Speedo driven gear for a 1984 Fiero base 4 speed (Page 1/1)
tomres NOV 24, 03:07 PM
Hello. New to forum.
I am looking for the speedo driven gear part number that fits in my 1984 Fiero base 4 speed Muncie MY8 3.32 axle 185/80R13, Mandatory Canadian (primary speedo dial in kmh, secondary in mph).

RPO codes:
13B
13I
139
71L
71U
AAA
AR9
C41
C49
D4T
D60
D9D
E5Z
F25
K81
LR8
MM4
MY8
NA5
NB1
N46
PON
QHS
UL5
VK3
V73
WS9
WV1
WV9
W82
YT9
Z49

I have no idea what color is, but drive gear is beige (or natural, or aged white maybe)
I have found a lot of information on this topic, but it is sometimes contradictory. Specifically RPO codes D9D and D4T, that I think speedo gears related, are usually listed as "unknown" and "Fleet Sales Ambulance"(?)

Any help would be appreciated. Thanks.
Forrest NOV 24, 05:15 PM
I found this digging through many threads....
MD9 TH125C Automatics will have the large GREEN 10 tooth drive gear.
The smaller VSS speedo gear will be:
BLUE 30 tooth - tire sizes P185/80R13, P185/75R14, P195/70R14, P215/60R15
WHITE 31 tooth - tire size P215/60R14

MG2 Muncie/Getrag 5-speed transmissions will have a NATURAL (tan) 35 tooth drive gear.
The smaller VSS speedo gear will be:
RED 29 tooth - tires sizes P185/80R13, P185/75R14, P195/70R14, P215/60R15
PURPLE 30 tooth - tires sizes P215/60R14

M17 Muncie 4-speed transmissions will have a NATURAL (tan) 35 tooth drive gear.
The smaller VSS speedo gear will be:
RED 29 tooth - tires sizes P185/80R13, P185/75R14, P195/70R14, P215/60R15
PURPLE 30 tooth - tires sizes P215/60R14

MT2 Isuzu (?) 5-speed transmissions will have a 35 tooth drive gear (color unknown).
The smaller VSS speedo gear will be:
RED 29 tooth - tires sizes P185/80R13, P185/75R14, P195/70R14, P215/60R15
PURPLE 30 tooth - tires sizes P215/60R14

Myself ...they are super rare so I just bought what I could. Car shows 5 miles under what I am actually doing but that is fine with me.

Honestly we need to get all these 3d scanned and shared with the community.
I have a blue one...if anyone else wants to team up I am willing to do my part to get the blue one scanned in. My library has a scanner.

[This message has been edited by Forrest (edited 11-24-2021).]

tomres NOV 24, 08:08 PM
Thanks a lot Forrest.

I assume that I will not find the exact part that fits my car, and I agree to buy what I can find. Accuracy is secondary for me, first is to bring the speedometer and odometer to life.
My gearbox is MY8 and I don't know if any of the parts described in your post will fit my car.
Anyway, I realize that I won't be able to get any of them from a parts supplier. It would be great to scan yours in 3D!
fierosound NOV 25, 11:29 AM
M17 Muncie 4-speed transmissions will have a NATURAL (tan) 35 tooth drive gear.
The smaller VSS speedo gear will be:
RED 29 tooth - tires sizes P185/80R13

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pmbrunelle NOV 25, 12:18 PM

quote
Originally posted by tomres:
My gearbox is MY8 and I don't know if any of the parts described in your post will fit my car.



It doesn't matter that your gearbox is MY8.

The VSS gears of all Fiero standard transmissions (Muncie, Isuzu, Getrag) interchange.

The choice of VSS gear only depends on the tire size you want to run, not the transmission.

From there, if your speedometer reads a bit off, you can change the VSS gear to fine-tune the speedometer reading.
tomres NOV 25, 02:52 PM
Thank you very much to all.


quote
The VSS gears of all Fiero standard transmissions (Muncie, Isuzu, Getrag) interchange.



This makes my first goal so much easier: getting the speedometer and odometer working, even if they aren't accurate.
Thanks again. I was pretty lost and now pretty hopeful.
theogre NOV 25, 08:27 PM
Any gear is better then none because VSS "data" is use by speedo, ECM, and Cruise at minimum. (More in other models.)
ECM can have weird problems besides setting codes w/o speed "data" making engine "problems."

Is/was an aftermarket VSS "adjuster" module to add/remove pulses for Speedo etc. to correct speed vs tire size. Maybe more then one version because several VSS methods. GM had VSS "generator" like use in Fiero and optical/digital for others. Try Jeggs etc for that.

If can't find one now... Many ways to do this w/ or w/o a MCU like "Arduino" boards.
While the Speedo and divider isn't very picky, you need to know output from VSS to make your output match in volts etc. So you don't fry them w/ over volts...
I have no data about VSS output volts, wave form, etc.

------------------
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(Jurassic Park)


The Ogre's Fiero Cave

tomres NOV 26, 01:51 PM

quote
Originally posted by theogre:
ECM can have weird problems besides setting codes w/o speed "data" making engine "problems."


You're right. The "check engine" warning comes on while driving, and goes off as soon as the car stops.


quote
Originally posted by theogre:
Is/was an aftermarket VSS "adjuster" module to add/remove pulses for Speedo etc. to correct speed vs tire size. Maybe more then one version because several VSS methods. GM had VSS "generator" like use in Fiero and optical/digital for others. Try Jeggs etc for that.



I had no idea about this device. Thanks a lot theogre.

I have found this one:

https://www.amazon.com/Dako...ometer/dp/B07YQ7P8SN

I wonder if it would work with the Fiero VSS.