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

67chevemall · 09-13-2012, 06:10 PM

Hey I have my tach on the bench to see why it stopped working.

Does anybody have a method to this?

It is a OEM one I bought on the board from Wes.

My other ? is does the whole instrument cluster need to be grounded?

Cheers

davepl · 09-13-2012, 07:17 PM

You could no doubt make some frequency generator, but wouldn't it be easier to just walk it over to any other vehicle you have and hook up the tach signal and power line to it under the hood? Then you could also compare it to the in-dash tach of that vehicle (if it has one).

Should be trivial if you have anything with HEI or a coil. If you're lucky enough to have a Mercedes V12 BiTurbo, you're on your own, we could never find a tach signal on the dyno! But an older vehicle should be ok.

JimKshortstep4x4 · 09-13-2012, 07:32 PM

Thje dash housing should be grounded as the tach gets its ground from the instrument housing. I would check to make sure the power wire and the wire from the distributor are connected and that you have power to the tach. Tachs seem to hold up well so I would look for something outside of the tach first.

Checking with an ohm meter does not seem to work as the readings from the tach are all open or close to being open. If you decide the tach is bad then sending it to someone in the business is a good option.

Jim

67chevemall · 09-14-2012, 09:03 AM

Thanks guys. My bezel is wood so I am thinking I just need a ground. My power wire is good and so is the dizzy wire. Just changing the glass on the cluster and I'll try it all out.

09-13-2012, 06:10 PM	#1
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Bench testing a Tach?? Hey I have my tach on the bench to see why it stopped working. Does anybody have a method to this? It is a OEM one I bought on the board from Wes. My other ? is does the whole instrument cluster need to be grounded? Cheers __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

09-13-2012, 07:17 PM	#2
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Bench testing a Tach?? You could no doubt make some frequency generator, but wouldn't it be easier to just walk it over to any other vehicle you have and hook up the tach signal and power line to it under the hood? Then you could also compare it to the in-dash tach of that vehicle (if it has one). Should be trivial if you have anything with HEI or a coil. If you're lucky enough to have a Mercedes V12 BiTurbo, you're on your own, we could never find a tach signal on the dyno! But an older vehicle should be ok. __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

09-13-2012, 07:32 PM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: Bench testing a Tach?? Thje dash housing should be grounded as the tach gets its ground from the instrument housing. I would check to make sure the power wire and the wire from the distributor are connected and that you have power to the tach. Tachs seem to hold up well so I would look for something outside of the tach first. Checking with an ohm meter does not seem to work as the readings from the tach are all open or close to being open. If you decide the tach is bad then sending it to someone in the business is a good option. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

09-14-2012, 09:03 AM	#4
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Re: Bench testing a Tach?? Thanks guys. My bezel is wood so I am thinking I just need a ground. My power wire is good and so is the dizzy wire. Just changing the glass on the cluster and I'll try it all out.



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