Not far from my house there is a stretch of road with a 35 mph limit and a radar sign that shows big numbers and says "Your Speed Is ... ".
A couple of years ago I noticed that when my speedometer said 36 mph, the sign said that I was doing 39 mph.
I finally got around to correcting it. For my speedometer to read slow meant that I needed a gear with fewer teeth. That would spin the gear faster would send a faster signal to the speedometer. I looked at the Mac's Auto Parts site and they listed a 17-tooth speedometer gear with part number C3DZ-17271-C. An article about how to read Ford part numbers explained that C3 meant 1963, D meant Falcon, and 17271 meant speedometer. That sounded like just what I needed. Someone on e-bay was selling that part for $6.49 with postage included. Cool! I ordered one and installed it this morning.
New Gear:
C3DZ-17271-C.jpg
The old gear was tan and had 19 teeth. The new gear is white and has 17 teeth.
on counter top 4-DCP_0078.jpg
Going from 19 to 17 teeth makes the speedometer and odometer go faster. This will multiply the speedometer, odometer, and indicated gas mileage by 19/17 = 1.118, or 12%. Before, my speedometer said 36 mp when it should have said 39 mph. With the correction 1.118 * 36 mph should read 40 mph.
My wife and I drove to where I work and the odometer registered 12.7 miles where it had previously measured about 11 miles. Then we drove to the radar site and made three passes at 38 mph, 24 mph, and 50 mph. The speedometer compared near spot-on to the radar. When I made the pass with 50 mph on the speedometer, the radar read 49 mph. Yay!
This means that when I thought that the car was maxing out at 88 mph, it was actually hitting 98 mph! (Don't tell my wife!)
And my gas mileage is better than what I had thought!
Yay! I'm doing the happy bannana dance!
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