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On my 4bt, I do not believe there is anything for a tach. at least we sure can't find anything... What are my options? possibly a different alternator with a pickup or a pickup on the crank pulley? What is my best option?
Thanks!
 

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How many spade terminal connectors are there on the tach? If there's three with 2 side by side and one behind the one behind is for tach hookup.
 

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every b series engine has a provision for a mechanical tach. but its $$$$$$$ for the correct parts to do it. contact me if you need more info on this. i put them on all my personal engines so i know exactly whats going on. that alt. stuff is kids stuff .
bob in tn.
1 423 384 8938
 

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Can you tap into the circuit of the alternator before the rectifier?

If so then a wire with a diode on that will give you a strong 0-7v ripple which is what your normal tacho feed is.
 

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There are a few routes you can go. Alternator pulse type or a programable using a probe and flywheel tooth count. OR a mechanical as previously mentioned. I also priced mechanical out once at approx. $200 bucks and that did not include a Tach! Bob, did you accomplish this for much less than that? The Angle Drive Adapter for $130 is what makes this expensive. I have seen Stewart Warner angle drives cheaper but do not know if they would work, I don't need an expensive lesson either...

I went on the cheap, I found a 3 3/8 programmable off a semi tractor, bought a probe from Napa and made my own brackets etc. Under $75 total.
 

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My plans (hopes) are to use the stock tach in my Durango. As far as i can tell from the FSM, the tach is driven off of the crank position sensor. I am planning on mounting the stock CPS on the 4bt's flywheel housing. It just counts the teeth on the flywheel.

Since the tooth counts are different and the tach will read high, i'm just going to replace the backing on the tachometer.

I think this will work, I will find out in a couple of months for sure.
 

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There is also a universal tachometer controller available if I remember correctly, use any tach then. I'll search for it again, I think it is a Dakota Digital product even, made right here in the city I live in coincidentally. That would make your life easier going with OEM in-dash I assume.
 

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While we're on the subject, if the alternator is used (tach lead), then there must be a ratio that has to be maintained to get a reading that corresponds to crank rpm? how is that calculated and how accurate are they? Think "mixing and matching" alternators when doing these swaps. I'd prefer a magnetic pick up and sensor mounted to the crank pulley or flywheel...any sources for, and experience with?
 

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While we're on the subject, if the alternator is used (tach lead), then there must be a ratio that has to be maintained to get a reading that corresponds to crank rpm? how is that calculated and how accurate are they? Think "mixing and matching" alternators when doing these swaps. I'd prefer a magnetic pick up and sensor mounted to the crank pulley or flywheel...any sources for, and experience with?
I know people who've swapped alternators and report about 10% variation.

Obviously all alternators are set to charge at a standard idle speed (700rpmish) and seem to produce a similar frequency when they do.

My truck has a DC rev counter (it was converted from pulse), I made an adjustable frequency-voltage converter to plug the gap.

Picking up flywheel teeth will give you the same calibration issues, except they won't change if you swap alternators.
 

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1989 Jeep Wagoneer, 360v8, 727, stock for now,
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Isspro makes a tach that uses gets its signal from magnets attached to the front pully, just like the Dodge unit. Page 14 in the catalog

You can down load the Isspro catalog from here isspro catalog
 

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i just picked up a multimeter that reads rpms....
it was about $60 but you can get cheaper ones...
it read about 650rpms on idle
in gear it read 600rpms
25 mph it read 1200-1300rpms
40mph it read 1400rpms
55mph it read 1500-1550rpm in overdrive
dose this sound about right???
i have the alternator with the pickup terminal.
jbox
 

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Programing Dakota Digital

How many teeth are on a 4bt flywheel i am going to set my tach today and need to know probally will count myself but would like to see if i am in the right ball park :happyfinger:
 

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I used a VDO Tach on my M37 that gets its signal from the tach output pin on my Delco Alternator. The VDO Tach has dip switchs that must be set and then the tach is calibrated with a calabration pot. You must have a known tach source to calibrate it against. I used my General Instruments Strobe Tach.

Another option is Autometer. Autometer makes a 0-4000 rpm diesel tach that is driven by a pickup that is attached to the outside of an alternator. A large hose calmp that will fit around the entire tach body holds the sensor. I have one of these on my test stand and am very pleased. However, once again it must be calibrated against a know Tach source. The Autometer the type that the case clamps on the steering column, while the VDO is panel mount.

If your interested in wither of these two options, let me know and i will dig out part numbers and post.

Paul
 

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The Autometer type that the sensor clamps on the alt case are on ebay all the time, just search for "diesel tach"
 

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Another option which gets some mileage on the iH8mud forum is a tiny tach. I've never used one but it sounds like it picks up injector pulses.
 

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Another option which gets some mileage on the iH8mud forum is a tiny tach. I've never used one but it sounds like it picks up injector pulses.
I have a tiny tach under the hood on my carryall. It does infact have a transducer that clamps on an injector line. Besides digital display of Engine RPM, it also shows Max Rpm until reset, also engine on hours etc. Nice little unit, BUT.......its a throw a way. It has a internal battery that is part of the PC Board that can not be replaced. When the internal battery finally quits, buy a new one. I have had mine running since 2004. The Tiny Tach also requires external 12 volts along wiht the battery.

Paul
 

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Where do you get the ones with the transducer?

The only ones I can find on the 'net are for spark engines.
 
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