Comparison Photos:

280z on left 240z on right

Front (note 280z screw hole)



Bottom



Top



Back



Back Harness (Note white current loop on 240z and red voltage pickup wire on 280z)



280z back (Green is 12V and black is ground)



280z and 240z connector comparison. (Note the different locations for Gnd and +12V. It is neat to see the location for the tach signal input is in the same part of the can...clever engineering and evolution).

 

Edited December 3, 20159 yr by Blue

Disassembling the 280z donor tach

Remove bezel, lens and trim pieces

Front face

Angle showing needle

Carefully pry off needle.

Remove two black screws holding face plate.

280z "can" with tachometer workings fastened to bottom.

Remove two screws in back and press on the brass studs to "push" workings out. There is a double sided foam tape also holding the workings so you may need to apply heat to soften it. Prying up by starting at the sensor post seemed to work best for me.

Removed.

Empty 280z can.

Edited September 4, 201212 yr by Blue

Date code stamps on the tachs:

240z:

70-11-23

280z:

24-5-77

Disassembling 240z Tach:

Remove pick-up current induction loop.

Connectors removed.

Remove bezel and lens and spacer.

240z face.

Side view of needle.

Workings in the can. (note the white turn indicator hoods)

Workings removed.

The Swap:

280z "guts" in 240z tachometer.

Align the posts on the back side. (match the holes to the white foam indentations)

The securing screws are different. Use the 280z ones.

Secured.

Different connectors. Use the 280z. (Burnish the brass fittings)

Installation detail. Star washers lock connector.

Install face plate.

Install 240z harness to connector. (Black is ground)

Button-Up

240z "sand" inside the bezel. I think it may be from the paint inside.

"Gravity grime" and dirt on the lens...especially at the bottom. (wash with soapy water and polish with plastic polish)

Installed front needle.

I used goop to secure it. I read a post saying NOT TO USE CRAZY GLUE.

Installed needle.

Install the side screws.

Done!

Back of completed tach showing white loop, power connector, and red sense wire that will be soldered to a longer one that will be routed to the coil -neg terminal.

Closing photo: Very dirty lens from 280z tach.

Follow up.

Tach works great.

Here is a clever use of spoons I found on the net:

How to remove the needle from a tachometer.

Edited October 15, 201410 yr by Blue

Awesome discussion. I have a '73 that I put together from parts. It runs great but I too am trying to get the tach working. I upgraded to the Pertronix ignition. From the discussion above I understand where to connect a gnd and the +12volt wire, but I am confused as to how to hook up the "current loop" I bought a spare tach, was told it was working and was planning to "test wire" it under the hood before pulling the old one out of the dash. One side of the current loop has a piece of red tape and the other side has a piece of black tape. Where do I connect these two wire?

Edited October 14, 201410 yr by Burto

Hi Burto,

The above really is for wiring a 280z. There are only 3 connections (Ground, +12V and the tach. signal from -neg coil)

This may help with your '73 tach:

https://www.google.ca/search?q=site%3Aclassiczcars.com+73+tach+wiring&oq=site%3Aclassiczcars.com+73+tach+wiring&aqs=chrome..69i57j69i58.13917j0j7&sourceid=chrome&es_sm=122&ie=UTF-8

I know it's been a while since this article was written and it's very good. Including the photos makes it a lot easier to understand. I've made this conversion several times without problems. The one comment I have is the 280z unit that was used is from a 77 or 78 280z. The 75-76 280z has the same font and face plate as the 240 including the 6500 red line. If you use a 75 or 76 280z tach for this swap you don't have to touch the face plate or needle. Makes things a lot easier.

Zclocks

 

Used this to swap mine. Tach reads perfectly, thanks for the write up.

only problem is now the backlights for the tach do not work, neither do the blinker lights. Any ideas ? Thanks