speedometer prob.....

[gebasgt]

I have 3:55 gears in the rearend of my 1993 cobra and my speedo is off by i'm guessing 8-10 mph. How can I fix this problem? I don't know if I need to reprogram the computer or if there is something else I need to do. Any help would be greatly appreciated.

 

[tording]

You can get a new speedo gear that goes on the end of the speedo cable that goes into your transmission. This will correct the problem. I don't know what gear you need exactly for 3.55's but I bet somebody will know and post it up here.

I think I found it and I believe you need a 23 tooth speedo gear. You can get them off of ebay for like 10 bucks.

http://cgi.ebay.com/ebaymotors/Must...hZitem180063775255QQihZ008QQitemZ180063775255

 

[gebasgt]

Ok, now what if I want to have my speedometer read 10 mph less than actual speed. What gear do I need then??

 

[JChalfan]

Ok, now what if I want to have my speedometer read 10 mph less than actual speed. What gear do I need then??

Probably a speedo gear designed for 4.11's?

Why do you want your speedo to read low?

Do a search for "speedo gear" and you will find a lot of info, I think there's some charts out there about which speedo gear you need for what rear end gears.

But no, you don't need to reprogram the computer.

I have 3.55's in my '90, and I beleive I used the "white" gear. I don't remember for sure how many teeth it has.

Jeff

 

[Roland69]

there is a thread I made about this in the sticky in 5.0 tech....all the info you need for speedo gears

 

[Roland69]

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

 

[5.0 Nostalgia]

You need the 23 tooth white gear. They are usually more expensive. If that doesn't work, you will need to change the drive gear in the tailshaft of the transmission.

 

[TRWXXA]

Why do you want your speedo to read low?

Perhaps he thinks if he gets enough points on his license, he wins a prize.

You can't get your speedo to read exactly 10 mph too low or too high. An incorrectly geared speedometer will be off by a percentage, not a specific mph. A speedometer that reads 60 mph at an actual speed of 70 mph is off by about 15%. The same speedometer will read 34 mph at an actual speed of 40 mph.

Once you understand this relationship, it's easy to figure out what gear you need to correct your speedometer. The formula is this:

current speedo gear / actual speed = required speedo gear / indicated speed

EXAMPLE:
You currently have a 19-tooth gear, and your speedo reads 88 when your actual speed is 80 mph.

19/80 = x/88

Cross multiply and solve for x.

80x = 19*88 = 1672

x = 1672/80

x = 20.9

You'd need a 21-tooth speedometer gear for a correct reading.

And you thought you'd never find a use for algebra in real life.

 

[Roland69]

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

 

[MikeC]

If you want the white 23 tooth gear, go the the Chrysler/Dodge dealer and get part number (P)J3167393. I recently got one, it was about $9 and they had it in stock. I read years ago that it's a good idea to reduce the diameter because it's a little larger than the other Ford gears because of the larger tooth count. I put the end of mine in a drill and while it was spinning, used some sandpaper to shave 0.020" off the dia. Then cleaned up any burs from the teeth. It's worked great so far.