Speedometer gear Question

[fastback68cuda]

I tried posting this in the other trans form but it kept blocking me so here i am...

I have a 727 in the shop being rebuilt for my 68 barracuda that originally came with the 904. it now has the 727 (year and source unknown to me) with a 3.55 sure grip rear end. the speedometer needle kinda dances up and down when i drive so i think it could be a bad calble, bad speedo gauge or maybe a bad gear??? the cable seems ok so the speedo gear is the easy fix right now so i'd like to try it out. Does this seem like a probable cause for the "dancing" of the speedometer needle?

the trans has a black 32 tooth gear and i have some 15 x 7 cop car wheels that ar going to go on soon. Does anyone know if this is the correct speedo gear for mr setup?

I know tire size matters but haven't got that far. i know i will be putting in the biggest tire i can run with SS springs if that helps.

Thanks for the help,

Robert

 

[redfastback]

total tire diameter is what your looking for (i.e. 26", 26.5" etc) as well as gear ratio. if the needle bounces around during low speed operation but steadys out at higher speed, it usually is a bad cable. if it is bouncy all the time thru all speeds its in the gears in the speedometer, not the trans. the trans speedo gear only job is to properly tell the speedo what actual speed is.

 

[340mopar]

A 245/60-15 tire is in the 26 -26.5" range. A 26" tire coupled with a 3.55 gear would be a 36 tooth (red) gear. If you jump up to a 28" tire you would need a 33 tooth (yellow) gear. Any tire size in between would require a gear somewere between the 36 and the 33 tooth gears. Your 32 tooth gear will make the speedo read faster than you are going.

Chuck