If your speedometer will only go to 35 mph, you probably have a problem with the speedometer head. The speedometer gears only makes small changes.
I would hook a working speedometer head to the cable under the dash and see if that ones reads correct, if it does you know the problem is in the gauge itself, if it reads the same (35mpg) the problem is in the drive gear in the transmission not the gear on the cable.
You can test the speedometer in place with a drill and short piece of cable, its not easy but is easier than removing the whole speedometer.