Diesel Tach Idea.

[dennis]

I have found a couple of early (pre 81) Instrument clusters with 100 mph speedos, with 7000 rpm tachs. I was thinking of deleting power brakes, and using a 69 Bus master cylinder which should stop a Caddy ok I would think, and mounting a gasser distributor in the vac pump hole along with a coil to generate a very accurate tach signal.

Thoughs, flames?

[Rabbit on Roids]

i thought a bout that a long time ago. but there has to be easier, and less complicated ways to make it work. you honestly dont even need a coil, just something to drive the coil, and pick up the pulse from the coil neg- wire. then you wouldnt have to have a useless coil in your engine bay.

it would be cool to see it done, but it might not be worth the time, and it might not be possible.

what are you going to do about the intermediate shaft spinning the wrong way? gassers spin CW, diesels spin CCW. im pretty sure the oil pumps spin the same way tho, so that leads me to believe that one of the engines has reverse cut gears. probably the diesel, because they were less common compared to the gassers.

hope this helps some...

[truckinwagen]

yep, the diesel has reverse cut gears to spin the oil pump the right way.

you cant install a distributor with a diesel IM shaft, and if you installed a gasser IM shaft on a diesel the oil pump would spin the wrong way.

[Rabbit on Roids]

so, basically it was a good idea, but it just isnt going to work.

(i thought about putting a dizzy in my diesel too, but then i found out about those problems.)

[dennis]

Oh well. Guess I'll read that article on converting the tach for the W terminal.

[745 turbogreasel]

Might be able to swap drive gears?

[truckinwagen]

the issue is that the distributor and vacuum pump shafts are very different diameters, I already thought of swapping them(for a different project) but they don't change out right.

[745 turbogreasel]

Is there any reason alternator revs are less accurate than engine revs?
I'd bet on the instrument being the leas accurate part of the system either way.

[dennis]

Is there any reason alternator revs are less accurate than engine revs?
I'd bet on the instrument being the leas accurate part of the system either way.

Probably not except at least with my truck the pulley ratios probably don't match up with the doner alternator. I guess it could be dialed in with a variable resistor once the tire size gear ratios ect.. are calculated to determine rpm at a certain road speed to have a reference to adjust to.  Mechanical engine rpm is engine rpm. Im gonna make this work without modifying the tach. Im already thinking that Tectonics Tuning sells a crank pickup to change CIS 16 valve engines to EFI.

[maxfax]

I wish I still had my old rabbit to snap some pics..  I welded two little tabs on the inner edge of the crank pulley and mounted a magnetic pickup to read them..  A transistor and such (equivelent to a GM ignition module) and I could trigger any gasser tach...   It worked well, easy to build, and cheap!!!

[truckinwagen]

I wish I still had my old rabbit to snap some pics..  I welded two little tabs on the inner edge of the crank pulley and mounted a magnetic pickup to read them..  A transistor and such (equivelent to a GM ignition module) and I could trigger any gasser tach...   It worked well, easy to build, and cheap!!!

I have all the parts to do that, and intend to do it.
but really wish there was an easier way to do it, I can just imagine to many ways it could fail(break off, etc...)

-Owen

[foxracer1]

I wish I still had my old rabbit to snap some pics..  I welded two little tabs on the inner edge of the crank pulley and mounted a magnetic pickup to read them..  A transistor and such (equivelent to a GM ignition module) and I could trigger any gasser tach...   It worked well, easy to build, and cheap!!!

So use a HEI ign module? I might have a chance to get some dyno time and i'd like to have a rpm signal for the dyno for more accurate graphs and tuning. What all parts are needed?

[maxfax]

 I started with an aftermarket tach then later found a gasser cluster... It worked quite well for several years until the tach in the cluster took a poop..

I had a rather stubby output speed sensor from a Ford AODE / 4R70W trans..
 Found a few unused bolt holes in the back of the block to mount a piece of angle iron, and screwed the sensor fast to the piece of angle iron.. It stuck out no further than the crank pulley, the sensor itself protruded from the bracket no more than 1"...  The accessory belt flying apart would have probably been the only thing that would have damaged it...

I had a friend build the adapter to take the pulses from the magnetic pickup and amplify them for the tach.. It was basiclly a crude ignition module..  I dunno if a GM HEI module would work without some sort of load to simulate a coil.. Although if you could find the proper resistor, or possibly an 1156 bulb hooked up as a coil, it might work..  I think...  (I had an ignition module tester that used the 1156 bulb )

[foxracer1]

I'm interested to figure out how to do this! Is there any way you could make up a wiring diagram? I appreciate the info thus far!

[truckinwagen]

I got my hands on a hall effect sender that sends a pulse whenever a magnet passes it, should just wire up to the sensor lead on the back of my tach(one wire to ground, the other to the tach's sensor lead)

it is rather bulky, however,(about 3.5" long, and 3/4" thick)  so I am a bit worried about it hanging out and getting broken off.