PT'S 70 CST "GO DAWGS" Join Date: Oct 2003 Location: Batesburg, SC. 29006 Posts: 5,410	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 __________________ 70 CST SWB 70 NOVA 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 God Bless Our Troops

06-07-2005, 11:31 PM	#2
Roberty Hot Damn - Here I Am!! Join Date: Feb 2000 Location: Ringgold, Georgia Posts: 726	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. __________________ My vehicles: '90 Silverado Sport '71 Chevelle SS Convertible '70 C-10 - My Grandfather bought it new - original un-restored

06-08-2005, 12:33 AM	#3
lamar Registered User Join Date: Apr 2004 Location: Covington,Ga Posts: 453	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. __________________ 72 C-10

06-08-2005, 05:42 AM	#4
PT'S 70 CST "GO DAWGS" Join Date: Oct 2003 Location: Batesburg, SC. 29006 Posts: 5,410	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 __________________ 70 CST SWB 70 NOVA 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 God Bless Our Troops

06-08-2005, 07:41 AM	#6
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	The tachs are basically the same. They are marked as to whether they are calibrated for a 6 cylinder or an 8 cylinder. Jim

06-08-2005, 08:08 AM	#7
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,269	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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