[dbruce222@gmail.com]

I have a 2000 40 Express. My port tachometer is jumping allover the place or not working at all. Where do the wires pick up the signal from.
Any ideas on how to look for solution.

 Dave

[MC1600]

You have CATS or Cummins?

Not sure about the Cummins, but the CATS connections start right in the front of the engine, centered, above the belt cage. Directly connected to the block is the Aetna sending unit (P/N 8901). There are two wires from that but also a mechanical tach cable that goes to your synchronizer. The location is horrible because the cable gets kinked making a very tight turn between the sending unit and the belt cage. If I were you, I would do the following:

1. Have Glendinning make you a 12" extension (I'd just do both engines). The extension pushes the sending unit outside the belt cage and gets rid of any pressure on the cable.
2. If #1 doesn't fix it, I'd replace the sending unit. Super easy swap-out. They run about $135
3. If #1 and #2 fail, I'd send the tach to Lauderdale Speedo for a rebuild. They're awesome.
4. Last thing I'd try is replacing the tach cable between the sending unit and the synchronizer.

If you have a Cummins, I suspect it's a similar trouble-shooting process, but without the need for #1 above.

[dbruce222@gmail.com]

You have CATS or Cummins?

Not sure about the Cummins, but the CATS connections start right in the front of the engine, centered, above the belt cage.  Directly connected to the block is the Aetna sending unit (P/N 8901).  There are two wires from that but also a mechanical tach cable that goes to your synchronizer.  The location is horrible because the cable gets kinked making a very tight turn between the sending unit and the belt cage.  If I were you, I would do the following:

1.  Have Glendinning make you a 12" extension (I'd just do both engines).  The extension pushes the sending unit outside the belt cage and gets rid of any pressure on the cable.
2.  If #1 doesn't fix it, I'd replace the sending unit.  Super easy swap-out.  They run about $135
3.  If #1 and #2 fail, I'd send the tach to Lauderdale Speedo for a rebuild.  They're awesome.
4.  Last thing I'd try is replacing the tach cable between the sending unit and the synchronizer.

If you have a Cummins, I suspect it's a similar trouble-shooting process, but without the need for #1 above.

Thanks. I have Cats 3208 435 HP. I got rid of my the belt cages. I will try the sending unit. Is that part number a VDO part or a Cat part,or Glendinning.

[MC1600]

That’s an Aetna part number.

Be real careful getting rid of those cages. If you have pss seals that tap into your HEX, there are water lines that can get easily cut.

[dbruce222@gmail.com]

That’s an Aetna part number.

Be real careful getting rid of those cages. If you have pss seals that tap into your HEX, there are water lines that can get easily cut.

Thanks again. I do have PSS but the cooling lines are not near the belts