Just changed the gears in my rearend to 3:55 and my speedometer is now off. Does anyone know the correct speedometer gear to use and where I can get one? The car is a 68 442 convertible,400 engine,th 400 trany. Thanks

 

http://www.tciauto.com/Products/Tech...eedo_gears.asp

Heres a link to the math to figure it out. You must know the amount of teeth on the drive gear. This may require you to remove your speedo cable and housing at the transmission to count the teeth. Then, you can purchase the correct driven gear.

Most of the time you just need a new driven gear....its pretty cheap under 20 bucks.

Sometimes you have to replace the drive gear...depends. There are two housings for 400 trannys depending upon drive teeth. One housing only allows up to 39 teeth, the other allows up into the 40's, If I recall correctly.

Hope this helps.

 

Since you didn't tell us the tire size or even what transmission you have, no it is not possible for us to tell you what speedo gear to get. You can buy new ones here:

http://www.transmissioncenter.net/sp...n_______va.htm

EDIT: Oops, sorry, I didn't read the OP closely enough. It does say it's a TH400. We still need to know the tire size, however.

 

I am currently running 225/70r15 but I may be switching to 215/60r15 or 205/60r15. Thanks

 

225/70-15s are 27.40" in diameter and have a section width of almost 9". The 215/60s are over 2" smaller in diameter and are only 8.5" wide. The 205/60s are less than 24 3/4" in diameter and only 8" wide. Do you really intend to use those sizes?

I've run 255/60-15s, which are about the same diameter as you current tires.