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Old 03-09-2020, 09:30 AM
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vertbird vertbird is offline
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Default Testing a tach....stops at 4500rpm

In my '76 TA the tach seems to function fine until it reaches 4500rpm then seems to stop. I seldom run it up that high but I don't want to keep my foot in it thinking I'm at 4500 and actually be at 5500rpm about to blow the thing up. Anyone know an easy way of testing the tach without running the engine that high just to see if the tach will physically go past the 4500rpm mark? I know other gauges can be ground to verify the needle moves all the way but not sure if that's applicable to a tach. Thanks

  #2  
Old 03-09-2020, 10:18 AM
"QUICK-SILVER" "QUICK-SILVER" is offline
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Without some kind of machine you can't make and break contact (on the coil lead) fast and consistant enough to make a tach work. Four pulses from the coil is ONE crank revolution.

I would hook up a known good tach and see what the engine is really turning.

If you're close to Chattanooga I've got a test tach you can borrow
Clay

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Old 03-09-2020, 01:30 PM
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STEELCITYFIREBIRD STEELCITYFIREBIRD is offline
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Factory tach?
If aftermarket, switch it to 4 or 6 cylinder.
Factory, nada clue how to test except maybe wiring it to another vehicle, or wire in another tach, in series or parallel?? Maybe??

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Old 03-09-2020, 01:32 PM
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STEELCITYFIREBIRD STEELCITYFIREBIRD is offline
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My 76 Formula factory tach has been to 7k + FWIW. There is an inline fuse in the brown wire, maybe clean up/ reseat that and coil connector.

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Old 03-09-2020, 04:32 PM
70GS455 70GS455 is offline
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More than likely you have a piece of debris in the meter movement physically preventing it from moving any further. Any ignition simulator or function generator (like i have on my test bench) can be used to determine proper and accurate tach functioning.


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Old 03-09-2020, 08:29 PM
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george kujanski george kujanski is online now
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I have found critter remains in tach movements

George

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Old 03-10-2020, 11:39 AM
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vertbird vertbird is offline
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Thanks everyone. Thanks Clay for the offer. I have an older GTECH pro that I may try to use as a tach. If it indicates beyond 4500, I guess I'll be pulling out tach and try to clean it. It was calibrated and repaired by the Tachman in 2006....guessing it's out of warranty by now.

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Old 03-10-2020, 01:21 PM
"QUICK-SILVER" "QUICK-SILVER" is offline
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This car got a 6K or 8K tach?

6K tachs are solid on back. 8K's have a hole on back that's covered by a paper sticker. When that sticker gets old and falls off...Here comes the dust and bugs. Fairly common to have tach failure because of it.

Clay

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Old 03-11-2020, 01:00 PM
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It's the 8K, but the sticker is still on there.

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