After completing my B Body,, total restro,, My speedometer is reading about 10 mph slow.. I pretty sure I've got 355 gears,,, 15'' tires,, about what gear do I need to put in the transmission,,, Speedometer was completely rebuild.. Thank you for any help..
10 mph slow at what speed? 40 ? 60 ? 100?
Errors in accuracy are directly proportional to speed as they are the result of an incorrect ratio.
The link Stumpy posted will help. Telling us 15" tires isn't enough, the diameter of the tire is the key. A super thin sidewall 195-50-15 tire will surely be shorter than a 235-75-15.
A speedometer that reads too slow needs a speedo-pinion gear that is smaller. This will spin faster.
The opposite is also true.
In many cases, a single tooth difference can be worth 2-3 mph of change.
I have a variety of used speedometer gears that I've used to correct errors. They are easily found on ebay for under $25.
