Rather than mess with the gears in the tranny, i'd like to install a calibration box if possible. I need to take off my inst. panel anyway to silence a noisy speedo cable and can install the box while i'm in there. Does such a thing exist?
Yes! they do make them. I got a speeding ticket in my 68 Firebird. Took it to a place in Norfolk, Va that did speedo calibration. They chart the speedo indication at various speeds then send the data to a company that makes a little gear box the goes down at the tranny. The speedo cable comes out, the box goes in, then the cable goes into the box. It worked perfectly. My speedo indicated within 1-2 miles an hour at all speeds. Was thinking of doing this to my car. I got a ticket here in Florida-first speeding ticket in 20 years...now I have to sit through a whole Saturday of driver improvment to get the three points removed and the fine reduced. ANyway, I know what the speedo was indicating at the time and it must be at least 7 MPH slow. So I am going way to fast to stay under the 10 MPH buffer.
I found that place in the yellow pages.
Here is one in California...http://www.speedometershop.com/
The device is called a ratio adapter. Hope that helps.
Oh, the problem with the Firebird was the speedo, but it was going to cost $200 to fix it...only cost me $60 for the ratio adapter...
There's also a company in Atlanta that makes calibration kits. They didn't exactly get mine right, but they're now at 10% off instead of 20% off... I think it's my fault for specifying the wrong tire diameter.
Anyway, make sure you have your tire diameter, final drive ratio, and number of teeth on the output gear of the tranny available when you call them...
The company is "Speedometer Service Co. and the number is 770-569-8255.
It's also a gear box, and it cost me $124.47 after shipping. You can't buy a calibration module like the newer cars have available to them... Our older cars use a direct mechanical linkage to the speedometer cluster. You can't just electrically divide the signal coming from the tranny like you can with the newer cars...
Check to see if there is a speedometer shop in your area. If there is, ask about the Stewart-Warner speedometer gearbox. I believe it is either a 777 Series Drive Joint Kits and Parts or 666 Series Drive Joint Kits and Parts. It is a small gear box that fits between the speedo pickup gear on the transmission and the speedometer. It has quick change gears that allow you to choose almost any tire size and rear end gear ratio you want. This will allow you to get the accuracy with within 2%-3% or less. The drawback is that it isn't cheap.