#1  
Old 07-12-2020, 09:22 PM
racerx23 racerx23 is offline
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Default 1972 Formula tach issues

My 72 Formula tach is NOT reading correctly.It is off about 1800-2000 rpms too low. The cluster I bought from a fellow PY buddy said it came from a 72 or 73 TA. Who can test it ? Or where can I buy a new 72 tach ?
Thanks guys

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Steve Thomas
Dallas, GA
1950 Chevy truck red/original drive train
1967 Camaro SS silver w/black stripes 8.91@153mph
1969 Camaro SS 350 white w/black stripes
1971 Firebird 350 matching #'s white/blue int.
1975 Trans Am Blown 509 blk.
1975 Trans Am 400 matching #'s silver,loaded
1979 Trans Am 301 matching #'s,black
1980 Trans Am 301 matching #'s,t-tops,blue
1982 Mitsubishi drag truck 383 sb runs 9.92@ 133mph
  #2  
Old 07-12-2020, 11:19 PM
Formulabruce's Avatar
Formulabruce Formulabruce is offline
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72 is still a 1 wire tach as I recall. Make sure cluster is grounded as it needs that to work correctly. Our sponsor Ames sells new tachometers I believe. There website has a free catalog you can download even to your phone for reference. You need catalog F25. There are a few places that repair and recalibrate them. Usually the windings can degrade and cause readings that are incorrect. Make sure you know what you have, a stock harmonica connector for a 72 cluster does Not plug into a 1973 cluster.
What type of ignition are you running?

  #3  
Old 07-13-2020, 08:35 AM
racerx23 racerx23 is offline
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Default tach

I have the stock unitized distribtor.I hooked up a temp tach to make sure the distributor was sending correctly and it was. The cluster I have has a 2 wire connector and my harness is a 2 wire harness.I do have 2 additional ground straps on the cluster.
Thanks

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Steve Thomas
Dallas, GA
1950 Chevy truck red/original drive train
1967 Camaro SS silver w/black stripes 8.91@153mph
1969 Camaro SS 350 white w/black stripes
1971 Firebird 350 matching #'s white/blue int.
1975 Trans Am Blown 509 blk.
1975 Trans Am 400 matching #'s silver,loaded
1979 Trans Am 301 matching #'s,black
1980 Trans Am 301 matching #'s,t-tops,blue
1982 Mitsubishi drag truck 383 sb runs 9.92@ 133mph
  #4  
Old 07-13-2020, 08:53 AM
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FrankieT/A FrankieT/A is offline
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Location: USA
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I believe the '72 is the first year of a 2 wire tach.

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1978 Black & Gold T/A [complete 70 Ram Air III (carb to pan) PQ and 12 bolt], fully loaded, deluxe, WS6, T-Top car - 1972 Formula 455HO Ram Air numbers matching Julep Green - 1971 T/A 455, 320 CFM Eheads, RP cam, Doug's headers, Fuel injection, TKX 5 Spd. 12 Bolt 3.73, 4 wheel disc. All A/C cars
  #5  
Old 07-13-2020, 12:52 PM
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Peter Serio Peter Serio is offline
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The 2nd Gen trans am had a special meter (which is the part that moves the white pointer).

Those early 2nd Gen Firebirds use old school analog meters with a forced zero position as prior year tachometers on all Pontiac cars including cars with a hood tach had a zero position that was assisted by the weight of the pointer (to return to zero). The 1970 Trans Am was the first attempt at a tachometer with an forced zero in that the springs inside of the meter provide zero as the weight of the pointer does not assist in zero return, it actually opposes it. Over time (and use) or lack of use the springs inside of the meter movement wear out and the tachometer loses calibration. This affects not only the return to zero (after you turn the engine off) but also the arc across the rest of the dial. There is no way to repair a 48 year old tachometer meter where the springs have gone weak. The only cure would be to replace the meter. Modern aftermarket tachometers are not made with meters that are balanced using weights & springs, they are made completely different, so it takes a totally different type of circuit board with a computer chip on it to drive that meter. The old school tachometers had a small ivory colored circle shaped circuit board that drives the analog meter. Sometimes those boards go bad over time. They actually disintegrate in the air; and the aluminum pathways (used to made from copper) corrode.

You can buy an improved ( made with all copper pathways) 2nd Gen Trans Am replacement circuit board for the older GM car tachometers. They make new boards for a car with the points distributor tachometer and they also make new circuit boards for cars with Delco electronic ignition.

Unfortunately the wire plug-ins on the new circuit boards sometimes will not fit the trans am wire plug-ins. The guy who designed the new boards used as his sample part a circuit board from a 1971 Chevrolet Camaro Z28. Same electrical circuit, however the Chevrolet board had different shape & length plug-ins. (To fit the Camaro Meter assembly.) So you have to un-solder the new pins and solder on the trans am wires. For 2nd Gen cars the points tach board has 3 wire plug-ins, GM-HEI has 4.

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Peter Serio
Owner, Precision Pontiac

Last edited by Peter Serio; 07-13-2020 at 12:59 PM.
  #6  
Old 07-13-2020, 01:42 PM
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FrankieT/A FrankieT/A is offline
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Location: USA
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Quote:
Originally Posted by Peter Serio View Post
The 2nd Gen trans am had a special meter (which is the part that moves the white pointer).

Those early 2nd Gen Firebirds use old school analog meters with a forced zero position as prior year tachometers on all Pontiac cars including cars with a hood tach had a zero position that was assisted by the weight of the pointer (to return to zero). The 1970 Trans Am was the first attempt at a tachometer with an forced zero in that the springs inside of the meter provide zero as the weight of the pointer does not assist in zero return, it actually opposes it. Over time (and use) or lack of use the springs inside of the meter movement wear out and the tachometer loses calibration. This affects not only the return to zero (after you turn the engine off) but also the arc across the rest of the dial. There is no way to repair a 48 year old tachometer meter where the springs have gone weak. The only cure would be to replace the meter. Modern aftermarket tachometers are not made with meters that are balanced using weights & springs, they are made completely different, so it takes a totally different type of circuit board with a computer chip on it to drive that meter. The old school tachometers had a small ivory colored circle shaped circuit board that drives the analog meter. Sometimes those boards go bad over time. They actually disintegrate in the air; and the aluminum pathways (used to made from copper) corrode.

You can buy an improved ( made with all copper pathways) 2nd Gen Trans Am replacement circuit board for the older GM car tachometers. They make new boards for a car with the points distributor tachometer and they also make new circuit boards for cars with Delco electronic ignition.

Unfortunately the wire plug-ins on the new circuit boards sometimes will not fit the trans am wire plug-ins. The guy who designed the new boards used as his sample part a circuit board from a 1971 Chevrolet Camaro Z28. Same electrical circuit, however the Chevrolet board had different shape & length plug-ins. (To fit the Camaro Meter assembly.) So you have to un-solder the new pins and solder on the trans am wires. For 2nd Gen cars the points tach board has 3 wire plug-ins, GM-HEI has 4.
A lot of good info there. My 1970 T/A tach worked with points, HEI and now LS. It has worked flawlessly until it gets to 6500 RPM where sometimes it gets stuck. Never was problem with a Pontiac motor for obvious reasons, lol. However, my tach is dead balls on compared to the FI system. I checked it at 500RPM increments.

__________________
1978 Black & Gold T/A [complete 70 Ram Air III (carb to pan) PQ and 12 bolt], fully loaded, deluxe, WS6, T-Top car - 1972 Formula 455HO Ram Air numbers matching Julep Green - 1971 T/A 455, 320 CFM Eheads, RP cam, Doug's headers, Fuel injection, TKX 5 Spd. 12 Bolt 3.73, 4 wheel disc. All A/C cars
  #7  
Old 07-15-2020, 10:34 PM
racerx23 racerx23 is offline
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Join Date: Dec 2006
Posts: 190
Default tach issues

I ordered a new circuit board for the tach which should be here nextweek.I will keep you guys posted whether it works or not.If it is a meter issue where is the best and quickest tach repair shop ?
Thanks in advance

__________________
Steve Thomas
Dallas, GA
1950 Chevy truck red/original drive train
1967 Camaro SS silver w/black stripes 8.91@153mph
1969 Camaro SS 350 white w/black stripes
1971 Firebird 350 matching #'s white/blue int.
1975 Trans Am Blown 509 blk.
1975 Trans Am 400 matching #'s silver,loaded
1979 Trans Am 301 matching #'s,black
1980 Trans Am 301 matching #'s,t-tops,blue
1982 Mitsubishi drag truck 383 sb runs 9.92@ 133mph
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