speedometer off

I just bought a 74 firebird w/turbo 350 trans . The speedometer is off so I replace the it with a new one but it still off @35 mphs its show 55 mphs. I don't if tires, rims, or gear have been change. I heard I could replace the plastic speedometer output drive in the transmission. If so what size to get the any other help or ideals would be great.

Mike

I wish I could help you, but all I can say is my '79 has the same problem. But its only off be 5-10 Km's. So when were doing 100 it says 90, etc! Also ours can go right around...

We were out making some video of it burning out, donuts etc, then came the "see how fast it can go" segment.

So, we got it up past 190, then it kept going, and going and eventually went all the way around and back to 20....lol. So I don't know how fast we were actually going... probably like 210 or something. Anywho....I wouldn't worry too much about your speedo for now, just watch your speed and don't get caught! ;)

There are too many variables to say that this or that speedo gear will do it. You may be able to find a shop that can calibrate it. If there is not a speciaty type place in your area that can do it I would start with tranny shops.