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Discussion Starter #1
I bought my car 10 years ago and the speedometer has ALWAYS been jumpy. When I installed a T5 along with a new 3.55 rear gear in my 68 a couple years ago I made sure to use a new 4 speed speedometer cable and a new 23 tooth driven speedometer gear to correct my speed. Even with all the new equipment my speedometer is still jumpy, so I pulled the speedometer gear out of the car the other day and it was chewed to shreds.

I spun the speedometer cable by hand and it seems to spin freely. I also made sure to get the correct gear orientation and tooth count for my setup so I'm really confused why the gear is chewed up. I have a T5 out of a 1990 Mustang GT so I have an 8 tooth driven gear (I confirmed this by looking up into the transmission, I have a white driven gear which looks in good condition). I'm running a 3.55 rear with 195/75-14 tires which according to online calculators I need a 22.5 tooth gear (23 tooth gear) which is what I was running. Any thoughts as to why my speedometer driven gear is chewed up?
 

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The teeth get thin with the 23 tooth gear and the aftermarket ones can be poor quality.. Either try a 22 or look for a factory Ford 23
 

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I found that the 23 tooth gear life span was short. I pulled the T5 and replaced my drive gear so I could go with a fewer tooth gear. I put a 6 tooth drive gear (black) and a 17 tooth driven gear. I run 3.50's in the rear. Speedo is pretty accurate.
 

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Maybe juggle the drive and driven gears. I just put 3.55's in my 66. With a 215/60/15 tire at 25.2" I needed a 20 tooth gear with my 6 tooth drive gear IIRC.
 

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Discussion Starter #7
I found that the 23 tooth gear life span was short. I pulled the T5 and replaced my drive gear so I could go with a fewer tooth gear. I put a 6 tooth drive gear (black) and a 17 tooth driven gear. I run 3.50's in the rear. Speedo is pretty accurate.
This seems to be the consensus. i hate to pull the transmission back out of the car, but it looks like i may have to. Thanks everybody for the replies.
 

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The black 23 tooth speedometer gear is really a quick-and-dirty fix. The gears don't mesh. It just sort of jams against the other gear and rolls around. It really doesn't belong in Fords. I read it is a Mopar part.
 

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Use a 7 tooth drive on the trans and a 20 tooth driven gear on the cable. Should work just right for 3.55s.
Supposedly there's something about angle or diameter or teeth too thin on the 23 tooth gear. (depends on who you talk to)

quik should be in the clear on the cable as it's new. The speedo itself can drag and really cause some issues for the cable, etc.
I'd scrutinize that too.
 

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I bought my car 10 years ago and the speedometer has ALWAYS been jumpy. When I installed a T5 along with a new 3.55 rear gear in my 68 a couple years ago I made sure to use a new 4 speed speedometer cable and a new 23 tooth driven speedometer gear to correct my speed. Even with all the new equipment my speedometer is still jumpy, so I pulled the speedometer gear out of the car the other day and it was chewed to shreds.

I spun the speedometer cable by hand and it seems to spin freely. I also made sure to get the correct gear orientation and tooth count for my setup so I'm really confused why the gear is chewed up. I have a T5 out of a 1990 Mustang GT so I have an 8 tooth driven gear (I confirmed this by looking up into the transmission, I have a white driven gear which looks in good condition). I'm running a 3.55 rear with 195/75-14 tires which according to online calculators I need a 22.5 tooth gear (23 tooth gear) which is what I was running. Any thoughts as to why my speedometer driven gear is chewed up?
Hmmm… Why would you use a 4-speed cable? That's way too long for a T5. The 4-speed plug is on the RH side, and has to go all the way around the trans. The T5, like the C4 and 3-speed, cable plugs on the left side.

I hope you didn't use a 4-speed gear. Oddly it will work, for a while, but the helix of the gear goes the wrong way and will be eaten pretty quick.

The gear inside the trans is the drive gear. The one on the cable is the driven gear. The 23 tooth gear is a delicate little flower, and prone to early death. You'd be better off with, say, a 17T gear, and a reduction drive adapter. That's what Ford did on the Drag Pac cars.

 

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Hmmm… Why would you use a 4-speed cable? That's way too long for a T5. The 4-speed plug is on the RH side, and has to go all the way around the trans. The T5, like the C4 and 3-speed, cable plugs on the left side.

I hope you didn't use a 4-speed gear. Oddly it will work, for a while, but the helix of the gear goes the wrong way and will be eaten pretty quick.

The gear inside the trans is the drive gear. The one on the cable is the driven gear. The 23 tooth gear is a delicate little flower, and prone to early death. You'd be better off with, say, a 17T gear, and a reduction drive adapter. That's what Ford did on the Drag Pac cars.
There are left-hand and right-hand driven gears depending on which side of the case the cable goes into. If you have the wrong one the gears will be cross-hatched and just be destroyed in no time.
 

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The 23 tooth gear is a Jeep part and as others have said, will fail. And since you will have the transmission out, it's also a good idea to flush it out. and put in new lube. All those shredded gear teeth can block some of the lube passages. You will find a bunch of them at the bottom of the trans case. The 7/20 tooth combination is recommended.
 

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And if you used the wrong gear, ie LH instead of the RH, the driving gear in the trans is probably trashed. ask me how I know.
 

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Discussion Starter #15
Well, it's unanimous! The 23 tooth gear is junk and shouldn't be used with a Ford T5!

I did some research on the different driven gears when I installed the T5 a couple years ago, so I made sure to use the correct orientation gear for a T5. However, I did not come across any articles that mentioned the weaknesses of the 23 tooth gear.

What really sucks is now I have to pull a fresh transmission out of the car just to swap a plastic gear! It's not like I had any other projects I wanted to do this Spring.
 

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Just be glad that the transmission has a drive gear that can be changed. On some transmissions, the drive gear is part of the output shaft and not a sperate part. It might be possible to change the gear without pulling the whole transmission. The gear is "weak" because it is meshing with the wrong drive gear.
 

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Discussion Starter #17
Update: After receiving the new speedometer 7 tooth drive and 20 tooth driven gear I went ahead and installed the 20 tooth gear for testing and learned a lot during the install.
  1. The speedometer doesn't jump when driven by an electric drill, so the problem definitely is within the system before the speedometer.
  2. The LH driven gears for the 3 speeds and C4's are shorter than the RH driven gears for the 4 speeds. Therefore the cable inside of the sheath for the speedometer cable for the 4 speed is longer that those for 3 speed and C4. When I installed the 23 tooth driven LH gear I forced fit it onto the the 4 speed cable which bound up the cable inside the sheath causing an enormous amount of drag on the cable.
  3. I shortened the cable inside the sheath by about 1/4" and greased the inside of the new 20 tooth gear and the teeth of the gear. The new combination spun much more freely.
  4. A test drive produced a jump-free speedometer.
 

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Discussion Starter #20
So you didn't need to install the drive gear?
I do need to install it, I'm just being lazy for now and testing out the system to see what works and what doesn't. I'll have to pull the transmission and swap the drive gear sometime soon. Till then my speedometer will just be off by about 10%.
 
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