Trying to get speedo working - 911SC w/ 97 C2S Drivetrain

[sirdaft1]

The speedometer in my ‘79 911SC w/ a 1997 C2S drivetrain (3.6L VR + 6-speed G50), hasn’t worked since purchasing the car last year. I speculate the speedo was never setup due to the car being a club race car for the past decade and a half. Any insights into how we might get the speedo working? Is the speedo driven by the trans or wheel speed sensors?

And the speedo was just rebuilt by North Hollywood.

Thank you in advance.

[timmy2]

2 brown/red wires from speedo run through body harness to a location under the shift coupler cover plate in the tunnel, connect to the sender wires from the transmission.

[Bill Verburg]

Originally Posted by sirdaft1

The speedometer in my ‘79 911SC w/ a 1997 C2S drivetrain (3.6L VR + 6-speed G50), hasn’t worked since purchasing the car last year. I speculate the speedo was never setup due to the car being a club race car for the past decade and a half. Any insights into how we might get the speedo working? Is the speedo driven by the trans or wheel speed sensors?

And the speedo was just rebuilt by North Hollywood.

Thank you in advance.

an original 993 trans has no provision for a speedo, 964 and newer all get the speedo signal from one of the front wheel speed sensors used for AABS

[Jim2]

As Bill says the 993 drove the speedo from the ABS system, these G50 transaxles do not have a provision for the speedo magnet ring inside the transaxle.

I used a 911 speedo in another brand of car and recreated the magnet ring around the perimeter of a cv joint, then added a bracket to hold the sensor. My magnet ring is just a strip of aluminum with the magnets epoxied in place and held onto the cv with a hose clamp.

If you are handy you might be able to come up with something similar.

[sirdaft1]

Oh wow... thank you for the responses! Glad to hear I wasn’t going crazy when trying to figure out how to make this work. It appears there might be a reason the PO didn’t setup the speedo! Curious... anyone have experience with GPS speedometers? My concern is that I may go through all of the above, only to have the speedo off by miles due to the difference in wheel circumference over stock. GPS would potentially be an easy solve.

[sirdaft1]

Curious if anyone has fit a GPS sender with their stock speedo...

https://www.egaugesplus.com/gps-speedometer-senders.html

[jpnovak]

I too have done the "epoxy magnet to the CV joint and run a VR sensor" thing. Worked well.

GPS will ultimately be more accurate. The usual gauge houses can probably retrofit for you. Would have to check carefully to see if the linked GPS sender could replicate the same pulse signal as the stock magnetic pickup ring. I *think* that is 7 magnetic pulses per revolution.

[GaryR]

My first thought was to contact the gauge guys in CA and see if they can convert a stock speedo to GPS somehow, but i'm more curious to see pics of this conversion! 385 HP / 6 speeds in an SC? Thing must be a handfull!