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Re: 74 Rallye tach adjustment questions
[Re: cougar_cat_25]
#984444
05/02/11 10:27 AM
05/02/11 10:27 AM
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Joined: Jun 2008
Posts: 1,822
Colorado
denfireguy
top fuel
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top fuel
Joined: Jun 2008
Posts: 1,822
Colorado
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Quote:
My tach needle doesn't start to move until my engine rpm is 1500-2000ish. I have it out, apart and see that it has one phillips head adjustment screw. Anyone know which way to turn it and ballpark how much?
I have searched for years on information repairing and calibrating the factory tachometer. I have found no schematics and no information on calibration. I know that they were never very accurate even when they are new. They only had two transistors in a rudimentary amplifier that put out more current with more and more closures on the input. Todays technology is much better.
You might consider changing the innards to a Dashworx electronic version. If you send it to him for the install, he will calibrate it for you for an extra fee.
The state of the art method of calibration is to use a function generator to simulate the open and closing of the points or the reluctor triggering the control module. The frequency of the generator is set to 4000 Hz for 1000RPM (8 cylinder engine)indicated on the tach. Calibrating it to another tach works but is not as accurate. It is like setting your watch to the city hall clock. It is fine if it is accurate but it depends on someone else's accuracy in setting it and how long ago it was set. A stuck clock is right twice a day.
Craig
2014 Ram 1500 Laramie, 73 Cuda
Previous mopars: 62 Valiant, 65 Fury III, 68 Fury III, 72 Satellite, 74 Satellite, 89 Acclaim, 98 Caravan, 2003 Durango
Only previous Non-Mopar: Schwinn Tornado
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Re: 74 Rallye tach adjustment questions
[Re: denfireguy]
#984445
05/02/11 04:00 PM
05/02/11 04:00 PM
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Joined: Sep 2004
Posts: 6,906
IL, Aurora
ademon
master
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master
Joined: Sep 2004
Posts: 6,906
IL, Aurora
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Quote:
Quote:
My tach needle doesn't start to move until my engine rpm is 1500-2000ish. I have it out, apart and see that it has one phillips head adjustment screw. Anyone know which way to turn it and ballpark how much?
I have searched for years on information repairing and calibrating the factory tachometer. I have found no schematics and no information on calibration. I know that they were never very accurate even when they are new. They only had two transistors in a rudimentary amplifier that put out more current with more and more closures on the input. Todays technology is much better.
You might consider changing the innards to a Dashworx electronic version. If you send it to him for the install, he will calibrate it for you for an extra fee.
The state of the art method of calibration is to use a function generator to simulate the open and closing of the points or the reluctor triggering the control module. The frequency of the generator is set to 4000 Hz for 1000RPM (8 cylinder engine)indicated on the tach. Calibrating it to another tach works but is not as accurate. It is like setting your watch to the city hall clock. It is fine if it is accurate but it depends on someone else's accuracy in setting it and how long ago it was set. A stuck clock is right twice a day.
Craig
 turn the screw any way it will be evident to which way you need to go, if your racing the car don't go by the stock gauge, or even the stock gauge with modern internals, mine is fine for spirited street driving.
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