Does Anybody's Speedometer Go Crazy?

[moe&michelle]

can anybody help me? i have an sc 400 1995, and ever since i bought the car the speedeometer goes crazy? i've been told its becuz i have 18"tires is this correct, and can it actually make my odometer count the miles faster? does my trans. have a worm gear inside that needs to be adj.?

[esska11]

i know thats a common problem for these cars mine started going crazy now it doesnt work at all...i got gps installed and that tells me my speed so ive put off fixing it for now haha...but i know that there is another section on this forum that deals with this problem matter of fact i need to go find it while im thinking about it