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06-15-2010, 04:53 PM
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#1 |
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not enough hours in the day
Join Date: Jan 2009
Location: Axtell, NE
Posts: 550
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Factory tach accuracy
My factory tach has read fast at higher RPM's since it was installed 4 or 5 years ago.
It has always read about 2500 PRM when another known good tach read 2100 RPM at highway speed. Now it reads over 3000 RPM at the same speed. \ I have an HEI distributer, I know that GM cars from the mid 70's to mid 80's used a tach filter with HEI distributers. Could not using one cause the tach to not read correctly? Or if this is a problem with the tach itself is there some way to correct it? |
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06-15-2010, 05:16 PM
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#2 |
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Under Construction
Join Date: Oct 2007
Location: Midlothian,TX (DFW)
Posts: 4,555
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Re: Factory tach accuracy
If i recall correctly you need an updated tach wire for HEI vs. using the original wiring
.... here is a thread on the topic: http://67-72chevytrucks.com/vboard/s...=hei+tach+wire
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Heath subscribe to the board here: http://67-72chevytrucks.com/vboard/payments.php http://67-72chevytrucks.com/vboard/s...d.php?t=157669 FAQ how to's 1956 Chevy Apache 1967 C10 SWB FleetSide (under construction) 1969 K10 SWB FleetSide (Future Build) 1972 C10 SWB Stepside (Future Build) 56 chevy truck : http://www.cardomain.com/ride/2955823/1 67 truck build: http://www.67-72chevytrucks.com/vboard/showthread.php?t=281357/1 69 k10: http://67-72chevytrucks.com/vboard/s...d.php?t=389470 Last edited by my67chevytruck; 06-15-2010 at 05:19 PM. |
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06-15-2010, 05:24 PM
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#3 |
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not enough hours in the day
Join Date: Jan 2009
Location: Axtell, NE
Posts: 550
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Re: Factory tach accuracy
When I installed the tach I ran new wiring, 18ga if I remember correctly. From some of the other replies on that thread I may need a tach filter.
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06-15-2010, 10:28 PM
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#4 |
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its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: Factory tach accuracy
stock tachs sucked 40 years ago.
Sucks + 40 years = craptastic at best. While I have no first hand info on the reproduction ones... I suspect they are sub par too |
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06-15-2010, 10:37 PM
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#5 |
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Senior Member
 
Join Date: Jan 2002
Location: Williston, ND
Posts: 2,999
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Re: Factory tach accuracy
Exactly what andy said, factory tachs are not known for accuracy.
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68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi |
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06-15-2010, 11:21 PM
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#6 |
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Member #1049
Join Date: Jun 2000
Location: Troy Montana
Posts: 3,940
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Re: Factory tach accuracy
I agree, stock tachs are an "ornament" with a needle that moves..
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06-16-2010, 07:20 AM
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#7 |
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its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: Factory tach accuracy
live rat.... i love the way you put that!
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06-16-2010, 07:51 AM
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#8 | |
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Its a Truck Thing......
Join Date: Dec 2004
Location: Sierra Vista, Arizona
Posts: 3,159
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Re: Factory tach accuracy
Quote:
Smitty
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71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 71 C20 Longhorn/Ole Yellor 69 C30 Former Motor Home, Flat Bed time |
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06-16-2010, 02:06 PM
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#9 |
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not enough hours in the day
Join Date: Jan 2009
Location: Axtell, NE
Posts: 550
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Re: Factory tach accuracy
I'm not expecting 100% accuracy, but over 1000 RPM off is a little excessive. I was hoping there was something I could try to get it closer.
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06-16-2010, 02:22 PM
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#10 |
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Registered User
Join Date: Jan 2009
Location: Las Cruces, New Mexico
Posts: 86
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Re: Factory tach accuracy
Dang, I just got my hands on a 69 with a factory tach. You mean to tell me it's just there to look pretty? Well, I'm taking the whole thing back!
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06-16-2010, 02:46 PM
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#11 |
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Registered User
Join Date: Aug 2001
Location: SOMERSET KY.
Posts: 6,427
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Re: Factory tach accuracy
I'VE HAD 6 OR 8 FACTORY TACH.S IN 6 OR 8 DIFFERENT TRUCKS I'VE OWNED & DRIVEN OVER THE LAST 25+ YEARS. SOME WERE VERY ACCURITE, & SOME WEREN'T SO PRETTY ACCURITE. LATELY (LAST 10 OR 12 YEARS) I USSUALLY PULL EM OUT & SELL EM CAUSE OTHERS SEEM TO VALUE THEM MUCH MORE THAN ME. I TEND TO USE AUTO-METER INDASH GAUGES IN MY TRUCKS BECAUSE I LIKE ACCURITE INFORMATION ON THE OPERATION & INNER WORKINGS OF THE TRUCK I DRIVE. NOT 40 YEAR OLD FACTORY GAGES THAT WERE MARGINAL AT BEST WHEN THEY WERE NEW. I'VE NEVER USED A FILTER OF ANY KIND ON ANY TACH. EITHER.
 JOHN
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junkyardjohn 69 1 TON TOW TRUCK // 84 4WD CUCV BLAZER// 85 1 TON 4WD STAKE TRUCK// 86 M1031 5/4 TON 4WD CUCV// ALOT OF OLD TRUCKS FOR ONE OLD MAN TO DRIVE. THERES ROOM FOR ALL OF GODS CREATURES RIGHT NEXT TO MY MASHED POTATOES//LIFE MEMBER OF P.E.T.A (PEOPLE EATING TASTY ANIMALS) DON'T RENT U-HAUL ALWAYS TELL THE TRUTH IT WILL AMAZE PART OF THE PEOPLE & ASTONISH THE REST |
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