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

Sklptrljay · 07-30-2013, 12:35 AM

I installed a cluster I bought (year and a half ago--always takes longer than you think to get these things together), and It's giving me a few issues. Mostly I am concerned about the tach needle bouncing around. It's all over the place.

I grounded the cluster, I followed the HEI installation instructions (constant 12V instead of the resistance wire), It has a new pcb that's made in the USA ( I checked that the pcb had continuity internally).

I'm just stumped, so I was hoping someone has worked this out before. I'm wondering if it's just a bum tach? I didn't see a brand name on it.

Any thoughts?

68gmsee · 07-30-2013, 09:33 AM

Best thing to do is use a dwell/tach meter if you have one and hook it up to the tach part of the HEI to see if it does the same. If you don't have one maybe you can buy one or maybe borrow one.

Sklptrljay · 07-30-2013, 03:53 PM

I think my dad may have a dwell meter. Thanks for the idea, I'll post the results.
Posted via Mobile Device

Square_78 · 07-30-2013, 07:06 PM

I would be interested to know. My tach does the same thing
Posted via Mobile Device

*Mister-B* · 07-30-2013, 07:27 PM

This is a bit of a shot in the dark, but I wonder if your engine and chassis isn't properly grounded with the copper ground straps, and that's introducing electrical noise into your system?
Posted via Mobile Device

Sklptrljay · 07-30-2013, 07:45 PM

I did run ground straps. I might check to make sure they all have a good surface connection.

HSRACER · 07-31-2013, 04:04 PM

Mine does the same thing. I bought a new one thinking the old one must be bad. Havent installed it yet.

MARKDTN · 07-31-2013, 05:03 PM

Can't speak for these trucks, but late 70's Corvettes and Camaros/Firebirds have to have a tach conditioning module/filter between the HEI and the tach. If you don't have it, the needle bounces. That may be the issue with using this with an HEI.

http://forums.corvetteforum.com/c4-g...1990-vert.html

*Mister-B* · 07-31-2013, 05:59 PM

Quote:

Originally Posted by MARKDTN

Can't speak for these trucks, but late 70's Corvettes and Camaros/Firebirds have to have a tach conditioning module/filter between the HEI and the tach. If you don't have it, the needle bounces. That may be the issue with using this with an HEI.

http://forums.corvetteforum.com/c4-g...1990-vert.html

I have HEI, and this tac that I installed, and it works great. I don't believe I have this module you referred to.

Posted via Mobile Device

Sklptrljay · 07-31-2013, 08:42 PM

Mister B, my tach looks exactly like yours. If that means anything, I don't know.

I still haven't located a dwell meter, but I do have an extra HEI. I'm gonna swap the guts when I get some time, hopefully tonight.

Sklptrljay · 08-02-2013, 12:07 AM

*Update* --- Problem solved.

I changed out the cap and coil and everything is working great. I was a little worried I would have to buy a new tach.

Hope it's as simple a fix for you guys with the same problem.

**bigmac73** · 08-09-2013, 11:26 AM

i have a similar problem with my tach, i went out and bought the corvette HEI tach filter and installed it , no bouncing but it seems that mine is off about 1000 rpms, and the range between actual and indication gets higher as you increase RPMs. any thoughts ????

07-30-2013, 12:35 AM	#1
Sklptrljay Registered User Join Date: Apr 2012 Location: Stillwater, Oklahoma Posts: 874	Tach needle bouncing I installed a cluster I bought (year and a half ago--always takes longer than you think to get these things together), and It's giving me a few issues. Mostly I am concerned about the tach needle bouncing around. It's all over the place. I grounded the cluster, I followed the HEI installation instructions (constant 12V instead of the resistance wire), It has a new pcb that's made in the USA ( I checked that the pcb had continuity internally). I'm just stumped, so I was hoping someone has worked this out before. I'm wondering if it's just a bum tach? I didn't see a brand name on it. Any thoughts?

07-30-2013, 09:33 AM	#2
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Tach needle bouncing Best thing to do is use a dwell/tach meter if you have one and hook it up to the tach part of the HEI to see if it does the same. If you don't have one maybe you can buy one or maybe borrow one. __________________ 68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive...

07-30-2013, 03:53 PM	#3
Sklptrljay Registered User Join Date: Apr 2012 Location: Stillwater, Oklahoma Posts: 874	Re: Tach needle bouncing I think my dad may have a dwell meter. Thanks for the idea, I'll post the results. Posted via Mobile Device

07-30-2013, 07:06 PM	#4
Square_78 Registered User Join Date: Mar 2012 Location: Okanagan Valley, BC, Canada Posts: 1,237	Re: Tach needle bouncing I would be interested to know. My tach does the same thing Posted via Mobile Device __________________ #teamlongbed "I refuse to go disc brakes. I actually love drum brakes. It makes for an adventure." - 50bomb 1978 Chevy shop truck - static 6/8" 1970 GMC 1500 - Accuair eLevel Resto-mod http://67-72chevytrucks.com/vboard/s...d.php?t=537497

07-30-2013, 07:27 PM	#5
Mister-B Account Suspended Join Date: Oct 2012 Location: Salt Lake City, Utah Posts: 3,331	Re: Tach needle bouncing This is a bit of a shot in the dark, but I wonder if your engine and chassis isn't properly grounded with the copper ground straps, and that's introducing electrical noise into your system? Posted via Mobile Device

07-30-2013, 07:45 PM	#6
Sklptrljay Registered User Join Date: Apr 2012 Location: Stillwater, Oklahoma Posts: 874	Re: Tach needle bouncing I did run ground straps. I might check to make sure they all have a good surface connection.

07-31-2013, 04:04 PM	#7
HSRACER Registered User Join Date: Sep 2007 Location: Katy TX Posts: 1,268	Re: Tach needle bouncing Mine does the same thing. I bought a new one thinking the old one must be bad. Havent installed it yet. __________________ HSRACER Slammed 53 5 window Blown/Bagged 54 Pickup Patinaed 67 LS stepside Supercharged 67 Nova Bagged 69 Suburban Turbo'ed 5.3 LS

07-31-2013, 05:03 PM	#8
MARKDTN Registered User Join Date: Jan 2011 Location: Chattanooga, TN Posts: 2,165	Re: Tach needle bouncing Can't speak for these trucks, but late 70's Corvettes and Camaros/Firebirds have to have a tach conditioning module/filter between the HEI and the tach. If you don't have it, the needle bounces. That may be the issue with using this with an HEI. http://forums.corvetteforum.com/c4-g...1990-vert.html __________________ '83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project

07-31-2013, 08:42 PM	#10
Sklptrljay Registered User Join Date: Apr 2012 Location: Stillwater, Oklahoma Posts: 874	Re: Tach needle bouncing Mister B, my tach looks exactly like yours. If that means anything, I don't know. I still haven't located a dwell meter, but I do have an extra HEI. I'm gonna swap the guts when I get some time, hopefully tonight.

08-02-2013, 12:07 AM	#11
Sklptrljay Registered User Join Date: Apr 2012 Location: Stillwater, Oklahoma Posts: 874	Re: Tach needle bouncing Update --- Problem solved. I changed out the cap and coil and everything is working great. I was a little worried I would have to buy a new tach. Hope it's as simple a fix for you guys with the same problem.

08-09-2013, 11:26 AM	#12
bigmac73 Senior Member Join Date: Mar 2012 Location: Chesapeake, Va Posts: 1,275	Re: Tach needle bouncing i have a similar problem with my tach, i went out and bought the corvette HEI tach filter and installed it , no bouncing but it seems that mine is off about 1000 rpms, and the range between actual and indication gets higher as you increase RPMs. any thoughts ????

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