Is this common?

[max.b]

found the culprit to no speedo

is this common?

[Reverb]

Mine went on my Jeep - if your drive doesn't match the speedo gear then it will rip it. If it's not in properly it will too.

[fmyth]

yes

[Ascaris]

White color is a 23 tooth speedo gear. These are known to have a short service life in Mustang applications.

The highest tooth count made by Ford is a 21 tooth. I think the 23 tooth is intended for Chrysler applications, but happens to fit Mustangs also.

The 23-tooth is used in Mustang applications when the gears are changed and the standard (up to 21 tooth) driven gears no longer work with the drive gear used in the transmission. If it is an automatic, I think you are stuck with the drive gear, as it is part of the shaft, but the T-5 can have the plastic drive gear removed from the output shaft to allow the use of a 21 or less tooth driven gear.

This page has a table showing the drive/driven gear combos possible.

[max.b]

Originally Posted by Ascaris

White color is a 23 tooth speedo gear. These are known to have a short service life in Mustang applications.

The highest tooth count made by Ford is a 21 tooth. I think the 23 tooth is intended for Chrysler applications, but happens to fit Mustangs also.

The 23-tooth is used in Mustang applications when the gears are changed and the standard (up to 21 tooth) driven gears no longer work with the drive gear used in the transmission. If it is an automatic, I think you are stuck with the drive gear, as it is part of the shaft, but the T-5 can have the plastic drive gear removed from the output shaft to allow the use of a 21 or less tooth driven gear.

This page has a table showing the drive/driven gear combos possible.

car is an 85 so it came with a 7tooth drive. i swapped in a 21 tooth to correct for the 3.73s so hopefully im good. its a t5 even though the drive gear is changeable its not as easy as swapping the driven haha

[SlowBox]

Originally Posted by Ascaris

White color is a 23 tooth speedo gear. These are known to have a short service life in Mustang applications.

The highest tooth count made by Ford is a 21 tooth. I think the 23 tooth is intended for Chrysler applications, but happens to fit Mustangs also.

The 23-tooth is used in Mustang applications when the gears are changed and the standard (up to 21 tooth) driven gears no longer work with the drive gear used in the transmission. If it is an automatic, I think you are stuck with the drive gear, as it is part of the shaft, but the T-5 can have the plastic drive gear removed from the output shaft to allow the use of a 21 or less tooth driven gear.

This page has a table showing the drive/driven gear combos possible.

That's some good information. What's the difference between the T5 tailshaft and C4/C5? I have 3.55 gears and the speedo reads around 10mph high.

[max.b]

the t5 tailshaft has a plastic changeable grive gear. the autos have it machined into the shaft.

[Michael Yount]

If you can pair up the 21 or 23 tooth driven gear with a 7 or better yet, an 8 tooth drive gear, they'll generally hold up ok. But if it's with a 6 tooth drive gear, they generally get chewed up pretty quickly. When I was originally setting up my car I had a 21 tooth on a 6 tooth drive gear - lasted 17.8 miles. Went with an 18 tooth and recalibrated the speedo. The 18 tooth/6 tooth combo lasted for 10 years/35k miles. Changed from the stock Dana rearend to a Ford 8.8, went with 3.55's and a bit of a taller tire - and dropped down to a 16 tooth.

Moral of the story - if you have to use a high tooth count driven gear, pair it with a high tooth count drive gear in order to make it live. Changing the drive gear requires pulling the tailshaft housing off.