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G3GM 1973 to 1977 A-bodys. Chevelles, Monte Carlos, El Caminos, Laguna, 442, Cutlass, Malibu, GTO, LeMans, Century, Regal, Grand Am, Grand Prix, Sprint, Gran Sport, Can Am, Hurst-olds, and other 73-77 A-bodies


Test Tach

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Test Tach Empty Test Tach

Post by RossK73 Fri Jan 12, 2024 9:47 am

Hi - I have a couple of 73 tach clusters and was checking to see if the tachs can be tested before I put them up for sale. My SS came with the famed round idiot lights and I will probably leave these as they are correct to the car. Does anyone have a testing procedure that you can share? Thanx!
Happy New Year!
-Ross
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Test Tach Empty Re: Test Tach

Post by Mcarlo77 Fri Jan 12, 2024 1:38 pm

I've got a half dozen tach clusters where I've replaced the circuit board and to my knowledge, there is no way to bench test the accuracy of them unless you have the proper equipment. You can, however, briefly touch the leads to a 12V battery to confirm the needle drops to Zero. This is a pretty good indication that at least it works. There was a well-known company named Wilcox Corvette that dealt in Corvette parts and also sold a machine they developed for something like $175 that would accurately test tachometers. Unfortunately, the business no longer exists. Kinda wish I'd have bought one...could have had a little side business.
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Post by RossK73 Fri Jan 12, 2024 5:40 pm

Thanx Mcarlo77 - I'll give that a shot - don't care if they are precise as long as they work.
Cheers!
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Post by zucchi Tue Jan 16, 2024 9:18 am

Study the wiring diagram in your shop manual then hook up the tach accordingly with test leads.
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Post by g3chevy / Mr Pontiac Mon Jan 29, 2024 12:08 pm

This video might help. I did a "bench test" on the vehicle to make sure everything was working properly. That test starts at the 25 minute mark.


https://www.youtube.com/watch?v=kU8ZpvgKDFc
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Post by REVINKEVIN / Mr. 600+HP Tue Jan 30, 2024 5:28 am

Great info Mr. Head Honcho of the Poncho crowd. I will take a look at it.
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Post by RossK73 Tue Jan 30, 2024 8:33 am

Thanx for the tip G3 - It looked like only 2 terminals were used in the test. I don't have the gauge package to connect the cluster so I will have to connect to my aftermarket tach lead to do this. I'll give that a shot when I can get my car out of storage. Much appreciated!
Cheers!
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Post by g3chevy / Mr Pontiac Tue Jan 30, 2024 3:20 pm

RossK73 wrote:Thanx for the tip G3 - It looked like only 2 terminals were used in the test. I don't have the gauge package to connect the cluster so I will have to connect to my aftermarket tach lead to do this. I'll give that a shot when I can get my car out of storage. Much appreciated!
Cheers!

There's actually 3 connections to make to test your tach. The 12 volt, the negative and the tach lead going to the distributor. Here's a pic for reference. When you connect your tach to the 12 volt positive lead with your ground (negative) already connected, it should move the needle to "0". When the positive is disconnected it should float up a little bit to around 500 - 1000 rpms.
Test Tach Tach_c11
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Post by g3chevy / Mr Pontiac Tue Jan 30, 2024 3:21 pm

REVINKEVIN / Mr. 600+HP wrote:Great info Mr. Head Honcho of the Poncho crowd.  I will take a look at it.

Glad to see you're still kicking! You're missing some great weather up here lol!
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