My ODOMETER is reading/registering about 10 mph slower than its actually going. At 50mph its reading 40. At 60 mph its reading 50. I am sure is off that much because I had my wife get up to those mph and my 72 442 registered 10 miles slower. The transmission is 350 and the rear end is 10 bolt posi with 3.42 gear ,at least that is what the previous owner told me. I will check that tomorrow to verify. Anyone have an idea why I am getting a difference in the readings.

thanks
Gary

 

Are you saying that if you go 60 mph, for one hour, your odometer shows you as only having gone 50 miles?

Or do you mean that your SPEEDOMETER is registering 50 mph when you are going 60 mph?

If that is the case, you probably have the wrong size tires and or wheels on the car. Does the car have 15" or bigger wheels? That car was made for 14" wheels and if you increase the wheel or tire size from stock, it will affect your speedometer reading.

If you have a smart phone you can download a speedometer app so you don't have to have your wife double checking. I run the wrong size tire on my '87 442 and I use this app to make sure what my proper speed is. I have found that when my speedo says 70, the car is actually going 74.

 

Yes I am saying if I am driving the car @60 mph,the odometer/speedometer reads 50. I do have 15 inch tires.

 

Wheel size does not matter, just overall tire diameter. I'll bet the 3:42 posi is not original and it came with higher gears (lower number). Common upgrade but it throws the speedo off. You can change the driven gear at the transmission end of the cable but may also have to change the drive gear in the tailshaft to get it right. Can also get a ratio adaptor, that's what I did to avoid messing with the drive gear in the tailshaft