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  #1  
Old 06-30-2008
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Default Tach Sending Unit Location - 6V92TA (1986)

I've looked at the DDA manual and it states there are two possible locations for the Tach Sending Unit.

1) To the Right of the water pump on the end closest to the engine bay door.

2) Below the alternator drive pulley, on the end fartherest from the engine bay door.

I can't seem to find the sending unit in either location. I have the access open in the bedroom and have looked for the sending unit with no luck. I do see the "Port" next to the water pump but it has a cover plate and no sending unit.

My wife says I can't find anything right under my nose. Can someone give me some clue where to look.

I'm am trying to track down the source of an inop tach. I planned to start with the sending unit so I could check the drive pin. If it looks good, I am going to check the pulse at the sending unit. If that checks, then I am going to pull the dash and check the pulse at the tach. If that is good, then I will replace the tach.

Any guidance?

Thanks,

Glenn
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Old 07-01-2008
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on the 84pt40 it was under the bedroom hatch.
while laying on the bed,facing the rear of the bus,its straight down and a little to the left,its an electric gizmo,its shaped like a banjo with a wide neck,has 2 wires coming out of the neck and it mounted flat,on top but to the rear of the engine.
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Old 07-01-2008
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the round part of the banjo is about as big as a 50cent peice.
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Old 07-01-2008
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I think I remimber seeing what you describe. Not the snake I was expecting. I'll head back to the Bird later this morning. Does it have a mechanical interface to the engine that can fail? Do you know a test proceedure for the electrical side?

Thanks Randy.

Glenn
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Old 07-01-2008
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it does have a mech interface,a short drive of some kind.
its been years since i had one off,so i really don't remember what it is.
i don't know how to test it either.
Hey,at least i knew what it looked like!
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  #6  
Old 07-01-2008
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I found the Banjo! Just like you described....Now to figure out if it is working.....

Thanks,

Glenn
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Old 07-01-2008
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if you figure out how to test it,let us know!
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  #8  
Old 07-02-2008
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I got a replacement at Napa, I will have to look up the part no# or just take it in as I did.
If I remember on the mech. one the rod wears down so if you do a continuity test from the wire and that is ok then it has to be the sending unit.
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Old 07-10-2008
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Update on the Banjo...Tach sending unit.

I pulled the complete unit off the engine. The gearbox would rotate easily. Connecting the two banjo wires to a scope yielded nothing. Removed the Mechanical-to-Electrical transducer aka banjo (probably a coil). This unit would not turn freely. Removed the hex tube connecting the gearbox to the transducer and found the short cable was "stripped" in its holder. I resoldered the cable into the cable holder using a propane torch. I then used penetrating oil and a drill to loosen up the transducer. Then I lubricated the transducer. Re-assembled everything and tested with a drill and o-scope. Nice sine wave. Reinstalled and I now have a working tach.

It is clear that the tach transducer should be lubricated frequently (I recall someone saying about every 3k miles). There is a rubber boot on top of the transducer. Removing the rubber boot and placing some oil in the port should provide lubrication to the transducer. I not sure what oil would be best, but I would think that the 40wt we use in the engine would be fine. The oil will leak past the transducer into the gearbox and being the same weight as the engine oil would be compatible with the oil in the gearbox.

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  #10  
Old 07-10-2008
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Quote:
Originally Posted by guysmalley View Post
I got a replacement at Napa, I will have to look up the part no# or just take it in as I did.
If I remember on the mech. one the rod wears down so if you do a continuity test from the wire and that is ok then it has to be the sending unit.
Guy,

I checked with my local NAPA. The only Tach Sending Unit they have is a VDO unit that was cylindrical shaped. If it would fit on the gearbox, it will probably work. I believe it is VDO Part No: 340-008 with a 7/8 x 18 thread and sells for about $130 at NAPA. The VDO puts out 4 pulses / rev...I did not check what the existing one outputs.

Is this the one you purchased?

Thanks,

Glenn
VDO Sending Unit
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Last edited by RAGster; 07-10-2008 at 12:41 AM.
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