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I have been runnning the last few years with the speedometer off calibration. My running gear is all Mazda RX7 but I have smaller dia tires than was originally on the car. This makes me constantly do mental math for speedometer correction and MPGs.

I tried to source close to the correct Mazda "drive gears" but the only one close is from a car some 30+ years old. They are no longer available. The one common website says the 22 tooth gear I need is from a Miata. Which should work but their pitch is RH and I need LH pitch. So that site is lacking on full info.

There are many companies out there that do correction boxes. I have found only one company that manufactures one with a Metric M22-1.5 thread; Clark Brothers. I tried to contact them but they did not return my email. I contacted another company but they said they do not make adapters with Metric threads. I contacted a 3rd small company that assembles adapters using parts from Clark Bros. I just got off the phone and ordered a stright thru geared adapter with a .9183 reduction ratio which should put me right on the mark. So my setup will be an OLD Toyota rt angle drive feeding the new ratio adapter and then to the mechanical cable that feeds the speedo. I should have it in a few days. I will report on how this all worked out.

This might be a good choice for those of you with Toyota transmissions too.

For $95+ shipping($12) maybe I won't have to do anymore mental math while driving and I'll be able to enjoy the ride just a little bit more. The Company's name is:

APT Instruments Intl Inc
9632 Humboldt Ave S, Bloomington MN 55431

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

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OK. I am here to report success! I had the adapter 2 days after I spoke to the guy on the phone. I changed my approach because I didn't want my Toyo angle adapter, which is cable based, drive the gear train friction of the ratio adapter. I figured that it should have as little force on it as possible. So now it is : transmission - ratio adapter - angle adapter - cable. Things fit in there with no room to spare, literally. The speedo cable's nut is wedged in a corner between the tunnel sidewall and the tunnel frame member. But it does fit!

But, on to the report. My speedo is now dead nuts on. From 25 to 50 MPH as the speedo reads exactly as it should when compared to the GPS speedometer app on my Android . And the odometer is only off about 0.1 mile out of a 15 mile trip, so <1% error there. This again, as compared to the app on my android phone. Except for any long term reliability issues that may, or may not crop up, this was 100 bucks well spent IMO. Had I gone with my original plan of a different driven gear in the trans, I would have been 1-2% off for both speedo and odo. But that was not an option as those parts were made of unobtainium.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Is there a pulse generator that will fit that metric thread? I want to use an electronic speedometer.
Fred V

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Fred V
www.jzrusa2.blogspot.com

Brings back memories, 1974 Australia went through the changeover to metric and popular were stickers to go over your MPH speedo to show the KMH. others just marked the important spots, 35 and 60 MPH (60 and 100kmh respectively) speed limits with Whiteout.

Fred, is this what you are looking for?

http://www.ebay.com/itm/Speed-Sensor-Ca ... b0&vxp=mtr


Not 100% sure if the threads are M22-1.5 or not, but being Toyota, they probably are. You can also look up Standard Motor Parts SC172, I think that is the same part. Do a where-used and then search the local yards for one of those cars if that is your preference. It would appear that early 90's Toyota transmissions (probably Mazda too since mine was metric and I use a toyota rt angle adapter on it) used the electrical adapter version first, then went to a complete replacement assembly that included everything from the driven gear to the electrical connector. Those, you need to be concerned about the teeth and pitch direction. later they dropped that whole scheme and use different sensors all together.

This might also work for you: http://www.btbprod.com/GENERATOR-8-PULSE-FOR-ELECTRIC-SPEEDOMETER.html

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

chuck
I ran in to the same problem with my electronic speedo which was design for a GM trans, vs a Toyota. I just ran a 7/8-14 die over the M22x1.5 speedo cable mount. There is not a lot of difference between the two threads. You probably end up with over 80% thread engagment, and we are not talking about any kind of loads thru the cable mount. Dave W

True Dave. As a matter of fact the guy I was talking to at APT told me that years back, before there were metric thread adapters, people would just thread them on as far as they would go. He had some crazy story of one end would thread on all the way (not sure which end) and the other only a couple of turns. Not sure exactly why that would happen. Unfortunately, I was not happy with getting a thread interference with less than 1 turn which was my experience in my setup. AS soon as I take a tight bend in the cable, I may be causing undue strain in the system somehow. I chose to go the metric thread adapter route where everything seats up according to design.

Even with the die solution, you are still only getting that 1 turn of fit. the other threads are just there for the ride.

I thought I'd share my solution to this obscure issue. As in everything in life, YMMV.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Thanks for the info guys.
Fred V

_________________
Fred V
www.jzrusa2.blogspot.com