The 'E' Type Forum

Does anyone know what the thread size is on the speedo output at the transmission? I need to get a mechanical to electrical adapter so that I can feed speed data into my MS3 Pro fuel injection ECU. I see common thread sizes advertised for GM as 7/8"-18 and 5/8"-18. Not sure if either is a match for the Jag.

Or . . . maybe the thread size at the speedo itself. That might be a lot easier installation.

It's BSB, British Standard Brass. Yes it is a thing. Speedo drive is 3/4" x 26 TPI. I'm imagining that Jaguar speedo transducers, e.g. DAC4569, would screw straight on ...

Thanks for the thread info. The DAC4569 is a bit pricey at over $200 and doesn't really solve my issue(my speedo wouldn't work). There are adapters that are what you might call "pass through" in that the mechanical drive from the speedometer can still be attached and in between is a device that will provide an electrical signal proportional to the speed. Usually this is some type of toothed disc and sensor in between the male and female speedo connectors.

I'm probably going to have a hard time, if not impossible, finding anything that uses a 3/4-26 thread.

Example here:

https://www.summitracing.com/parts/dak- ... LdEALw_wcB

https://store.gaugemagazine.com/speedom ... ns-3-wire/

Oh, so its not a digital speedo project … What ru going to do with the signal, it will only there when yr moving, nothing when stationary/idling?
My interpretation, that Summit Racing/Dakota unit would hog yr speedo drive also?
Imo easy solution would be to make yr own union adapters; I bought my 3/4-26 thread cutters on-line from India for very good price ...

No, not digital speedo. I need the signal to feed into my fuel injection ECU (MS3 Pro) so that when I look over the data logs I'll know what speed I was at.

I've been searching around and think I have found what I need. A little more research is needed to confirm, but Daytona makes what they call a "Speed Pulse Converter Twin Signals Output Universal", which is for use on motorcycles. Can be seen here:

https://daytona-europe.com/en/sensors-a ... 87430.html

In their description they say "Joint for speedometer cable is same as X1 type sensor". Turns out that the X1 type is what is used(I THINK) on the backside of the Jag speedometers. Lots more discussion about that connector's thread size over on the Jag Forums

https://forums.jag-lovers.com/t/speedom ... ize/453839

I'm only about halfway through that thread but so far it looks promising. If this pans out it will be a much easier solution since it will all be tucked away behind the dash.

lowact wrote: ↑

Thu Feb 05, 2026 2:34 am

It's BSB, British Standard Brass. Yes it is a thing. Speedo drive is 3/4" x 26 TPI. I'm imagining that Jaguar speedo transducers, e.g. DAC4569, would screw straight on ...

Hey Colin is this the same as British Cycle with the 26tpi or different?

I've gotta have one of these taps :-)

Steve, Marek did similar, except he took it off the speedometer end, Dunno the details, you should PM him.

Andrew, nah, BSC is 60 degrees. BSB is 55 degree whitworth

lowact wrote: ↑

Thu Feb 05, 2026 6:34 am

Andrew, nah, BSC is 60 degrees. BSB is 55 degree whitworth

Right. Off to EBay.

Edit. I'm getting senile. We've had exactly the same discussion before viewtopic.php?f=3&t=20798

Don’t you just love these old British threads

My final solution was at the other end of the speedo cable. I bought a Daytona Motorcycle Speedometer Conversion Adapter to Convert Mechanical to Electric Speedometer (93390). Turns out that the rear of the speedo uses the same connector as is common on most motorcycles and is pretty much the standard for most speedometers. Maybe this is what Marek used. I don't know since I did not get in touch with him. Out of curiosity I may still do that since he is so very helpful.

I stuck a Hall effect sensor into the speedo unit itself, as this was an easy way to get the required digital speed pulses into the MS3 unit without getting my hands dirty or crawling under the car. You can see a picture of it at viewtopic.php?f=6&t=17086&p=142437&hili ... or#p142437

Ignore the "I want to half run my fans half of the time" argument and just look at the picture.

kind regards
Marek

Slick!