A WHAT IF SENARIO

[chucky]

Say for instance you wanted to put in a remote manual tach on an AO 3116 where and how would you do it and what/where do you get the signal from to drive a manual tach ?

 

[Keith Knight]

Seems I’ve read that there is a hole on the transmission housing and the flywheel starter ring acts as a tone ring and you put a sensor there. That was a really long time ago. So I may be completely wrong.

 

[GeneralDisorder]

You already have a tach sensor. It's on the bell-housing IIRC and is necessary for the transmission. I believe there is also wiring already in the truck to support a tach as it is part of the winch package on the A0 trucks since the winch operation requires raising the idle speed with the hand throttle. Later electronic trucks deleted the hand throttle and use an idle up switch through the engine ECM and thus also deleted the tach from the winch package.

Also - semantics and all that - but a "manual" tach would be a cable driven tach. Which I haven't seen on any vehicle made in the last ~60 years. All tach's are electric from the era our trucks come from. I assume you meant to say "analog" - which indicates the type of display - in this case a needle gauge. It's an electrically driven analog gauge that I assume you are after.

 

[Ronmar]

There is actually 2 RPM sensors, one lower right belongs to Allison for transmission control, and one top left just to the rear of the primary fuel filter/primer, to drive an electric tach.

a mechanical tach? Cant think of any place to get rotary motion from to drive one. One reason no one uses them any more as you need the 1:1 rpm output or appropriate gearing. The engine basically needs to be built for it. Electrics are far easier, and as General mentioned, sensor and wiring is already in place up to the dash on the A0.

 

[chucky]

This truck wasnt a winch truck so no luck there but do you think the sensor by the fuel filter would run a generic electric tach like a SUN tach ?

 

[MatthewWBailey]

What about the ac terminal on the alternator?

 

[Ronmar]

This truck wasnt a winch truck so no luck there but do you think the sensor by the fuel filter would run a generic electric tach like a SUN tach ?

Not an automotive tach, those are typically sensing ignition and are only looking for 1/2 pulse per revolution per cylinder, I E: a V8 has 4 pulses per revolution.

you need a flywheel/magnetic pickup tach that can sense the 133 pulses per revolution created by the sensor monitoring the passage of the flywheel ring gear teeth.

google flywheel tach or magnetic pickup tach or diesel tach, and you will find some.

 

[Ronmar]

What about the ac terminal on the alternator?

On the A0, that second terminal on the reg is not labeled AC, it is labeled F- and is intended to monitor the duty cycle/pulse width of the pulses used to excite the field (How hard the alt is working). Not sure what freq it is being pulsed at by the regulator, but I suspect it is not coincident with RPM, but I have also never checked it. Just as easy if not easier, to sample the tach sensor output, under the drivers dash at the left or under the center dash forward of the heater where the aux panel harness connector can be found…

 

[Lostchain]

What about the ac terminal on the alternator?

That terminal only gives you alternator shaft speed not engine speed, I suppose if you knew all the diameters of the pulleys you could do math to get the engine speed. The output of the AC terminal is Hz X 10 = Shaft RPM

 

[flyfishtrailer]

This truck wasnt a winch truck so no luck there but do you think the sensor by the fuel filter would run a generic electric tach like a SUN tach ?

Behind the heater is a pair of connectors on the harness behind the heater for the tach and all of the switches that were used for the winch. You just don't have the branched harness that plugs into it that was included with the winch kit.

 

[chucky]

Not an automotive tach, those are typically sensing ignition and are only looking for 1/2 pulse per revolution per cylinder, I E: a V8 has 4 pulses per revolution.

you need a flywheel/magnetic pickup tach that can sense the 133 pulses per revolution created by the sensor monitoring the passage of the flywheel ring gear teeth.

google flywheel tach or magnetic pickup tach or diesel tach, and you will find some.

Thanks so much Ronmar your why i check here first if i dont know ! ADMINS you should rename FMTV section to FMTV/RONMAR with out him in here we would suffer !

 

[Ronmar]

That terminal only gives you alternator shaft speed not engine speed, I suppose if you knew all the diameters of the pulleys you could do math to get the engine speed. The output of the AC terminal is Hz X 10 = Shaft RPM

Yep, that's how you do it. Old school but fairly common way of getting engine RPM off a diesel... I just don't think the A0 alt is capable of it. They have that terminal configured for AC on the A1 alt and the LBCD monitors alt RPM using it to make some of its decisions...

 

[MatthewWBailey]

That terminal only gives you alternator shaft speed not engine speed, I suppose if you knew all the diameters of the pulleys you could do math to get the engine speed. The output of the AC terminal is Hz X 10 = Shaft RPM

I'm doing that now with the delco alt but it labels that terminal "R"