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Old 12-14-2006, 12:19 AM   #1
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How to retrofit tachometer on Cummins 5.9?

Boy, this Cummins 5.9 sure runs sweetly. But I would like to know my RPMs, and there is no tach. I have searched this and a couple other sites, and all I find is that it may be possible to buy a tach that runs off the alternator. That does not sound real accurate. Anybody know a way to run a tach off the flywheel or off the front pulley or some other place...?Maybe the injection pump -- I have the "P" style inline pump.
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Old 12-14-2006, 07:25 PM   #2
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The alternator tachs are accurate--semis used them for decades. I thought the TC's had tachometers, though?
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Old 12-14-2006, 09:07 PM   #3
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I don't have a tach either. I thought about getting on but I just used this to figure out my RPM's at a given speed.

http://www.idavette.net/tech/ratioc.htm
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Old 12-14-2006, 10:13 PM   #4
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No tach in my TC2000. I guess I'll call a couple of the gauge manufacturers about an alternator tach.

The other gauges are commonly used by the Dodge pick'm'up crowd. You'll find them on http://www.cumminsforum.com/index.php.

Hey, WOW! That idavette calculator is fabulous! Seems I was only turning about 2200 RPM at 55 MPH. Now, what's a conservative safe redline for a 5.9? 2600? That would be 63 MPH with my new 39 inch tall tires -- maybe 65 if the tires are 39,5. I could make myself a little chart and tape on the dash. Thanks!!!!
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Old 12-14-2006, 11:36 PM   #5
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Engine tachometers

These units are available for every engine. The alternator type units are easy to connect and reliable. Most of the big diesel engines use a sensor that is screwed into a threaded hole in the bellhousing, that is in alignment with the teeth on the starter ring gear. Many tach makers will offer a diagram exactly where to drill a new hole and size of drills to use, and tell size of tap and thread pitch. After the hole for the sensor has been tapped, the sensor is screwed into new hole untill the sensor touches the ring gear teeth, then the sensor is unscrewed about 3/4 to 1 turn. This is a very good method of mounting the sendor. Another simple method for mounting the sendor is glue two small button magnets opposite each other on any rotating pulley, harmonic balancer, altenator, generator, or water pump. Mount the tach sensor near magnets very rigidly and the tach will work excellant.
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Old 12-14-2006, 11:57 PM   #6
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Thanks Frank, that rings a bell. I've seen glued-on magnets used for aftermarket cruise control systems -- glued onto the driveshaft.

Drilling a hole in the bell housing sounds scary, but I'm also wondering what the sensor would "focus on". Or does it count the teeth somehow?
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Old 12-15-2006, 12:16 AM   #7
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If they are like other electronic speed sensors I've seen, they will use a tone ring that will count the number of magnetic pulses over a given time. It also very well could be optical.
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Old 12-15-2006, 12:30 AM   #8
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Here we go: A company called ISSPRO has all kinds of tachs for diesels; glue-on magnets, alternator drive.... I'll study their web site for a while now.
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Old 12-15-2006, 12:59 AM   #9
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This might work for me:
http://www.isspro.com/installation/IS236A.pdf
The dial is only 2", but it would serve.
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Old 12-15-2006, 10:52 AM   #10
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Auto Meter has one that uses an inductive sensor strapped to the alternator, but it must be calibrated with another tach. And, being me, I would have trouble trusting such a calibration. Part numbers 2888 (black), 3788 (silver/white). 2 5/8 diameter, goes to 5000 RPM.
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Old 12-15-2006, 06:39 PM   #11
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Quote:
Originally Posted by Elliot Naess
What's a conservative safe redline for a 5.9? 2600? That would be 63 MPH with my new 39 inch tall tires -- maybe 65 if the tires are 39,5. I could make myself a little chart and tape on the dash. Thanks!!!!
I called a diesel performance shop and asked them what they though a safe redline would be for a 5.9 and they said "you can run those motors at 3,000RPM's all day long and not hurt them"

Maybe call around and see what you hear is a safe redline.

I figure that once I have the governor set where I want it I can check my top speed - therefore RPM's at wide open throttle. If it's safe then I don't really care what then engine's turning while I'm driving. I mean I kinda care but not enough to spend lots of money on a tach.
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Old 12-15-2006, 07:14 PM   #12
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When figuring out how tall your tires are, don't go by the sidewall rating or the overall height. What you need to do is measure from the road surface to the center of the hub. This will give you your effective overall radius taking into account sidewall squish, differences in rim widths, etc etc etc. Then you just need to multiply by two to get the effective overall diameter. You'd be surprised how much of a various there might just be...
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Old 12-15-2006, 07:54 PM   #13
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Right. Many years ago I worked in a shop that did speedometer/odometer calibrations. They would mark the tire then drive the vehicle down the alley some ten or 20 tire-revolutions and measure the distance and calculate from that.
That reminds me that there is a commercial speedometer shop in West Sacramento. I think I'll drop in on them.
Sure appreciate all the input here, guys!
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Old 12-20-2006, 12:57 PM   #14
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Frank, you were right (of course!). Commercial Speedometer in West Sacramento has an ISSPRO tach, 3 3/8 diameter, 3000 RPM, with a sensor that screws into the bell housing. He knew right off the top of his head how many teeth the 5.9 has on the starter ring gear, and he told me I should have a hole in the bell housing with a red hex head plastic plug in it. He even knew the size of the thread in that hole. So I went out to Millicent and opened the dog house, and sure enough, that red plastic plug is right there, at 11 o'clock on the bell housing. About $150,-. And he has it IN STOCK. Next trip to Sacramento!
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Old 01-31-2007, 01:23 PM   #15
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And here they are.

Tach: Isspro R8530M. 3 3/8", 3000 RPM, lots of little switches on the back so it can
be used for a wide variety of applications. $117.57.

Sender: Isspro CS4-106. Magnetic sensor. $25.00. Screws into the existing
hole in the bell housing.

An old hot rodder's gotta have a tach!

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Old 06-19-2010, 11:35 PM   #16
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Re: How to retrofit tachometer on Cummins 5.9?


Oooohh... Kayyyyy.... So it took me a while to get around to installing this tach. More than three years!

It's installed and I will take pictures and blah, blah.... But it reads wrong. It reads something on the order of double the true RPMs. Shows 1100 at idle, and goes to the maximum of 3000 with just a light revving up. I calibrated it for 103 teeth on the flywheel. It's dark out now, so I'll recheck a couple of things tomorrow -- voltage, ground and the calibration switches, I suppose. Meanwhile... any clues? Is 103 the correct number of teeth on the ring gear of a 1992 Cummins 5.9 with an Allison MT643?
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Old 06-19-2010, 11:40 PM   #17
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Re: How to retrofit tachometer on Cummins 5.9?


Meanwhile... researching....

WHOA! Lookit!:

http://www.valeoclutches.com/media/docu ... Brakes.pdf

Says 173 teeth. I'm going out there with the calibration chart and a flashlight.
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Old 06-20-2010, 12:02 AM   #18
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Re: How to retrofit tachometer on Cummins 5.9?


Bingo! Idles at 600 - 650. I didn't rev it all the way up with the engine cold, but I took it to 2000, which sounded just right for such revs. Next time it's warmed up, we'll find out what it is governed at.

I'm installing the pyrometer and the turbo pressure also. Most of the work is done.
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Old 06-20-2010, 10:57 AM   #19
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Re: How to retrofit tachometer on Cummins 5.9?

makes me want to get one for my bus and for my liteace
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Old 06-20-2010, 11:20 AM   #20
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Re: How to retrofit tachometer on Cummins 5.9?


A bit early -- obviously -- for a complete opinion on this tach, but I can report that the calibration procedure is easy enough, SO LONG AS YOU KNOW HOW MANY TEETH THERE ARE ON YOUR FLYWHEEL. The instruction sheet has a chart for any number of teeth from 1 to 255, so no mathematics needed. Just set eight tiny switches on the back of the tach according to the chart and off you go.

Wiring was easy with a plug-in harness. Wire up the harness, then plug into the gauge. None of the awkward old method of attaching wires to studs on the gauge.

The tach needle moves very smoothly -- no jumping or chattering at all.
Just one odd thing -- it stays at idle speed when you shut the engine off. But if this bothers you, you can turn the key back on for a couple of seconds, and it will go to the new idle speed, which is now zero, and stay there when you shut the key off for good.

Installing the sensor on the bellhousing was a bit of a chore, since there is so little room to work down there -- on my (naughty word) flat-nose front-engine bus.

Edit; add pictures:

The tach sending unit is the thing that resembles a big bolt with gold threads and black head, with a chrome nut at the base, and one white and one yellow wire, at the left side of the bell housing:




Here it is up close:



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