First yes I searched and read the forums. I'm still confused and am just trying to clarify things. The car is a 92 Z28 with a T-5 G80 GU4 RPO codes for the rear end (as verified off of the service tag). Posi and 3.08 gears if my reading was right. The rear gears where changed to 3.73 throwing off my speedo and as I understand it the VSS input to the ECM. So I need a blue 7 tooth drive gear and a red 21 tooth driven gear to correct everything right? Will these work? http://www.thegearbox.org/catalog/item/3819132/3532517.htm
http://www.thegearbox.org/catalog/item/3819132/10161222.htm
If not an I looking for one without the shaft? Any idea what drive gear is in the tranny or should I order a blue gear just in case? Anything else I should be trying to track down? Any suggestions on where to track down the right parts if these aren't it? Thanks for your help.

 

Your car uses and electric speedo sensor,... but the gear that you posted is for a cable speedo sensor. AFAIK: GM never made a red 21 tooth T5 gear for an ELECTRIC speedo sensor.

Here is what you need :

http://www.dakotadigital.com/index.c...rod/prd126.htm

The firs time I ever saw the new model with an LED window in it !!

 

Remove your VSS, mark the mainshaft gear with a marker and count teeth by rotating things. Red usually = 9 tooth. Purple usually = 7 tooth.

The VSS for the third gen is harder and harder to find. So is the 21 tooth gear meant for the VSS. Instead of original style, you can use the gears you posted and change VSS style which threads onto a speedo gear setup. The parts will be easier to find and service later.

4004 pulse per mile sine wave is needed. https://www.thirdgen.org/forums/tran...-vss-help.html

7 / 21 is correct for most third gen tire sizes and 3.73.

 

So instead of changing gears in the tranny this just corrects the out put signal to the speedo and ecm? Seems a lot easier.

 

Not only can you use your original electric Speed sensor, DRIVE and DRIVEN gears,.... ( stuff that you already have ) but the DD SG5 is more versatile and cheaper. It can be used not only to calibrate for gear changes and tire sizes, but it's even compatible with most (all?) types of electric speed sensors. Right now I'm using it now for a stock 95' T56 sensor - to - stock 84' digital cluster ( + an aftermarket speedo )

Use the SGI-5 & you'll never have to hunt for another speedo gear again !!!

 

Good stuff planning on a T-56 swap in the future anyway.

So looking over the instructions application 2 for my use I would want out 1 for the ECM out 3 for the speedo? And I should be trying to mount this under the dash on the passenger side or where ever is closest to the wires? Sorry man wiring is not my strong suit. Thanks again for your help.

 

Just an update in case anyone else comes across this issue;

I used a Dakota Digital SGI-5E box (this is the current version). It turns out on my setup that the Yellow wire to the 4-out box is the sender signal, the Purple is ground (perhaps someone reversed the wires somewhere in the harness at some point, I didn't go digging through everything). So;

As per the "Application #1" in the Dakota Digital documentation (High-High signal)

-Yellow wire from speed sensor cut by 4-out box and run to "Signal In" on DD unit.
-"Out 1" (calibrated ac output signal) on DD unit wired back to Yellow input on 4-out box.
-Power (positive, ignition 'on' only) and ground connections for DD unit spliced off from stereo wiring harness
-Purple (ground wire) left in place on 4-out box (i.e. not cut-it was left as it was found).
-everything tied up behind panel on dash, DD unit then calibrated as per instructions for the modified rear gear/speedo setup and everything is working A-Ok.
-lower front dash cover reinstalled- no one will ever know there is a modification unless they go looking for it.

The above was copied from another post by Eric2ndgen

Just to make sure I have everything right. Use application 1 set up. After verifying the signal wire route it into the SGI box (signal in) and from out 1 back to the 4-out box. For power I can tap the 12v ignition hot and ground from the 4-out box that the signal wire is taken from. Then it's on to calibration.

I'm really unsure about the application 1 and 2 on the SGI-5E instructions. I thought I read the VSS used a 4000 ppm signal and application 1 states the range of 32000 to 250000.

 

I would agree with you the Application 2 using "OUT1" is more in line with the PPM count of the signal you will be converting. You're roughly 120% of what the VSS reading should be.

BTW, what speedo gear tooth count is on the VSS?

 

Haven't pulled the car apart yet to find out what gears are in there. My understanding with this little unit I wouldn't have to. Just hook it up and calibrate as per the instructions provided correct? Calibrating this thing seems like it might be tricky. Never states what the stock cal number is to complete the formula they provide.

 

VSSs and speedo gears do fail; taking 5 minutes with a mirror and a ratchet to count teeth is for information. And on the rare chance it's a 21 or 22 tooth outer gear, you'd only need to buy a single drive gear; swap it out and be done.

Calibration is easier on the newer SGI-5; with the old versions it was all about setting the dip switches and it could be tricky. Now you can gradually change it slowly towards ideal. Much easier.

 

Does the SGI also correct the odometer and work with the cruise control? I saw one video where there was an output for the speedo, odometer, and cruise control all separate coming out of the yellow speed buffer thats attached to the ECM.

 

Put the SGI-5 box between the VSS and the 4-out buffer box. Use a sine wave (magnetic) output from the SGI box to the yellow buffer box.

RBob.