Tachometer Question....... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ts71281 · 04-01-2004, 12:12 PM

I bought a restored instrument cluster from a member on here (who I will not name) with a camaro tach installed. Other than the bezel being in 40 million pieces from no packing materiel

and the bezel being a 67 with a choke hole (which I asked about) and the printed circuit board that had corroded and de-laminated, the rest of the cluster works. However when idling at 850 the tach only reads about 500-550 RPMS. I'm pretty sure I got the wrong tach and that it's for a 6 cylinder. Can someone please give me some positive insight to this and tell me this tach can be converted to a 8 cylinder tach easily? I have more money in this stupid instrument cluster than if I bought a new one from LMC!!

Is there some kind of resistor I could take out of another 8 cyl gm tach (I have lots of oldsmobile ones laying around) and just swap it over. It seems all across the whole tach it's always about 400 RPM's slow. Anyone ever just bend the needle?

I'm just trying to get by cheap is all. Thanks guys!

Joe

bpmcgee · 04-01-2004, 01:12 PM

The tach that I have has a way of switching from 6 to 8 cylinders. I don't recall exactly what it was, but it was marked "6" and "8" on the back.

Brian

stelth2002 · 04-01-2004, 01:17 PM

I wouldnt recommend switching modes, but form the sounds of it yours is just not right. A 6clyinder tach would read about 1150 rpm if your v8 was idleing at 850. What about at upper rpm, is it right?

ts71281 · 04-01-2004, 01:35 PM

Can you change the modes on a factory tach? Well, at 60 MPH, I'm turning 2800 RPM's (according to the tach) in direct drive 1:1 ratio, 3.73 gears and a 29" tall tire. does that sound about right? It just torques me off that I have to deal with this crap! I paid good money for this thing and I could have bought a new one for the time and work I have invested in this one. I'm sick of dishonest people that lie just to sell something. ::end of rant:: Are you sure a 6 cyl tach would read higher at a given RPM than a 8 cyl tach at the same rpm? I thought it'd be the other way around.

stelth2002 · 04-01-2004, 02:35 PM

Well i know what you mean about quality of parts. I try and describe mine the best i can. However, from the looks of your tach, it is showing about 200 rpm to high. And im pretty sure a 6 tach would read higher. Its easy math..... v8 = 8*2000 = 16000
6 = 6*2000 = 12000 so it will rap the 6 clyinder tach higher.

Brad · 04-01-2004, 02:36 PM

If it is a Camaro 6 cyl tach, I could trade you for a Camaro 8 cyl tach. PM me if you're interested.

JimKshortstep4x4 · 04-01-2004, 02:37 PM

I am not familiar with the tach that you have but some of the originals had adjustment pots on them and with a small screw driver, they can be adjusted. Might be worth looking at the back of the tach to see if there is an adjustment.

The 6 cylinder tach should read higher on an 8 cylinder engine since it has two more impulses to the tach for a given rpm.

Jim

ts71281 · 04-01-2004, 08:48 PM

hmmmmm............I'm confused because my digital tachometer (on my multi-meter) says 850 and my camaro tach says like 500-550. Maybe I'll have to look at the back and see if there's a selector. Hopefully there is! If I can confirm it's a GOOD working 6 cyl tach, I might take you up on your offer Brad. Tach is in the truck however. I won't trade you junk! I know how it feels to be SOLD junk and don't want to ruin anyone elses trucking hobby by trading them junk either. I'll have to take my bezel out again and take a look at the back of that tach. I wonder why it's reading low then............... Can factory tachometers have a calibration screw? Maybe from lack of shipping the numbers on the tach got shifted? Although it appears fine. Anyone suggest a good tach rebuilder guy in Minnesota?

Joe

JimKshortstep4x4 · 04-01-2004, 09:08 PM

From my experience it will probably be cheaper to get another tach rather than to have it rebuilt. (If your tach is fairly common).

I have seen the needles drag when the bearings that support the needle get loose. If that is the case, the bearings are adjustable. Like I said, I am not familiar with the tach you have,
just making suggestions based on the tachs I have worked on.

Jim

Longhorn Man · 04-02-2004, 01:16 AM

it is a 20 year old tach...you didn't think it would be dead nuts on acurate did you?
They can go out of calibration in a few years. Some were off while still on the show room floor.
Not the seller's fault...I'd blame GM personally.

ts71281 · 04-02-2004, 12:30 PM

$375 for a cracked bezel, delaminated printed circuit, and a tach that's not accurate I think I can point a finger

Joe

stelth2002 · 04-02-2004, 01:20 PM

wow, id send it back and want my money back, even if it was minus shipping

Longhorn Man · 04-02-2004, 02:16 PM

Well, OK, i was just refering to the tach its self, it does kinda sound like you got a bad deal on that one.

Mudder · 04-02-2004, 02:39 PM

Damn for a few more bucks you could have had all Autometers. Not trying to make ya feel bad. Just seems like for that price it should have been pretty damn sweet.

ts71281 · 04-02-2004, 04:05 PM

I know it! That's why I'm kind of torqued right now! Trying to not sink another penny into this thing. That's why I said I should have just bought a new one! All I was trying to do was keep a clean factory look but with a tachometer that went higher than 5 grand. Too bad for me

I'm still sore from this, the member should have shipped me a jar of vasoline as well.

Joe

Mudder · 04-02-2004, 04:15 PM

Dont be too hard on yourself Joe......If I had all my mistakes back I'd be well on my way to another truck.

04-01-2004, 12:12 PM	#1
ts71281 Registered User Join Date: Apr 2003 Location: Maple Grove, MN Posts: 497	Tachometer Question....... I bought a restored instrument cluster from a member on here (who I will not name) with a camaro tach installed. Other than the bezel being in 40 million pieces from no packing materiel and the bezel being a 67 with a choke hole (which I asked about) and the printed circuit board that had corroded and de-laminated, the rest of the cluster works. However when idling at 850 the tach only reads about 500-550 RPMS. I'm pretty sure I got the wrong tach and that it's for a 6 cylinder. Can someone please give me some positive insight to this and tell me this tach can be converted to a 8 cylinder tach easily? I have more money in this stupid instrument cluster than if I bought a new one from LMC!! Is there some kind of resistor I could take out of another 8 cyl gm tach (I have lots of oldsmobile ones laying around) and just swap it over. It seems all across the whole tach it's always about 400 RPM's slow. Anyone ever just bend the needle? I'm just trying to get by cheap is all. Thanks guys! Joe

04-01-2004, 01:17 PM	#3
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	I wouldnt recommend switching modes, but form the sounds of it yours is just not right. A 6clyinder tach would read about 1150 rpm if your v8 was idleing at 850. What about at upper rpm, is it right? __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

04-01-2004, 02:35 PM	#5
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	Well i know what you mean about quality of parts. I try and describe mine the best i can. However, from the looks of your tach, it is showing about 200 rpm to high. And im pretty sure a 6 tach would read higher. Its easy math..... v8 = 82000 = 16000 6 = 62000 = 12000 so it will rap the 6 clyinder tach higher. __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

04-01-2004, 02:36 PM	#6
Brad Out of the carpool lane. Join Date: Jan 2000 Location: Clark Co, WA Posts: 5,673	If it is a Camaro 6 cyl tach, I could trade you for a Camaro 8 cyl tach. PM me if you're interested. __________________ 1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten...

04-02-2004, 01:20 PM	#12
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	wow, id send it back and want my money back, even if it was minus shipping __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

04-01-2004, 01:12 PM	#2
bpmcgee Registered User Join Date: Mar 2003 Location: Northern Illinois Posts: 2,181	The tach that I have has a way of switching from 6 to 8 cylinders. I don't recall exactly what it was, but it was marked "6" and "8" on the back. Brian

04-01-2004, 01:35 PM	#4
ts71281 Registered User Join Date: Apr 2003 Location: Maple Grove, MN Posts: 497	Can you change the modes on a factory tach? Well, at 60 MPH, I'm turning 2800 RPM's (according to the tach) in direct drive 1:1 ratio, 3.73 gears and a 29" tall tire. does that sound about right? It just torques me off that I have to deal with this crap! I paid good money for this thing and I could have bought a new one for the time and work I have invested in this one. I'm sick of dishonest people that lie just to sell something. ::end of rant:: Are you sure a 6 cyl tach would read higher at a given RPM than a 8 cyl tach at the same rpm? I thought it'd be the other way around.

04-01-2004, 02:37 PM	#7
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	I am not familiar with the tach that you have but some of the originals had adjustment pots on them and with a small screw driver, they can be adjusted. Might be worth looking at the back of the tach to see if there is an adjustment. The 6 cylinder tach should read higher on an 8 cylinder engine since it has two more impulses to the tach for a given rpm. Jim

04-01-2004, 08:48 PM	#8
ts71281 Registered User Join Date: Apr 2003 Location: Maple Grove, MN Posts: 497	hmmmmm............I'm confused because my digital tachometer (on my multi-meter) says 850 and my camaro tach says like 500-550. Maybe I'll have to look at the back and see if there's a selector. Hopefully there is! If I can confirm it's a GOOD working 6 cyl tach, I might take you up on your offer Brad. Tach is in the truck however. I won't trade you junk! I know how it feels to be SOLD junk and don't want to ruin anyone elses trucking hobby by trading them junk either. I'll have to take my bezel out again and take a look at the back of that tach. I wonder why it's reading low then............... Can factory tachometers have a calibration screw? Maybe from lack of shipping the numbers on the tach got shifted? Although it appears fine. Anyone suggest a good tach rebuilder guy in Minnesota? Joe

04-01-2004, 09:08 PM	#9
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	From my experience it will probably be cheaper to get another tach rather than to have it rebuilt. (If your tach is fairly common). I have seen the needles drag when the bearings that support the needle get loose. If that is the case, the bearings are adjustable. Like I said, I am not familiar with the tach you have, just making suggestions based on the tachs I have worked on. Jim

04-02-2004, 01:16 AM	#10
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	it is a 20 year old tach...you didn't think it would be dead nuts on acurate did you? They can go out of calibration in a few years. Some were off while still on the show room floor. Not the seller's fault...I'd blame GM personally.

04-02-2004, 12:30 PM	#11
ts71281 Registered User Join Date: Apr 2003 Location: Maple Grove, MN Posts: 497	$375 for a cracked bezel, delaminated printed circuit, and a tach that's not accurate I think I can point a finger Joe

04-02-2004, 02:16 PM	#13
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Well, OK, i was just refering to the tach its self, it does kinda sound like you got a bad deal on that one.

04-02-2004, 02:39 PM	#14
Mudder Registered User Join Date: Feb 2001 Location: East Central, MO Posts: 11,336	Damn for a few more bucks you could have had all Autometers. Not trying to make ya feel bad. Just seems like for that price it should have been pretty damn sweet.

04-02-2004, 04:05 PM	#15
ts71281 Registered User Join Date: Apr 2003 Location: Maple Grove, MN Posts: 497	I know it! That's why I'm kind of torqued right now! Trying to not sink another penny into this thing. That's why I said I should have just bought a new one! All I was trying to do was keep a clean factory look but with a tachometer that went higher than 5 grand. Too bad for me I'm still sore from this, the member should have shipped me a jar of vasoline as well. Joe



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04-02-2004, 04:15 PM	#16
Mudder Registered User Join Date: Feb 2001 Location: East Central, MO Posts: 11,336	Dont be too hard on yourself Joe......If I had all my mistakes back I'd be well on my way to another truck.

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