1991 Mustang 5.0 Auto Speedometer

[Ebhardt]

A friend of mine has a 1991, 5.0L Ford Mustang Automatic.
The speedometer goes "haywire" at about 40 mph. It bounced from 0 - 100 mph
He put in a new speedometer cable and the problem got worse!!!!
Any ideas?
Any information would help.
Thanks!!!
Jen

 

[Nicoleb3x3]

Does the speedo gear teeth look ok?

 

[LiquidGT]

+1 The speedo gear is the next best place to look.