Can I install an sc speedo on a 75
 

Been reading a lot. It can't find find an easy answer to this. Obviously the 75 speedo is cable driven and I've seen a sending unit that mounts to the 915 with the SC. Can someone fill me in and walk me through steps if possible.

You would need the magnetic "wheel" that bolts to the ring gear inside the transmission. Then you'll need the pickup on the outside. Don't know if you can do it with the 75 case.

-Andy

I have done the electronic speedo conversion on my 75 Targa but did so in conjunction with fitting a later transmission. The later trans has a mounting recess to hold the magnetic pickup. The case for the transaxle that was originally in my Targa did not include the mounting recess cast into the case housing of the later trans. (The recess is directly in the trans case and is not on the replaceable differential cover).

If you end up doing the trans swap, then it's a fairly straightforward mod:
- Pull the speedo drive cable.
- Run some two-conductor wire from the speedo to the trans through the tunnel (follow the path of the speedo cable); connect the conductors to the pickup on the trans.
- Wire in the speedo according to the SC wiring schematic; you'll have to run a new wire for switched 12VDC power from the fuse box.

I did this on my 74. No need to run wires from the fuse box. They are already present in the dash harness. Simply splice in the appropriate connections.

If you like projects, it wouldn't be that hard to make an adapter. The electric speedo expects its signal line to be grounded 8 times per wheel revolution. So you need to find out how many revolutions the mechanical cable rotates per wheel rev with your 7/31 r&p. And build an interrupter which will do that. Porsche uses bar magnets and reed switches, but I think optical would be the way to go.

Thanks for the responses but I think with and early 915, probably not enough reason not to use the mechanical speedo.

Thanks again for taking the time.