Okay, all you transmission know-it-alls! I need to pick your brain! As we all know, the Fiero has an electronic sender at the trans end, and solid state speedo in the dash pod.
All well and good. Only in my kit car rebody dash, I am using vintage analog guages ! So the fiero guage and sender are out, and a long, snaky flex cable drive are in! You with me so far ? Naturally, the revolutions per mile for my new speedo will not be the same as the revolutions per mile coming out of the speedo drive port on my Fiero Transmission, so a small gear box will be needed to adjust the ratios to match. I know how many revs per mile the new speedo needs. I DO NOT KNOW THE REVS PER MILE COMING OUT OF MY FIERO TRANSMISSION OUTPUT! The trans is a stock 4-speed Muncie, ala 1985 GT. I suppose I could rig up a way to find this number with a mechanical system, but that would be a real pain in the backside. So I am hoping one or more of you already knows this magic number ! or where we can find it !!

to clarify - I need to know how many revolutions the speedo output drive will rotate if the car goes one mile -

all assistance will be very greatly appreciated !! Thanks !!

[This message has been edited by Fastfocusguy (edited 09-02-2010).]

2 numbers come to mind: 2000 pulses per mil & 4000 pulses per mile

But then one has to ask, How many pulses does the sender maker Per Revolution ?????

My haynes manual shows 4000 pulses per mile

if the sender has a 2 pole magnet, then it should send 2 pulses per revolution ( right ??? )

which would mean the output shaft driving it is turning only 2000 revolutions per mile ( right ??? )

but that is only my assumption, and we know what happens when we ASSUME !!!!! :0

[This message has been edited by Fastfocusguy (edited 09-02-2010).]

Fiero MUST use VSS if it got a ECM. Fiero Need a speedo/buffer between VSS and ECM to /2. VSS output = 4000 ppm but ECM needs 2000 ppm.

only Fiero 87-88 L4 w/ 1227748 ECM can use a FWD car PROM to use VSS directly w/ no speedo/buffer.

quote Originally posted by Fastfocusguy: if the sender has a 2 pole magnet, then it should send 2 pulses per revolution ( right ??? ) which would mean the output shaft driving it is turning only 2000 revolutions per mile ( right ??? )

no and no

"2 pole" made for easy diagram.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

[This message has been edited by theogre (edited 09-02-2010).]

all good and well, but does not help me to figure out what the transmission speedo output shaft is doing -
I need to know how many revolutions per mile the actual mechanical speedo drive dog is doing !

Research the trans... You maybe over thinking it... Some have a cable and VSS option. In old Carb car, Cruse uses a VSS and Speedo uses a cable.

Or redesign speedo to make it work with digital/electronic.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

Okay , here is what I have done - - -
Dismantled the speedo drive gizmo far enough that I can see the rotating element
Marked the rotating element with flourescent paint
Installed a thin wire pointer, aimed at the paint mark
installed marker arm on car body and marked starting point on garage floor
rolled car slowly forward until rotating element made one full revolution
made new mark on garage floor
measured between the marks
divided this number into the number of inches in one mile
End result shows output shaft in speedo drive gizmo turns 1000 revolutions per mile ! !

So now I can do the math to figure the gear ratio I need in my speedo adapter so my DeTomaso Pantera Analog Speedometer will read correctly even though it is being driven by the Muncie 4 speed in the 1985 fiero GT my repica is built upon.

another fun option maybe to to keep the VSS, and have the pulses spin a electric motor, the more pulses - the faster the motor. and this motor can be right at the speedo to feed it the spinny analog speed. this way you dont have to feed a sheathed speedo cable 8 feet thru the car.

but, I think ogres idea is the best. pull the mechanics out, and install the electronics. you can keep the cluster.

quote Originally posted by theogre: Research the trans... You maybe over thinking it... Some have a cable and VSS option. In old Carb car, Cruse uses a VSS and Speedo uses a cable.

Agreed. No need to reinvent the wheel.

Look for a Cavalier etc. Their 4-speeds/5-speeds had gear drive for a cable driven speedo. Just swap the VSS for it.
Something to check. See here: http://www.fierosails.com/TransMan.html

[This message has been edited by fierosound (edited 09-02-2010).]

So after doing the math, and correcting for my oversize Pantera Rim/Tire package, I have found that I need a 1:1.66 ratio adapter gear box.

Abbott enterprises will sell me one for $125.oo plus S&H

So now we know how to put a DeTomaso Pantera Speedometer into a Fiero GT and make it read correctly !!

Also thanks to fierosound ! I will see if a Cavalier speedo drive will work in the Muncie 4 sp. If so, it will save me from having to modify my butchered VSS !