jvandyke Posted January 21, 2019 Share Posted January 21, 2019 i've searched, honestly. The aftermarket tach in our '72 is junk. Is it possible to make the OEM tach work with the V8? I see some "adapters" out there. The 350 has an HEI dizzy. The OEM tach is still sitting in the nacelle and it would be so nice just to make it work with the V8, ya know? Something like this? https://www.ebay.com/itm/UNIVERSAL-TACH-ADAPTER-CONVERTER-COP-1-2-3-4-5-6-8-10-cyl-to-any-4-6-8-Tach/141931549970?hash=item210bc79512:g:wqgAAOSwNX1b~MNz:rk:1:pf:0 Quote Link to comment Share on other sites More sharing options...
calZ Posted January 21, 2019 Share Posted January 21, 2019 There might be cheaper options, but this would 100% work and is still reasonably priced. http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=127/category_id=694/mode=prod/prd127.htm Quote Link to comment Share on other sites More sharing options...
jvandyke Posted January 21, 2019 Author Share Posted January 21, 2019 I did see the dakota one too. I contacted the "widget man" ebay one linked above, he responded immediately and said it would work but only if I also added a widget to increase the voltage: https://www.ebay.com/itm/TACHOMETER-SIGNAL-BOOSTER-3-16V-Input-48-63V-Output-compare-to-MSD-8920/142171581596?epid=3012319916&hash=item211a162c9c:g:d9kAAOSwjoFb~Mao So that's about $80 in his stuff, whereas if the Dakota works, there ya go. Can't really get a whole tach for that anyway, let alone one that already fits the car and looks correct. I'm leaning this route but I should probably try to see if the stock one still reads, it won't be correct but it should read something, which means another few hours crammed under the dash trying to decipher the rat's nest nightmare of wires 40 years of hackers have built up, it's something else, my turn! Quote Link to comment Share on other sites More sharing options...
jvandyke Posted January 21, 2019 Author Share Posted January 21, 2019 Here's what he says, I hope doesn't mind the re-post. He seems knowledgeable and quick to respond, that's two ++ already. Yes, but you'll also need one of our voltage boosters to drive the tacho (see our listing# 142171581596). Tachos on all pre-300 Z's were back-EMF types that needed the "spike" from a coil discharge to trigger. The 12V square wave from this BTA adaptor won't drive them, so you'll need to add the BTAC2 booster on the adaptor's output. The adaptor and booster can mount together and share the same power and ground (most of our customers use piggyback fastons). For an HEI distributor, you'll probably also want a filtering resistor (free, but you'll need to request one with purchase). Lastly, since the tacho has been out of use, we recommend you test it first to make sure it's working. If the HEI is an OEM type, the HEI tach output should trigger it (albeit with a wrong reading), since OEM HEI outputs use an internal connection to coil-negative. If it's an aftermarket HEI with digital output, you can test using a different vehicle with an external coil by jumpering signal and ground between the vehicles. We do bundle shipping, just pay full postage at checkout and we'll refund the excess to your PayPal when the items ship. In this case you'll pay $10.50 with $3.50 refunded. Thanks for your interest!Best Regards,Gene K Quote Link to comment Share on other sites More sharing options...
jhm Posted January 22, 2019 Share Posted January 22, 2019 I've never had a problem running the stock tach with a GM HEI or the stock Chevy distributor. Typically, some additional resistance is required in the signal feed line; but no other changes required IIRC. Quote Link to comment Share on other sites More sharing options...
jhm Posted January 22, 2019 Share Posted January 22, 2019 P.s. It's easy to remove the stock tach through the front of the dash, which will make it much easier to work on vs killing yourself working on it from underneath the dash. Quote Link to comment Share on other sites More sharing options...
jvandyke Posted January 22, 2019 Author Share Posted January 22, 2019 47 minutes ago, jhm said: I've never had a problem running the stock tach with a GM HEI or the stock Chevy distributor. Typically, some additional resistance is required in the signal feed line; but no other changes required IIRC. So all you do is add a resistor and the 6 cylinder tach reads correct for the 8 cylinder? Quote Link to comment Share on other sites More sharing options...
jhm Posted January 22, 2019 Share Posted January 22, 2019 Yep, I've done with two different cars in the last few years. It's discussed in the JTR manual, if you happen to have a copy handy. Quote Link to comment Share on other sites More sharing options...
jvandyke Posted January 22, 2019 Author Share Posted January 22, 2019 9 minutes ago, jhm said: Yep, I've done with two different cars in the last few years. It's discussed in the JTR manual, if you happen to have a copy handy. This one? https://www.amazon.com/Datsun-Z-V-8-Conversion-Manual/dp/B0006EVOAK/ref=sr_1_2?keywords=jtr+manual&qid=1548178839&sr=8-2-spell $263.84 (I've seen it for $40ish elsewhere) Care to share what you did? Quote Link to comment Share on other sites More sharing options...
Miles Posted January 22, 2019 Share Posted January 22, 2019 (edited) Per JTR page 10-2, the 240z tach will not work with an HEI distributor. The 260z and 280Z tach will work with the addition of a 15k 1/2 watt resister and some wiring changes. The guts of the 260Z/280z tach have to be swapped into the 240Z tach housing because the 240Z/280Z tachs mount differently. Edited January 22, 2019 by Miles Quote Link to comment Share on other sites More sharing options...
jvandyke Posted January 22, 2019 Author Share Posted January 22, 2019 alright, thanks, I think I might just chase the signal converter then, I should consider getting a copy of that book, although it's not my car (my kid's) and he may or may not be in it for the long haul, I 'should' just buy it from him, I freak'n love this thing. I"ll be along in a week or so with rear suspension questions, maybe later today. Quote Link to comment Share on other sites More sharing options...
jhm Posted January 23, 2019 Share Posted January 23, 2019 My bad....I completely missed the fact that you have a 240. My apologies. A 260 or 280 tach should be relatively easy to come by, if you decide to go that route. The JTR manual is available for $39: https://jagsthatrun.com/products/copy-of-v-8-conversion-manual-for-volvo-200-series (Yes, I know the hyperlink says Volvo; but it should work and get you to the correct manual on the JTR website.) Quote Link to comment Share on other sites More sharing options...
jvandyke Posted January 23, 2019 Author Share Posted January 23, 2019 We fired her up and the old Drag'n Tach actually still works. I had shorted out the bulb holder in it during an instrument lighting upgrade (LEDs). So for now I'm going to try to resurrect this abmonination. I tore it all down and a trace on the PCB was burned, I'll repair that and if it all still works and lights up then we'll live with it for now. It's one of these from the 90's (as is the whole car so I guess it's "period correct". BTW Does anyone have extra heater control cable clamps to spare? We're missing one. Quote Link to comment Share on other sites More sharing options...
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