Speedo adjustment

[Stinky]

I changed my rear dif from 3.7 to 4.10 and my speedometer is off.  It was off before that.  What is the easiest way to adjust it?

 

 

[Charlie69]

when I pull a set of rear end gears I also pull the speedometer drive that is in the side of the transmission, the speedo cable is attached to it.  It also needs to have the factory height in tires for it to be correct.

[datzenmike]

Charlie is right. If you pull a different differential always get the transmission gear that is 'mated' to it. Ive done exactly the same thing a 3.70 to a 4.11 on my car. The tires are not stock but close. 

 

What I would do is find a way to get your exact speed at a known speed. This will include any difference in the tire diameter. Lets just say that you get 55 when you are really going 50. That would be 11% error. 110 at 100. Next you need to disconnect your speedometer cable and unbolt the speedometer pinion and pull out of the transmission. (avoid having the front jacked up too high or the oil will pour out the hole. You need to count the teeth on the plastic gear to know where you are to know where you are going

 

 

You may find that you have a Blue 18 tooth gear and you need more teeth to slow the speedometer cable down. Divide 18 into 19 and its 5.5% and not quite enough, but 20 divided by 18 is exactly 11%. Now all you need is a larger red 20 tooth pinion sleeve, pop it in the speedometer reads 11% slower. 

 

Each increase by one tooth is around 5%, not exact but close. If you have the stock tire you can also divide the known differential ratios 4.11/3.7 = 11%

 

 

 

My car I was able to find a red 20 tooth but was still out by 3 at 30 using those drive through radar displays. That's 10% so a 22 tooth fixed this. Thanks again Charlie for finding one for me.

 

 

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