[Marshall Kroft (Trafficop]

I have a 73' Challenger that has 15" wheels on it as opposed to the stock 14" and the speedometer is not working correctly. Is there anybody that can explain in laymans terms what size or kind of gear I need to swap to make the correct adjustment. I am not an auto mechanic, so please speak in terms for dummies.

Any help is appreciated, Thanks

Marshall

[Dave-R (Roppa440)]

You just swap the plastic gear wheel that drives the speedo cable from the trans output shaft.

Tell me what your tire size is and what ratio gears are in your axle and I can tell you which speedo drive gear you need.

There is a thread (or two?) about how to work out what your axle gears are.

[Dave-R (Roppa440)]

This link should help you find which axle gear you have.
http://www.challenger440.pwp.blueyonder. co.uk/cgi-bin/disc/show.cgi?tpc=6&post=1 0019#POST10019

The plastic gear you have to change is very cheap and to change it is a simple one-bolt job. It is on the end of the speedo cable where it joins to the trans.

[Marshall Kroft (Trafficop]

Looked on the rear end but no numbers were there. My miscue is that I do have 14" tires but the speedometer is reading higher then the actual speed. I have a standard or stock rear end according to my mechanic (904) or something like that with 24" tires 235/60r14's. Cant figure out why the speedo wont read right? Thanks very much for your help.

Marshall

[Dave-R (Roppa440)]

OK. Now I know your tire size. Good so far.

The 904 is the transmission.

To sort you out I need to know the gear ratio in your axle. The link I gave you above tells you how to jack up one or both wheels and count how many times the wheel rotates for exactly one rotation of the driveshaft (sometimes called propshaft).

Jacking up one or both wheels depends on if you have a limited slip differential or not. The link discusses how to do that.