Tachie no workie

[MMeier]

Went to hook up my old tach since it had to be disconnected during the 4500 install. Tach is a S. S. White Technologies unit... 3500 RPM , full sweep, model #5401. On the Getrag there was a sending unit installed in the bellhousing at the bottom with 2 wires coming out of it, one was ground the other I take was the pick up wire. Plugged the wire that goes to "send" on back of tach to the factory plug grey terminal... . no tach!#@$%! Any ideas!!?? Is this a tach that only works off that sender? :{ I'd really like to keep it. Can I tap into the factory CPS up front... if so, which wire do I need?

 

[PToombs]

IIRC, the factory CPS uses a square wave signal. Not compatible with most tachs. I remember Philip said that, or something close. He knows for sure, he'll most likely give his few cents worth.

You could wire the alternator, I think it will read off that. Or find a way to install your pickup back on. Did the old pickup read the teeth on the flywheel?

 

[MMeier]

Pete, not quite sure what it read off there, after din din here in a few I'll go measure how far back it was from the front. Damn, this 4500 is SSSSWWEEEEEEEEETTT!Oo. Just measured... looks to be back 1 1/8 - 1 1/4" from the front of the bellhousing, so that sounds like it must've been reading off the flywheel.

 

[PToombs]

I've never seen a 4500, does it have a shield on the front? Just wondering if you can pull it and look and see if there is a spot to drill?

I looked at that on mine, and there wasn't enough room inside for a nut on the pickup, and I didn't want to buy a tap with that thread.

I wired mine off the alternator. After I did, a bunch of guys did it too.

https://www.turbodieselregister.com...1993/132600-wiring-alternator-tach-drive.html

 

[MMeier]

So Pete. . and others, were these tachs origianlly designed to operate off a magnetic pick up? Oh, and what do you mean by "W" wire?

 

[PToombs]

Mark, actually don't know much about your Tach, how it operates. The pickup you had is most likely a Hall-Effect sensor. It senses the tooth going by and reads the difference in the magnetic field.



I don't know why it's called a "W" wire. That's the letter the terminal on the alternator is marked with. Alot of the older heavy equipment alternators had that terminal so it could have a tach in the dash.

 

[MMeier]

Mark, actually don't know much about your Tach, how it operates. The pickup you had is most likely a Hall-Effect sensor. It senses the tooth going by and reads the difference in the magnetic field.



I don't know why it's called a "W" wire. That's the letter the terminal on the alternator is marked with. Alot of the older heavy equipment alternators had that terminal so it could have a tach in the dash.

How do you tell ? Has a very strong magnetic pull to it and had 2 wires going to it, one was definitely ground.

 

[PToombs]

Well, that's a new one to me! I've never seen one with a magnet in it.

 

[MMeier]

Here is a nasty pic

. . came out bad, but i think you can tell what it is. Piece in the middle is a spacer of sorts to position it I guess. Thread is a whopping 5/8" diameter. see why i don't want to drill my new bellhousing!!

 

[PToombs]

That looks like what I've seen. You want that 1 mm from the teeth on the flywheel, that's what the spacer is for. The nut is thin enough to go inside. Just drill it! I's only a little hole! :-laf

Or try the alternator method. You can do the alternator and try it to see if it works. I didn't solder anything when I did it. Just don't cut the back cover, and leave it off to try it.

I can't think of any other way to do it.

 

[MMeier]

When you do up the alternator, is it picking up an electrical pulse, or... ? WTH is Philip??? With it alll back together now, no way to get the nut inside the bell. On the getrag the bell was threaded, then the plastic spacer thingie, then the nut sucked it up against the bell.

 

[PToombs]

He's usually keeping watch on these things, I'm surprised he hasn't chimed in. I believe it picks up the pulse, not real sure on the workings of that. I just know it works. Weird the spacer was on 1st, must be to conform to the slight curve of the bell.

I wonder if you could go to a machine shop, and have them tap it if you drill the hole? Or have them drill too? They should have a tap that size. should be cheaper than buying one too.

 

[MMeier]

OK OK , enough of driving my beloved '93 with no stinkin' tach !!!#@$%! Just recieved some info that "I think" applies to my tach. Next stupid question, how many 'poles" do these alternators have?? 6? Need to know so I can set one of the DIP switches in the back of tach... theres like 11 of them !! Have to measure crank pulley diameter, divide by alternator pulley diameter,multiply by number of poles... . gives me a "program number" then set switches accordingly.

 

[MMeier]

Pete... someone

... sure one of you has a balancer lying around from a first gen... what diameter are these, can't get down there close enough to read the tape measure, looks to be 8" in diameter?

 

[PToombs]

Ya know, yer frickin killin me here! #@$%!

:-laf

8 or 8. 25. I just went and measured mine. Anything else I can do for you? Milk? Cookies?



Let us know how it goes.

 

[MMeier]

Ya know, yer frickin killin me here! #@$%!

:-laf

8 or 8. 25. I just went and measured mine. Anything else I can do for you? Milk? Cookies?



Let us know how it goes.

Thanks Pete... ummm did you see my question above?

 

[PToombs]

About poles? Yup, clueless on that. Sorry Mark.

I don't know it the FSM says or not. A little to whipped to check tonite.



I did like the flywheel on the pulley idea.

 

[MMeier]

Well, appears it is going to work that way. . Just have to get the 9 DIP switches where they belong, can't imagine the endless combinations to that!! Looks like it is reading 1/2 of what it should be, going to call my lady at Mr. Speedometer first thing in the morning, hopefully she will have the correct "combination" . Maybe call the local alternator repair shop and see if they know or not. thanks for your help Pete!! Too bad i won't be able to make it back to SOP... taking on full time employment with the county starting next week !:{

 

[MMeier]

I did like the flywheel on the pulley idea.

Actually what I was starting to envision was a tone wheel from a 3rd gen "affixed"to the front of the balancer.

 

[MMeier]

Tachie workie !!!

... YAY... that is all! Oo.