Do you think circumference matters? Wouldn't it count 4 triggers as one revolution and call it a day?

If the prop shaft is thick enough, drill, tap and use bolt heads as a triggers.

Sixto
87 300D

Circumference is irrelevant.

Here's a picture of my Ford EDIS trigger wheel with a ruler. I don't think you could go wrong by using the basic dimensions and shape of it's teeth.

http://www.peachparts.com/shopforum/...1&d=1329177939

Hmmm, might even be able to cut up the wheel and use it's teeth. It's made of some kind of sintered metal so I don't know how it will cut and grind.

Don't you think the teeth on the 36 minus 1 wheel are a little tall? I'm thinking the flat pieces of steel used as balancing weights should get the job done, keep a low profile and they'll be pretty tough if spot welded, brazed or epoxied on correctly. I might even try welding 4 beads on the driveshaft, minding heat, of course.

I would not even think about drilling and tapping for screws. That sounds too risky.

Maybe a bit tall, but the taller the teeth the better the signal, to a point. Too flat and you'll have signal problems as well needing to run a gap that is going to be too small.

Drilling and tapping are not a direction I'd go, nor would I just try to run a bead.

For a first go, my working plan is to try to cut the teeth on my Ford EDIS wheel and epoxy them to the drive shaft and then do some form of reinforcement with flox or microballoons and some glass cloth.

During my test the nuts were affixed to my "driveshaft" with two runs of electrical tape and I got the speedometer up to 70mph with no hassle so there is not much force exerted on them. The issue, I think, is more to protect them from getting banged by a sideways force that could pop them loose.

I spent some time cutting and grinding the teeth off my Ford EDIS trigger wheel to see if that concept would work and I must say it looks rather promising.

I cut them in such a way that I had a bit of a lip to provide some additional grip to the composite material I plan to attach them with. It also provided a visual reference for how much to grind to get a matched set. Here's a macro of one of the teeth I cut.

http://www.peachparts.com/shopforum/...1&d=1329346108

It was quite time consuming to try to get 4 that would match, but I managed pretty well.

http://www.peachparts.com/shopforum/...1&d=1329346302

I weighed them and they all turned out the same - unfortunately the most sensitive scale I had only read in grams and all were 4 grams.

Here's a shot of one tooth on the driveshaft. The seam is in a perfect position to provide an accurate point of reference for alignment.

http://www.peachparts.com/shopforum/...1&d=1329346542

I'll need to source some epoxy to be able to mount the teeth permanently, but I'm very optimistic that this strategy will work. I'll also need to make another trip to the JY to be able to pick up a sensor that I can use for fabricating the mount for the pickup. The air-gap between the trigger wheel and pickup needs to ideally be 1mm, so it needs to be both sturdy and have a fine adjustment capability. Here's a sketch of what I'm using as a concept.

http://www.peachparts.com/shopforum/...1&d=1329347827

After pondering the various options for mounting the trigger wheel teeth, I decided to do a test of the welding option. I took a couple of my rejected teeth and welded them to some scrap metal. I tapped on them with a hammer and I'm convinced that they are quite secure. I also don't think that this will introduce any appreciable balance issues, particularly if I attempt to use a consistent trigger time for each weld. Here's a sample...

http://www.peachparts.com/shopforum/...1&d=1329419486

I am glad you tried it this way, because I was planning to weld the tabs on myself. I just need to make sure I get all the paint off the shaft where I am going to weld. I thought about using a strip of sand paper that is used by plumbers for sanding copper pipe.

An angle grinder would do a fine job of getting the paint off and down to bare metal.

I'm starting to get a good idea about how I'm going to fabricate my sensor mount. Here's a sketch of my current thinking.

http://www.peachparts.com/shopforum/...1&d=1329462058


The transmission mount bolt provides a very stout place to tie into. It's a 19mm nut and there is a channel that will provide support against any lateral movement. There is not a lot of room for anything over about 1/4" so it makes sense to make the attach point steel. I want to be able to take the mount apart in segments, so that is why I'm using aluminum and allen screws to form the sensor support. The sensor is a metal cylinder 18mm in diameter, so an 18mm hole with a clamp feature will provide the fine adjustment needed vertically to maintain 1mm of clearance between the trigger wheel and the sensor.

The sensor is quite similar to this in design. (Don't have a picture of the one on the car yet)
http://www.peachparts.com/shopforum/...1&d=1329462684

WOW! You are just getting too fancy LOL!

If it doesn't cost an arm and a leg, I would request that you make a bunch of these! I could sure use one, and I am sure you could sell a few more. I was thinking I would not get that fancy, but just bend something up out of flat CRS stock.

Don't plan on doing that, but as I go through the fabrication process, I'll add dimensions, photos and notes on how I built mine.

Not even sure this is the final design yet, just part of the solution process.

Having the parts bolted together will definitely help, as the trans mount bolt is hard enough to tighten as it is.

That was exactly the reason for a design that could have the vertical part of the bracket installed after the transmission mount bolt was installed and tight. Since the "base" is relatively thin (1/4") steel, the aluminum part of the bracket needed to be fastened from the bottom. I don't have the capability to weld aluminum so attaching the final piece had to be with allen screws.

Barring any modifications as a result of the process of finishing the fabrication and installation, here is the design and the dimensions of the bracket. For best results cut the piece for the transmission mount fairly rough, and then grind to a snug fit.

http://www.peachparts.com/shopforum/...1&d=1329634648

I made a trip to the junk yard today and grabbed a speed sensor to use in finishing the fabrication of the bracket. I didn't want to cut the original and then have to re-splice the wires under the car and worry about polarity. It's easier working on the bench rather than under the car. Here's the actual sensor

http://www.peachparts.com/shopforum/...1&d=1329635188

I'll most likely cut the tab with the mounting hole and just use a cinch bolt in the bracket to hold it in place with a 1mm air gap.

By the way, we can now verify that the sensor is a VR (variable reluctor) rather than a Hall effect sensor because it is a two wire device.

Well after all this R&D (mostly on your part mach4), it looks like the car that needs the electric speedo will become a parts car. Another (much nicer) '81 300SD became available that has a bad engine. This thread: http://www.peachparts.com/shopforum/diesel-discussion/312704-broken-camshaft-617-81-sd-how-could-happen.html
is about the car. I tried to feed in a new timing chain, but it seems there is more damage somewhere else inside the engine. This car has a good trans, decent interior, and a pretty good looking exterior. The engine from the other car ('81 SD with mechanical speedo trans) will go in this one, and the trans will go in a friends 300D that needs it. The rest will be for parts. It is still nice to know that the mod can be done if needed in the future.