Speedometer way off

[88Stang331]

The guy i bought the car from 88 GT, said it had 3.73 gears in the back, and when i was driving it it sure felt like it. However he said the speedo gear hadn't been adjusted. I bought the appropriate speedo gear and installed it correctly. However the speedometer gauge still reads double the speed i'm actually going (did this before and after i installed the speedo gear). I'm thinking that the needle may have been bumped, seeing as it has white gauge faces. Any suggestions? Any way to tell what gears are actually in it? This is getting annoying really fast.

 

[Roland69]

put the rearend on stands. Mark a line on the drive shaft and spin the tire one full turn and count the yurns the D/S makes....3 1/2=3:55's ....3 3/4=3:73's.... a little over 4 turns=4:10's and so on

 

[Roland69]

If this helps here ya go

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

 

[88Stang331]

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

I Purchased this gear from latemodel resto, and installed it, but when i put it in, it didn't change the speedometer at all. So i will try to put it up on stands and see that way. I just want to know if its the needles that are off, or the wrong speedo gear.

If its the wrong speedo gear, and there really isn't 3.73's then when i build the rear end, i'll put 3.73's along with a auburn LSD. If it is the needles...well then i guess i'm buying a new gauge cluster =\

If it is the needle, anybody have a 140mph gauge cluster for 1988 GT?

 

[RaceDvr50]

If it's the needle it will be off at zero, is it? Otherwise they may have just installed the wrong drive gear. Check that table Roland gave you and just buy the gear from Ford, they cost all of about $10 that probably is your problem but you need to know the rear end ratio, if your tire diameter has changed from stock you'll need to compensate for that and you need to know if the tranny is a 6,7 or 8 teeth drive gear.

 

[SteedaGT9150]

maybe its the cable?

 

[88Stang331]

anyway to tell if its the cable? It is a little off on the gauge at zero, but thats usually off by a certain amount, not double the speed no matter what speed your going. I figure if its off by 200% no matter how fast i'm going, then i would suspect it would be the gear ratio or what not.

 

[mkk50]

hmm didnt 88 have the 85 mph speedos? Does the white faced gauge he put on go up to 140?

 

[88 Fox GT]

'89 GTs were the only ones that had 140mph speedos (with no airbags.) You MUST get a speedo out of a '89 if you want the 140. '90-'93s had air bags and the speedo cluster was a totally different shape on the bottom.

 

[mkk50]

what im thinkin happened is the previous owner put a 140 mph face on top of an 85 mph speedometer, if u take the cluster out, try lifting up on the edge of the white faced overlay, if you see a black one underneath, try to see if it goes up to 85 or 140.

 

[Roland69]

he wanted a cool looking gauge over a gauge that worked lol

 

[Shinlee]

lol

 

[Roland69]

Sir do you know how fast you were going ..... 55 no 25 lol

 

[88Stang331]

but another thing that makes me think its the gauge cluster is the fact that the gas gauge needle is way off too. When i have a full tank, the needle is so far up and over, its no longer viewable.

 

[Flavadave4]

what im thinkin happened is the previous owner put a 140 mph face on top of an 85 mph speedometer, if u take the cluster out, try lifting up on the edge of the white faced overlay, if you see a black one underneath, try to see if it goes up to 85 or 140.

I think thats what happend

 

[88Stang331]

SOB thats what i figured happened, but i didn't want that to be the case =\. Anyway, i will check out the gauge cluster and see if its black underneath and if it goes up to 85. *sigh* i hate it when people do things wrong.

I thought it was all GT's came with 140MPH speedos?

 

[savegoodautonfg]

I have a stock t-5 what one will i need?

 

[88Stang331]

?? What gears do you have? and what year is your car?

 

[88Stang331]

if it actually is a 140 overlay on a 85mph speedo do i have to change the gear in the transmission that connects to the speedo cable? or just get an actual 140mph cluster?

 

[savegoodautonfg]

I have stock right now but im gonna get 3.73's and my car is 1990 GT