Hello, I have an MGB with a 1983 RX7 transmission (and a 1985 RX7 12A engine)

I have been looking for a way to convert the speedometer flexshaft output into a digital sender so that I can use a digital Auto-meter guage. The square drive end on the flexshaft is about 3/16" and on the MGB original guage it is more like 1/4". I can stick it in, and it will turn, but it bounces all over the place, and I'm sure is inaccurate as all get out.

Before I get flamed, I did try searching, but unfortunately the words, "speed" and "sensor" are so incredibly vague that I get nearly the entire site for a search result...none of which seems to have anything to do with what I was asking.

Does anybody know of a bolt on speed sensor for the 1st gen transmission output?

 

Most AutoMeter gauges have an option to use a driveshaft sensor. That's probably the easiest thing to do.

Or, you can braze a big blob onto the Mazda cable and then shape it with a Dremel so that it fits into the MG gauge.

 

I hadn't thought of the blob...

On the point of using the driveshaft sensor...where do I get one to attach to the driveshaft? I was figuring that somebody made a screw-in replacement to the stock sender that instead of spinning the speedo cable, just sent out the signal. But if I could find some magnetic attachment to the driveshaft with pickups, I'm sure that could work. I'm just a little disappointed, I was hoping for the elegant solution of just screwing in a sensor...

 

I think they just use a sort of metal zip tie-thingie to secure a magnet to the shaft, and then you mount a Hall sensor nearby.

As the RX-7 transmission shares some stuff with the T5 (sort of...), a Ford adapter may work but I have not tried it.

 

well thanks Aaron,

I'm gonna call up the local mazda dealership, see if they know of any solution (who knows, maybe a sensor off of a mid nineties transmission would work)...

 

I did a little searching but there seems to be very limited information on aftermarket speedometers. There is an indication that the VSS from an FD may do the job and bolt up to the 1st gen transmission.

From the 2nd gen forum (the transmissions are very similar) I found these threads:
https://www.rx7club.com/forum/showthread.php?t=840979
https://www.rx7club.com/forum/showthread.php?t=638737

 

Woohoo Aaron!

I checked one of those links you posted and found this solution:

http://www.speedometersolutions.com/

has the screw-in VSS for our transmission, with power, ground, and signal wires...absolutely perfect!