quick speedo gear/axle ratio question

riceslayer302 · Feb 11, 2007

i have been having problems with my speedo lately, i just got the car this october and really dont know what was put into it, i know it has gears and assume they are 3.55's, i turned the tires and the driveshaft spun about 3 1/2 times. the speedo wasnt working so i pulled the VSS sensor off and there was no driven gear to be found, there is a 7 tooth yellow drive gear.

so i went to mustangs unlimited today and used their speedo gear chart, according to them, 3.55's in a manual tranny use a 20 tooth black driven gear. so i bought it, it was all of 7 dollars. installed it, and my speedo works, but its about 20mph off... when im going 60mph, my speedo reads 80mph.

i was looking at my friend andy's gear today, his is red, and he has 3.55's too, and his speedo is dead on... but mustangs unlimited says red is 3.73...

what should i try now? if the car had 3.27s would it make the speedo read higher than im going or would it read lower??? should i get 3.27 driven gear and try that? or get the red one?

my friends tranny also has the same 7 tooth yellow drive gear... maybe i should get the red?

what do you guys think? how can i figure this out without buying all the driven gears at mustangs unlimited and breaking my wallet haha

eagleautosports · Feb 11, 2007

Speedo gears are affected by the height of the tires too. If your car and his are the same, along with trannys and tires, get the red.

Roland69 · Feb 11, 2007

if your car is a 1990 than you need a White 23 tooth Speedo Gear

Roland69 · Feb 11, 2007

Manual Transmissions with 6 Tooth Drive Gear

Not found in OEM applications

Item Number
Description
N/A
3.08 Gear Ratio / Not possible

C0DZ-17271-A
3.27 Gear Ratio / Maroon 16 Speedo Gear

C3DZ-17271-C
3.55 Gear Ratio / White 17 Speedo Gear

C0DD-17271-B
3.73 Gear Ratio / Yellow 18 Speedo Gear

C0DZ-17271-B
3.90 Gear Ratio / Pink 19 Speedo Gear

C1DZ-17271-A
4.10 Gear Ratio / Black 20 Speedo Gear

C4OZ-17271-A
4.30 Gear Ratio / Red 21 Speedo Gear

Manual Transmissions with 7 Tooth Drive Gear

1983-1989 T-5 OEM
Pre 1993 T-5 Aftermarket
1996-1998 Cobra T-45 OEM
All Tremec Transmissions

Item Number
Description
C0DZ-17271-A
2.73 Gear Ratio / Maroon 16 Speedo Gear

C0DD-17271-B
3.08 Gear Ratio / Yellow 18 Speedo Gear

C0DZ-17271-B
3.27 Gear Ratio / Pink 19 Speedo Gear

C1DZ-17271-A
3.55 Gear Ratio / Black 20 Speedo Gear

C4OZ-17271-A
3.73 Gear Ratio / Red 21 Speedo Gear

Jeep Part #j3167393
4.10 Gear Ratio / White 23 Speedo Gear

Manual Transmissions with 8 Tooth Drive Gear

1990-1995 T-5 OEM
1996-1998 T-45 OEM Except Cobra

Item Number
Description
C0DD-17271-B
2.73 Gear Ratio / Yellow 18 Speedo Gear

C1DZ-17271-A
3.08 Gear Ratio / Black 20 Speedo Gear

C4OZ-17271-A
3.27 Gear Ratio / Red 21 Speedo Gear

Jeep Part #j3167393
3.55 Gear Ratio / White 23 Speedo Gear

Jeep Part #j3167393
3.73 Gear Ratio / White 23 Speedo Gear (Not 100% accurate. This combination will offer the best accuracy without changing the drive gear. Change drive gear to a 6 tooth for complete accuracy. See 6 tooth table.)

Jeep Part #j3167393
4.10 Gear Ratio / White 23 Speedo Gear (Not 100% accurate. This combination will offer the best accuracy without changing the drive gear. Change drive gear to a 6 tooth for complete accuracy. See 6 tooth table.)

Automatic Transmissions with 7 Tooth Drive Gear

1983-1989 Automatic Transmissions

Item Number
Description
D0AZ-17271-A
2.73 Gear Ratio / Blue 16 Speedo Gear

C7AZ-17271-B
3.08 Gear Ratio / Gray 18 Speedo Gear

C7VY-17271-A
3.27 Gear Ratio / Tan 19 Speedo Gear

C8SZ-17271-B
3.55 Gear Ratio / Orange 20 Speedo Gear

D0OZ-17271-B
3.73 Gear Ratio / Purple 21 Speedo Gear

Jeep Part #j3167393
4.10 Gear Ratio / White 23 Speedo Gear

Automatic Transmissions with 8 Tooth Drive Gear

1990-1998 Automatic Transmissions

Item Number
Description
C7AZ-17271-B
2.73 Gear Ratio / Gray 18 Speedo Gear

C8SZ-17271-B
3.08 Gear Ratio / Orange 20 Speedo Gear

D0OZ-17271-B
3.27 Gear Ratio / Purple 21 Speedo Gear

Jeep Part #j3167393
3.55 Gear Ratio / White 23 Speedo Gear

Jeep Part #j3167393
3.73 Gear Ratio / White 23 Speedo Gear (Not 100% accurate.)

Jeep Part #j3167393
4.10 Gear Ratio / White 23 Speedo Gear (Not 100% accurate.)

Now if you really want to change the internal drive gear of your manual tranny you can match it according to the table below. Be aware that the 6 tooth will offer the most combos for numerically higher gear ratios and offer the greatest degree of accuracy. The 6 tooth gear selection table for a manual tranny is the first in the page.

Item Number
Description
E3ZZ-17285-B
6 Tooth Internal Drive Gear / Black

E3ZZ-17285-A
7 Tooth Internal Drive Gear / Yellow

F0ZZ-17285-A
8 Tooth Internal Drive Gear / Green

riceslayer302 · Feb 11, 2007

my car is a 1990, but i dont think the 90 has a 7 tooth drive gear, i believe it is an 8, my guess is being though the car is an early 90, the tranny is either a carryover from 89 or it was swapped at some point in the cars life.

i am running street tires, 225, 15's

riceslayer302 · Feb 11, 2007

so what gear would you recomend to get it to drop to the correct speed, as i said, at 60mph, my speedo reads 80mph and is running about 2500 rpms in 5th gear

Roland69 · Feb 11, 2007

well if you checked the gears and by the sounds of it you did it right.....if it was 7 bucks try the 23 tooth...it only takes about 5 min to change

Roland69 · Feb 11, 2007

I have a 23 tooth gear in the ashtray of my car (in storage) but I would ship it out to you since they are so small and light I bet it would only cost me like $2

riceslayer302 · Feb 11, 2007

so if i get a driven gear with more teeth on it, it will bring the speed reading down some?

do you think i might not have 3.55's??? what should i expect in my situation? if the gear for 3.55's is 20mph fast, would i have higher gear ratio such as 373s? or lower like 308s???

sorry for these damn technical questions, im trying to figure it out on my own but there isnt much info, just charts that dont give the WHY factor

riceslayer302 · Feb 11, 2007

sent you a PM about the gear

Roland69 · Feb 11, 2007

a for sure way to tell is take the rear diff cover off and have a look see. and also look and see what coulur the speedo drive gear is when you pull the small speedo gear out using a small light

riceslayer302 · Feb 12, 2007

the drive gear looks white, but it is probably a faded yellow. i counted the teeth, looks to be 7. i am going to try my friends red gear today, and if that makes it worse, my best guess is that the car has 3:08 or 3:27. or maybe it just has stock gears and im just an idiot. im pretty sure its got gears though it pulls ALOT harder than a stocker. could be aluminum flywheel and driveshaft doing it, idk

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