johnbell Posted July 26, 2011 Share Posted July 26, 2011 I am working on a 74 260 with a gen 1. I cannot get the tach to work at all. the moment I turn the key on it goes to max. Oh, it may wiggle around a bit after the engine is running but I am pretty sure it is toast. I have tried JTR's suggestions to no avail. I really want all of my original gauges to work. I am kind of a nut that way. We are going to have a heater, air conditioning and stock gauges that work!! period. I pulled the tach and see that the case is absolutely huge..Why cant I find a new tach, rob the movement and change it out. It looks like the needle swing is 255 degrees on the old one, a new tech sun super is 250 degrees. My watchmaker friend says he has the tools to pull the needles, may have to do some adaptation there but probably do able. Anybody ever tried this before..Sun tach is about 40 bucks. Worth trying?? Quote Link to comment Share on other sites More sharing options...
beermanpete Posted July 26, 2011 Share Posted July 26, 2011 If you have the 4-wire tach then the problem is likely the electronics inside the tach. My tach did the same thing as what you described. The problem seemed to be heat related. When the weather got hot it would go to full scale as soon as I turned on the key. I replaced the 2 transistors and it works fine now. I found some information on the internet about the Smith meters used in British cars in the 60s. The Datsun tach appears to be a close copy of the Smith tachs. The Smith gurus seem to think the timing capacitor is the primary problem when the tach goes full scale. Either way it is an easy fix for a capable electronics repair technician. Quote Link to comment Share on other sites More sharing options...
johnbell Posted July 27, 2011 Author Share Posted July 27, 2011 I took the old tach apart. I managend to get the hand off with finger pressure. there is. after you pry off the cap on the middle of the hand a hole for a puller, I took this to my watchmaker friend, but while he was looking for his puller, I pulled it off. I went ahead down to auto zone and bought a sun super tach, o to 8000 rpm, just like the original. about 50 buck tax title and license. anyway, I tested the sun before I ripped it apart and it worked as adversitsed. I pulled the movement off the Z tach, down to the dial (bezel) In order to adapt the Sun movement to the Z bezel I fount that it had to be rotated 90 degrees in order to clear the stock turn signal lighting. so the stock dial must be drilled with two holes 90 degrees from the original holes.(p.S. the original holes will almost line up on the horizontal, but, due to the turn signal light tubes are unusable. I had to cut the needle off the Sun with a dremal tool. I supported the axle with a hemostat while doing this. I drilled the new mounting holes in the bezel 90 degees from the original holes, and mounted the movement on the bezel. the original axel measured about .36 inches in diameter the new sun axel is about .40. I will redrill the z needle to the correct size, orient it on the axle in the correct position, I am sure after several tries and then glue it. the original mount holes will have to be delt with. And I assume, if all goes well, I wil have all of my original instrumets working with the V8 chev. Wish me luck!! Quote Link to comment Share on other sites More sharing options...
Leon Posted July 27, 2011 Share Posted July 27, 2011 Sounds like way more work than necessary. Why not just buy a 280Z tach? My 260Z had a dead tach, that worked only when it wanted to. I bought a 280Z tach off ebay and no problems since. Quote Link to comment Share on other sites More sharing options...
johnbell Posted July 27, 2011 Author Share Posted July 27, 2011 All gauges are now working. Stock gauges with a V8 chevy. the clock was the most expensive to repair at about 100.00 tach, 50 bucks, temp and oil 20 bucks for a used gauge, volts and fuel 20 bucks. 40 bucks for oil and temp senders. I feel good. now when the taurus fan controller gets here tomorrow, (139.00) for full auto control to control the 20 buck taurus fan,, I will be streetable.. Insurance here we come! Quote Link to comment Share on other sites More sharing options...
rejracer Posted August 15, 2011 Share Posted August 15, 2011 I did the 280z tach when i upgraded to electronic ignition. Has worked ever since, I did the mod in 1995. Quote Link to comment Share on other sites More sharing options...
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