When I am going about 40mph the speedo spikes to about 60mph. and at higher speeds ( I guess about 60-?? ) it spikes to like 120mph or so... Any Ideas?

 

is it at only those speeds?

 

My guess is your speedo cable is broke. Replace it.

 

The speedo cable might be partially disengaged from the speedometer. If the plastic retainer is cracked, the cable can be slightly pulled away from the meter.

 

I think your car is just super fast.. I still have to fix mines too

 

My speedometer is about 5mph fast, if it says 70, I'm doing 65. Is there a way to adjust this or what?

-Lukas

 

The cable is most likely Loose, at the Transmission itself or the Back of the cluster..another couple guesses: is that it is Kinked,and it will stop then Spike..bent somewhere and the cable casing hinders the Inner Cable from spinning.(you can always throw some kind of Lube down the Cable and spin it to lubricate it).
OR: the Speedometer Gear Inside the Transmission is getting worn out,at the Cable inlet(due to being loose).
and the Last Guess(or what to check for..haha) would be the where the Cable meets the Inside of the cluster.
..someone Mentioned the Cable being Broke..NO,,if it was,the speedometer would not Work at all..Remember the speedometer is Cable driven,NOT Electrical.like the Tach or the other gauges in the cluster
..have Fun..Buy a coffee and check it out..cheers!..STYX!~

 

stock rims/tires????

 

..well there is..
you can get another Speedometer Gear for the transmission that has a Closer Ratio.
If I am not mistaken though,the stock speedometer is not all that accurate.(..about 5mph,sounds "normal". if you are doing 70 and Really you are doing 65 that is good,in a way.you get charged for being 5 MPH less,when they ticket you!)
You have to take into account If you are running different size tires,Other than stock size.
If you then Toss a set of 17's in and alter the Rubber,the Speedo will definitely be off.