Old Kenworth 849 tach not working.

[LandonRobinson]

Year: Unknown (est late 1960's - early 1970's).
Model: 849
Make: Kenworth
Engine #: 27161992
Engine: Cummins; NTC350FFCRX
Tachometer: Stock; electronic.

A quick backstory on this is that the engine is possibly not the original engine and has a "1987" rebuild date tag on it along with the NTC350FFCRX model number.

But anyway... the problem that I am having is that the tachometer in the cab does not work, when you turn the ignition on the needle jumps, and if you slowly wind up the engine somewhere in the mid-range RPMs the needle wavers a little bit but otherwise you get nothing, so I think the tach works it is just not getting a signal from the engine.

I have cleaned up all the wiring on the back of the tach and verified that it is getting 12 volts when the ignition is turned on, I have looked the engine and the alternator over and there is no obvious place where the tach signal is coming from, so my question is... does anyone know where the tach signal comes from on this engine?

 

[Truck Shop]

More than likely tack sensor is located on bell housing, reading flywheel. I have seen sensors
located in various spots on the bell, but normally at the bottom. There was also a type that
was incorporated into original mechanical drive at or in the area of PT pump, I've only seen
one like that. Signal from alternator was not used in those years as I recall. If it is a late 60's
early 70's it should have been mechanical. A photo of tach head would help.

 

[petepilot]

More than likely tack sensor is located on bell housing, reading flywheel. I have seen sensors
located in various spots on the bell, but normally at the bottom. There was also a type that
was incorporated into original mechanical drive at or in the area of PT pump, I've only seen
one like that. Signal from alternator was not used in those years as I recall. If it is a late 60's
early 70's it should have been mechanical. A photo of tach head would help.

Check rt.side bellhousing below motor mt.

 

[Truck Shop]

Another waste of time.

 

[LandonRobinson]

Sorry for the delay, two log loaders in the sorting yard blew hydraulic hoses on Friday and I was offsite all weekend, yesterday involved tipping the cab forward on one of them.

Anyway... here are some pictures of the dash and the tach.

The tach is definitely electronic it only has wires going to the back of it and no spinny cable.

I'll look around on the bell housing again.

The late 60's to early 70's is just an estimate no one really knows.

Thank you for the replies.

 

[crane operator]

Tach sender unit may be long gone from the last time, or the first time, they swapped transmission. Someone said "stupid thing doesn't work anyways" and clipped the wires and threw it in the trash.

 

[trucker1]

This is what it looks like, and what it looks like in the bell housing.
This one is above the starter, but it also has another hole below the starter, common for them to go bad, couldn't get them out and just drilled a new hole. I think the hole is tapped 3/4 fine thread. If I remember right (from 20years ago) you thread it in until it touches the teeth on the flywheel and them back it out one turn and lock the nut there. I have had trucks that had 3 or 4 in the bellhousing, only one of them hooked up. It will have 2 wires on the sending unit.

George

 

[Truck Shop]

By design that's a 80's vintage tach-- no longer available.

 

[LandonRobinson]

I have looked the whole entire tranny over and there is no sending unit anywhere on it, the only hole that I could find anywhere was the water drain hole at the very bottom (which is a plain old hole with no threads at all), I did however find the speedometer drive at the very back (which the operator doesn't care about).

 

[LandonRobinson]

Well... What I ended up finding out late this afternoon was that buried back in the dark and covered in grease on top of the fuel assembly on the driver's side of the engine was the coupler for the mechanical spinner cable, and with that getting the electronic tach to work is not going to happen.

So with that I am considering this resolved, thank you again to everyone that replied I greatly appreciate you taking the time to do so.