83-84TC tach modification - input needed June 11, 2007, 10:14:17 PM OK, I have an instrument cluster from an 83-84TC in the '80 XR-7. Great, right? Anyway, obviously the tach is set up for a 4 cyl engine, but the XR-7 currently has a V8 and eventually will have a V6, so I want to make the tach useable instead of having it read 50-100% higher.I'm just trying to figure out the "best" way to alter the signal and perhaps make it adjustable to boot.I have a tach from a 79-80 turbo Mustang and those had a small adjustable pot on them which could be used to "adjust" the input signal, but the 83-84 TC tach does not. Of course electronics is not my strong suit and I'm trying to sort out what resistor to replace, or figure out a way to alter the signal before it gets to the "SIG" input to the tach itself. Is it possible to put a resistor in the line from the coil to the tach? Will that reduce the signal impulses?Anyone modified one of these, or something similar? Quote Selected
83-84TC tach modification - input needed Reply #1 – June 11, 2007, 11:40:13 PM Chuck - I do know that a resistor inline with the coil will not work - the tach works by counting pulses, not by the strength of those pulses. You would have to replace a resistor or capacitor (or both) on the tach's circuit board to modify it. Without having one to play with I'm afraid I can't offer much help other than that... Quote Selected
83-84TC tach modification - input needed Reply #2 – June 12, 2007, 12:35:43 AM here's it on Eric's Site http://www.coolcats.net/tech/advanced/4to8tach.htmlbut, it's only for the 87/88. When you do find out, let him know, so he can get it on his site Quote Selected
83-84TC tach modification - input needed Reply #3 – June 12, 2007, 09:44:43 AM Quote from: Thunder Chicken;153680Chuck - I do know that a resistor inline with the coil will not work - the tach works by counting pulses, not by the strength of those pulses. You would have to replace a resistor or capacitor (or both) on the tach's circuit board to modify it. Without having one to play with I'm afraid I can't offer much help other than that...Yeah, I kind of figured that.I'm guessing I need to figure out which resistor on the board alters the SIG before it hits the chip (OP AMP?). Quote Selected
83-84TC tach modification - input needed Reply #4 – June 12, 2007, 09:46:16 AM I have no clue what that means, but if you figure out a mod, let me know. I would love to have a stock guage pack in my dash. 83-4 TC is the same look just with a tach. Quote Selected
83-84TC tach modification - input needed Reply #5 – June 12, 2007, 10:59:21 AM Youre swapping to a V6? Of what sort? Quote Selected
83-84TC tach modification - input needed Reply #6 – June 12, 2007, 11:00:29 AM Me or chuck? I think he's doing the SHO V6 Quote Selected
83-84TC tach modification - input needed Reply #7 – June 12, 2007, 05:56:56 PM /thread shiznitting..Chuck maybe if you posted up a picture of the back of the Tach it would help. A lot of us haven't seen the back of an old school turbo cluster. Quote Selected
83-84TC tach modification - input needed Reply #8 – June 12, 2007, 06:17:16 PM Quote from: CougarSE;153866/thread shiznitting..Chuck maybe if you posted up a picture of the back of the Tach it would help. A lot of us haven't seen the back of an old school turbo cluster.Ok Mr. Poopy The second pic is with parts removed for clarity. The post in the middle marked "SIG" is where the input from the coil comes in. Quote Selected
83-84TC tach modification - input needed Reply #9 – June 12, 2007, 06:26:49 PM I'm intrested in how this turns out!! Quote Selected
83-84TC tach modification - input needed Reply #10 – June 12, 2007, 07:26:32 PM Ok, I'm trying to find some info on that op amp. I'm thinking maybe if I can figure out the inputs, I may be able to figure out the proper pieces that need to be changed.I'm not having any luck though. Quote Selected
83-84TC tach modification - input needed Reply #11 – June 12, 2007, 07:40:23 PM More digging.It appears to be a DIP-14 type OP AMP. Looking at data sheets, pins 2,3 5,6,9,10,12 and 13 are inputs and 1,7,8 and 14 are the outputs.PIn #1 is lower right in the pic Quote Selected
83-84TC tach modification - input needed Reply #12 – June 12, 2007, 07:53:16 PM Hmm, hardwood floors, granite countertops, where do you live again? :hick:I have NO clue about any of this, but I DO have an 83/84 TC cluster to play with. Maybe Jeff K over on NATO has an idea? Quote Selected
83-84TC tach modification - input needed Reply #13 – June 12, 2007, 08:00:14 PM Chuck, what will you do with the "Turbo" and "Overboost" LEDs in the cluster?Quote from: Aerobird Motorsports;153890Hmm, hardwood floors, granite countertopsIt looks like a kitchen table and spray-painted particle board to me. :D Quote Selected
83-84TC tach modification - input needed Reply #14 – June 12, 2007, 08:08:35 PM IMO I can live with the turbo and overboost lights in the cluster if I have a factory looking Tach. It's alot better then having an aftermarket one that doesn't match the rest of my int. Who ever figures this out, I wana know how to do it Quote Selected
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