a real tach

[92EcoDiesel Jetta]

Of course Andrew, it would never work otherwise. Can you measure the resistance of your Ford probe? I am curious how it compares to the Mercedes pickup at around 70 ohms.

[92EcoDiesel Jetta]

I didn't mean any offense, it's usually something little.  You're sure you haven't gotten the 12+ and ground reversed?

Can you measure the resistance of your Ford probe? I am curious how it compares to the Mercedes pickup at around 70 ohms.

1,130 ohms.

Andrew, no offense taken. 
I am 100% sure I didn't reverse the + and ground since that would have fried it. As I said earlier I was able to make the tach needle move by manually pulsing the input with 12V. I think the problem is I need a higher voltage from the pickup. I'll see if the distributor pickup will be good enough. It is 1.1k ohms, close to your Ford probe.

[92EcoDiesel Jetta]

Finally got around to test the new distributor mag pickup with the Mk I tach and it's working!!!!!
 Here's a pic of the pickup temporarily installed. Note that I changed the "tooth" to a small round super magnet in hopes of getting a higher output. I epoxied the magnet in place so it does not fly off at high PM (ask me how I know  ).  I bypassed the RC network on the input of the tach which attenuates the input signal and went direct to pin 2 which is the input to the chip and it worked!!!



Here's a video of it under test. Click on it and it should play. I also took out the clock in my MK II cluster to see how the tach will fit and it looks like I have to cut a big round hole in the back of the cluster plastic housing in order for it to fit. There's also the empty space of the fuel gauge which I will have to cover up, or, if it'll fit, I will put the LCD clock from the MK I cluster there. Oh yeah and I have to spray paint over the "unleaded fuel only".

[92EcoDiesel Jetta]

Andrew, can you be more specific on which gasser tach will fit my cluster better?

I forgot to mention that in the video, there's only one "tooth" rather than two. I was surprised that the rpm was correct when it should have been 1/2 of that with only one tooth.

[92EcoDiesel Jetta]

Hi Andrew, sorry I' been busy and have not done much with the tach. My cluster has 1 connector like the pic you posted. Maybe it's easier to swap the speedo instead of the tach like I am trying to do. I am wondering what else will not work other than the glow plug light and whether I can safely plug in the connector without frying anything?

Anyway I tried the tach again and it stopped working! Turned out the magnet I glued onto the crankshaft pulley was missing! I will clean the mating surface better and try again with crazy glue and epoxy. If that doesn't work I will get 2 studs welded and use a nut to secure the donut magnets.

I also tried to calibrate the tach with a 1725 rpm ac motor. At first I tried to cut a v notch in the motor pulley for the mag pickup but it didn't work- it did not generate enough voltage. So I bolted the magnet to the pulley and the tach works, but was reading only 1400 rpm. I tried adjusting the potentionmeter but could only get it to go lower than 1400 rpm but not higher. I need to get another magnet and add it 180 degree apart then do the calibration again.

Once itcalibrated, I am going to try to fit it in my current cluster and see how that goes. If it's not physically possible then I will look for a CE1 cluster as you suggested.

Can you post a picture of your cluster?  I imagine it's like this:



How about swapping out the whole cluster for one like this?

You could swap in your speedo.  You might need to adjust the wiring in the connector and add the glow plug led.

[92EcoDiesel Jetta]

Here's my calibration setup:
1725 RPM motor with 2 donut supermagnets as the "trigger tooths" I turned the adjustment pot till I got 1725 RPM. The range of adjustment was 0 to 2400 RPM.
Now it's just a matter of fitting the tach into my cluster and attaching the 2 donut magnets to the crankshaft pulley so they don't fly off again. lol

[Smokey Eddy]

so they don't fly off again. lol

THAT is the key. Anyone have any ideas? i doubt a glue of any kind would work?

[92EcoDiesel Jetta]

I have glued a magnet to a flywheel before with just crazy glue and it stayed. I think I just have to do better surface prep before apllying the glue. I will sand it down then clean with solvent and see if that'll do it. If it still don't stick, I will either weld or tap two 6-32 studs in the flywheel and put a nut on the donut magnets.

[Smokey Eddy]

ah! good idea!
Where again does one find the sensor that counts the magnets passing? I know someone said off of a different car but any examples so i can narrow my search in the junk yard?

[92EcoDiesel Jetta]

ah! good idea!
Where again does one find the sensor that counts the magnets passing? I know someone said off of a different car but any examples so i can narrow my search in the junk yard?

Mine is from a distributor from a gasser but I do not know which car it came from. I think your best bet is just find one and try it, or get the Ford probe that Jimbote recommends. It seems having a higher resistance correlates to higher output. The tach needs a certain level before it will trigger. The one I used did not put out enough voltage with a ferrous "tooth" but I was able to increase it by using donut magnets instead.

[Smokey Eddy]

Yeah using magnets is definitely the way to go. I have an external tach i'd like to drive with it. You know, like one of those ricer tachs but its not massive and its not in front of my face on the dash.
So im looking for a photogate type deal that will either be actually on a distributor? I was thinking it would be on one of the spark plug wires? If anyone has any pictures I'd really appreciate that!

[92EcoDiesel Jetta]

I haven't updated this thread because I haven't been working on it lately. Anyway, I bought a CE2 gasser cluster a few weeks ago and been trying to get the tach in it to work the last few days. I connected the 28 pin connector on the dash to the cluster, connected the hall effect sensor to pin T28/10 tach signal. The hall effect sensor was driven by 2 magnets on the pulley of a 1725 RPM AC motor and the tach didn't move. This was using the same setup I used to get the CE1 tach working. I kind of expected the CE2 tach not to work because I have not bypassed the RC network on the tach circuitry on this CE2 tach like I had to do with the CE1 tach. The tachs on the CE1 and CE2 cluster use the same chip but the layout is different. The CE1 tach has its circuitry on a small round PC board on the tach itself while the CE2 tach has  its  circuitry on the same board as the rest of the electronics for the cluster. So I went ahead to trace out pin T28/10 and it went no where near the tach chip on the PC board. Not wanting to waste time to figure why pin T28/10 does not go to the tach chip, I soldered a wire directly to the input of the tach chip and made the same mod as I did to the CE1 tach. It works!!! In the video, as I turn the key on, the tach jumps to 1725 RPM reading the speed of the AC motor, then I started the engine and the temp and fuel gauge registers and oil pressure comes up. Oh, how do you like the location of my oil pressure gauge? I still have more work to do such as fastening the 2 trigger magnets to the crank pulley, hooking up a glow plug light which I will do when I move the glow plug relay out of the fusebox and into the engine bay. I will connect the glow plug LED directly across the glow plugs instead of to the glow plug relay.

[92EcoDiesel Jetta]

[92EcoDiesel Jetta]

When I started this tach project, I first used a tach from a Mercedes, then one from a Peugeot, then a tach from a VW CE1 cluster and finally the CE2 cluster. I have a lot of parts I have bought for this project and they are for sale. The Mercedes and Peugeot tach will work on any engine once you have a trigger set-up and sensor installed. The Mercedes and Peugeot tach comes with the tach, mag pickup, and whatever electronics so it is complete. The CE2 cluster from my Ecodiesel has the CE1 gasser tach installed, an LCD clock has been put in place of the vacant temp gauge under the tach and the unleaded fuel decal has been sprayed over with flat black paint. It looks pretty good. I have no need for it since I have a CE2 gasser cluster in my car now so it is also for sale. If you want a cluster with a tach and LCD clock here's your chance. Send me a PM if interested. I will post some pics later.

[92EcoDiesel Jetta]

I've got the 2 trigger magnets installed. I used a Dremel flex disc and hit the crankshaft pulley down to the bare metal, then use crazy glue on the magnets. After it's dry, I added JB Weld to the hole of the donut magnet and also the outside of the magnet so it's well supported by epoxy. Click on the pic below to play the video (in case you don't know). I tried to not rev it too much since the epoxy won't be fully cured for 24 hours.