Hi I have an 87 mustang gt and over the summer I replaced the clutch in it and now the speedometer doesn't work right. At first the speedo just bounced a lot but now it doesn't work at all except when I'm on the gas in 5th then it bounces around but when I let off it drops right back to 0. Does anybody know what may be causing this.

 

Speed gear sounds like. Possibly speed cable.

 

Speedo* stinkin smart phone

 

I took the cable and gear out and brought it to a auto parts store and they said that it all looked fine. I looked at the gear and it was a little worn but they said that it wasn't enough to mess anything up. The thing that gets me is that the speedometer only moves in fifth almost like the gear inside the tranny only spins in fifth.

 

Well, did you look at the gear in the tranny? It's plastic too, wears out.
Also don't ever bring anything to a parts store to be "checked out", unless it's Napa.
The prerequisites for working at a parts store include: a pulse. I've made purchases from about 150 parts stores over the years, and I can say with confidence that MAYBE 4 employees total had any clue what they were talking about.

 

the speedo drive gear is clipped on the output shaft. if your trans moves the car in all gears...it moves the speedo cable in all gears.

if the driven gear is not chewed up.....

it MUST be a broken cable.