Speedo gear
 

My speedometer is off by 5 mph when I reach 35 + mph. Slower speeds its still not accurate. It's a stock 31 with 19 in tires. Where do I begin to see if I have the right gear? By looking in the catalogs I need to know what gear ratio I have. Isn't there a way by jacking up the rear and turning the wheel to find the gear ratio? Can you explain how it is done.
Thanks

Re: Speedo gear
 

hmm its going to be a bit tricky but put the car in 3rd, jack up one wheel, and mark the tire - then count how many times you need to hand crank the engine to get the tire to rotate one revolution. like a ratio of 3.54. Its really 3.54:1 meaning it takes 3.54 turns of the input(driveshaft) to get the output (wheel) to turn one revolution.

Re: Speedo gear
 

How is your odometer? If it is correct then you need to fix your speedometer and not mess around with the gear on the torque tube.

Charlie Stephens

Re: Speedo gear
 

Okay how do I check my speedometer for accuracy ?

Re: Speedo gear
 

I had tried some of those roll the car or lift one wheel and crank the engine by hand..

I finally jacked up the rear end, removed the fill plug, cleaned one of the ring gear teeth with a swab and marked it...then turned the rear end one tooth at a time and counted the teeth....I'm not sure if you could see the mark if the rear end were full

34 teeth you probably have a 3:78 to 1

other ratios here.

http://www.fordgarage.com/pages/rearaxleratios.htm

I used a hand held GPS to check speedo accuracy.....I realize you may not have one....

Re: Speedo gear
 

I use a gps that's how l know that is not accurate.

Thanks for the chart that shows me the different gear ratios. That will be the best way to see witch ratio I have.

Then I can check witch speedo gear I have.

Re: Speedo gear
 

The Judging Standards have a chart showing the different speedo gear turtles..Section 4 page 15...revised 2011

I needed a 19 tooth turtle gear for my 3:78 ..I have 21" wheels but the outside diameter may be the same as 19's

Also there is this..

Re: Speedo gear
 

I did not understand initially, but a recent thread advised to count TWO turns of the tire when one wheel is jacked up. I used this method to confirm that 3.78 is my ratio.

Re: Speedo gear
 

Look at post #22.....and then read some of the others as there were some additional things to do..

https://www.fordbarn.com/forum/showt...=177353&page=2